Also, this what happens if I don’t multiply the ratios back at the output of filmic (filmic’s defaults with auto-set black/white exposures, so max RGB norme):
Smooth.
Now, look at the ratios:
Non-smooth.
Now, change the norm to luminance:
You have to recover highlights at least to get a color consistent with the neighbourhood. That magenta is simply too opinionated in terms of its chroma, considering how off the hue is to begin with.
The reason v5 hides it better is that the ratios are massaged to degrade progressively to { 1, 1, 1 } when we reach display white. Problem is that this “desaturation” is not hue-linear… (pick your poison).
This how the ratios = RGB / max(RGB) look like after only the filmic HL’s reconstruction:
Note that the reconstruction is not smooth at the edges of the clipped region because it’s a stupid 1st order in-painting, so the guided laplacian essentially inherits the same logic but at the 2nd order, which better respects gradients and output smoother results.