A standard monochrome video signal has additional modulation frequency bands (sidebands) added in order to convey color information. These are the color subcarrier components. Using the color burst as a reference, the ratio of the color subcarrier of the video signal to the burst indicates the intensity of the colors (in PAL and NTSC). Thus, when there are relatively limited color subcarrier components in the video signal, the colors are weak or pale. The system is, in fact, a little more complicated than this since in PAL and NTSC the color subcarrier contains red and blue information simultaneously which must be further processed to RGB by a color decoder in the monitor.The color subcarrier frequency in PAL is about 4.43 MHz and in NTSC it is about 3.58 MHz. Since it resides outside the highest luminance frequency, the relevant usable luminance frequency is limited to about 4 MHz in PAL and to about 3 MHz in NTSC (when using simple analog filters.) The luminance frequency response after separating chrominance from luminance may be much higher when using a digital Comb Filter.
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