Ansco Color negative / positive process
1950 – 1957
Subtractive 3 color: Chromogenic monopack, negative / positive
(Ansco Division of General Aniline and Film Corporation)
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Original Technical Papers and Primary Sources
Duerr, Herman H. (1952): The Ansco Color Negative-Positive Process. In: Journal of the Society of Motion Picture Engineers, 58,6, pp. 465-479.
Duerr, Herman H. (1954): Letters to the Editor, “Feature Films on Ansco Color”. In: The British Journal of Photography, January 15, 1954, p. 33.
Mitchell, Robert A. (1953): The new Ansco Color film and process. In: American Cinematographer, 34,4, April 1953, pp. 166.
Ross, Rodger J. (1951): Duplication of Color Images With Narrow-Band Filters. In: Journal of the Society of Motion Picture and Television Engineers, 57,9, pp. 267–274.
Rowan, Arthur (1952): ‘The Wild North’ introduces MGM’s new Ansco Color process. In: American Cinematographer, 33,3, March 1952, pp. 106-107, 122-124.
Schadlich, Karl (1956): Professional Printing Techniques for Ansco Color Negative-Positive Motion Picture Film. In: Journal SMPTE, Vol. 65, July 1956, pp. 375-377.
Andrew, Dudley (1980): The Post-War Struggle for Colour. In: Angela Dalle Vacche and Brian Price (eds.): Color. The Film Reader. New York: Routledge, 2006, pp. 40-50, on p. 46.
Anonymous (1956): Current Techniques of 35mm Color Film Photography and Printing. In: American Cinematographer, 37,1, January 1956, pp. 26-27 and p. 58.
Brune, Wolfgang (1954): Ein altes farbenfotografisches Verfahren unter neuen Gesichtspunkten. In: Bild und Ton, 7,10, pp. 293–295. (in German)
Idelson, Martin (1950): Note on Metol Analysis In Photographic Developers. In: Journal of the Society of Motion Picture and Television Engineers, 54,4, pp. 492–493.
Koshofer, Gert (1966): Fünfundzwanzig Jahre deutscher Farbenspielfilm. In: Film – Kino – Technik, Vol. 20, No. 10, 1966, pp. 259-262, on p. 261. (in German)
Merritt, Russell (2008): Crying in Color. How Hollywood Coped When Technicolor Died. In: Journal of the National Film and Sound Archive, Australia, 3,2/3, pp. 1–16, on p. 1, on p. 6 and on p. 7.
Pierotti, Federico (2016): Un’archeologia del colore nel cinema italiano. Dal Technicolor ad Antonioni. Pisa: Edizioni ETS, on p. 165. (in Italian)
Pinel, Vincent (1992): La forêt des techniques. In: Michel Ciment (ed.): Ciné mémoire. Colloque international d’information (7-9 octobre 1991). Paris: Femis, pp. 17-24, on pp. 21-24. (in French)
Ryan, Roderick T. (1977): A History of Motion Picture Color Technology. London: Focal Press, pp. 139-142.
“The Wild North Introduces MGM’s New Ansco Color Process
Single color-negative requires no special camera, is developed and printed by the studio. Prints are marked by unusual clarity, richness and definition.
By ARTHUR ROWAN
The Wild North, first full length feature production made with the new Ansco Color professional film, is Metro-Goldwyn-Mayer’s answer to a long search for and the development of its own color filming process.
Scheduled for general U. S. release late this month, The Wild North recently was previewed in Hollywood. Its first foreign presentation took place in London, late in January. The accolades resulting from these initial showings are attracting wide interest in the longheralded Ansco Color professional film, and compliments for MGM’s technicians who achieved such remarkable results with it.
The new Ansco Color process consists of a combination of camera, duplicating and printing films of the multilayer, complementary color type. Each film has a “pack” of three color-sensitized emulsion layers and a filter layer coated on safety film base, the individual layers being so thin that the total thickness of the pack exceeds only slightly that of most black-and-white negative emulsions.
In the process, four Ansco films are employed:
Type 843 Ansco Color negative camera film.
Type 846 Ansco Color negative duplicating film.
Type 848 Ansco Color positive printing film.
Ansco Color Compensating travelling matte film.
The laboratory processing sequence of these color films is similar to that of black-and-white motion picture films, with only a bleach solution added between the developer and the fixer. No complicated processing equipment is required.
There is an interesting two-phase story in the production by MGM of its initial Ansco Color feature film: first the studio’s development and adaptation of the Ansco Color process for its feature-length productions, and second the actual photography of The Wild North.
As have other Hollywood major studios, MGM long had the desire to develop its own color filming process, which would enable it to achieve greater studio control plus increased speed in the making of color pictures. Simultaneously, with MGM’s initial developments, 20th Century-Fox and Warner Brothers set out to explore other color film processes for similar reasons.
Metro’s initial exploration of Ansco Color began several years ago when John Arnold, the studio’s executive director of photography, chanced to see one of the first feature productions in Ansco Color made in this country. The picture, Sixteen Fathoms Deep, was photographed on the old Ansco reversible 35mm color film. Although, photographically, the production left a lot to be desired, still, Arnold saw possibilities in it as the medium for MGM’s color process. He was especially attracted by the fact the studio could process the film in its own laboratory and make the release prints, enabling it to maintain complete control over color productions from beginning to end.
Arnold arranged a screening of Sixteen Fathoms Deep for MGM production heads; their reaction encouraged him to continue further study of the film. A supply of Ansco color film was obtained and there ensued many months of experimenting, with the object of determining the most desirable lighting and photographic procedure for the medium. Having extensively studied all the color films that have been developed to date, Arnold holds that satisfactory screen results can be had with most of them providing that the matters of correct color temperature for set illumination and the proper filters for photography are properly dealt with, and the correct procedures for each are established for those who are to work with such films. Some color processes possess certain attributes that are not found in others, such as simplicity of use in the camera and in the laboratory, which are important to the final screen result.
In the early days of MGM’s exploration of Ansco Color, the studio had no developing equipment for the film. The laboratory work, therefore, was done by a local commercial film lab specializing in Ansco color processing. Later, John Nicholaus, MGM’s film laboratory head, converted some of the studio’s developing equipment for processing Ansco Color. Other equipment was built for making duplicate prints. All during this initial stage of exploration, Ansco factory technical men worked in close cooperation with Arnold and Nicholaus; and when, later, Ansco brought out its newer Ansco Color negative-positive process, MGM studio was made the principal testing ground for the new product.
All of the studio’s work on the old Ansco reversible film was promptly abandoned, and the color project was begun all over again from scratch with the new films. “One of the first things we discovered,” said Arnold, “was that the new Ansco Color negative was superior in many respects to the old reversible film. It had truer color, was sharper on the screen, and especially important was the fact it possessed unusual ability to render remarkable definition in shadow areas. Now, more than ever, we seemed to have hit upon a color process that had every quality we desired.”
All this generated renewed enthusiasm in the studio for the development of MGM’s own color filming process. Ensuing months saw the Ansco film put through every conceivable test. One of the most conclusive resulted from photographing Ansco Color right along side the production cameras on several important sets of MGM color films then in course of shooting. The object of these tests, of course, was to determine how Ansco Color negative would respond to the set lighting and makeup currently in use for color at the studio.
Similar research continued for several months, culminating in what proved to be, perhaps, the most decisive test of all. This was the test made in the Hawaiian Islands during the time the studio was making one of its big color productions there. Ray Rennahan, A.S.C., shot a thousand feet of the Ansco Color negative on the rich Hawaiian exteriors which Charles Rosher, A.S.C., simultaneously was shooting for MCM’s Pagan Love Song.
After evaluating the results of all tests made to date, it was decided that the studio had gone about as far as it could in its explorations with Ansco Color. The next step was to put the film to use in an actual production.
The Wild North, then titled The North Country, was the first production on MGM’s color film schedule to be considered. Here was a story that had everything necessary for an exhaustive test of any color film: dark, rugged interiors of a north woods cabin; rich exteriors in majestic mountains, both in summer and winter; and snow – always a challenging condition for the color cinematographer.
Because a great deal of the story was to be shot in snow, Arnold decided to find out first how Ansco Color negative would respond to snow photography, and especially to the extraneous light snow reflects. Taking a camera and crew into the mountains north of Los Angeles, he photographed snow scenes at all hours of the day; in bright sunlight and in shade; at high noon and at dusk; at the same time testing the various filters which he had previously developed especially for Ansco Color during earlier studio experiments.
MGM executives were so elated over the results, they sent the film to the studio’s New York office for its reaction. While awaiting approval, Arnold turned his attention to solving a serious problem that arose while filming the snow scenes in the mountains. This was the matter of sluggish camera movement caused by congealed lubricant, resulting from low temperatures in cold weather.
A small electric heating unit operated by an ordinary 6-volt storage battery, was attached directly to the vital center of the camera mechanism.
Following local tests, the unit was found to work perfectly and cameras thus “winterized” were shipped to Idaho, where the second phase of this story – the actual photography of The Wild North – begins.
METRO-GOLDWYN-MAYER chose one of its most illustrious directors of photography to photograph its first Ansco Color feature-length production – Robert Surtees, A.S.C., who won an Academy Award last year for his Technicolor photography of King Solomon’s Mines, and who subsequently was assigned to photograph Quo Vadis in Rome. In The Wild North, he had another picture calling for shooting off the lot, away from the usual studio conveniences – a story calling for both summer and winter locales in rugged mountains; long sequences to be shot in snow – real snow, not studio prop stuff. Thus the frozen north became the exciting panorama against which a man hunted for murder saves the life of and nurses back to health the Mountie sent into the desolate wilderness to bring him to justice.
The winter scenes were filmed near Sun Valley, Idaho. The summer sequences, except for the rapids scenes, were photographed in the vicinity of Jackson Hole, Wyoming. Because it was impractical to ship electric generators and booster lights to these rugged location sites, Surtees had only reflectors for booster lighting. In the winter, this posed no problem because of the light reflected from the snow. But he was apprehensive at first when shooting exteriors in summer in the wooded country near Jackson Hole without booster lights. His fears were dispelled, however, when first studio bulletins on the dailies reported “perfect results”. “This proved that Ansco has the rare quality of ‘reaching into the shadows’ to bring out detail,” said Surtees, “a quality possessed by no other color film.”
“And speaking of quality,” Surtees continued, “this was proved further when we were shooting the winter sequences in snow. Heretofore, it has been difficult to shoot action scenes in snow on location and get good photographic quality. With Ansco, after determining the stop that gave the desired rendition of skin tones, the snow and other objects in the scenes registered perfectly normal – something I have not found possible with other color films. Moreover, there is none of the bluish cast of reflected skylight on the snow. Snow looks like snow in Ansco Color!”
Perhaps the most remarkable photography was the sequence of scenes shot after six-thirty one evening, just as a blizzard started. “We had just so many days to shoot,” said Surtees. “We had to gamble on whatever light was available. So, we kept on shooting. To insure getting some contrast in the scenes, I had logs and other objects protruding from the snow painted dead black. The effect secured was actually more realistic than the scenes appeared to the eye. I don’t believe we could have equalled the contrast result with fast pan film.”
When Surtees first started shooting in the dazzling brilliance of the snow country, the first thing he noted was the extreme readings given by his light meter – the result of light reflected from the snow. Thereafter, he followed the old reliable practice of taking a meter reading from the palm of his hand – holding the meter about 8 inches away. The result: perfect skin rendition every time.
Surtees found that Ansco Color is remarkable for its ability to produce excellent day for night shots. Using a Pola screen on the lens, and stopping the lens down a little, perfect black skies resulted without the additional use of blue filters. “Of course,” he says, “you have to have the sun just right to achieve the best effect. That’s one of the advantages of being able to shoot Ansco Color with a regular Mitchell camera. With the camera racked over you can see the result in the camera viewfinder through the taking lens, and compose the scene, adjust focus, and set your Pola screen at the right degree – the same as in black-and-white photography.”
There are two dramatic and photographic highlights in the picture – the first, the attack of Stewart Granger and Mountie Wendell Corey by a pack of wolves. This exciting sequence was photographed by Surtees on an MGM sound stage with telling results. Here skillful lighting and camera manipulation, thanks to the remarkable characteristic of Ansco Color to render detail in low-key illumination, make this a breathtaking event to watch on the screen.
The second dramatic highlight is the trip through the rapids in a canoe, when Granger exposes Corey to the same ride on the rapids he himself experienced when the man for whose murder he is being sought was shot. True to Granger’s conviction, Corey, faced with a threat to his life, aims a shot at Granger.
This remarkable action footage was photographed by another MGM cinematographer, Harold Lipstein, A.S.C. Some of it was achieved by process photography, but for this, Lipstein also furnished the background plates.
The script called for recording the two desperate men in the canoe in closeup in order to capture the emotion in their faces contrasted with the turbulent rapids boiling all around them as they fought to keep the craft afloat. To photograph this with all the punch and reality demanded of the script, Lipstein had dolly tracks built out over the river, from the bank, so the camera could be pulled back as the canoe approached.
For still other closeup shots, Lipstein had two canoes lashed together and a platform placed across the two on which the camera was mounted. This formed a camera-dolly-on-water, which enabled the camera crew to ride the rapids just ahead of Granger and Corey – with the camera focused upon them for some of the most realistic footage in the picture.
The major advantages of the Ansco Color negative-positive process, according to Surtees, are that processing can be accomplished in the studio’s own film laboratory, and that the new material makes filming a relatively lower cost operation, because standard black-and-white equipment may be used for filming and processing. Among the cameraman’s advantages is the film’s higher speed which makes it possible to “stop down” and thus gain depth of field and sharper definition in both foreground and background. Skin textures and color rendition in general seem a little softer – a bit on the pastel side – and more like that seen by the eye. Colors never obtrude on the scene; there are never any exaggerated blue skies or blatant reds.
With general press reviews of The Wild North lacking because the film has yet to be released in the United States, it is interesting to note the comment of one critic on the London Daily Herald which sums up succinctly the views also of his British contemporaries: “This sturdy film has one quality to be most highly recommended. It is shot in a new color process called Ansco Color, which is crisper, clearer and less like strawberry jam. It made the film a pleasure for me!”
(Rowan, Arthur (1952): “‘The Wild North’ introduces MGM’s new Ansco Color process”. In: American Cinematographer, 33, 3, March 1952, pp. 106-107, 122-124.)
“The New Ansco Color Film And Process
Ansco Color film possesses photographic latitude ranging from realistic highlights to the detail inside deep shadows.
By Robert A. Mitchell
NOTE – It was just a year ago that American Cinematographer magazine reported on Metro-Goldwyn-Mayer’s initial Ansco Color production, The Wild North. Since then, MGM has completed its second Ansco Color feature, Ride Vaquero, and is currently in production on two more, Take The High Road and Arena. The following article, which is condensed and reprinted from International Projectionist, for December, 1952, treats the subject of Ansco Film more technically than did our initial report. Omitted is the author’s description of the processing procedure. – EDITOR
A new consciousness of the unlimited possibilities of color is making itself felt in the motion-picture industry. Not only are more feature pictures filmed in color than ever before, but newer full-color processes which permit greater photographic freedom, studio color-film processing, and release-print manufacture by regular “black-and-white” laboratories, are very much in evidence.
Among the foremost of these new processes is Ansco color, used for filming and printing MGM’s The Wild North. In this production the full range of tone and color faithfully reproduced the freshness and ruggedness of the Canadian Northwest. The blue of sky and water, and the innumerable tones of green in natural foliage, flashed forth clearly and brilliantly on the screen to give a perfect illusion of reality.
In some color film the deep shadows in a photographed scene are actually a fog of dark red in which all pictorial detail is hopelessly lost. To prevent obliteration of the shadow detail in such films, it is necessary for the producer either to decrease the overall density (which unfortunately transforms the wispy texture of the highlights to a featureless glare) or else to reduce the photographic latitude making the picture “thin” and “flat.”
In The Wild North pictorial grandeur is enhanced by a range of light-value contrasts in perfect color balance from the eye-dazzling highlights to the wealth of pictorial detail simultaneously visible in deep shadows. With film of such range of response, exterior color scenes need no longer appear as though photographed at high noon – flat and uninteresting; but producers can capture the flavor of time, locale and atmospheric and seasonal mood in the color medium. Color, that is, becomes a dramatic medium, to be treated as such by the more sensitive masters of movie-making.
Of direct importance to the projectionist in his own immediate responsibility is the fact that Ansco color film possesses the same consistently sharp focus as black-and-white; and comparable resolving power – the ability to separate and present small details.
These prints require no special projection technique. Color on the theatre screen is always at its best, however, when the projectionist gives adequate attention to the arc lamps to avoid faulty screen illumination resulting from discolored or uneven light; and, of course, when all projection gear in the light path is kept immaculately clean.
Ansco color prints are made on high-acetyl base of first quality and are, therefore, readily spliced with the same safety cements or double-purpose cements that give satisfactory results on black-and-white high acetyl-prints.
There are three main types of color film: (1) those that have color built into the photograph emulsion, and hence are exposed and printed photographically; (2) those that have the images stamped on the film by dye-soaked, relief-image matrix films, and (3) those that utilize chemical dye-toning of black-and-white emulsions, usually coated on both sides of the film-base.
Ansco color, the subject of this article, belongs to the first class. Its camera is an ordinary camera, without color filters or beam-splitting optical system. Only this and other “monopack” films can be exposed in ordinary single-aperture, single-magazine movie cameras, developed on ordinary black-and-white processing machines and printed on ordinary black-and-white printers. This simplicity is possible only when the color has been built into the emulsion during manufacture of the raw stock.
All natural-color photography involves some method of splitting up the vari-colored light of the scene to be photographed into three primary components, thus forming three separate images, or “color records.” The light is analyzed in the camera into its components; while in the print these components are brought together again to synthesize the colors of the scene photographed.
The color-photographic analysis may be accomplished by simultaneously exposing three negatives, each through a separate color-filter, which, of course, requires a special beam-splitting camera having three picture-apertures, three sprocket-trains, etc.; or else through a simplified variation that permits two records to be made through a single aperture. In Ansco color, however, the color-analysis is accomplished inside the emulsion of the negative.
There are three color-receptors in the human eye. These are sensitive to red, green (a very slightly yellowish green), and indigo (violet-blue). When colored lights are mixed on a white screen, it is possible to reproduce all colors (including hueless white) by combining red, green, and indigo in various proportions. R, G, and I, therefore, are the three primary colors.
Painters, however, have a different set of ”primary” colors which they use when mixing pigments. These are cyan (a slight greenish blue), magenta (a moderately purplish red), and yellow (very slightly greenish yellow). Actually, C, M, and Y are not primary colors but complimentary to the primaries.
In Ansco color negatives the light-sensitive emulsion contains built-in cyan, magenta and yellow “process colors” sensitized to the same spectral bands, or regions, to which the three color-receptors of the human eye are sensitive, just why C, M, and Y dyes are used for building up the images on color film, instead of the true primaries R, G, and I, will become clear when the process is examined in detail.
To do this, let’s forget Ansco and other color processes in commercial use, and invent one of our own. It may not have much practical value; but it will clarify the principle involved in making a natural-color print from the three-color records. Suppose three negatives are exposed in a beam-splitting, 3-aperture color camera. These color negatives will develop black-and-white, of course, and all three will look exactly the same except that the densities of all colored objects photographed will be more or less different on each negative. In other words, the color values are “latent” in the three simultaneously exposed negatives.
We then make a black-and-white print from each negative. Now if the black-and-white image on the positive printed from the “red-record” negative is converted – by chemical toning, let’s say – to that color which ABSORBS red light from white light, the image will then subtract red from all the areas where no red was present in the original scene. The color which is completely red-subtracting happens to be cyan!
Remember – we are not tinting our red-record positive all over with cyan; we are only toning the photographic image from a black silver image to a cyan image.
The same idea is carried out with the other two positives. The silver image on the film printed from the green-record negative will be toned to a magenta image because magenta absorbs all green. And the image printed from the indigo-record negative will be toned yellow.
We now have three very pretty positives, one with cyan pictures, one with magenta pictures, and one with yellow pictures. But still no natural-color pictures. How can we get them?
Place the three positives one over the other in exact registration and glue them together so they won’t slip out of line – that’s all we have to do. Each process color (C, M, or Y) will subtract its proper primary color (R, G, or I) from the white light of the projector, and lo! we obtain a picture in perfect natural color. Now three thicknesses of film glued together admittedly might be loo bulky for the smoothest projection results; so the best commercial processes superimpose all three colors (C, M, and Y) in one coating of emulsion.
In imbibition-process color films the image is built up in three printings on a single film. In Ansco color films there are three very thin color-sensitive and color-forming emulsions coated on one side of the film-base. The total thickness of the Ansco color multilayer emulsion “pack” is not appreciably greater than that of regular black-and-white emulsion.
1. The Indigo-Sensitive Layer. The Ansco color multilayer emulsion is surfaced by a thin layer of glossy gelatine which protects the emulsion from accidental scratching. Directly underneath this invisible protective coating is a layer of photo emulsion which is affected only by indigo-violet light, and does not respond to green or red. This emulsion, therefore, constitutes the indigo record.
Below the indigo-sensitive emulsion is a yellow filter-layer which screens indigo light from the two emulsions which lie below it. The deep yellow color of this gelatine layer is produced by colloidal silver – dispersed silver grains much smaller than those in a black or gray silver image. Red and green light pass practically unimpeded through this filter-layer, since yellow represents white light from which indigo rays have been removed (leaving red and green).
2. The Green-Sensitive Layer. Under the filter-layer lies an emulsion which is sensitive to both green and indigo light. Indigo light, however, is prevented from reaching this emulsion by the yellow filter-layer. This emulsion, accordingly, photographs only green light, and is known as the green record.
3. The Red-Sensitive Layer. Under the green-recording emulsion there is a special emulsion which is “blind” to green, but photographs red light. This emulsion is, of course, also protected from indigo-blue by the yellow filter layer. It therefore constitutes the red record.
The red-sensitive emulsion is coated on the clear high-acetyl safety-film base. But coated on the non-emulsion side of the base is a dark “antihalation” coating which prevents the light passing through to the back of the film during exposure in camera or printer; from being reflected and scattered into the light-sensitive emulsions, spoiling the image with glare-spots and halos. All camera film, whether color or black-and-white, has an antihalation backing which washes off when the film is developed.
A “pack” of three microscopically thin emulsions, each sensitive to a different primary spectrum-color, is not enough, by itself, to produce a picture in natural color. If this were all there were to Ansco color film, it would, behave exactly like black-and-white film even though latent color values reside in the three sensitive layers. Something more must be put into the film to transform color values into actual color that we can see. Ansco must “tone” the three sensitive layers to their latent color values of cyan, magenta, and yellow. To accomplish this, there are added special chemicals called “color-formers,” a yellow color-former being incorporated in the indigo-sensitive emulsion, a magenta color-former in the green, and a cyan color-former in the red-sensitive layer. The color-formers have no color of their own, but they react, during development of the film, with “dye-couplers” in the developing solution to form the desired yellow, magenta, and cyan dyes.
Because these dyes are complementary in color to the primaries recorded, the new Ansco color film is called a multi-layer complementary-color film. The triple-layer cyan, magenta, and yellow images are entirely equivalent to the three glued-together positives we imagined a few paragraphs back, but thin enough throughout their triple ply for accurate focusing and flexible enough for practical, ordinary projection. And they are characterized by extreme stability of the dye images.
Ansco Color Negative Film Type 843 is exposed in the usual way in any 35-mm motion-picture camera. This camera film is intended for exposure with day-light-quality light-sources, although overall color balance on a movie set is not critical. It is only necessary to have all light sources – low-intensity arcs, high-intensity arcs, and incandescent lamps – balanced to the same color temperature except where special effects are desired. Standard filters used in all interior color filming enable a proper balance to be obtained.
The exposed camera film is developed in the same manner as black-and-white film, the only addition to the process being a bleach bath and a second “fix.”
In a regular black-and-white negative all tones are reversed – shadows and dark objects in the photographed scene coming out light on the negative, and the highlights coming out dark. So also with Ansco color negative film. And because all photographic values are reversed, the colors of the photographed scene are reversed to their complementary colors – blue sky appearing as orange, red blood as pale blue-green, etc. Ansco color negative, therefore, is a true negative, and from it Ansco color positives are made.
So far nothing has been said of the sound-track. Sound is not recorded directly on the picture negative in professional movie-making, but on sound-recording stock by a recording head driven in synchronism with the picture cameras. The original sound recordings may have either photographic or magnetic tracks, magnetic recording being in favor at the present time because of its high fidelity and low noise-level.
Whichever recording method is used, independently recorded sound-effects and background-music tracks are properly “dubbed” into the principal record of the dialogue and sounds that originated on the set during shooting. Sound mixing is accomplished by means of an apparatus which has several soundheads (reproducers) feeding their combined output into a single recorder. The chief recordist sits at the console of the mixer like an organist and manipulates the volume controls which regulate the strength of sound from all the simultaneously-playing tracks. The resultant, or mixed, sound is recorded photographically on a single film.
This film is the master sound negative from which a master sound positive and a number of duplicate sound negatives, used for printing the soundtrack on the theatre-release prints, are derived by contact-printings.
This brings us to the matter of making Ansco color sound film prints for theatre projection. Now, release prints are only very rarely made from the original camera negatives, not even in black-and-white work. As is the case with the soundtrack recording, a number of duplicate negatives are prepared for printing the release positives. The preparation of these picture dupe negatives is an interesting process, and provides a peep behind the scenes of professional film make-up.
Just as the rolls of processed negative film for a black-and-white movie must be harmonized and balanced for consistent density and contrast in the release prints, so also must the negatives for a natural-color movie be photographically adjusted. And with color film there is the additional problem of color-balance. (That is, the overall tone of the scenes must not vary in tint except for desired pictorial and dramatic effects. The color must be balanced to give the most natural results with the white light of the projection arc.)
These problems can be solved very simply and satisfactorily.
”But why,” it may be asked, “is it necessary to make duplicate negatives from which to print the release positives? Why not print them directly from the original camera negatives, making all light and color-balance corrections during printing?”
This can be, and is, done on occasion; but professional productions involve optical effects which are not present in the camera negatives. These include fades, dissolves, wipes, photomontages, multiple exposures, travelling-mask shots, etc. It is considered unwise to cut these optical effects into the original camera negative, a mighty precious commodity.
Then, too, it would be extremely foolhardy to risk damage to the original negative through the routine printing of several hundred release positives. In fact, in order to speed up the work and maintain good picture and sound quality, it is mandatory to make a dozen or so duplicate negatives, some of which are sent to foreign countries for release-printing overseas.
From the original Ansco Color Type 843 Camera Negative Film a master positive film is printed. This may either be in full color by printing on Ansco Color Type 848 Positive Motion-Picture Printing Film, or (as is preferred in professional practice) the master positive is made in the form of three black-and-white positives, one for each primary color.
The development process for Ansco color release prints is the same for the negative, except that special treatment is given to the soundtrack in order to obtain a regular silver-image track.
Interesting is the fact that the sound-track may be printed in any one, any two, or all three of the emulsion layers of Ansco color film. If, for example, an indigo filter be placed between the light and the sound negative in the printer, the track will print only in the top indigo-sensitive emulsion. If the filter be cyan, transmitting both indigo and green light, the track will print in both the top and middle layers. With no filter all three layers will print.
The top indigo-sensitive layer was used for printing the soundtrack of MGM’s The Wild North. This layer has the finest grain and does not require any electrical high-frequency equalization to equal the frequency-reponse characteristics of black-and-white prints. Other laboratories, however, are obtaining good results with 2- and 3-layer tracks.
This description concerns the new Ansco color film as it is being made and used at the present time – a fact to bear in mind in view of continued progress in the popular and rapidly expanding process of making motion pictures in full natural color. Further improvements are inevitable. It is quite possible, for example, that the yellow filter-layer of colloidal silver may soon be eliminated.
(Mitchell, Robert A. (1953): “The new Ansco Color film and process”. In: American Cinematographer, 34, 4, April 1953, pp. 166.)
“THE ANSCO COLOR NEGATIVE/POSITIVE PROCESS
The Ansco Color Negative/Positive Process was a three-color subtractive system for color cinematography introduced in 1953 by the Ansco Division of General Aniline and Film Corporation.1 When it was introduced the process consisted of three elements that could be used singly or together: a coupler-incorporated three-color negative film for an original photography, a coupler-incorporated three-color duplicating negative film, and a coupler-incorporated three-color release print film.
The first feature picture photographed in the Ansco Color Negative/Positive Process was the MGM picture, The Wild North. The negatives and release prints for this picture were processed in the MGM laboratory on converted black and white processing equipment.2 The success of this first venture into color processing was followed by several more features in Ansco Color at MGM.3
Seven Brides for Seven Brothers
The Student Prince
Kiss Me Kate
Take the High Ground
The Long, Long Trailer
Following the introduction of its color negative film the Ansco Company continued to improve its product. Three different camera negative films were manufactured before the film was eventually discontinued.
The camera negative films manufactured under the name of Ansco Color Negative were multilayered color films which consisted of three light-sensitive emulsions sensitized to red, green and blue light respectively, and coated on a single film support (Fig. 49). Incorporated in the emulsion layers were dye couplers which reacted simultaneously during development to produce a separate dye image in each layer, complementary to the sensitivity of the layer. The light and dark areas of the image were reversed with respect to those of the original subject. Also the various color areas of the negative were complementary in color to the corresponding areas in the original scene. In order to obtain maximum image sharpness it was necessary to produce a dye image in closest proximity with the originally exposed silver halide grain. To accomplish this it was important that the color coupler surround the grain so that the coupling reaction can take place in situ with the silver halide grain. The Ansco Color couplers were anchored in the emulsion layers by means of the specific chemical configuration of the color coupler molecules. A fatty acid molecule of large molecular size was chemically combined with the dye coupler molecule through a short linkage.
Three different color negative films having the general characteristics described above have been manufactured as Ansco Color Negative Film:
Ansco Color Negative Film, Type 843
A color negative film balanced for use under average daylight conditions, that is, for a mixture of sunlight and some blue sky. The speed of this film was E.I. 16. For daylight or arc light exposure it was recommended that an ultraviolet absorbing filter such as the Ansco UV 16 be used on the camera lens. Normal contrast for this film was Red 1·00, Green 1·00, and Blue 1·25.
Ansco Color Negative Film, Type 8444
A color negative film balanced for use with 3200°K tungsten quality illumination. The speed of this film was E.I. 16 tunsten. According to the manufacturer this film could be used with daylight illumination without loss of speed by using a suitable conversion filter such as the Wratten 85 B. Normal contrast for this film was Red 1·00, Green 1·00, Blue 1·25.
Ansco Color Negative Film, Type 8455
A color negative film balanced for use with 3200°K quality illumination. The speed of this film was E.I. 25 tungsten and 16 daylight, with a Wratten 85 filter. This film was manufactured with a safety base which contained an orange tint which remained after processing. The purpose of this tint was to match the camera negative to inter-negative films which have a dye mask and thus permit intercutting of the camera negative and inter-negative. Normal contrast for this film was obtained by developing to a green gamma of approximately 0·70.
The Ansco color duplicating negative film was a multilayered color negative film similar in layer arrangement and color absorption characteristics to Ansco Color Negative Film. Its color sensitivity, however, was different from the camera negative film. It was similar to the color print film.
Ansco Color Duplicating Negative Film, Type 8466
A duplicating negative film which consisted of three light sensitive emulsions sensitized to red, green and blue light, respectively. The sensitivity of this film was balanced for exposure by a tungsten light source of approximately 3000°K. The exposure index was 0·60 to 1·0. Normal contrast was 0·90 to 1·20; however, development could be carried to gamma 1·5 or higher, if necessary.
The print film manufactured to be used with Ansco Color negative and duplicate negative films was multilayered color film which consisted of three light sensitive emulsions sensitized to red, green and blue, respectively, and coated on a single film support. Incorporated in the emulsion layers were dye forming couplers which react simultaneously during development to produce a separate dye image in each layer. When printed from a color negative, a color duplicate negative or a set of tri-color separation negatives, a three-color reproduction of the original was obtained. The couplers used in this film are similar to those described previously for the negative film.
Ansco Color Positive Release Printing Film, Type 8487
A color positive film balanced for printing with filtered tungsten illumination. The speed of this film was similar to black and white positive, approximately E.I. 1·5.
The processing steps and times for the negative and positive processes are given in the following tables:
1 DUERR, H. H., “The Ansco Color Negative-Positive Process,” Journal of the Society of Motion Picture and Television Engineers, June, 1952, pp. 465-479
2 ROWAN, A ., “The Wild North Introduces MGM’s New Ansco Color Process,” American Cinematographer, March, 1952, pp. 106-107, 122-124.
3 Variety, January 6, 1954, p. 51.
4 Technical Service Bulletin # 6.41 (Professional Motion Picture Department, Ansco Division, General Aniline and Film Corporation, Binghamton, New York, December 1, 1957).
5 How to Use and Process Ansco Color Negative (Professional Motion Picture Department, Ansco Division, General Aniline and Film Corporation, Binghamton, New York, April, 1957).
6 Technical Service Bulletin # 6.31 (Professional Motion Picture Department, Ansco Division, General Aniline and Film Corporation, Binghamton, New York, October 15, 1951).
7 DUERR, H. H., “The Ansco Color Negative-Positive Process,” loc. cit. , p. 470.”
(Ryan, Roderick T. (1977): A History of Motion Picture Color Technology. London: Focal Press, pp. 139-142.)
“Nevertheless it was two years before Anscocolor, a multi-layered reversal stock in which each layer would absorb its proper colour and filter the light before it penetrated to the next layer, was ready. Processing Ansco involved nothing other than activating the dye-couplers already present in the film. This made it far quicker to develop than Technicolor. The German wartime inventions included a sturdy but very thin base on which could be attached three layers plus two separation filters. Given this, Anscocolor could be employed in conventional cameras and under much lower light levels than Technicolor where, to begin with, the light was split to expose two strips of film.
Ansco’s first commercial film, Climbing the Matterhorn, was made for Monogram Pictures in 1948.24 The ability to take advantage of outdoor light and colour conditions was well displayed, winning Ansco an immediate contract with MGM. With a secure part of the expanding US market, Ansco set up a laboratory, in Paris in 1949 hoping to claim the market vacated by the failing additive processes. But by this time Agfa’s other child, the Belgian Gaevert Co., had perfected its Gevacolor and it too moved confidently into Paris. Gevacolor and Anscocolor were comparable economically and aesthetically; Ansco was perhaps a bit sharper, but Geva was available in negative as well as reversal.
24 James Limbacher, Four Aspects of the Film (New York: Brussel and Brussel, 1969), p. 55.”
(Andrew, Dudley (1980): The Post-War Struggle for Colour. In: Angela Dalle Vacche and Brian Price (eds.): Color. The Film Reader. New York: Routledge, 2006, pp. 40-50, on p. 46.)
“4. LES PROCÉDÉS SOUSTRACTIFS
Autour des années trente, on assiste à la naissance presque simultanée des principaux procédés modernes qui relèvent tous du système soustractif. Dans ce système, la couleur est matérialisée sur la copie destinée à la projection. Le quasi-monopole exercé par les procédés soustractifs tient à un fait très banal : il ne demande aucune transformation du matériel de prise de vues et de projection. Mais cette simplification d’utilisation résulte d’une complexité accrue au niveau de la fabrication et du traitement des émulsions. C’est là que se situe le problème du point de vue de la conservation : les trois couches qui composent la structure de la plupart des films soustractifs sont composées de matières colorantes beaucoup plus instables que l’argent réduit de l’émulsion en noir et blanc.
e. Les procédés chromogènes négatif/positif : ces procédés apparaissent en 1941 avec le nouvel Agfacolor dont les brevets seront dispersés après la guerre et donneront naissance à tous les procédés modernes (Gevacolor, Ferraniacolor, Fujicolor, Anscocolor, Sovcolor, Eastmancolor…).
La prise de vues s’effectue sur un négatif comportant trois couches argentiques sensibles respectivement au rouge, au vert et au bleu. Au cours du développement chromogène, des coupleurs ancrés dans chaque couche produisent des colorants cyan, magenta et jaune. L’argent est ensuite entièrement éliminé. On obtient ainsi une image négative où couleurs et valeurs sont complémentaires de celles du sujet. Pour le tirage, on utilise un film du même type qui rétablit les couleurs et les valeurs du sujet. Les procédés chromogènes négatif/positif sont quasiment les seuls utilisés aujourd’hui dans le cinéma commercial. Leur traitement est relativement simple mais cet avantage comporte une contre-partie : l’usine n’est plus à l’extérieur du film comme dans le Technicolor ou le Kodachrome, elle est à l’intérieur. La complexité des multiples réactions qui se produisent dans ce très faible volume fragilise le produit final. Les procédés chromogènes ont été longtemps instables. Les fabricants nous promettent maintenant des émulsions susceptibles de durer plusieurs siècles (sous la réserve du respect des procédures de traitement, d’une bonne utilisation et de conditions de stockage correctes). Il reste néanmoins à sauver quarante années de cinéma en couleur et la tâche n’est pas mince.”
(Pinel, Vincent (1992): La forêt des techniques. In: Michel Ciment (ed.): Ciné mémoire. Colloque international d’information (7-9 octobre 1991). Paris: Femis, pp. 17-24, on pp. 21-24.) (in French)
“Kinefilmmaterialien wie Ansco Color (nur 1950-1956), Ferraniacolor (seit 1950) und Gevacolor (seit 1948) verdanken den Pionierleistungen der Agfa ihr Erscheinen;19 allerdings hatten die ausländischen Hersteller auch bereits eigene Vorleistungen erbracht. Im Vorspann und auf den Plakaten des am 14.11.1951 uraufgeführten ersten deutschen Gevacolor-Spielfilms Grün ist die Heide war daher auch zu lesen: “Gevacolor nach Agfa- und Gevaert-Patenten”; ihm folgten bis 1953 sechs weitere deutsche Gevacolor-Filme.
19 Koshofer, G.: Die Geschichte der modernen Farbfotografie. Bild u. Ton Bd. 2 (1966) Nr. 2, S. 60.”
(Koshofer, Gert (1966): Fünfundzwanzig Jahre deutscher Farbenspielfilm. In: Film – Kino – Technik, Vol. 20, No. 10, 1966, pp. 259-262, on p. 261.) (in German)
“There are several color negative films manufactured by different companies throughout the United States and Europe. These negative films can be used in any ordinary black-and-white camera. They have three emulsion layers superimposed on a cellulose acetate base. These three emulsion layers are differently sensitive to different colors of light. This means that the photo-sensitive silver halide particles in the separate emulsions are exposed by different colors of light. Generally, color negative films have a filter layer between the top two emulsions. Where the color sensitivity is not complete, this filter aids in separating unwanted colors from a particular emulsion.
In the United States the most widely used color negatives are Eastman and Ansco.
Both Eastman Color Negative and Ansco Color Negative have only one strip of film surfaced with three layers of emulsion, each being sensitive to a different primary color. Either film can be used in a conventional 35mm camera.
Similar to color negative, 16mm color positive film has three layers of emulsion, each sensitive to a different primary color – red, green and blue, The commercial film is low in contrast and differs from color negative in that a positive color image is obtained by reversal development rather than a negative.
From it three 35mm separation negatives are made when dye transfer release prints are to be made for 35mm exhibition.
In Europe, there are three additional color negatives, Agafcolor, Gevacolor and Ferraniacolor. These negatives are similar to those used in the United States in that three layers of emulsion are superimposed on a single film base.
The Technicolor laboratories, in both United States and England, manufacture release prints from all of these color negative systems.
When photographing with 35mm Eastman or Ansco color negative, any standard 35mm camera may be used, including the “hand-held” or portable models. Specific “color” cameras are not required. After the negative is developed, positive prints may be made in a manner similar to that for black-and-white film, or by the dye transfer method from the color negative, or from separation negatives, as will be explained later.
Only Technicolor offers the producer the alternative of having film printed on color positive stock or by the dye transfer method. Dye transfer release prints offer a cost advantage when a large number of prints are required for worldwide release. And by dye transfer printing from matrices valuable negative is saved from constant re-use.
Color positive release prints are manufactured only from color negative. Color positive stock is similar to color negative in that it has three super-imposed emulsion layers. Color positive stock is contact-printed by light coming through the color negative. Color negative has different colors correlated to the sensitivities of color positive emulsion layers.
Color positive stock records one color image aspect in each of its three emulsion layers and, after printing, is developed.”
(Anonymous (1956): Current Techniques of 35mm Color Film Photography and Printing. In: American Cinematographer, 37,1, January 1956, pp. 26-27 and p. 58.)
“Long after it stopped providing three-strip cameras, Technicolor continued to offer its services as a lab to process and print a wide variety of color films made from negatives manufactured by its competitors and successors – notably Eastman, Ansco, Agfa, Ferraniacolor, Gaevert, and eventually Sovcolor and Fuji – film stocks that all used ordinary cameras. While Eastman and its competitors provided camera negatives, Technicolor after 1954 limited itself to the highly lucrative business of processing and making dye transfer prints.”
(Merritt, Russell (2008): Crying in Color. How Hollywood Coped When Technicolor Died. In: Journal of the National Film and Sound Archive, Australia, 3,2/3, pp. 1–16, on p. 1.)
“With practically no fanfare, but with meticulous planning and extraordinary discretion, Eastman commandeered the manufacture of color motion picture film negative. Its single domestic competitor, Ansco film, secured an exclusive contract with MGM, and with the release of The Wild North in March 1952 actually beat Eastman to the gate in exhibiting the first Hollywood monopack feature.22 But by the end of 1954, after the last stragglers had finally returned their Technicolor cameras, Ansco was out of the movie business, and through the rest of the decade Eastman provided the color negative to all the major studios and virtually all the independents.
22 For Ansco Color Film and MGM, 22 American Cinematographer (February, 1950), p. 42; Arthur Rowan, “‘The Wild North’ Introduces MGM’s New Ansco Color Process,” AC (March, 1952), 106–107, 122–124. Also Robert A. Mitchell, “The New Ansco Color Film and Process,” AC (April, 1953), 166, 177–183.”
(Merritt, Russell (2008): Crying in Color. How Hollywood Coped When Technicolor Died. In: Journal of the National Film and Sound Archive, Australia, 3,2/3, pp. 1–16, on p. 6.)
“But in the 50s, not only did color come to the modern world. Domestic melodrama – the quintessential black-and-white genre of the 40s – became the new cutting edge for color experimentation. Although the sudden surge in color westerns at the start of the decade meant that, numerically, Eastman Color westerns far outnumbered so-called women pictures in color, by the time the studios hit their stride in developing their own color aesthetic, the new lords of color were the melodramatists: Sirk, Minnelli, John Huston, Otto Preminger, George Cukor, and Fritz Lang – directors who quickly created signature styles, while dramatically broadening the range of color applications to narrative.28 At the same time younger Turks [Elia Kazan and Nicholas Ray in particular] collaborated with their cinematographers to create color experiments of their own. Minnelli is an especially interesting case because he had been the leading director of Technicolor musicals in the 40s, and then with Ansco and Eastman Color created a brand new color style for his 50s melodramas – notably Lust for Life, Tea and Sympathy, and above all in his masterpiece Some Came Running.29
The Technicolor codes did not suddenly evaporate. Particularly in the early transitional years, expensive CinemaScope and VistaVision spectacles faithfully followed the Technicolor formulas, making their color designs all but indistinguishable from the Kalmus model [the widescreen illustrations I have used from The Robe, Knights of the Round Table, and How To Marry a Millionaire, all shot on Eastman Color or Ansco, are classic examples of Technicolor practice being used verbatim during the new regime].30 But, by the mid-1950s, conspicuous shifts appear.
28 Eastman Color western and melodrama counts derive from The American Film Institute Catalog, 1951–1960, Chadwyck-Healey/American Film Institute, 2003–2008. The rise of the color western in the early 1950s was particularly dramatic. By my count, a total of twenty westerns filmed in color were released from 1940 to 1949, none during America’s war years. At the end of the decade, the number shot up from three in 1949 to 11 in 1950, then to 23 in 1951, 21 in 1952, 21 in 1953, and 20 in 1954. In short, as many color westerns were shot each year in the early 1950s as were shot in the entire preceding decade.
29 For Minnelli and Technicolor, Scott Higgins, “Color at the Center: Minnelli’s Technicolor Style in Meet Me in St. Louis ,” Style (Fall, 1998). For Minnelli and his color 1950s melodrama, Minnelli with Hector Acre, I Remember It Well (Garden City, NY: Doubleday, 1974), 288–290.
30 Minnelli, in fact, resisted Eastman color for Lust for Life because in its first years the Eastman color style so closely resembled Technicolor’s that Minnelli assumed Eastman could not reproduce subdued tones. Its palette, he claimed, came “straight from the candy box, a brilliant mixture of blues, reds, and yellows” [I Remember, 288–89]. So he used Ansco Color along with the single color consultant with no Technicolor background, Ansco’s Charles Hagedon.”
(Merritt, Russell (2008): Crying in Color. How Hollywood Coped When Technicolor Died. In: Journal of the National Film and Sound Archive, Australia, 3,2/3, pp. 1–16, on p. 7.)
“Anscocolor (1945). La prima versione dell’Anscocolor consiste in una doppia pellicola invertibile (in cui, cioè, il passaggio dall’immagine negativa a quella positiva avviene su un unico supporto mediante il processo chiamato, appunto, di inversione). La prima pellicola invertibile è quella utilizzata nella macchina da presa (Camera Film, Type 735, sensibilità 6 ASA); da essa è poi ricavato il numero di copie desiderato su un secondo supporto invertibile, usato al posto del tradizionale positivo (Print Film, Type 732). La Ansco commercializza anche un terzo tipo di pellicola invertibile (Duplicating Film), destinata alla realizzazione di copie (del Camera Film) ed effetti ottici. Nel 1950 questo sistema, molto complesso, è abbandonato in favore del tradizionale metodo basato su un supporto negativo e uno positivo74.
74 Cfr. H.H. Duerr, H.C. Harsh, “Anscocolor for Professional Motion Pictures”, in SMPE Journal, 1946, 5, pp. 357–367; “Ansco’s New Film for Use in Color Motion Picture Production”, in American Cinematographer, 1947, 2, p. 65.”
(Pierotti, Federico (2016): Un’archeologia del colore nel cinema italiano. Dal Technicolor ad Antonioni. Pisa: Edizioni ETS, on p. 165.) (in Italian)
“Note on Metol Analysis In Photographic Developers
By Martin Idelson
Technical Dept., Pavelle Color Inc., New York, N. Y.
The method of Brunner, Means and Zappert1 for the determination of metol in Ansco Color Positive first developer, A-502, was found by us to give a titration curve with no true inflection point. Instead, there was a region of about 0.5 ml in which the inflection might occur; therefore, the error in the determination may be quite large. By substituting acetic acidfor water as solvent for the titration, and 0.1 N sulfuric or perchloric acid in acetic acid for the conventional 0.1 N hydrochloric acid, a better inflection point may be obtained. No changes except those already mentioned were made in the procedure given by Brunner, Means and Zappert.
Briefly, the theory is that whether a substance is an acid or base depends on the solvent in which it is dissolved.2,3 Nitric acid is commonly regarded as a strong acid, but when nitric acid is dissolved in concentrated sulfuric acid it acts as a moderately strong base.
Metol is an amino phenol. In water the amino group is a weak base and the phenol group is a very weak acid. The net effect is a weakly basic reaction towards acids. If, however, acetic acid is used as the solvent, the acidity of the phenol group is completely masked while the basicity of the amino group is enhanced.
The titrant must be a stronger acid than acetic acid; sulfuric and perchloric acids are very convenient and a 0.1 N solution of either in glacial acetic can be accurately standardized against diphenylguanidine potentiometrically or with methyl violetindicator.
A comparison of two titrations, one in water and the other in acetic acid, is shown in the accompanying graph. On calculating the change in emf per milliliter at the equivalence point, it was found that for water the ratio was 64 mv per ml and for acetic acid, the ratio was 112 mv per ml. Furthermore, these values applied over a region of 0.5 and 0.2 ml respectively. It can be seen that the end point can be found more closely with acetic acid as solvent.
It should be noted that a precipitate forms when the titration with ceric sulfate is performed. The end point is not as sharp as in water, and either a separate sample should be prepared or an aliquot part of the combined extracts of metol and hydroquinone may be used.
1 A. H. Brunner, Jr., P. B. Means, Jr., and R. H. Zappert, “Analysis of developers and bleach for Ansco Color Film,” Jour. SMPE, vol. 53, pp. 25–35; July, 1949.
2 L. P. Hammett, Physical Organic Chemistry, Chap. II, McGraw-Hill, New York, 1940.
3 N. F. Hall and J. B. Conant, “A study of superacid solutions: I,” J. Amer. Chem. Soc., vol. 49, p. 3047; 1927.
A Contribution: Submitted December 28, 1949.”
(Idelson, Martin (1950): Note on Metol Analysis In Photographic Developers. In: Journal of the Society of Motion Picture and Television Engineers, 54,4, pp. 492–493.)
“The Ansco Color Negative-Positive Process
By Herman H. Duerr
The basic principles of the Ansco Color Negative-Positive Process are outlined. The paper deals with the essential characteristics of the color film materials used for the process and outlines the printing and processing steps required. Methods used to comply with the requirements of the motion picture industry in regard to color dupes for optical effects, protection masters, color negative master dupes, and color release printing are described. Requirements of sound and procedures to produce silver sound tracks are discussed.
In 1945,1 the Ansco Color Process for professional motion pictures was proposed. This process was based on the principle of reversible development of monopack materials. Several motion pictures have been produced using this process. It was realized, however, that a color process using the negative-positive approach would be preferable for a number of reasons. In the first place, such a process would follow more closely the long established black-and-white practices of the motion picture industry. More important, however, a color film process using the negative-positive cycle is superior due to the higher speed attainable and the considerably greater latitude in exposure, processing and printing.
The Color Negative-Positive process, however, presented many problems, particularly in regard to methods of providing dupes for optical effects, protection masters and other essential requirements for the production of feature motion pictures. These problems have now been satisfactorily solved and the Ansco Color Negative-Positive process will now replace the older process using film types 735 and 732, requiring reversible development.
The Ansco Color Negative-Positive Process, like the earlier reversal process, is a subtractive color process, using the principle of color-forming development.
There are three different 35mm color film materials involved in the process:
Color Negative Film Type 843,
Color Dupe Negative Film Type 846, and
Color Positive Release Printing Film Type 848.
In addition to these color film materials, a panchromatic fine grain dupe film, such as the Eastman Panchromatic Separation Film, Type 5216, can be used for making separations.
The three multilayer color film types used in the negative-positive cycle are similar in structure, although quite different in other characteristics.
Figure 1 shows the layer arrangement typical for the three color film types used in the process. The conventional layer arrangement, with a red-sensitive bottom layer, a green-sensitive middle layer and a blue-sensitive top layer, is being used. This figure illustrates the Color Negative Film Type 843 before processing.
As has been described before,2 the three colors, cyan, magenta and yellow, in the Ansco Color Process are formed in their respective layers during one color developing step. It is one of the important characteristics of the Ansco Color Process that the nondiffusing, colorless color couplers are dissolved and uniformly distributed in the gelatin of the photographic emulsion layers and completely surround the individual light-sensitive silver halide grains. After exposure and during the color development, the developing agent becomes partially oxidized by reducing exposed silver halide grains to metallic silver. The partially oxidized developing agent reacts with the color couplers to form dye deposits. The oxidized color developing agent is soluble and can move freely in the layer. In order to produce a dye image in closest proximity with the originally exposed grain, it is, therefore, important that the color coupler surround the silver halide grain so that the coupling reaction can take place truly in situ with the silver halide grain. This characteristic of the Ansco Color Process is important and is responsible for the good image sharpness and definition.
A schematic illustration of the mechanism of dye image formation taking place in closest proximity to the exposed silver halide grains is shown in Fig. 2. The Ansco color couplers are immobilized in the emulsion layers by means of the specific chemical configuration of the color coupler molecules. To provide the characteristics of complete solubility and at the same time immobility and nondiffusing properties, the molecular structure has been arranged in such a way that a fatty acid molecule of large molecular size, through a short linkage, is chemically combined with the dye coupler molecule.3 The fatty acid molecule acts somewhat like an anchor, preventing the diffusion of the dye coupler and of the formed dye image within the layer, as well as from one layer to another.
A typical cyan color former of this configuration, with substitution referred to as “fat-tail,” is:
Ansco Color Negative Film, Type 843
Camera Requirements: The Ansco Color Negative Film, Type 843, can be exposed in conventional motion picture cameras as they are used for black-and-white photography. The only additional requirement is that, for maximum image definition, the lenses used should have good color correction.
Film Characteristics: The layer arrangement of the Color Negative Film, Type 843, before processing has been shown in Fig. 1. The layers after processing are shown in Fig. 3.
More recently the Type 843 film has been supplied on gray base instead of on clear base with the soluble antihalo back layer, and results regarding halation in motion picture practice have been quite satisfactory. The gray base does not interfere with the subsequent printing operations and the absence of a soluble back layer on the negative film has certain advantages in processing.
Sensitometry: The sensitometric curves of the three emulsion layers of the Color Negative Film, Type 843, are illustrated in Fig. 4. When developed to the proper contrast for direct printing on Color Positive, Type 848, or for the preparation of black-and-white tricolor separations, the gamma values for the three layers, measured as integral densities on the Macbeth-Ansco Color Densitometer Model 12, should be approximately as follows:
Blue-sensitive layer (yellow) 1.25
Green-sensitive layer (magenta) 1.00
Red-sensitive layer (cyan) 1.00
Spectral Sensitivity: The spectral sensitivity of the color negative film is shown in Fig. 5. The sensitivity peaks are at 450, 555 and 655 mμ, respectively. The film is balanced for light of daylight quality. For interior illumination the overall color balance should be approximately 5400 K. While the overall color balance is not critical, it is important that the different light sources on a set be balanced to the same spectral quality. The use of ultraviolet filters, such as Ansco UV-16 or Wratten Filter No. 1, for outdoor exposures and indoor exposures with arc lights is recommended.
Absorption Characteristics: The dye images recorded in the color negative film are in colors complementary to the colors of the original. The absorption characteristics of the dyes in the color negative film are illustrated in Fig. 6. The absorption maxima are: yellow, 440 mμ, magenta, 540 mμ and Cyan, 675 mμ.
Sensitivity and Resolving Power: The color negative film has an exposure index of 16. The resolving power, as measured by the method proposed by Sayce,4 is 44–48 lines/mm.
Ansco Color Duplicating Negative Film, Type 846
Film Characteristics: The Color Dupe Negative Film is similar to the Color Negative Film Type 843 in layer arrangement and color absorption characteristics. However, the color sensitivity is different from that of Type 843, but it is similar to that of the Color Positive Film Type 848, as shown in Fig. 9. In order to produce dupe negatives with fine grain and good resolution, the emulsions used for this film type are much slower. The exposure index is approximately 0.6 to 1.0. This film type is also on gray base of the density of the Negative Type 843 so that it can be readily interspliced with it. The resolving power is approximately 66 lines/mm. The sensitometric characteristics of the color dupe negative film are shown in Fig. 7.
The color dupe negative film is used to make color negative dupes from tricolor separation positives made from the color negative originals. Optical effects, fades, lap dissolves and other special effects can be introduced via these color dupe negatives. The various methods which can be used to obtain a color positive release print will be described later, below.
Ansco Color Positive Release Printing Film, Type 848
Film Characteristics: In emulsion layer arrangement the color positive release printing film is similar to the color negative film shown in Fig. 1. The color positive film can be exposed either directly from color negative originals, from color negative dupes or from black-and-white tricolor separation negatives. The sensitometric curves of the individual layers of the color positive film, plotted as integral densities, are shown in Fig. 8. In Fig. 9 the spectral sensitivity of the color positive printing film is illustrated. Good separation of the spectral sensitivity ranges with a minimum of overlaps is desirable for good color reproduction in the printing film.
Dye Absorption: The absorption characteristics of the dyes produced in the color positive film are different from those in the color negative and dupe negative film. The absorption maxima are: 440 mμ for the yellow layer, 540 mμ for the magenta layer, and 660 mμ for the cyan layer.
Film Speed and Resolving Power: The sensitivity of the color positive film is similar to black-and-white positive, approximately exposure index 1.5. The resolving power is 64–66 lines/mm.
All three color film types used in the Ansco Color Negative-Positive Process are on low-shrink, safety base.
Color Processing Procedures and Solutions
The three color film types used in the process require very similar processing steps and processing solutions. Only the Color Negative Film, Type 843, requires a different color developing solution. The color dupe negative film and the color positive release printing film can be developed in the same solutions throughout. The color developing time of these two types is different, as shown in Table I.
For uniform processing of all types of color film materials good control of the processing solutions at all times is very important. Basic control procedures which apply also to the handling of color negative-positive have been described by Bates and Runyan,5 while analytical procedures to control and maintain solution strength and uniformity have been presented by Brunner, Means and Zappert.6 General information in regard to color sensitometry may be found in the report of the SMPTE Color Sensitometry Subcommittee.7
Methods of Release Printing From Ansco Color Negatives
Methods of release printing from Ansco color negatives for the printing of Ansco color negative originals from different methods and certain variations thereof can be used to produce color positive release prints. These methods are summarized in Fig. 10.
Not all of these methods are equal in regard to color quality and cost. A more detailed discussion of the advantages and disadvantages of each of these methods is, therefore, in order.
Method A. Printing From Original Color Negatives Interspliced With Opticals on Color Dupe Negatives
This method, shown schematically in Fig. 11, comes closest to present black-and-white practices, at least as far as domestic releases are concerned. The color negative originals, which may represent 60–75% of the total footage, are interspliced with optical effects such as fades, lap dissolves, etc., made on Color Dupe Negative Film Type 846 Tricolor separations on Fine Grain Duplicating Pan Film are made from the full-length negative. They are used as protection masters. The optical effects are produced from sections of these black-and-white separations by printing on Color Dupe Negative Film Type 846. Method A, which involves a minimum of color printing by the use of color negative originals except for opticals and effect shots, leads to the best color quality. This method would be first choice for domestic releases.
Method B. Printing From Full-Length Master Dupe Negatives
In Method B, as shown in Fig. 12, release printing is done from master color dupe negatives. This method is recommended where the original color negatives cannot be made available for release printing. This is frequently the case for foreign releases. Tricolor separations on panchromatic duplicating film are made from the cut negative. Master color dupe negatives on Type 846 are made from all scenes, including opticals and special effects. Scene-to-scene conformance can be attempted in making the separations, as well as in printing the master dupe negatives, so that only minor color balance and light corrections have to be made during the release printing steps. The black-and-white separations also serve as protection masters.
As in Method A, the release printing is done by contact printing. In both methods conventional equipment, such as a Model D or Model E Bell & Howell or similar printers, can be used.
The filters required to correct for the overall and scene-to-scene color balance variations in printing are determined by the use of a color scene tester similar to the one described by F. P. Herrnfeld.8
On the Model D printer provisions should be available for the insertion of color balance filters.8 Following a suggestion made by the Metro-Goldwyn-Mayer Laboratory, a special material for colored traveling mattes for the Model E Bell & Howell printer has been made available. Film base dyed uniformly to produce various color filter combinations, coated with positive fine-grain emulsion, is exposed and processed by the Laboratory to produce a “variable width” type light control strip in the center of the film, as shown in Fig. 13.
Appropriate lengths of different colored matte negatives, representing the various light and color balance changes are spliced together. This colored traveling matte automatically corrects for scene-to-scene variations in color balance and density and the full speed of the printer can be utilized.
In the preparation of master color dupe negatives on Type 846 film, the following sensitometric conditions are representative:
Sensitometric test strips exposed with a light source approximately 3200 K, using an intensity scale sensitometer and measured on a Macbeth-Ansco Model 12 Color Densitometer.
*Black-and-white separations exposed on an Eastman Type IIb Sensitometer and measured on Western Electric RA-1100B Densitometer.
The method described next requires optical printing and is shown schematically in Fig. 14.
Method C. Release Printing From Black-and-White Separation Negatives
In Method C three-color separation positives on fine-grain Pan Duplicating Film are made from the color negative originals. These positives are printed on the same fine-grain duplicating film, this time developed to a lower gamma negative. Optical effects can be introduced during this printing step. The black-and-white three-separation negatives, including the optical effects, are used for release printing on Ansco Color Positive Film Type 848, preferably using multihead printers with good registration.
Method C avoids one color printing step as compared with Method B, and if very carefully controlled allows somewhat higher color brilliance. However, due to the fact that optical printers have to be used, the release printing is considerably slower and the method requires great accuracy in sensitometric and registration control, and for that reason is not generally recommended. A fourth method not requiring tricolor separations should also be mentioned. Although the color degradation produced by this printing Method D is definitely noticeable, results have been better than expected. This method is briefly outlined in Fig. 15.
Method D. Release Printing From Color Dupe Negatives via Color Dupe Positives
In Method D color positive prints on Color Dupe Film Type 846 are made from the original color negatives using sharp cutting filters. The filters recommended are Ansco UV-16 for all printing steps in addition to the three-color separation filters:
Wratten Filter No. 70;
Wratten 16 plus Wratten 61; and
Wratten 23 plus Wratten 48A.
These filters are also recommended for making the three-color separations in Methods A, B and C.
The Color Dupe Film Type 846 is developed as a color positive. Optical effects can be introduced at this step or the next one, in which the color positive dupe is again printed on Color Dupe Stock 846 with the same sharp cutting filters. This time the 846 Film is developed as a low-contrast color negative. The contrast of this dupe negative should be kept as closely as possible to the same contrast as the original color negative. This second generation color dupe negative can be used for release printing on a conventional contact printer. The Method D does not provide for black-and-white protection masters. For this reason this method is not recommended for feature pictures. A description of this method has been included because there may be occasions where this procedure may offer certain advantages; also, the fact that color rendition is still quite acceptable is a good indication of the flexibility of the Ansco Color Negative-Positive Process.
Sound on Ansco Color Release Printing Film Type 848
The reproduction of sound from multilayer color films using developed dye images has for some time presented a problem, especially in connection with the red sensitive photocell, which is today the standard for 35mm motion picture projection.9 In order to obtain a track which is efficient in absorption in the infrared region of the 868-type phototube, a method to produce a combination silver-plus-dye track having response characteristics similar to the conventional black-and-white silver tracks has been worked out.
Sound Track Development
As shown in Table I, the Color Positive Release Printing Film Type 848, after color development, fixing, bleaching and washing, is surface-dried by effective air squeegeeing. At this stage the sound track area carries a sound image consisting of a dye image from the original color developing step plus a silver ferrocyanide image, produced in the silver bleaching step. Using an applicator wheel or a pen-type applicator, a high viscosity rapid developer solution is applied to the sound track area only. This developer reduces the silver ferrocyanide-plus-dye sound image to a metallic silver + dye image. For the selective treatment of the sound track area, the following steps are important.
1. Effective air squeegeeing to remove surface moisture. The air squeegee should be close to the applicator station to prevent diffusion of moisture to the surface of the emulsion before developer solution is applied in the form of a bead covering the sound area only.
2. Application of high viscosity sound track developer, treating time approximately 30 sec.
3. To accelerate the development of silver track, infrared heat lamps at this stage are advantageous.
Cross-modulation and listening tests have indicated that variable-area sound negatives used for printing Color Positive 848 should have about the same densities as used for printing on black-and-white positive fine-grain film. Densities between 2.40 and 2.70, as read on a Western Electric RA-1100 Densitometer, are satisfactory. Sound printing with filtered light to confine the sound image to the two top layers is preferable. The top layer alone may be used for variable-area tracks.
The variable-area silver-plus-dye track of the edge-treated color positive film shows very good cancellation, fully equal to black-and-white tracks. The contribution of, and the effect of the dye image underlying the silver track image is insignificant in terms of the 868-type phototube response. A yellowish stain in the track area reduces the volume only by about 2 db.
Experience with variable-density recording is still somewhat limited, although satisfactory recordings have been made. In order to produce satisfactory gradation and resolution characteristics, the sound track should be confined to the two top layers, with equal contributions by both layers.
The development work reported in this paper represents the combined efforts of many people of the Ansco Research and Development Dept., as well as the Ansco technical staff in Hollywood. The valuable assistance of the Metro-Goldwyn-Mayer Laboratory, in particular J. M. Nickolaus, J. Arnold and D. Shearer, in cooperating on the various phases of the process and in supplying sample negatives and dupes for this presentation, is gratefully acknowledged.
1 H. H. Duerr and H. C. Harsh, “Ansco Color for professional motion pictures,” Jour. SMPE, 46: 357–367, May 1946.
2 F. Wing, “Ansco Color Film,” Ansconian, 3–11, Sept.-Oct. 1943. J. L. Forrest, “Machine processing of 16mm Ansco Color Film,” Jour. SMPE, 45: 313–326, Nov. 1945.
3 W. Schneider, A. Fröhlich and H. Schultze, “Die diffusionsfesten Farbbildner des Agfacolor Films,” Chemie, 57: 113–116 (DEZ.) 1944.
4 L. A. Sayce, Photographic Journal, 80: 454, 1940.
5 J. E. Bates and I. V. Runyan, “Processing control procedures for Ansco Color Film,” Jour. SMPE, 53: 3–24, July 1949.
6 A. H. Brunner, Jr., P. B. Means, Jr., and R. H. Zappert, “Analysis of developers and bleach for Ansco Color Film,” Jour. SMPE, 53: 25–35, July 1949.
7 A Report of the Color Sensitometry Subcommittee, “Principles of color sensitometry,” Jour. SMPTE, 54: 653–724, June 1950. (Reprinted as a booklet.)
8 F. P. Herrnfeld, “Printing equipment for Ansco Color Film,” Jour. SMPTE 54: 454–463, Apr. 1950.
9 R. Görisch and P. Görlich, “Reproduction of color film sound records,” Jour. SMPE, 43: 206–213, Sept. 1944. A. M. Glover and A. R. Moore, “Phototube for dye image sound track,” Jour. SMPE, 46: 379–386, May 1946. R. O. Drew and S. W. Johnson, “Preliminary sound recording tests with variable-area dye tracks,” Jour. SMPE, 46: 387–404, May 1946. A. B. Jennings, W. A. Stanton and J. P. Weiss, “Synthetic color-forming binders for photographic emulsions,” Jour. SMPTE, 55: 455–476, Nov. 1950. J. L. Forrest, “Metallic-salt track on Ansco 16mm Color Film,” Jour. SMPE, 53: 40–49, July 1949.
J. G. Frayne: Dr. Duerr mentioned a variable density track density of 0.85. This would be high for unmodulated density and would yield low level output. Do you propose using variable density tracks that are that dark?
H. H. Duerr: The density of 0.85 obtainable in the top layer alone referred to, is the maximum density. The unmodulated, unbiased operating density would, of course, be considerably lower and closely related to regular black-and-white practice. The best median density has to be established by further tests.
Dr. Frayne: Does this density figure 0.85, include the base?
Dr. Duerr: No. This is the maximum density obtainable in the top layer.
C. R. Daily: Do you intend to produce a tungsten-type film for use with a color temperature of approximately 3350 K?
Dr. Duerr: We are now producing only a film for daylight-type illumination, but expect to have a tungsten-type film available later on. Whether it will be balanced for 3350 K or a somewhat lower color temperature is not yet certain.
Frank E. Carlson: You referred to a color temperature of 5400 K for the negative film. Is the film balanced to the spectral emission of a black body radiator at that color temperature?
Dr. Duerr: Yes.
Richard H. Ranger: I have no question, but would like to compliment Dr. Duerr on his presentation, because the work shown here tonight represents great strides over the results demonstrated to a group of engineers in Wolfen shortly following the end of hostilities in Germany several years ago.
Presented on October 18, 1951, at the Society’s Convention at Hollywood, by Herman H. Duerr, Ansco Division of General Aniline & Film Corp., Binghamton, N.Y.”
(Duerr, Hermann H. (1952): The Ansco Color Negative-Positive Process. In: Journal of the Society of Motion Picture and Television Engineers, 58,6, pp. 465–479.)
“Ein altes farbenfotografisches Verfahren unter neuen Gesichtspunkten
Dipl.-Chem. Wolfang Brune, Berlin-Grünau
In der Praxis der Farbenfotografie und Farbenkinematografie haben sich in den letzten Jahren ausschließlich subtraktive Verfahren durchsetzen können. Die Ursache dafür, daß die farblich befriedigenderen additiven Verfahren gegenwärtig noch keine Anwendung finden, liegt in ihrem beträchtlich höheren Lichtbedarf bei der Projektion, der sich zur Zeit lichttechnisch noch nicht ausreichend realisieren läßt.
Für die subtraktive Farbenfotografie sind verschiedene Lösungswege aufgefunden worden, die sich charakteristisch voneinander unterscheiden und im folgenden kurz betrachtet werden sollen.
Die erste Gruppe der subtraktiven Verfahren bedient sich eines Filmes mit mehreren, unterschiedlich sensibilisierten übereinander gegossenen Schichten. In diesen werden bei der Entwicklung aus der in ihnen oder im Entwickler enthaltenen Komponente (auch Farbkuppler genannt) und dem Entwickleroxydationsprodukt die Bildfarbstoffe durch Synthese aufgebaut. Bei dieser Gruppe unterscheidet sich das Aufnahmematerial prinzipiell nicht vom Kopiermaterial, wenngleich natürlich die Praxis in bezug auf Sensibilisierung, Reihenfolge der Schichten usw. zu einigen Unterschieden geführt hat. Bei solchen Mehrschichtenmaterialien besteht, ähnlich wie bei der Schwarzweiß-Fotografie, die Möglichkeit zur Durchführung eines Umkehrverfahrens oder eines Negativ-Positiv-Prozesses. Trotz einiger Unterschiede zwischen Umkehrmaterial, Positivmaterial und Negativmaterial bleibt das Prinzip, nämlich das Vorhandensein mehrerer, im allgemeinen dreier, unterschiedlich sensibilisierter lichtempfindlicher Schichten, die übereinander gegossen sind, erhalten. Zu dieser Gruppe gehören die Verfahren Agfacolor, Anscocolor, Kodacolor, Ektacolor, Gevacolor u. a., die letzten Endes alle auf die sogenannte “chromogene Entwicklung” nach Fischer (DRP 253335 und DRP 257160) zurückgehen, wenn sich jetzt auch die einzelnen Verfahren in verschiedenen technischen Einzelheiten in stärkerem Maße voneinander unterscheiden1. Diese Verfahren haben sowohl in der Kinematografie als auch in der Amateurfotografie Eingang gefunden.
Eine zweite Gruppe subtraktiver Verfahren geht in ihrer ursprünglichen Form beim Negativprozeß auf die Methoden der Schwarzweiß-Fotografie zurück. Mittels einer Spezialkamera und normaler Schwarzweiß-Entwicklung werden drei negative Farbauszüge (Blauauszug – Grünauszug – Rotauszug) hergestellt, von denen nach dem Auswaschrelief-Verfahren drei Matrizen hergestellt werden. Nach ihrer Anfärbung mit den zugeordneten subtraktiven Grundfarben (gelb – purpur – blaugrün) unter Benutzung fertiger Farbstoffe folgt die Bilderzeugung durch einen Druckprozeß auf einer geeigneten Unterlage. Diese besteht aus einem Schwarzweiß-Positivfilm, in welchen bereits ein schwaches Silberpositiv und die Silbertonspur fotografisch übertragen sein können. Diese Gruppe ist durch das Technicolor-Verfahren gekennzeichnet, nach welchem bisher wohl mehr als die Hälfte aller Farbfilme hergestellt wurde. Dieses Verfahren dient jedoch ausschließlich kinematografischen Zwecken. In der letzten Zeit soll das Technicolor-Verfahren insofern eine Modifikation erfahren haben, als es sich zur Aufnahme nicht mehr einer Strahlenteilungskamera bedient, mit der man sofort zu den drei negativen Farbauszügen kommt.
Vielmehr soll neuerdings die Aufnahme mittels einer normalen Kamera auf ein farbfotografisches Material der zuvor besprochenen Gruppe gemacht werden, was nach der entsprechenden chromogenen Entwicklung zu einem Farbnegativ führt. Von diesem Farbnegativ können durch dreimaliges Kopieren unter Zwischenschaltung der erforderlichen Filter (blau, grün, rot) drei positive Farbauszüge hergestellt werden, die durch einen weiteren Kopierprozeß zu negativen Farbauszügen führen. Von diesen ausgehend wird der Positivprozeß, wie weiter vorn beschrieben, durch den dreimaligen Druckprozeß mittels Matrizen durchgeführt 2.
Zu den subtraktiven farbenfotografischen Verfahren gehört auch eine nahezu vergessene dritte Gruppe, die sich zur Erzeugung des Farbbildes nicht der Farbstoffsynthese durch chromogene Entwicklung oder des Druckes mit fertigen Farbstoffen bedient, sondern bei denen der in der gesamten Schicht enthaltene Farbstoff partiell ausgebleicht wird. Die ersten Anfänge dieser Verfahren sind von der Beobachtung ausgegangen, daß bestimmte Farbstoffe unter dem Einfluß des Lichtes ausbleichen. Unter Zugrundelegung des Gedankens der Farbausbleichung durch das Licht ist versucht worden, farbenfotografische Materialien herzustellen, die solche ausbleichbaren Farbstoffe enthalten. Diese Versuche sind jedoch alle daran gescheitert, daß der Bleichprozeß relativ langsam verläuft und daß der verbleibende Farbstoff mit der gleichen Lichtempfindlichkeit behaftet ist wie das Ausgangsmaterial. Versuche, den verbleibenden Farbstoff (das eigentliche Bild) zu stabilisieren, haben nicht zu brauchbaren Ergebnissen geführt. Verfahren dieser Art, die als “Farbstoff-Ausbleichverfahren” bezeichnet werden, sind deshalb bald aufgegeben worden.
Dagegen haben Versuche mit einem anderen Ausbleichverfahren zu guten Ergebnissen geführt. Hier werden den bekannten lichtempfindlichen Halogensilberschichten Farbstoffe beigegeben, die nach Exposition und Schwarzweiß-Entwicklung (in einer noch nicht vollständig aufgeklärten Reaktion) in einem besonderen Bade gemeinsam mit dem entwickelten Bildsilber ausgebleicht werden können. Weiter unten wird dieses “Silberfarbbleichverfahren” noch etwas näher beschrieben. Zu dieser Gruppe gehört das von Gaspar ausgearbeitete Verfahren (Gasparcolor) und das Pantachrom-Verfahren der Agfa, das sich jedoch mit kleinen Einschränkungen für den Positivprozeß, eines dem Gasparcolor-Film ähnlichen Materials bedient. Nach beiden Verfahren ist in den Jahren von 1934 bis 1939 eine größere Zahl farbiger Trick- und Werbefilme hergestellt worden, die sich vor allem durch hohe Farbsättigung und Farbbrillanz ausgezeichnet haben sollen.
Dieses Gasparcolor-Verfahren verwendet ebenfalls ein mehrschichtiges Material, dessen einzelne Schichten unterschiedlich sensibilisiert sind und in deren jeder ein Farbstoff der drei subtraktiven Grundfarben eingelagert ist. In seiner ursprünglichen Form besteht der Gasparcolor-Film aus einer Unterlage, deren eine Seite eine unsensibilisierte Schicht mit eingelagertem Blaugrünfarbstoff trägt, während die andere Seite zunächst mit einer rotsensibilisierten Schicht mit dem Gelbfarbstoff und darüber einer unsensibilisierten Schicht mit Purpurfarbstoff begossen ist. Als Kopiervorlage werden positive Farbauszüge benötigt, wie sie von additiven Verfahren und vom Technicolorverfahren her bekannt sind.
Der Kopierprozeß geschieht dergestalt, daß zunächst der positive Grünfilterauszug mit blauem Licht auf die unsensibilisierte, den Purpurfarbstoff enthaltende Oberschicht übertragen wird. Danach wird der positive Blaufilterauszug mit rotem Licht auf die rotsensibilisierte, den gelben Farbstoff enthaltende Schicht kopiert. Abschließend wird die auf der Rückseite befindliche unsensibilisierte, den Blaugrünfarbstoff enthaltende Schicht mit blauem Licht hinter dem positiven Rotfilterauszug exponiert. Während des ersten Kopierprozesses mit blauem Licht ist die darunter liegende Schicht durch ihre Eigenfärbung vor unerwünschter Exposition geschützt, beim zweiten Kopierprozeß mit rotem Licht durch die obere Schicht hindurch erfolgt in dieser auf Grund der fehlenden Rotsensibilisierung ebenfalls keine Exposition, so daß es tatsächlich möglich ist, die drei Farbauszüge einwandfrei auf diesen Mehrschichtenfilm zu übertragen. (Das Kopiermaterial für das Pantachromverfahren hat auf die Zugabe des Blaugrünfarbstoffes in der unsensibilisierten Rückschicht verzichtet und dort nach Exposition hinter dem negativen Rotauszug eine Eisenblautonung durchgeführt3.)
Dieses Material wird nach erfolgter Belichtung zunächst einer normalen Schwarzweißentwicklung und anschließender Fixage unterzogen. Danach befindet sich in den einzelnen Schichten ein Silbernegativ des jeweils überkopierten positiven Farbauszugs. Im Anschluß daran wird das Material in einem besonderen Bleichbad weiter behandelt, dessen wirksame Bestandteile zum Beispiel Bromwasserstoff oder Thioharnstoff sein können. In diesem Bade erfolgt der eigentliche “Silberfarbbleichprozeß”, indem gleichzeitig mit der Ausbleichung des Silbers der Farbstoff in einer, dem ausgebleichten Silber proportionalen Menge zerstört wird. Das Silber scheint nicht nur in den chemischen Prozeß des Farbstoffabbaues mit einzugreifen, sondern ihn auch noch zu katalysieren, besonders in Anwesenheit reduzierender Substanzen. Anschließend an den Silberfarbbleichprozeß folgt eine Nachbehandlung mit einem Silberbleichbad, wobei das im Silberfarbbleichbad nicht umgesetzte Silber restlos entfernt wird. Nach einer abschließenden Wässerung ist die Verarbeitung des Materials beendet.
Der Film enthält nunmehr ein Farbstoffbild, dessen Dichte sich zur ursprünglich entwickelten Silberdichte umgekehrt, das heißt also wie das Positiv zum Negativ verhält. Die Restfarbe in den einzelnen Schichten ist komplementär zur Auszugsfarbe des überkopierten Farbauszuges. Aus der Tatsache, daß an den Stellen des entwickelten Silbers die Ausbleichung der Farbstoffe erfolgt und die Restfarbe der Schichten komplementär zum zugeordneten Farbauszug ist, geht hervor, daß es ein Direktpositiv-Verfahren ist und unmittelbar zum Farbpositiv führt, weswegen als Kopiervorlage stets ein Positiv benutzt werden muß. Die Verwendung eines ähnlichen Materials für Aufnahmezwecke scheitert an seiner zu geringen Empfindlichkeit, die ihre Ursache sowohl emulsionstechnisch in den verschiedenen erforderlichen Zusätzen hat, als auch lichttechnisch in der zu geringen Lichtdurchlässigkeit der einzelnen Schichten auf Grund des Farbstoffgehaltes. Auch hier wurden Versuche gemacht, die allgemeine Empfindlichkeit zu steigern, ohne jedoch praktisch anwendbare Ergebnisse zu erzielen. Infolgedessen kann ein nach dem Gasparcolor-Verfahren hergestelltes Filmmaterial nur für Kopierzwecke benutzt werden4. Wie ersichtlich, entsprechen Sensibilisierung und Bildfarbstoff in den einzelnen Schichten nicht der natürlichen Zuordnung, weswegen auch ein unmittelbares Überkopieren eines Farbpositivs nicht möglich ist. (Natürliche Zuordnung: rotempfindliche Schicht – Blaugrünfarbstoff, grünempfindliche Schicht – Purpurfarbstoff, blauempfindliche Schicht – Gelbfarbstoff.) Wegen des Fehlens eines entsprechenden Aufnahmematerials und wegen der Umständlichkeit des Kopierprozesses wurde das Verfahren aufgegeben, als das wesentlich einfacher zu handhabende Agfacolor-Negativ-/Positiv-Verfahren bis zur Produktionsreife entwickelt worden war und auf dem Markt erschien.
Von diesem Zeitpunkt an ist das Gasparcolor-Verfahren in Vergessenheit geraten und trotz ständiger Weiterentwicklung durch den Erfinder kaum noch angewendet worden. Erst in den allerletzten Jahren scheint es einen solchen Entwicklungsstand erreicht zu haben, daß seine Verwendung zumindest für einige farbenfotografische Zwecke durchaus ernsthaft wieder in Erwägung zu ziehen ist. W. Schultze5 teilt mit, daß neuerdings nach dem Gasparcolor-Verfahren Schmalfilmkopien von Kodachromfilmen sowie farbige Aufsichtsbilder von Farbdiapositiven hergestellt worden seien. Das dazu benötigte Material werde von der Firma E. I. Du Pont (USA) hergestellt, wobei sich nunmehr alle drei lichtempfindlichen Schichten auf einer Seite des Schichtträgers befinden und die einzelnen Schichten nach der natürlichen Farbzuordnung aufgebaut seien. Zur Herstellung der Aufsichtsbilder von Farbdiapositiven werde ein Material benutzt, das die lichtempfindlichen Schichten nicht auf der üblichen Papier- oder Kartonunterlage trage, sondern auf einer opaken Unterlage, die vermutlich aus mit Titanweiß eingefärbter Triacetat-Cellulose besteht.
Dem Verfasser ist weiterhin, bekannt geworden, daß eine französische Filmfabrik ebenfalls Versuche zur Herstellung eines farbenfotografischen Materials nach dem Silberfarbbleichverfahren in seiner modernsten Form macht und gegenwärtig bereits für Versuchszwecke ein Kopiermaterial auf opaker Unterlage für farbige Aufsichtsbilder herstellt, dessen Verarbeitung zu ausgezeichneten Ergebnissen geführt hat (private Mitteilung).
Diese Tatsachen sind besonders interessant und aufschlußreich in Anbetracht eines Vorteils der Silberfarbbleichverfahren, der bisher noch nicht erwähnt worden ist. Die den Schichten beigegebenen Farbstoffe gehören zur Klasse der Azofarbstoffe, insbesondere der sauren Azofarbstoffe, und zeichnen sich durch hervorragende Lichtechtheit und durch hohe Farbsättigung aus. In diesen Eigenschaften sind sie den Farbstoffen, die bei der chromogenen Entwicklung gebildet werden, weit überlegen. Es ist bekannt, daß die Farbstoffe, die beispielsweise in Agfacolor-Aufsichtsbildern entstehen, so lichtunecht sind, daß es nicht möglich ist, sie als Wandschmuck längere Zeit dem Licht auszusetzen. Unter solchen Umständen tritt nach relativ kurzer Zeit (nach längerer Zeit auch im Dunkeln) eine Ausbleichung der Bildfarbstoffe ein, die um so störender ist, als sie nicht in allen Schichten gleichmäßig erfolgt, sondern zunächst der empfindlichste Farbstoff, der Blaugrünfarbstoff, entfärbt wird, so daß das Bild immer rotstichiger und immer unansehnlicher wird. Demgegenüber besitzen die beim Silberfarbbleichverfahren verwendeten sauren Azofarbstoffe eine solche Lichtechtheit, daß sie ohne weiteres lange Zeit dem Licht ausgesetzt werden können, ohne irgendwelche Veränderungen zu erleiden. Außerdem sind die Azofarbstoffe wesentlich brillanter und farbsatter, so daß sie sich auch in dieser Beziehung vor den Farbstoffen der chromogenen Entwicklung auszeichnen.
Dem Verfasser haben solche Bilder auf opaker Unterlage vorgelegen, und zwar sowohl auf Material, das bei Du Pont hergestellt wurde, als auch auf solchem, das für Versuchszwecke von einer französischen Filmfabrik erzeugt wird. Auf beiden Materialien ist die Farbwiedergabe in bezug auf Sättigung und Brillanz so überzeugend, daß sie der Verfasser jedem anderen bisher bekannten Verfahren für Farb-Aufsichtsbilder vorzieht. Daneben führt die Verwendung einer opaken Unterlage aus angefärbter Cellulose automatisch zu einem Hochglanz, der die Brillanz der Farben erhöht, aber nicht die Empfindlichkeit des auf Fotopapier üblichen Hochglanzes besitzt.
Auf Grund dieser Vorteile ist der Gedanke sehr naheliegend, für Amateurzwecke ein Verfahren einzuführen, das sich (zumindest für Aufsichtsbilder) eines Kopiermaterials nach dem Prinzip der Silberfarbbleichung bedient. Bei Anwendung der natürlichen Farbzuordnung besteht ein solches Material aus einer Anordnung von drei Schichten, von denen beispielsweise die unterste rotempfindliche Schicht den blaugrünen, die mittelste grünempfindliche Schicht den Purpur- und die oberste, blauempfindliche Schicht den Gelb-Farbstoff enthält. Durch Anwendung von Chlorsilberemulsionen und durch Veränderung der Schichtenfolge kann die sonst notwendige Gelbfilterschicht vermieden werden. Auf dieses Material können infolge der “natürlichen Farbzuordnung” unmittelbar normale Farb-Diapositive kopiert werden, woran sich die vorher beschriebene Naßverarbeitung anschließt. Es resultiert unmittelbar das gewünschte Duplikatpositiv, wobei es belanglos ist, ob die Unterlage des Kopiermaterials durchsichtig ist und der Kopierprozeß ein Diapositiv ergibt, oder ob bei Verwendung einer opaken Unterlage ein farbiges Aufsichtsbild resultiert. Bei Betrachtung des Naßprozesses fällt ein am Rande liegender Vorteil des Verfahrens auf. Im Dunkelteil liegt nur die Schwarzweißentwicklung und die halbe Fixierzeit. Alle anderen Bearbeitungsstufen, vor allem der entscheidende farbgebende Prozeß der “Silberfarbbleichung”, können im Hellen stattfinden, befinden sich also unter ständiger Kontrolle. Im Gegensatz dazu muß bei allen Verfahren mit “chromogener Entwicklung” der entscheidende Prozeß im Dunkeln durchgeführt werden.
Mit der Benutzung eines solchen Materials, das, wie weiter oben bereits ausgeführt wurde, ein Direktpositivverfahren (jedoch ohne die bei anderen Verfahren erforderliche Umkehrentwicklung) darstellt, ist noch ein weiterer Vorteil verbunden. Es ist allgemein bekannt, daß die beispielsweise auf Agfacolor-Positivumkehrfilm aufgenommenen Diapositive hinsichtlich Farbbrillanz, Farbsättigung und Farbgleichgewicht wesentlich besser sind als die nach dem Agfacolor-Negativ-/Positivprozeß gewonnenen, da jeder Kopierprozeß zu Verlusten an Farbsättigung und Farbbrillanz führt.
Das Agfacolor-Negativ/Positiv-Verfahren hat sich wohl bei Fotoamateuren nur deshalb in steigendem Maße gegenüber dem Positivumkehrverfahren eingeführt, weil das dann vorliegende Agfacolor-Negativ die Herstellung einer beliebigen Zahl Farbdiapositive und Aufsichtsbilder, sowohl farbig als auch schwarzweiß gestattet. Es ist kaum daran zu zweifeln, daß der Amateur zum Positivumkehrverfahren zurückkehrt, das ihm farblich bessere Diapositive als das Negativ/Positiv-Verfahren liefert, wenn er von diesen Diapositiven beliebig viele farbige Aufsichtsbilder herstellen kann, die sich dann noch bei Anwendung des Silberfarbbleichverfahrens durch Lichtechtheit und höhere Farbsättigung auszeichnen. Auch die Herstellung weiterer Farbdiapositive würde bei Vorliegen eines Unikats auf Agfacolor-Positivumkehrfilm keine prinzipiellen Schwierigkeiten bereiten, da, wie bereits begründet, mittels der natürlichen Farbzuordnung Materialien hergestellt werden können, die als Kopiervorlage nicht mehr der drei Farbauszugspositive bedürfen.
Diese Überlegungen zeigen also, daß es für die Fotoindustrie durchaus sinnvoll und lohnend ist, sich erneut mit den Möglichkeiten des Silberfarbbleichverfahrens im Rahmen der aufgezeigten Möglichkeiten zu beschäftigen. Ob dieses Verfahren, nachdem es nunmehr auch das unmittelbare Kopieren von Farbpositiven zuläßt, wieder für den Farbenfilm in Betracht zu ziehen ist, bedarf weiterer Überlegungen. Es kann jedoch beim gegenwärtigen Stand des Silberfarbbleichverfahrens nicht mehr kritiklos als veraltet und überholt abgelehnt werden. Dem Farbfotoamateur, dem ein irgendwie entstandenes Farbdiapositiv zur Verfügung steht, liefert das Silberfarbbleichverfahren auf jeden Fall farbige Aufsichtsbilder, die infolge ihrer Lichtechtheit, ihrer besseren Brillanz und größeren Farbsättigung denen auf dem Wege der chromogenen Entwicklung hergestellten weit überlegen sind.
1 Näheres über diese Gruppe subtraktiver farbenfotografischer Verfahren siehe z. B.
a) Cornwell-Clyne: “Colour Cinematography”, London 1951.
b) W. Schultze: “Farbenphotographie und Farbenfilm”, Springer-Verlag 1953.
c) K. Meyer in “Fortschritte der Fotografie II”, Leipzig 1940.
d) J. S. Friedman: “History of Colour Photography”, Boston 1947.
2 Näheres über Technicolor in den unter 1 a und b genannten Werken.
3 a) siehe 1 c.
b) Heymer, Veröff. wiss. Zentrallabor Agfa, V (1937) 37.
c) Eggert u. Heymer, Veröff. wiss. Zentrallabor Agfa, VI (1939), 46.
4 Näheres über Gasparcolor in den unter 1 genannten Werken.
5 siehe 1 b, Seite 97.”
(Brune, Wolfgang (1954): Ein altes farbenfotografisches Verfahren unter neuen Gesichtspunkten. In: Bild und Ton, 7,10, pp. 293–295.) (in German)
“Duplication of Color Images With Narrow-Band Filters
By Rodger J. Ross
Outlined are some of the problems of the users of direct-positive subtractive color films, such as Ansco Color and Kodachrome, in producing acceptable duplicate images which in some cases may be third-generation reproductions. An experimental project will be described in which it was found that it is possible to produce duplicate images which may be directly compared with the camera originals by exposing the duplicating film with filters transmitting three relatively narrow spectral bands. While no attempt has been made in this paper to deal in any detail with the theoretical aspects of color reproduction, a number of factors which are of great concern to the users of color materials have been noted – particularly the establishment of visual acceptance limits for color images, and the influence of processing upon the shape and relationship of the three-color density curves representing an image of a neutral wedge.
In the normal white-light printing of color film, deliberate alteration of the color balance may be employed to produce duplicate images which are quite satisfactory for some purposes. In the hands of a skillful technician, the results which can be achieved in this way are quite surprising. For instance, large numbers of excellent 16-mm motion picture prints have been produced by direct printing from the camera originals.1,2
The problems involved in the reproduction of larger still transparencies are considerably more severe. Here it is possible for the observer to relate the appearance of individual colors in an image to objects in the immediate vicinity, or to make side-by-side comparison of images. In addition, there is ample opportunity for leisurely evaluation of different image areas.
The appearance of a color image is often described by the term “color balance.” This term is at best an uncertain indication of the characteristics of a color image, for it is well known that color balance may be influenced by such factors as the conditions of viewing. Visual evaluation, while suggesting the direction in which correction should be made, provides no indication of the degree of correction required, or the nature and extent of the factors which are responsible for unsatisfactory appearance.
In any attempt to improve the quality or appearance of color images, it is very difficult to demonstrate conclusively the degree of improvement that is obtained in a particular case. The best that can be done is to say that, as a result of visual evaluation, the image is a pleasing representation of the original object or scene, or that a duplicate image closely resembles the original image from which it was made. This might be defined as a process of establishing acceptance limits within which satisfactory images may be obtained. Since the eye is particularly sensitive to differences in colors in side-by-side comparisons, the acceptance limits established in direct comparison of duplicate and original color images might be expected to be severely restricted, as opposed to a condition under which an image is evaluated in respect to its pleasing appearance.
The Color Sensitometry Subcommittee of this Society, in a report published in the Journal,3 describes the progress that has been made in extending black-and-white sensitometric procedures to the evaluation of color materials and color images. One of the requirements of a color process might be said to be the reproduction of a neutral gray scale or wedge as a neutral image. The image of a neutral wedge might be represented by three curves on graph paper, derived from color density measurements on the image. Any system of this kind, however, must take into account the differences in the effects of a color image upon the eye and its influence upon another color material when duplicates must be made. There is the problem, too, of representing just-visible differences between color images of objects or scenes by significant quantitative differences in measurements upon a wedge image. Furthermore, a neutral image of a wedge is by no means an absolute requirement of a visually satisfactory image of a colored object. It should be possible eventually, however, to describe a color image in terms of a series of numbers, or as patterns upon a chart or graph paper, and to apply this information in the control of exposure and processing of color materials, in order to ensure that an image will be obtained within the acceptance limits established as a result of visual evaluation.
The deficiencies of the dyes of subtractive color materials have been described in detail in the literature. In brief, it may be said that as the result of the unsatisfactory transmissions and absorptions of available dyes, the colors in duplicate images will become degraded or desaturated.4 In addition, the contrast of a color image must be relatively high to obtain satisfactory color saturation.5,6 When a color image such as this must be reproduced on another color material with similar contrast characteristics, the contrast of the duplicate image will be further increased. Masking has been recommended as at least a partial solution for these problems. While it has been shown that it is possible to overcome completely the deficiencies of the subtractive process by masking, this would require the use of multiple masks. It is seldom practical, however, to utilize more than one mask in duplication. The practical difficulties involved in making and registering even a single mask have limited the use of masking procedures, particularly in motion picture printing.
Requirements for Two Languages
A basic problem of the National Film Board of Canada is the production of 16-mm color films in English- and French-language versions – one of which must be printed from color masters. When the Technical Research Division first undertook a study of the problems of color reproduction in the autumn of 1947, it appeared that no worth-while contribution could be made by further work on conventional color-correction methods. The possibilities were considered, however, of reproducing color film with three narrow spectral bands instead of white light. The idea of printing color film in this way was not a new one, even at that time. The Schinzels had proposed in 1937 that positive color prints might be made in this way from Agfa color negatives.7 Dufaycolor, an additive process, was being printed with three filters.8 Since then, however, interest in three-filter exposure techniques, especially in motion picture printing, has increased. Eastman Kodak has recommended recently that positive color prints from their new color negative should be produced in this way. Kendall was one of the first to propose that direct-positive subtractive color film might be printed with three filters instead of white light, and described a modified 16-mm step printer which could be used for this purpose.9 No attempt had been made before this project was initiated, however, to determine the most suitable spectral bands or the degree of improvement which might be obtained with this method of exposure.
The results of the experimental work on this project over the past three years would indicate that this method of reproducing direct-positive subtractive color images has some important advantages. The reproduction of individual colors can be improved and it is possible to exercise considerable control over image contrast. It is very difficult, as previously noted, to specify the exact degree of improvement that may be obtained. Since dye deficiencies are merely reduced and not entirely eliminated by this method of reproduction, duplicate images, identical with the camera originals, cannot be obtained. However, demonstration material has been assembled to indicate that duplicate images representing average objects or scenes may be made to fall within the most critical acceptance limits referred to previously – and it is often difficult to select the camera original. In comparisons of this kind, image contrast is an important factor. Although it may not always be necessary or desirable to do so, the contrast of duplicate images may be reduced by variation of processing until it is actually lower than that of the original, with no adverse effects upon the acceptance limits.
The eye is influenced by color images in such a way that color arrangement is an important factor in obtaining satisfactory duplicate images. In the course of this project it was found that if the original image contains a significant red area, for instance, there may be some degradation or alteration of this area in the duplicate image, and the failure of the process to reproduce this color is immediately apparent. The same degree of degradation or alteration will be present, of course, in all duplicate images produced in the same way, but may not influence the acceptance limits. In determining the most favorable color balance, a number of camera originals with widely different color arrangements should be selected, and with this method of reproduction a balance may be found which is satisfactory for all average scenes, eliminating the necessity for scene-to-scene correction. Further alteration of color balance will not as a rule improve the appearance of duplicates which do not fall within the acceptance limits.
The filters which have been used in the experimental work transmit relatively narrow spectral bands (Fig. 1). The object of this exposure method is to produce an image with each filter which is confined to a single layer of the duplicating film. Therefore, the transmission bands of the filters must be selected and the widths of the bands must be restricted so that this objective may be achieved.
When a color image has been produced by exposure in a camera, it should no longer be necessary to consider this image in the same sense as an original scene for the purposes of further reproduction, but rather as a set of three dye images into which the scene has been separated. The object in duplication, then, is to transfer each individual dye image to the corresponding layer in the duplicating film. Because of the undesirable transmitting and absorbing characteristics of the color-film dyes, there must always be more or less dye in the various areas in the corresponding layers of the duplicating film than in the three layers of the original image.
When exposure is made with suitable filters, the light transmitted by the three superimposed dye images of the original film will be modified to that which will pass through these filters (Fig. 2).
The transmission of the magenta dye in a color film for red, green and blue is not sharply defined, but passes gradually from one color to another. For a given sensitivity band of the green-sensitive layer of a duplicating film, then, the effective green transmission of the magenta layer may be much greater than it might appear to be. It would seem to be obvious that, since the starting point in color degradation and distortion is to be found in this unwanted green transmission, considerable improvement should be obtained by restricting the transmission of the magenta dye in the green region by means of a narrow-band filter.
The possibility of lowering the contrast of duplicate images by alteration of the processing times was also explored. It was found that the processing times for Ansco Color film exposed with three filters could be reduced by as much as 30% from the recommended times, with no apparent adverse effects on the appearance of the duplicate images. Under these conditions, the contrast of the duplicates was somewhat lower than that of the original camera images. However, in lowering the contrast of duplicate images it is very important that the higher densities should be very nearly visually neutral – otherwise undesirable alterations in the appearance of the images will be introduced.
While it was not possible in this project to study in detail the influence of variations in processing times upon the color images, it is known that processing is a significant factor in determining the shape and relationship of the three-color density curves representing an image of a neutral wedge (Fig. 3). This aspect of color-image formation has received little attention in the literature, although the effects of variations in time of first development have been described in some detail by Morse.10
In addition, the precise control of color processing is not a simple matter.11 Slight variations in the constitution of the color developer will exert a strong influence upon color images, and the influence of a particular processing condition may not be the same with different color materials.12 When a small quantity of color developer is used to process exposed film, changes in the developer between two successive tests may be responsible for a change in the appearance of the duplicate images equal to a variation of 10% in the exposure for one of the filters.
There are, of course, some practical difficulties in applying the three-filter exposure technique in the reproduction of color images. When the exposure system consists of a white-light source with a particular spectral distribution, the illumination or the exposure time may be adjusted so that images will be obtained at a level suitable for viewing or projection, and the spectral distribution of the source may be altered to obtain the desired color balance by means of voltage changes or color-compensating filters. With a three-filter exposure system in which the light transmitted by each filter presumably affects only a single layer of the film, a different set of conditions must be fulfilled. While it is somewhat more difficult to establish the desired color balance and image level with an exposure system of this kind, it is much more flexible. For instance, tungsten or daylight-type color films may be exposed with the same system by suitably adjusting the ratio of the three-filter exposures. For the most critical purposes, this is a precise procedure compared to the use of color-compensating filters.
The method of exposure also presents some problems. In the reproduction of still images, successive exposures with the three filters may be made. Kendall has described a 16-mm motion picture printer9 employing an integrating prism and a three-filter exposure system in which narrow-band filters could be used. A single light source could be employed with some means for alternating the filters in the light beam. A number of methods might be used to alter the time or intensity of exposure through each filter to vary the color balance. It should also be possible to employ monochromatic illumination in which case the desired spectral lines or bands might be selected by filters or slits.
The three-filter exposure system has been used to produce duplicates of large still color images that are satisfactory for viewing or further reproduction. A somewhat unusual and successful application for this exposure method was found in the production of 35-mm color-film strips from 16-mm motion picture frames. These “cine-strips” are made in an optical apparatus in which provision is made for exposure through three filters. The color master obtained in this way was printed in a step printer, the lamphouse of which had been modified to expose the third-generation duplicates in the same manner. The three-filter exposure system has also been used successfully by the Banting and Best Institute, University of Toronto, to reproduce medical photomicrographs and color transparencies in which any alteration in color or contrast is particularly undesirable.
The three-filter exposure method is not limited to the reproduction of stills, as has been demonstrated in the continuous printing of film strips in a motion picture printer. The techniques of white-light release printing of motion picture color film, however, have been developed to the point where fairly satisfactory prints may be produced from good-quality camera originals. Any new technique which presents new problems might not prove to be technically or economically practical, in spite of the possibility of further improvements in color quality and contrast. When adequate means have been devised to control printing and processing operations by means of color sensitometric procedures, precise printing methods such as the three-filter exposure technique should prove to be of great value in improving the quality of color release prints.
There is one application in motion picture printing in which the three-filter exposure technique should prove to be particularly useful, however. The intercutting of optical intermediates with camera originals is seldom satisfactory, and such alternatives as A & B printing, and special apparatus for obtaining simple optical effects direct from the camera originals must be employed. Intermediates suitable for intercutting should match the camera originals as closely as possible in color balance, the appearance of individual colors, image level and contrast. It has been shown that duplicate images with these desirable characteristics can be produced with the three-filter process. The problems involved in establishing and maintaining processing conditions, in order that motion picture intermediates with these characteristics may be produced consistently, are such that the closest collaboration with the processing laboratory is required. Facilities for processing lengths of film suitable for screening were not available for this project, and while considerable experimental work has been directed toward the production of optical intermediates, the demonstration material is limited to still images.
Some attention was directed, in the course of this project, to the quantitative evaluation of changes in color balance due to variations in the three-filter exposures, but a satisfactory method for indicating just-visible differences in the appearance of duplicate images has not been found (Fig. 4). The nature and extent of correction, in terms of percentage variation of the filter exposures required to obtain the desired results, was estimated by visual evaluation of comparison images. This is unquestionably a very tedious and uncertain method, and much experimental work is involved in obtaining the best possible results. From the standpoint of the users of subtractive color films, it would be desirable to find some means of establishing acceptance limits for color images, and of interpreting these limits in terms of the nature and extent of the variations in exposure and in the processing conditions which might be required to produce images consistently within these limits.
When Ansco Color film is exposed with three narrow-band filters, there appears to be increased sensitivity to slight changes in the characteristics of the film and in processing. If this is true, this method of exposure might prove to be an advantage, in a form of color sensitometry, in detecting and evaluating film and processing variations of little significance under normal conditions of use. There would seem to be some advantage, too, in utilizing the three-filter exposure system to set up reproducible color exposure conditions which could be readily specified and which should require little maintenance. While variations in the spectral distribution of a light source, now commonly expressed in terms of color temperature, will influence the film whether exposure is made with white light or with narrow-band filters, it should be possible to specify more precisely the characteristics of an exposure system in relation to the energy in these three bands of the spectrum.
1 W. H. Offenhauser, Jr., “Duplication of integral tripac color films,” Jour. SMPE, vol. 45, pp. 113–134, Aug. 1945.
2 P. S. Aex, “A photoelectric method for determining color balance of 16-mm Kodachrome duplicating printers,” Jour. SMPE, vol. 49, pp. 425–430, Nov. 1947.
3 Report of the Color Sensitometry Subcommittee, “Principles of color sensitometry,” Jour. SMPTE, vol. 54, pp. 653–724, June 1950.
4 T. H. Miller, “Masking: a technique for improving the quality of color reproduction,” Jour. SMPE, vol. 52, pp. 133–155, Feb. 1949.
5 R. H. Bingham, “Sensitometric evaluation of reversible color film,” Jour. SMPE, vol. 46, pp. 368–378, May 1946.
6 W. T. Hanson, Jr., and F. A. Richey, “Three-color subtractive photography,” Jour. SMPE, vol. 52, pp. 119–132, Feb. 1949.
7 Karl Schinzel and Ludwig Schinzel, “Copies from Monopack Negatives,” Das Lichtbild, vol. 12, p. 137, 1937. (Translated by Joseph S. Friedman, Amer. Photography, vol. 32, p. 439, June 1938.)
8 A. B. Klein, “Color cinematography,” Chapman & Hall, London, 1939, p. 438.
9 O. K. Kendall, “16-mm film color compensation,” Jour. SMPTE, vol. 54, pp. 464–479, Apr. 1950.
10 H. G. Morse, “Color film exposure and first development timing,” PSA Jour., Sec. B., No. 1, vol. 17, pp. 2–6, Feb. 1951.
11 F. C. Williams, “Current problems in the sensitometry of color materials and processes,” Jour. SMPTE, vol. 56, pp. 1–12, Jan. 1951.
12 J. E. Bates and I. V. Runyan, “Processing control procedures for Ansco Color film,” Jour. SMPE, vol. 53, pp. 3–24, July 1949.
Presented on April 30, 1951, at the Society’s Convention at New York, by Rodger J. Ross, Special Effects Div., National Film Board of Canada, John Street, Ottawa, Ontario, Canada.”
(Ross, Rodger J. (1951): Duplication of Color Images With Narrow-Band Filters. In: Journal of the Society of Motion Picture and Television Engineers, 57,9, pp. 267–274.)