The international photographer (Jan-Dec 1935)

Sixteen The INTERNATIONAL PHOTOGRAPHER May, 1935 Eastman Kodak Company Announces Kodachrome Process ( The following material on the Kodacltrorne process was prepared by Dr. G. E. Kenneth Mees, vice-president of the Eastman Kodak Company in charge of research and development.) RAW FILM BLUE SENSITIVE EMULSION GREEN " -!!__ Ht^ RED " ':r~~~ COLOR POSITIVE ^-YELLOW IMAGE — MAGENTA IMAGE "—BLUE-GREEN IMAGE SAFETY FILM SUPPORT ANTIHALATIONBACKING CROSS-SECTION OF KODACHROME FILM From the very beginning of photography, experimenters have tried to make photographs in color instead of in monochrome, and numberless processes have been put forward for that purpose. The ideal process would he one in which the color picture would be as easy to take and as certain in result as the monochrome picture is; hut until now no color process has approached that ideal. The new Kodachrome process, so far as the photographer is concerned, not merely approaches but realizes that ideal. It is as easy to take 16-mm. color pictures by the Kodachrome process as it is to take 16-mm. black and white pictures, and the percentage of good results obtained is as high. All practical processes of color photography depend upon the division of the light into three components, red, green, and blue-violet. Pictures are taken by these three components and are then combined by some method in order to give the finished color picture. Color processes are divided generally into two classes: the additive processes and the subtractive processes. In the first, the three components are combined by direct addition of colored images; in the second, the three components are combined by printing each negative in a color complementary to that which was used in taking, and these colored prints are then superimposed. In the classic experiment in which Clerk Maxwell demonstrated the additive process of color photography at the Royal Institution, he showed three pictures of a colored ribbon taken by light of the three primary colors, and he projected positives from his original negatives in superposition upon a screen, each of the positives being projected through a color filter of the same color as that used in taking the negative. With modern materials and filters, this method will give an excellent reproduction of a colored object. It requires very complicated apparatus, however, and is obviously a clumsy method of obtaining a color picture. Another type of additive process is that which is termed the "screen-unit process." In this, a screen is used over the whole area of the film, which is composed of very small color units — red, green, and blue. A photograph is taken through the screen and is thus split up into tiny areas, each of them taken through one of the three preliminary filters. On projection, these areas cover the entire picture with little spots of colored light. If a red object be photographed, for instance, the film will be fully exposed behind the red units of the screen but will not be exposed behind the blue and green units, and after reversal, the green and blue units will be blocked out by the black deposit of silver, while the red units will be projected in full brilliancy and will thus produce a red area on the screen corresponding to the red object which was photographed. This process has the advantage that the film can be used in any camera, exposure can be controlled in the ordinary way with a diaphragm, and the film can be projected in any projector. Its practical disadvantages are confined to the screen pattern, which is apparent on projection, to the absorption of light by the screen unit, which involves a considerable loss in brightness, and to the cost of the special screen-unit film. In the Kodacolor process, which has been very successful for amateur cinematography, the color separation is obtained optically. In the lens of the camera is placed a multiple-color filter composed of red, green, and blue units; and the tiny lenses embossed on the film make multiple images of these three units on the film emulsion. In projection, the same three filters are placed on the lens and a color picture is obtained on the screen. A multi-color image in the form of microscopic colored strips is projected and reproduces the colors of the original. Turning to the subtractive processes, if the three negatives are printed as images in colored dye — the red negative as a blue-green image, the green negative as a magenta image, and the blue negative as a yellow image — and these three color images are assembled in register on top of each other, a color picture will result. It will be seen that a red color can be obtained either by the projection of light through a red filter on the screen, as in the additive processes, or by the projection of the light through successive magenta and yellow images, the superposition of the yellow on the magenta pro ducing red. In the same way, a green image can be obtained by putting a blue-green one on top of a yellow one, and a blue-violet image can be obtained by putting a blue-green image on top of a magenta one. In working the subtractive processes, the three negatives may be taken just as for the additive process, and then positives are printed in some way which enables them to be made of a colored material, the commonest being to make them by printing in bichromated gelatine. By this process, the three negatives can be printed in colored dye, the picture taken through the red filter being printed on gelatin dyed blue-green, the one taken through the green filter on gelatin dyed magenta, and the one taken through the blue filter on gelatin dyed yellow. If the three are superimposed in register, the resulting transparent color picture will reproduce the colors of the original subject. Subtractive processes of this kind are being used successfully for the projection of theatrical motion pictures in color, but it is clear that to make one print only by this method, as is required in amateur cinematography, ICTER^ In (/QprlJ-QOiJg Use ^Trecls in Daytime-F^ ScenesDiffused. F^ecjs.arcd many ^tt?er effects With any \7amera " In any Ulimate GcorciG H. ScReibe ORIGINATOR OF EFFECT FILTERS 1927 WEST 78th ST. LOS ANGELES. CAL Please mention The International Photographer when corresponding with advertisers.