Linear to Log2 Transform Correctness

[deggua]

aces-core/transforms/ctl/utilities/ACESutil.Lin_to_Log2_param.ctl

Line 19 in 518c27f

if (lin <= 0.0) return 0.0;

This line doesn't make sense to me, this would result in pure black having the same Log2 encoding as middle grey

I think it makes more sense to handle the singularity and set lg2 = -infinity, which with proper clamping will result in 0 after normalization

float lg2 = (lin <= 0.0) ? -INFINITY : log2(lin / middleGrey);

Nevermind, the original works because it returns the normalized value, I see that now

aces-core/transforms/ctl/utilities/ACESutil.Lin_to_Log2_param.ctl

Line 24 in 518c27f

if( logNorm < 0.0) logNorm = 0;

This line seems incomplete, it ensures the logNorm is >= 0, but there isn't a corresponding condition to ensure logNorm is <= 1

if (logNorm > 1.0) logNorm = 1.0;

i.e. clamp logNorm to [0, 1] so that lin values > middleGrey * pow(2, maxExposure) map to 1

I may just be confused, I'm not a professional, but I've been working with shader code related to color transforms and tonemapping.