The art of sound pictures (1930)

COLOR 245 filters had to be put in front of the film again in the same order that the original filters were passed over the lens of the camera. In other words, in the projection machine, when the red picture was illuminated, a red color filter had to be placed in front of it. When the green picture was shown, a green filter was swung into position, and when a blue picture came into line with the lens, a blue filter was similarly interposed between the picture and the screen. In this way, red, green, and blue pictures of the same object or the same movement of an object were thrown on the picture screen in rapid succession. At this point, we must mention another psychological law of color. Whenever the human eye is exposed to color, it goes on seeing that color for about one-eighth of a second after the color itself has been removed. We may call this the persistence or inertia of color vision. Because of this fact, as you can see, the motion picture audience who look at the red picture thrown on the screen would continue actually to see that picture for about one-eighth of a second after the color on the screen had changed. Thus, they would still be seeing the red picture when the green picture appeared. In the same way, they would continue to 'see both the red and the green picture when the blue picture appeared. Thus, the human eye itself would automatically blend the three differently colored pictures into a single unit experience of color. In short, the human eye had to serve as a color mixer for this kind of colored motion picture. The three separately colored pictures were, in fact, mixed in the human eye, with the result that the original natural colors of the object would be experienced by the