International photographer (Feb-Dec 1929)

September, 1929 The INTERNATIONAL PHOTOGRAPHER Thirty-one Qolor -BY EMERY HUSE, Motion Picture Film Department, West Coast Division, Eastman Kodak Co. A year ago the Motion Picture Industry generally, and Hollywood particularly, was just entering seriously the field in sound photography. At the present moment color photography, or rather the anticipation of it, is in the minds of all motion picture producers. It is the desire of the author of this article to call to the attention of those interested in the general subject of color some of the underlying physical facts of color photography together with an historical resume of what has been done in this field. One must first go back appreciably and review somewhat some of the fundamental facts in the study of light. From the physicist's point of view, the study of light is a study of activity which originates in luminous bodies and causes the sensation of vision when it enters the eyes. There are two distinct phases in the study of light, first, QUANTITY which deals with differences in brightness and, second, QUALITY differences are classified under the phenomena of color. Sir Isaac Newton made many advances in the study of light and his many experiments lead him to believe in a certain hypothesis. Newton was the first to get a clear idea of color, which idea he attained through a study of glass prisms. He was the chief advocate of the corpuscular theory which maintained that light consisted of very minute weightless material particles. It is rather a strain on the imagination to think of material corpuscles flying with enormous speed through a solid substance like glass with so little hindrance as glass seems to offer to the passage of light. It is also somewhat difficult to explain the phenomena of reflection and refraction under this theory. Color was accounted for by differences in size and shape or in some other characteristics among ths corpuscles. The newer, and at present accepted, theory considers light as made up of waves acting in much the same way awaves produced by disturbances in a body of water. Under this theory there is little difficulty in explaining reflection and refraction. Furthermore, color is accounted for very simply by the supposition that differences in color correspond to differences in the length of (he waves. The medium in which ihese waves act is termed "ether" which means that empty space has properties other than mere extension; properties that enable disturbances carrying energy to pass through, the passage requiring finite time. We know from absolute measurement that light travels at a rate of approximately 186,000 miles per second. Prior to actual work on the recording of color photography it is necessary to consider somewhat the theories of color vision. One, that of Young and Helmholtz, is a purely physical theory, while another, that of Hering, is psychological. These two theories are given consider able weight. The Young-Helmholtz theory considers that the retina consists of three distinct sets of nerve fibers, each giving a single sensation, one set a red sensation, another a green and the third a blue-violet sensation. The Hering theory deals with three primary sensations and postulates certain contrasts caused by chemical change^ under the influence of light in three hypothetical fluids. Our present existing knowledge teaches us that there are three primary colors and these three colors are blue, green and red. Newton at one time advanced the theory that there were seven primaries. However, based upon work by physicists and psychologists, it is pretty well established that blue, green and red are considered universally as the three primaries. Three-color photography is based on the fact first discovered by Clerk Maxwell about 1860 that all colors can be matched by a mixture of the three primary colors: red, blue, and green, if the proportion of these constituent colors be rightly chosen. The work of Maxwell was based on the discovery by Young in 1807 that all color perception is the result of three fundamental color sensations singly or in various combinations and proportions and it is safe to say that the work of Maxwell is the foundation upon which three-color process of natural color-photography is based. Prior to Maxwell's time such men as Seebeck, Becquerel and Daquerre did quite a little experimental work on the reproduction of color but they were handicapped by the fact that they could give only a partial reproduction and had no way to fix their images. Later on natural color photography necessitated the use of a light sensitive dye which dye faded out to a colorless substance. A dye is decomposed only by the light which it absorbs, which color is complimentary to its own color. Certain aniline dyes bleach comparatively rapidly in light, hence after three such dyes are chosen so as to form the three fundamental colors, red, green and blueviolet and these are coated on a white surface such as paper in three separate layers and the whole exposed to a colored object, in red light, the blue and green dyes are bleached out leaving the red. In the same way in blue light, blue will be left as red and green are bleached out and in the case of green, red and blue are bleached out, while the colors which are mixtures of these each will be bleached in direct proportion to the amount of the fundamental colors present. Processes based on this principle were conceived by such men as Cros in 1861, Leisegang in 1889, Ives in 1891 and others up until 1910. Despite the apparent simplicity of the process, it has never furnished a satisfactory solution to the problem of natural color photography. It was difficult to secure three dyes having the proper color and of identical light sensitiveness and it was further difficult to prevent further bleaching of the dye after exposure. In 1897 Prof. Lippman, of Paris, devised an ingenious process of color photographv dependent upon the principle of light interference. Lipman's method was to expose a specially prepared finegrained transparent emulsion of silver chloride in contact with a bath of mercury which reflected back into the emulsion, the waves of light which reached it, thus setting up in the sensitive film the phenomena of interference. This process, however, although extremely interesting, was little more than a laboratory experiment from the standpoint of producing photography in natural color. This brings us back to the time of Maxwell who, as previously stated, did the basic work on the principle of threecolor photography. In natural color photography there are two very general classifications, the additive and subtractive processes. As a general statement the additive process of color photography can be summed up in the statement that we start with a colored light from which we produce white by addition. In other words, we take red, green and blue and by an additive method produce a white light. Photographically, this process may be analyzed as follows: The color sensation negative records by density the presence of that particular color in the subject, i. e., the red sensation negative records the red of the subject in terms of greater or lesser density according to the amount of red present in the various portions of the subject. A positive transparency from this negative will reproduce the red sensation by means of its clearer parts. The parts of the subject containing the purest red will be represented by clear glass, those parts with some red by a medium density, while those parts containing no red whatever will be of maximum density. Now if this transparency is viewed in red light it will reproduce the red sensation of the original subject. In a like man Phone GLadstone 4151 HOLLYWOOD STATE BANK The only bank in the Industrial District of Hollywood under State supervision Santa Monica Boulevard at Highland Avenue