|
Composite video (one channel) is an analog video transmission (without audio) that carries standard definition video typically at 480i or 576i resolution. Video information is encoded on one channel, unlike the slightly higher-quality S-video (two channels) and the even higher-quality component video (three or more channels). Composite video is usually in standard formats such as NTSC, PAL, and SECAM and is often designated by the CVBS initialism, for color, video, blanking, and sync, or simply as video. == Signal components == A composite video signal combines on one wire the video information required to recreate a color picture, as well as line and frame synchronization pulses. The color video signal is a linear combination of the ''luminance'' of the picture, and a modulated subcarrier carries the ''chrominance'' or color information, a combination of hue and saturation. Details of the encoding process vary between the NTSC, PAL and SECAM systems. The frequency spectrum of the modulated color signal overlaps that of the baseband signal, and separation relies on the fact that frequency components of the baseband signal tend to be near harmonics of the horizontal scanning rate, while the color carrier is selected to be an odd multiple of half the horizontal scanning rate; this produces a modulated color signal that consists mainly of harmonic frequencies that fall between the harmonics in the baseband luma signal, rather than both being in separate continuous frequency bands alongside each other in the frequency domain. In other words, the combination of luma and chroma is indeed a frequency-division technique, but it is much more complex than typical frequency-division multiplexing systems like the one used to multiplex analog radio stations on both the AM and FM bands. A gated and filtered signal derived from the color subcarrier, called the burst or colorburst, is added to the horizontal blanking interval of each line, excluding the vertical sync interval, as a synchronizing signal and amplitude reference for the chrominance signals. The burst signal is inverted in phase (180° out of phase) from the reference subcarrier. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Composite video」の詳細全文を読む スポンサード リンク
|