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Scopes hdr scale - #22662
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nicknezis wants to merge 2 commits into
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Scopes hdr scale#22662nicknezis wants to merge 2 commits into
nicknezis wants to merge 2 commits into
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The scopes only had an SDR scale: the waveform tops out a little above 1.0 and the histogram bins 0 to 1, so the headroom of an HDR edit was squashed against the top and could not be judged. Add a button that cycles the histogram, waveform and RGB parade between the SDR scale, a PQ scale and an HLG scale. On an HDR scale the preview is converted to linear Rec2020 and encoded as the BT.2100 signal an HDR export would carry, using the shared transfer functions in common/hdr-transfer.h. PQ is gridded in nits from 1 to 4000 with 203 nit reference white marked; HLG in percent of signal with reference white marked at 75%. The vectorscope and split view keep the SDR path. The choice is kept in conf. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_018Hf5bYk6AYsiHXNmKFEr15
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_018Hf5bYk6AYsiHXNmKFEr15
This was referenced Oct 17, 2026
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scopes: PQ and HLG scales for histogram, waveform and parade
Branch:
nicknezis:scopes-hdr-scaleSummary
The histogram, waveform and RGB parade only show an SDR scale, so you can't see where highlights will land in a PQ or HLG export. A new button in the scopes cycles between SDR, PQ and HLG. In HDR modes the scope converts the preview to linear Rec.2020 and plots the PQ or HLG signal that an export would carry. The PQ scale is marked at 1, 10, 100, 203, 1000 and 4000 nits, and the HLG scale at 25, 50 and 75% signal. Reference white (203 nits, or 75% HLG) is drawn dashed. The button is hidden for the vectorscope, and the choice is stored in
plugins/darkroom/histogram/hdr_scale.Referenced issue
Related: #17710
Checklist
src/tests/integration/where the pixelpipe is touched, ordarktable-clias a headless smoke test._(), new preferences are registered indata/darktableconfig.xml.in.RELEASE_NOTES.mdentry was added (only needed if fixing an issue in a release). Do not reference GitHub issues.Test instructions
Done so far: every commit builds, and all modes were checked in the GUI under Xvfb on Linux.
Not verified: macOS and Windows. The scopes read the preview's display-profile output (
_scope_processinsrc/libs/histogram.c), so with an ICC display profile that clips above 1.0, the HDR scales would show that clip and not the export signal.AI assistance
The code, commit messages and this description were written with Claude Code. I reviewed the diff.