Moving Picture News (Jan-Jun 1912)

THE MOVING PICTURE, NEWS 13 same result would be obtained were the two cells, each containing one of the solutions, placed in front of one of the lanterns so that the light from the lantern must pass through both solutions. On analyzing, by means of a prism, the light which passes through each solution, it will be found that the yellow solution absorbs and quenches all the rays of the spectrum above the green, and the blue solution all those below the green. Green is the only color which is not absorbed by either substance. Hence, when light is allowed to pass through both substances, either by mixing them in one cell or by placing them in separate cells, one in front of the other, they absorb and quench all colors except the green, and, therefore, the disc on the screen is green. The hues of two colored substances are never blended when the substances themselves are mixed. One of the substances always absorbs and quenches a part of the rays which escape from the other. The Theory of Color Perception. — The theory of color perception at the pr-esent time accepted by nearly all authorities is that of Young modified by Helmholtz, and sometimes called the Young-Helmholtz theory. According to this theory there are three primary color sensations, namely, those of red, green and violet, and all our perceptions of color arise from the combinations of these three. Each minute portion of the retina is capable of receiving and transmitting these three sensations, because it is supplied with three nerve fibrils, one of which is especially adapted for the reception of each of these sensations. One set of these nerves is strongly acted upon by long waves of light, and produce the sensation of red, another set responds most powerfully to waves of medium length, producing the sensation which we call green, and finally, the third set is strongly simulated by short waves, and generates the sensation known as violet. The red of the spectrum, then, acts powerfully on the first set of these nerves; but according to the theory, it also acts upon the other two sets, but with less energy. The same is true of the green and violet rays of the spectrum; they each act on all three sets of nerves, but most powerfully on those especially designed for their reception. Still Pictures in Their Natural Colors Every pictorial representation endeavors to secure the nearest possible approach to nature. Rarely is it possible to give an idea of the nature of an object by simple outline drawing, it is, therefore, shaded to give it the impression of body; and color is introduced to lend life and truth to the representation, color intensifies the illusion just as a plastic representation does. It is certain that the first photographic picture created a desire for photographs in their natural colors, and to secure the colors of the picture as the camera sees it has always been a problem, on the solution of which men have labored since the earliest days of photography. We can divide all experiments in this direction into two groups, first we can prepare light sensitive surfaces which retain the color of the light reflected upon them, which is called the direct method of producing photocromes. The earliest experiments in direct color photography I were originated by Becquerel, Seebeck and Pirtevin. The basis of their experiments is the property which silver sub-chloride possesses to reflect light similar in composition to that which formed it. Lippmann was also one of the pioneer experimenters who did much to perfect the art of color photography. Lumiere deserves great credit in perfecting the autochrom plate which is constructed as follows: Interposed between the sensitive coating and the glass is a thin layer of transparent microscopic starch grains, dyed orange-red, green and violet, spread without overlapping, mixed in such proportion that the layer appears colorless when examined by transmitted light, and absorbs but a small percentage of the light received. The sensitive coating is extremely thin, and made of a special fine-grained panchromatic emulsion. When such a plate is exposed in the camera, the glass side toward the lens, the light, before reaching the sensitive coating passes through the colored starch grains, which act individually as minute screens, each one absorbing all colors but its own. A miscroscopical selection takes place, and after development there is found under each grain a corre sponding spot (reduced silver) of a density proportionate to the amount of color received and transmitted by this particular grain. Were the plates fixed at this stage, the picture when examined by transmitted light, would showonly the colors complementary to those of the original, since the true colors are marked by the black spots beneath the grains. But when the reduced silver is dissolved (in the permanganate solution) the image is reversed. The opaque spot under each grain becomes transparent and transmits colored light precisely of the same hue as the light transmitted by the grain when the plate was exposed in the camera, in other words the color is reconstructed just as it was decomposed during exposure. A special yellow screen must be fitted to the lens in order to equalize the action of the light and compensate for the predominant actinism of the violet and blue rays to which the panchromatic emulsion is most sensitive. A very original idea has been followed by Joly, of Dublin. He uses glass plates with a ruling of very thin transparent parallel lines, about 10 per millimeter. These lines are red, green and blue in color, which order is repeated, and the whole plate appears in transmitted light of a light grey color. If such a glass plate is pressed into contact with a photographic dry plate during exposure, the plate being one which is equallj^ sensitive to all parts of the spectrum, the red rays reflected by the original can only pass through the red lines and affect the plate, which will reduce the silver in development wherever light impressed the plate. The green part of the original will be only imprinted under the green, the blue under the blue lines, whereas, the white will act through all lines. If a positive is made from this negative and viewed in contact with a similar screen, we obtain, when the two plates are in perfect register, a picture of the object in almost natural colors. F. E. Ives' process may be briefly described as follows: By means of a very ingenious compound camera front, three photographic negatives of the object are made by simultaneous and equal exposure from the same point of view and upon the same sensitive plate. The photographic plate is sensitive to all colors of light, but by introducing light filters one of the negatives is made by such light rays only as excite the fundamental red sensation, and in due proportion; another by light rays as they excite the fundamental green sensation: another by light rays as they excite the fundamental blue-violet sensation. From this triple negative a triple lantern slide is made which, although it shows no color, contains such a graphic record of the natural colors that in order to reproduce them to the eye it is sufficient to superpose the three images, one with a red screen, one with a green, and one with blue-violet, by projection with a special projection lantern having three optical systems. The three images, being exactly superposed, appear as one only, in which the natural colors are exactly reproduced together with the light and shade. We now are able to , take up the question as to how motion pictures are reproduced in their natural color b3^ means of light and photography alone. I feel that I cannot explain this better than to quote from the patent specifications of the different experimenters in the field of natural colored motion photography. Specification 3232. February, 1897. Ives, F. E. Several plates, or different portions of one plate, are exposed in succession behind screens of different colors. The screens are mounted in a frame, to which the slide is attached. The frame with the screens are moved after each exposure. A motor maj' be fitted to the apparatus. Specification 21649. October, 1898. Friese-Greene, W. Producing magic lantern slides. Relates to a method of producing negatives by exposing successivelj^ through three colored screens, and then making transparencies from these for projecting in a magic lantern. A rotating screen made up of three colored sectors, representing three primary colors, is rotated rapidly behind the camera lens 7 (see Fig. 2) by means of a belt 12, and pulley 13 and 11. It is stated that the negative (N. B., not negatives) produced will produce a positive transparency, which, when placed in a magic lantern with a similar