NTSC Composite Video Signals, and the RS - 170A StandardsPart 6 - The Chroma Burst & the Vectorscope
Since the entire exercize is to time signals so they switch properly, and obtain the correct colors when finished, it would be a good idea if we understood a little more about vectorscopes and the color signal.In order for any color to be correct, it must be in line with a known color. One that never changes. What color is blue. Is it sky blue or navy blue. Perhaps midnight blue? What about white? Eggshell white, or tooth white (and who's teeth are really white anyway?) No we must use a color that never changes. Black. Black is what you see, when you open your eyes in a lightproof environment. For those of you who have had the opportunity to be in a photographic darkroom... you know what black is. And video signal-wise, black is what you see represented on the vectorscope above.  It is the green line along the 0º line on a 360º color scale. Once we start adding color, we see other lines appear on the vectorscope. Observe the pictures to the left, which represent color bars, both on a waveform monitor, and on a vectorscope. Note that there are only 3 true colors, Red, Green, and Blue. All other colors are derivatives of these. For instance, Yellow is a combination of Red and Green. Magenta is Blue and Red combined. Cyan (sky blue) is Green and Blue mixed.The important thing to keep in mind, is that the reference line lines up with the 0º line, and all the colors line up with their appropriate colors in the appropriate places. By the way, it might be interesting, as well as helpful to know that all people are the same color. Yes, American Indians, Africans natives, Oriental and Europeans are all the same color ( with extremely minor variation ). They are simply different intensities of that color. However, no matter who you point the camera at, you will see the same line appear on the vectorscope. I call it " negative Y ", as it is opposite the " Y " line on the vectorscope. Below is a representation of where people should be. If they aren't there, something's wrong!  |
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