GOING FOR GAMMA
In CG the gamma means the power function of how computers encode the colour data, but its past traces back to before the era of computers
Gamma originated from the photochemical era of photography and shows the relationship between the original incoming light values and the darkening of the film emulsion – the density. Thus we can alter the gamma of the final result with different techniques. However the crystals in the film emulsion are nothing to do with maths and their sensitivity to the light isn’t linear nor expressible with the maths power function, which is the gamma value in digital imaging. Additionally the saying is that painting and film-based photography use subtractive colour models. If we put layers of evenly exposed film frames on top of each other and each of them halves the trespassing light amount, then two layers will mean a quarter light, three means one eighth and so on. This is a non-linear multiplicative situation, and not simple subtraction. Summing all of the features of the process, the density of the film becomes more like an S-shaped curve in the function of the exposure level at the capture side, which is not linear but logarithmic.
In video and digital imagingm CRT monitors had special response characteristics to the input signal, the gamma curve – which has to be compensated to more or less have physically-linear gradation at the end. LCD and other contemporary displays adopted this because it is a benefit – there are more digital signal steps in the low and mid-tones than in the highlights, which is in correlation with the sensitivity of the human vision.