The art of sound pictures (1930)

242 THE ART OF SOUND PICTURES time, we may briefly describe the principles underlying both types, ADDITIVE PROCESSES The word additive, as used in this connection, means that other colors are added to white in the process of photographing and reproducing color. The word subtractive means that white, or some of the components of white, are subtracted from the colors which are left on the film and which are subsequently shown through the projecting apparatus on the screen. The general method of adding colors to white on the film consists of passing color filters between the camera lens and the film in such a way that only rays of a certain color are permitted to pass from the object to the film at any given moment. To understand color photography, you must first acquaint yourself with certain simple preliminary facts about color itself. There are about 230 separate colors. But if we arrange this whole series in the form of a circle or a rectangle, we find in it four high spots, or “nodal points” — red, yellow, green, and blue. Each of these gradually blends into the color next to it in the series, forming intermediate colors, which in turn change into the next of the nodal colors. This psychological view of color must be carefully distinguished from its physical description. Physics describes colors as wave lengths of light, the longest of which lie at the red end of the spectral series, and the shortest at the blue. Different wave lengths of light falling on the retina of the eye produce different color experiences in the brain. Three of these light waves differently combined are capable of producing the entire 230 color