QuoteIf you like, can you share an .exr which exhibits this behaviour?
Hi Martin -- The EXR file is a commercial file from Megascans . . . but I bet it wouldn't be hard to make a generic file that would trigger the error. Now, I think the error is benign (or it simply cancels any displacement or bump). At any rate it's probably not related to the artifacts as I first thought. But let me get back to you.
QuoteThis could an image filter problem where a sharpening filter produces negative pixel values. Try using the Cubic B-Spline filter, it might help.
Pokoy -- This makes sense. I can see how a filter might be the culprit. I've always used Mitchell-Netravali.
For post effects, Soft Clip Effect, Compensate Soft Clip, and Contrast (0.25) are all enabled. I believe these are the default settings. (Up until recently I always rendered straight to EXR and did not worry about the Tonemap tab. But I've started rendering to 16-bit TIFF because they import very nicely into Lightroom. So now, it seems, these settings are applied.)
It's probably best to try one thing at a time. I'll start by setting the filter to Cubic B-Spline.
Thanks!