S-Video (Separate video) is a video signal that carries video information in the form of two separate signals (brightness and colour). Also known as Y/C. With S-Video, the audio signal is not carried.
S-Video is not suitable for projection. Because S-Video gives very low quality image than VGA. The S-Video input is usually found on older computers. A 4-pin connector fits into a 7-pin jack, but a 7-pin connector won't fit into a 4-pin jack. Also, projectors still have an S-video port.
Standard analog television signals go through various processing steps on the way to broadcast, each of which discards information and degrades the quality of the resulting images.
The image is captured originally in RGB format and then processed into three signals known as YPbPr. The first of these signals is called Y, which is generated from all three original signals based on a formula that generates the overall brightness of the image or luma.
This signal closely matches a conventional black and white television signal, and the Y/C encoding method was key to ensuring backward compatibility. When the Y signal is generated, it is subtracted from the blue signal to produce Pb and from the red signal to produce Pr. To save the original RGB information for viewing, the signals are mixed with Y to produce the original blue and red, and then their sum is mixed with Y to produce green.
Broadcasting a three-component signal isn't any easier than the original three-signal RGB, so additional processing is required. The first step is to combine Pb and Pr to form the C signal for chrominance. Phase and amplitude of the signal represent the two original signals.
This signal is then limited by bandwidth to comply with broadcast requirements. The resulting Y and C signals are mixed together to generate composite video. To play composite video, the Y and C signals need to be separated, and this is difficult to do without adding artifacts.
Each of these steps is subject to deliberate or unavoidable loss of quality. In order to maintain this quality in the final image, it is desirable to eliminate as many encoding/decoding steps as possible. S-Video is one approach to this problem. Eliminates the final mixing of C with Y and then splitting it up during playback.
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