Question on the Gamma(mid-tone) value in levels adjustment layer

var input_low   = 0;
var gamma       = 0.46
var input_high  = 255;

var output_low  = 0;
var output_high = 255;

var input = 154;

output = Math.pow((input - input_low) / (input_high - input_low), 1/gamma) * (output_high - output_low) + output_low;

alert(output);

I remembered your avatar from some past and checked you showed up again after nearly 2 years 😉

This is the gamma-compensation function: x ^ (1 / gamma). It uses to describe how human perceives a different values of brightness

* gamma is the coefficient you see in the panel

* all brightness values should be reduced to relative (0-255)/255

for example  = 154 - (154-((154/255)^(1/0,46)*255)) = 85,19

* I don’t know why there is a difference in rounding - most likely Adobe uses a rougher calculation to speed it up. To check, you can try on other values of the coefficients:

0,17: 154 - (154-((154/255)^(1/0,17)*255)) = 13,12

2.76: 154 - (154-((154/255)^(1/2,76)*255)) = 212,41

etc..