Gamma Correction and Luminance Masking

Question

As per Weber's law, delta(L)/L is a constant where L is luminance measured in candela/m2 )i.e. (L2 - L1)/L1. This implies that a small change in lower luminance range (darker) is perceptually much more than a small change in higher luminance range (brighter).

The sRGB images which we have stored are gamma corrected i.e. they first undergo a non-linear transfer function which also partially simulated human perception.

I would like to know what happens to luminance masking after gamma correction? Does Weber law still hold on these sRGB images or are they perceptually uniform i.e. 1 unit of difference in pixel value is same be it in darker region or in brighter region? In other words, is delta(L) constant in gamma corrected images where L is gamma corrected pixel value.

Answer 1

Weber's Law does not apply to sRGB coded values to the extent it does apply to luminance. In other words, sRGB value is closer to being perceptually uniform than cd/m2.

To answer your question, I would NOT expect delta(sRGB coded pseudo-L) to be (even vaguely) constant.

However, keep in mind that both Weber-Fechner and sRGB are coarse approximations to perception. CIECAM02 is a more modern alternative worth exploring.