s7habo
November 8, 2022, 1:12am
688
Yes, this is a known issue. I have written a bug report about it:
opened 07:11PM - 08 Sep 22 UTC
closed 12:34AM - 15 Jan 24 UTC
priority: high
feature: redesign
difficulty: hard
bug: pending
no-issue-activity
release notes: pending
**Describe the bug/issue**
If the highlights of the photo are close to the li… mit of dynamic range, the highlight slider of the perceptual briliance grading in the color balance rgb module produces artifacts when a certain threshold is exceeded.
This only happens in the default _darktable USC (2022)_ color space. In JzAzBz (2021) color space the slider behaves as expected.
**To Reproduce**
1. increase the exposure of the photo with exposure module until the highlights are at the limit of the dynamic range.
2. in the color balance rgb module, increase the value of perceptual brilliance in highlights using the highlights slider.
3. After a certain value, the artifacts - wide white spots - appear (see screenshot/video below).
**Screenshots**
**Screencast**
Short demo:
https://user-images.githubusercontent.com/38165484/189202459-4b598eb2-263c-421e-ba1c-e04402929b3e.mp4
**Platform**
_Please fill as much information as possible in the list given below. Please state "unknown" where you do not know the answer and remove any sections that are not applicable _
* darktable version : 4.1.0~git272.5a1a1845-1
* OS : Linux
* Linux - Distro : Ubuntu Studio 22.04
* Memory : 31,3 GiB
* Graphics card : NVIDIA GeForce GTX 1070/PCIe/SSE2
* Graphics driver : 470.141.03
* OpenCL installed : yes
* OpenCL activated : yes
* Desktop : KDE-Plasma-Version: 5.24.6
**Additional context**
I can't say for sure, but I suspect that this problem may be related to the
https://github.com/darktable-org/darktable/pull/12233
since this behavior appeared after that commit.
The temporary solution to this is to turn off filmic highlight reconstruction (quoted from flannelhead’s post):
“[…] Turn the threshold all the way up to 6 EV and transition slider all the way down to 0.25. At least with those settings I could no longer reproduce this sort of artefacts. […]”