OTHER TECH

Q. I was a printer for many years, and in our business we always worked with the primary colors of red, blue, and yellow to derive other colors. Why does the television industry use red, green, and blue as its primary colors? Jack Phillippe Yeadon, PA

A. David Ranada, Technical Editor, says: You're correct that printing, painting, and other "reflected-light" media use different primary colors than "emitted-light" sources, such as video and film. But the actual primaries for printing are cyan, magenta, and yellow, which, with black thrown in, represent the "CMYK" color model that's commonly used to derive nearly all printed colors. This is the only scheme that produces a lifelike range of color on surfaces such as paper.

It's actually easier to explain why red, green, and blue (RGB) were chosen for video, because there's a biological basis for it. If you took a "frequency response" of the color-sensitive cells in the human retina (the "cones"), you'd find that they fall into three clusters, with the peaks of their sensitivity roughly corresponding to the red, green, and blue areas of the visible spectrum. This is why we need at least three primary colors to be able to create the illusion of full-color reproduction (a species with four peaks in its retina-cell responses would need at least four). It's also why mixing these three together provides for the widest possible range of colors. So an RGB color system is the most logical and simplest to do the job.

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