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I'm just getting started with Darktable 3.0.0 processing some RAW files out of my Canon 6D MkII.

One odd thing I noticed is that some of the modules seem to create hot pixel-like "sparkle" artifacts when using them. Here's an example:

dark table hot pixels

This particular example comes from using the "Haze removal" module and pushing the strength upwards. Below about 0.10, they seem to disappear, but I've not checked everywhere. I've also seen this using the equalizer module. These artefacts persist even when exporting to PNG or JPEG.

Is this a bug? Or am I using it wrong, and it's an artefact of something else?

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This sort of bug is usually caused by some computation getting truncated to fit within the range that can be represented by whatever data type they are using — likely an integer over/underflow, or perhaps an improper use of unsigned integer values at some point in the computation. It is almost certainly a bug, though it may or may not be an easy bug to fix, depending.

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  • \$\begingroup\$ darktable computes in 32 bits floating point. \$\endgroup\$
    – Aurélien Pierre
    Jan 5, 2020 at 17:17
  • \$\begingroup\$ The other possibility is that it is using an inappropriate color space and multiplying by out-of-gamut colors or other similar out-of-gamut issues: ninedegreesbelow.com/photography/… \$\endgroup\$
    – dgatwood
    Jan 6, 2020 at 8:01
  • \$\begingroup\$ darktable uses unbounded Rec 2020 as a default colour space, and the haze removal module works in linear camera RGB unbounded too. \$\endgroup\$
    – Aurélien Pierre
    Jan 8, 2020 at 19:40
  • \$\begingroup\$ Any time you're converting between color spaces like that, there's the potential for bad things happening. This is why pipelines probably should stay in a single color space from end to end. Obviously, I have no idea if that's actually the problem, though. \$\endgroup\$
    – dgatwood
    Jan 8, 2020 at 21:42
  • \$\begingroup\$ @AurélienPierre at some point the result has to be converted back to 24-bit integer RGB for display, that might be where the problem lies. \$\endgroup\$
    – Mark Ransom
    Jun 4, 2020 at 17:20

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