Hey, so gamma is not a logarithmic response. You claim that the delta you use in Figure 2 is a ratio, but your code, https://github.com/johnnovak/johnnovak.site/blob/master/blog... uses a fixed power. These are not the same thing.

f(x+eps)/f(x) ~= eps f'(x)/f(x) + 1

f(x) = x^2.2 f'(x) = 2.2x^1.2

f(x+eps)/f(x) ~= 1.2 eps/x + 1

Human response to light is not particularly well-modeled by a logarithmic response. It's --- no big surprise --- better modeled by a power law.

This stuff is confusing because there's two perceptual "laws" that people like to cite: Fechner-Weber, and Stephens's. Fechner-Weber is logarithmic; Stephens's is a generalized power-law response.