The following diagram illustrates how all of this fits together: Fortunately this second step (the “display gamma”) is automatically performed by your monitor and video card. In other words, the purpose of gamma encoding is for recording the image - not for displaying the image. This impacts how we perceive brightness.Ī gamma encoded image has to have “gamma correction” applied when it is viewed - which effectively converts it back into light from the original scene. In dark situations, our rods dilate our pupils so we can see better. The larger (more dilated) our pupils are, the more light enters our eyes. If images are not gamma-encoded, they allocate too many bits or too much bandwidth to highlights that humans cannot differentiate, and too few bits or too little bandwidth to shadow values that humans are sensitive to and would require more bits/bandwidth to maintain the same visual quality.Ĭones manage color receptivity, rods determine how large our pupils should be. The human perception of brightness, under common illumination conditions (not pitch black nor blindingly bright), follows an approximate power function (note: no relation to the gamma function), with greater sensitivity to relative differences between darker tones than between lighter ones, consistent with the Stevens’ power law for brightness perception. So, one needs to correct them, therefore the gamma correction function. (they are not linear)ĭifferent display devices (monitor, phone screen, TV) do not display luminance correctly neither. Our eyes, different camera or video recorder devices do not correctly capture luminance. In theory this should flatten back to 1.0 gamma. – System or Viewing Gamma which is the net effect of all gammas when you look back at a final image. – Display Gammas encoded in hardware and/or viewing time Generally Gamma is just about defining relationships. Basically, gamma is the relationship between the brightness of a pixel as it appears on the screen, and the numerical value of that pixel.
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