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.
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.