Popular Science, syyskuu 1929
By Alden P. Armagnac
Color television is here, at least in the experimental stage.In the darkened auditorium of the Bell Telephone Laboratories in New York City the other day, a young woman wearing a colored dress sat before a cabinet of frosted glass, part of a new radio vision transmitter developed by Dr. H. E. Ives and his associates in the Laboratories. A narrow beam of light from a powerful are lamp flickered across her face and figure so rapidly that it seemed to observes as if she were bathed in a steady glow of light.
At the opposite side of the auditorium, in a separate chamber, Dr. Ives peered into a telescopelike window. Through a frame scarcely larger than a postage stamp he saw the young woman, startingly likelife, with the color and pattern of her costume perfectly reproduced. Now she held up a ball of yarn, and its crimson hue was instantly visible in the peephole receiver. Other observers took turns at the magic window. They saw, in turn, an American flag, the Union Jack of Britain, a flowerpot of geraniums, each of the objects, in its distinguishing colors.
In this first demonstration of transmitting and receiving instruments for television in color, the images were sent by radio across the auditorium. The feat was accomplished by a modification of the principles on which all television - the art of seeing moving objects at a distance - is based. Suppose a beam of light falls on a bright object, and, reflected, illuminates an electric "eye," or photo-electric cell. The light permits electric current to flow through the cell. This current, transmitted by wire or radio, will light another lamp in a "receiving" television machine. But if the original beam of light is trained upon a dark object, little or no light is reflected. The electric cell does not pass a current. At the receiving end the lamp does not light.
In television the dirst beam of light, from an arc lamp in the transmitter, constantly zigzags back and forth across the face of the subject. Similarly a beam from the lamp at the receiving end is made to zigzag, exactly in step with the other, across a screen. So rapidly do the beams of light scan the entire picture, a streak at a time, that you seem to see the whole scene at once, recreated in black and white.
There were seemingly insuperable obstacles that stood between "black-and-white" and "color" television. Dr. Ives and his engineers conquered them all by inventing first, an electric eye sensitive to light of any color (most electric eyes are color-blind to red); then lamps that would glow in other colors than the pinkish-red of a tube filled with neon gas; and finally a way of transmitting and combining three pictures of a distant scene at one time instead of just one.
Photographers and color engravers know that with only three so-called primary colors it is possible to reproduce all the hues of a given scene. They make three pictures, each through a "filter" of glass or gelatin stained with one of those colors, of the colored object to be reproduced. When the three pictures are combined the object appears in its original, blended colors.
This same method now is applied to television. A girl, for example, sits before a cabinet, a beam from an arc light coursing over her. Behind panes of frosted glass are twenty-four electric "eyes," silently watching. Fourteen of them, sceened by panes of red-stained gelatin, are picking out the red spots in her dress and the tint of her cheeks. Eight others with green "filters" record the green pattern in the fabric, while two others with blue filters keep tabs on her blue eyes and anything else of a bluish tint in the scene. All three impressions are broadcast continuously and simultaneously, but on different radio channels or wave lengths.
At the receiving station three radio receivers, properly tuned, pick up the separate impulses of the red, green, and blue pictures. Newly devised lamps filled with argon gas reproduce the green and blue light with the aid of colored screens of those colors. A conventional neon lamp with a red filter used in front of it supplies the red parts of the picture. Through partly-transparent mirrors, the three lights are combined in a single beam.
The net result is a moving pencil of light that changes color, like a chameleon, to match the color of a spot touched by the arc lamp's beam in the sending machine.
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