The art of sound pictures (1930)

244 THE ART OF SOUND PICTURES screen are capable of producing all the natural colors. If we can photograph all the red, then all the green, and finally all the blue in a given object, we have a complete physical color record of the object photographed. To reproduce its original natural colors, then, we need only to combine these three separate color photographs in precisely the same proportion of light intensity as they existed in the original object. The human eye then sees it on the motion picture screen in its original natural color by means of this recombination. The first attempts at color photography made use of this principle. Three different pictures of the same object were taken in rapid succession — first red, then green, then blue. The pictures were made by passing colored glass or a colored gelatine slide, called a “color filter,” between the lens of the camera and the sensitized film. The process took place exactly as though the photographer first held a piece of red glass behind the lens and snapped a red picture of the object, and then photographed a green and a blue picture of the same object, using green and blue glass behind the lens. In the motion picture camera, of course, the film was cranked in such a way that three successive frames were exposed to the lens at precisely the same moment that the corresponding color filter revolved between the lens and the film. As a result, each object or movement of an object recorded on the motion picture film required three separate frames to complete the color record. This meant that the film and camera shutter had to be moved very much faster than in ordinary motion picture photography. When this same film was run through a projection machine, in order to throw the colors on the screen, color