Your eyes are not linear sensors. They perceive much smaller differences in dark/low luminance areas and in light/high luminance the differences must be much greater for us to perceive a difference. By a happy coincidence the phosphor in a CRT works the opposite way in that an incremental change in voltage has a much bigger effect on output luminance at the bright end of its range than in the light end of the range. The response curve of voltage in to luminance is called the gamma and is governed by the following formula:
Where I is light intensity in the range 0-1.
Vs is input voltage in the range of 0-1.
y (actually the Greek character gamma) is the gamma
In notations of color space luminance (linear light output) is denoted as a Y and the luma or gamma adjusted light output is denoted by Y’. In the RGB space R,G and B represent the luminance of each of there respective primaries and R’,G’ and B’ represent the luma of each primary. It should also be noted that the correct notation and terminology is rarely used making color space and color theory very confusing.
Great, what does this mean to me?
The net result is that all immage formats, except a few very special ones, have a gamma correction built in. The idea is that in the 8 bit per primary color space the difference between 0 and 1 should be perceived as the same change as 254 to 255.
It is also a form of perceptually lossless compression. A voltage range that is divided into 255 even steps (Represented by 8 bits) that has a gamma of 2.2 would take 16384 even steps (14 bits) linearly represented to have the same perceptual luminance resolution.
Blender Gamma Correction
I have not looked into it but I would guess it is an adjustment over its default gamma.
Preparing content for TV.
TV in the US uses 2 different color spaces IUT-BT.601 for NTSC and IUT-BT.709 for ATSC. Each one of these color spaces defines a white point/color temperature, gamma and formula to convert from the Y’UV to R’G’B’. The Y’ Value ranges for 16 to 235 and the U and V range for 16 to 240. When you produce you final output you need to be sure that the color conversion formula is set up to take as an input R’G’B’ values in the range of 0 to 255 and output Y’ form 16 to 235 and U,V form 16 to 240. While it is possible in NTSC to have values of Y’ less than 16 these values are considered blacker than black and are only useful in test signals.
I use and would recommend AVISynth http://www.avisynth.org/ as a frame server to my encoder applications.