TV Tweaks - Part Two: Behind the Numbers

Compared with the "in the lab" box for one of our test reports on, say, an A/V receiver, the lab data for a TV review may seem skimpy. While there aren't a lot of numbers, the ones we do generate can give you a pretty good idea of what to expect from the set - particularly its color reproduction, which is arguably the most important aspect of a TV's performance.

Why is accurate color reproduction important? First, you have to understand that all the colors we see (not just onscreen!) are combinations of the red, green, and blue primary colors (see "The CIE Chromaticity Diagram"). That includes black and white - white is an equal mix of the three primaries, and all shades of gray are simply white at different values of brightness. What all this means is that the images you see on TV, just like those in real life, consist of the primary colors in different combinations, brightness values, and intensities. If the combinations aren't accurate, the images won't look natural.

For a video display to reproduce colors accurately, you need to calibrate it to accurately reproduce white. Ideally, you want your TV's picture to look the same as those on the professional monitors used in postproduction facilities where films get transferred to video. Pro monitors are calibrated to display grayscale values - the luminance range from black to peak white (see "Test Pattern") - as close as possible to the NTSC standard for white, which is based on the color of sunlight on a summer day in the northern hemisphere. Exact definition of that standard gets fairly complicated (again, see the chromaticity diagram), but for all practical video purposes it is equivalent to a "color temperature" of 6,500 K, or kelvins.

Unfortunately, the grayscale on most TVs is factory set for a color temperature well above 6,500 K - usually somewhere in the range of 8,000 to 10,000 K, which lends images an unnaturally bluish cast. When the "color" of white on a video display is wrong, it means the primary colors that make it up are being distorted, so all of the resulting images will not only look unnatural or exaggerated but also very different from those approved by a movie's director during the video transfer session.

In The Lab


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