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Hi Andy,

This seems like a resolution issue in phisto. Comparing phisto to pcond, I noticed that pcond sets an upper limit of 1e5 for luminance (5.0 in the log luminance histogram file), then uses 100 bins between this maximum and the minimum (which can't be under 1e-7). The current phisto script looks at the minimum but not the maximum, so your sun throws the whole thing off and we end up with less resolution in the statistics gathering.

I don't know why this hasn't come up before, but the easiest fix is to increase the resolution of the histogram produced by phisto. That way, pcond doesn't generate gaps in its internal histogram, which can cause steps (banding) in the resultant tone-mapping curve.

I have checked in a fix to phisto that seems to resolve this issue.