The charts labeled “Gamma” show the relationship of the TV’s input signal (electrical) relative to it’s output signal (phosphor or light bulb output). This relates to how bright the display creates an image of various intensities. The gamma of a consumer television is intentionally non-linear so that it can mimic the characteristics of the original camera recording system. The result is linear, but our test signals do not pre-compensate for this camera-recording-characteristic gamma. Therefore, the graph will not have a straight line. In other words, as the video signal starts from 0 percent (black) and gets progressively higher (brighter), the image will get brighter, but slowly at first and progressively faster at higher light levels at a rate of the input to the power of 2.5.

What shape this curve should have is up for substantial debate and depends significantly on the black level and contrast capabilities of the display. The light level of the surrounding viewing environment also affects the qualitative perception of the results. We have printed the system-designated reference gamma of 2.5 as a guide for comparisons. A professional CRT monitor viewed under the same lighting conditions as used in a standardized video post-production facility, such as our reference Sony PVM20M2U broadcast monitor has a gamma characteristic that matches this curve.

A display with a gamma curve that is more linear or more straight than the reference curve (which is common) may appear brighter, or more washed out in dark surroundings, but could be more watchable in a bright room. Similarly, moderately bright scenes displayed on a TV with a curve that’s greater, or more curved than the reference line may seem too dark. Ideally, the curve will be consistent from dark to light and under no circumstance should it flatten out near the top, creating an “S” shape (though this is common). An S-shaped gamma will cause the display to lose detail in bright portions of the image.