Ansco One-Strip Color-Separation Film, type 155
Subtractive 3 color: one-strip color separation
(Ansco Division of General Aniline and Film Corporation)
Original Technical Papers and Primary Sources
Harsh, H. C.; Friedman, J. S. (1948): New One-Strip Color-Separation Film in Motion Picture Production. In: Journal of the Society of Motion Picture Engineers, 50,1, pp. 8–13.
Cornwell-Clyne, Adrian (1951): Colour Cinematography. London: Chapman & Hall, 3rd. ed., on pp. 395–397.
“New One-Strip Color-Separation Film in Motion Picture Production*
By H. C. Harsh and J. S. Friedman
Ansco, Binghamton, N. Y.
Summary – A description is given of procedures to be used with the new Ansco Film Type 155 – which is designed for making color-separation negatives. Equal gammas are obtained for the red, green, and blue filter exposures with the same developing time, making it possible to obtain the black-and-white separations as successive frames on a single strip of film and thus obviate much of the difficulty of registration. By varying the developing time or developer formula, it is possible to change the gamma over a range of 0.5 to 2.0 to suit the purpose for which the separations are intended, while still maintaining equal gradations for the different filter exposures.
The following are some of the applications for the film which are described: (1) to provide duplicates of Ansco Color originals for protection or (2) foreign release, (3) for special-effects and process photography in conjunction with Ansco Color motion picture films, and (4) for direct photography of animated cartoons which are to be printed in Ansco Color.
The use of monopack color films such as Ansco Color Types 735 and 732 for the original exposure and the release printing stock in the production of motion pictures, poses certain problems in providing the intermediate duplicates or masters which are necessary for protection of the original, for foreign release, or special effects. Methods for making such duplicates using Ansco Color Type 132 have been described by Duerr and Harsh.1 The present paper describes another method for making intermediate duplicates, utilizing a new black-and-white film designed especially for color separations.
The specific problem in motion picture color photography with monopack materials is the loss of color saturation when it is necessary to make second, third, or fourth generation duplicates to arrive at a release print as is often the case in black-and-white motion picture practice. Current use of monopack color processes such as Ansco Color has proved that a direct print from a color original gives color reproduction of satisfactory quality. The difficulty in making more than a first generation print is due to the absorption characteristics of the image dyes. Fig. 1 shows the spectrophotometric curves for the image dyes of Ansco Color Film in the proper proportion to give a gray density of one.
To achieve accurate color reproduction, the intermediate duplicates should have yellow, magenta, and cyan images that are the exact counterpart of those in the original. A glance at the absorption curves of the yellow, magenta, and cyan dyes shows that the cyan absorbs appreciable amounts of blue and green and that the magenta absorbs appreciable amounts of blue. These absorptions are undesirable and to the extent to which they take place they contribute to color degradation and poor color reproduction. From these curves it becomes evident that the blue component of the printing light will not only copy the yellow image in the transparency but also the magenta and cyan. Hence, the yellow image in a second generation print is no longer a true representation of the yellow in the original and the same is true for the magenta. If this is to be used for another intermediate from which release prints are to be made, further degradation of color will take place. The result is a loss of color brilliance which may not be acceptable to critical audiences. The difficulty is obviated if the intermediate duplicates are made in the form of black-and-white separations. By the use of sharp cutting filters it is possible to obtain accurate black-and-white records of the red, green, and blue densities as they are present in the original. These negatives after being converted to black-and-white positives can be printed with identical or similar tricolor filters onto Ansco Color Type 732.
The idea of making separation negatives from monopack color originals is not new and has been applied in imbibition and other color printing processes for many years. However, a black-and-white film which is designed especially for this purpose has not been generally available and it has been found desirable to develop a new type of film to meet this requirement. The new film is tentatively designated as Ansco One-Strip Color-Separation Film, Type 155.
Accurate registration of separation negatives is essential in motion pictures. The ideal solution would be a film base material with high dimensional stability, but such a base material which is suitable for photographic use has not yet been realized. This problem is solved in the new film by making the separations as successive frames on the same 35-mm strip so that any shrinkage or other changes or variations in physical properties of the film with handling and aging will remain the same for all three filter exposures. Hence, the term “one-strip color-separation film”.
Equally important is the need for balance in the gradations of the three separations. In the past this has been achieved by giving the different filter exposures differential development. Since the three separations are on the same strip of film in the new material it is essential that the same effective contrast for the blue, green, and red filter exposures be obtained when developed for the same length of time. This is the important feature of Type 155. The lower set of curves in Fig. 2 shows the characteristics for the red, green, and blue exposures when developed to a gamma of approximately 0.65. This is the desired value for separations from Ansco 735 Type originals. Where it is desirable to include the technique of color correction by masking, the separation film should be developed to an appreciably higher contrast. Therefore, the material must have a wide latitude of gradation. The upper set of curves in Fig. 2 shows the characteristics for a higher contrast and it is noticed that the curves still retain the same equal gammas with different filter exposures as obtained with the shorter developing time. The normal density differentiation of a Type 735 original is approximately 1.6. It is seen that this range is adequately covered in the straight-line portion of the H and D curves.
Another feature of this new film is the sensitization which is extended farther into the red than a normal panchromatic film. The spectral response of Type 155 is shown in Fig. 3. The reason for this is apparent when you refer to the spectrophotometric curves of Fig. 1. You will note that the cyan-dye image has a maximum absorption at 680 millimicrons which corresponds to the maximum of the red sensitivity of the film. This enables one to use an extremely sharp cutting filter such as the Wratten 70, the cutoff of which is well beyond the sensitivity range of a normal panchromatic film. The use of the extended red sensitization in conjunction with the 70 filter gives a red filter separation that is for all practical purposes perfect, thereby achieving a considerable increase in saturation especially for the reds and those colors in which red plays a part.
The following will describe briefly the application of the film in the production of Ansco Color motion pictures. Fig. 4 shows graphically the steps involved. The scene is photographed on Type 735 film. This is then copied on Type 155 film using a printer equipped with registration pins and capable of skip-frame printing. It will also be advantageous if the printer has a synchronized filter wheel so that the red, green, and blue filter exposures can be made on successive frames in one printing operation. However, the latter is not essential and the black-and-white film can be printed three times and still obtain the images successively by techniques well known in optical printing. At this stage, fades, lap dissolves, and other special effects can be included. The type 155 film is then developed to a gamma of approximately 0.5 to 0.6 in a buffered borax developer of the type used for variable-density sound film. The resultant film now is a conformed master containing all of the effects and with the color records as successive-black-and-white frames. It will serve as protection against damage to the original color transparency since it is a good permanent record. The latter point is an important one since present-day color originals, if not stored under the proper conditions, may be subject to fading.
To convert the separation negatives to color prints they are first printed on standard black-and-white duplicating positive film on the same optical equipment as used for making the negatives. That is, the one-strip separation negatives are now converted into separation positives using three separate films. The final step is to print the separation positives onto the Type 732 Ansco Color printing film. This can be done in a standard contact step printer equipped with registration pins by printing the Type 732 film three times, each time using the appropriate separation positive and filter. It is also possible to make the black-and-white positives by contact from the negatives. In this case, release printing would have to be made on a skip-frame printer. In either case, the result is a release print which is equal to a direct print from the original in color reproduction.
Because of its unique feature of maintaining the same gamma for all three filter exposures over a wide range of gammas, Type 155 can also be applied to the direct photography of animated pictures or used for background projection and process photography. Those skilled in motion picture methods will immediately recognize other important uses of this new film in the production of color motion pictures.
1 H. H. Duerr and H. C. Harsh, “Ansco Color for Professional Motion Pictures,” Jour. Soc. Mot. Pict. Eng., vol. 46, pp. 357–368; May, 1946.
Mr. S. P. Solow: Could you tell us to what extent different colors produce different gammas on ordinary film?
Mr. H. C. Harsh: Usually the blue separation is softer than the others, and requires about two minutes more development time to bring it into equal gradation. They vary on the red and green. One time the green might be a little different from the red and vice versa, depending on the film.
Mr. Herbert Griffin: Suppose your color original does not have the same red, green, and blue printing contrast, then how do you proceed?
Mr. Harsh: This film was designed especially for use with Ansco Color Type 735 which gives a balanced print on Type 732 printing film. We are using it only as an intermediate step. We want to retain the same gamma relation in our black-and-white dupes as we have in making a direct print. Ordinarily, in using a black-and-white separation film, you would proceed from a well-balanced original. In the case of a faulty original the development times for the black-and-white positive could be varied for correction without interfering with the one-strip negative.
*Presented October 21, 1946, at the SMPE Convention in Hollywood.”
(Harsh, H. C.; Friedman, J. S. (1948): New One-Strip Color-Separation Film in Motion Picture Production. In: Journal of the Society of Motion Picture Engineers, 50,1, pp. 8–13.)
“In 1946 Ansco announced a new monochrome film designated Ansco One-Strip Color-Separation Film, Type 155. It has the special property of giving identical gamma for red, green and blue recordings in the same development time. This is equally true for low contrast (0·50) and for high contrast (2·00). The cyan dye used in Ansco Color Film has a maximum absorption at approximately 6,800 A. This enables the use of a Wratten No. 70 filter to yield a red separation that is nearly ideal.
The following technique is employed. The scene is photographed on Ansco Color Film Type 735. This is then copied on Type 155 film using a printer which is equipped with registration pins and capable of skip-frame printing. At this stage fades, lap dissolves and other optical effects can be introduced. The Type 155 film is then developed to a gamma of approximately 0·65 in a buffered borax developer of the type used for variable density sound film. The resulting film is now a conformed master containing all the effects and with the colour records as successive black-and-white frames. It serves as a protection against damage to the original.
To convert the separation negatives to colour prints, they are first printed on standard black-and-white Duplicating Positive film on the same optical equipment for making the negatives, and developed to a gamma of approximately 1·4. The final step is to print the separation positives on to Type 732 film three times through the appropriate filters. The result is claimed to be a release print equal in colour reproduction to a direct print from the original.
This film has been designed to solve the specific problem in the case of monopack materials of avoiding the loss of saturation when it becomes necessary to make second, third or fourth generation duplicates which will yield good release prints.”
(Cornwell-Clyne, Adrian (1951): Colour Cinematography. London: Chapman & Hall, 3rd. ed., on pp. 395–397.)