Magazine article American Cinematographer

Cinema Workshop

Magazine article American Cinematographer

Cinema Workshop

Article excerpt

THE VIDEO SIGNAL

Motion picture film captures the entire image in one fell swoop. The lens forms the image, the shutter opens, and the image is captured in the film emulsion. So what's new? The point is that all elements of the image are captured by the film emulsion simultaneously and in the same instant. This is not the case with the video process. This difference in image forming technique is the very essence of the principle of television.

Any picture or image is really made up of many "bits of information." In film these building blocks are grains of silver and a newspaper or magazine picture is made up of dots of ink. If a picture is comprised of too few "bits of information", the image will appear coarse and grainy with a lack of fine detail. Ideally, the image should be comprised of "bits" significantly smaller than the finest detail of the picture. The television picture can also be considered to be made up of bits of information, as many as 250,000 in a high-quality image. For simplification, these bits may be thought of as dots that can be black, white, or any shade of gray between, similar to grains of silver on photographic film. (For the time being, only a B & W picture will be considered.)

The lens on the television camera forms the image on the target of the tube in the same manner as a motion picture camera lens forms the image on the film. While the entire image is present on the target of the tube during the "exposure" of one "frame", the image is captured one bit at a time sequentially.

A beam scans the target image looking at each dot of information. Starting at the upper left hand corner, the beam scans horizontally to the right. …

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