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kelannaandClaude Opus 5.5 3bcc265bf6 LR-PREF-DISPLAY: monitor ICC profiles (display colour management)

Previews were always sRGB, which wide-gamut monitors show oversaturated.
Settings > Display > Choose Profile... (and the UI command
app.displayProfile) now shows photos through the monitor's ICC profile,
matrix/TRC or LUT-based.

- codecs: DisplayProfile (moxcms): the display's primaries (colorant tags,
  or measured through the A2B tables of a LUT-only profile), the proxy ->
  device correction (per-channel curve tables for matrix/TRC profiles, a
  CMS transform for LUT profiles) and sRGB <-> display transforms.
- pipeline: DisplaySpace / RenderRequest::display: the per-pixel stage
  renders into the display's primaries and gamut maps into its gamut
  (CPU and GPU: only to_out / out_luma change). Soft proofing's display
  gamut warning uses the display's gamut.
- engine: RenderJob::with_display; display::present converts sRGB
  results (thumbnails, cached previews, embedded JPEGs). Histograms and
  the preview caches stay sRGB; exports are unchanged.
- ui: the loupe, Before, Compare, hover and second window render for the
  display; everything else is converted on the render workers. Settings >
  Display tab, ui.json setting, file picker opening in the system's ICC
  folder.

Tests: profile parsing and transforms (sRGB, P3, gamma 2.2, a synthetic
LUT-only profile, corrupted files), display renders equal 8-bit renders
into the matching output space, sampled histograms, and a headless UI test
of the whole flow. docs/display-profiles.md describes the design.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01WEuxxPyG8t6KcADbZSEAUj

2026-10-09 11:21:09 -07:00

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Display (monitor) profiles

LightCraft can show photos through the monitor's ICC profile, so colours are right on wide-gamut and calibrated displays. Without one, previews are sRGB, which a wide-gamut panel shows oversaturated.

Using it

Settings ▸ Display ▸ Choose Profile… picks an .icc / .icm file (the dialog opens where the system keeps them: ~/.local/share/icc on Linux, ColorSync's folders on macOS, …\spool\drivers\color on Windows). Use sRGB goes back to no profile. The choice is an app setting (ui.json, displayProfile) and applies at once; a file that can't be used is reported there and previews stay sRGB.

Agents and scripts: app.displayProfile {"path": "/path/to/monitor.icc"} ("" or null: none; no path: report only) returns {path, description, kind: "matrix" | "lut", primaries: {red, green, blue: [x, y]}}.

How it works

The loupe renders into the display's gamut. Views (Detail, Before, Compare / Reference, preset and profile hover, the second window) ask the pipeline for a render in the display's own primaries (lightcraft_pipeline::DisplaySpace, RenderRequest::display): the per-pixel stage converts from the working space to the display's linear RGB, gamut maps into its gamut and encodes with the sRGB curve, on the CPU and the GPU alike (only FinishParams::to_out / out_luma change). Colours an sRGB render would clip stay as saturated as the display can show. For a display that is exactly a standard space the result equals an 8-bit render into that space.
Then to the display's device values (lightcraft_codecs::display::DisplayProfile::correct): for a matrix/TRC profile, three 256-entry tables from the sRGB curve to the profile's tone curves (nothing at all when they are the sRGB curve, as for Display P3); for a LUT-based profile, a moxcms transform through its B2A tables. A LUT-only profile (no colorant tags) gets its primaries measured through its A2B tables.
Everything made for sRGB is converted (lightcraft_engine::display::present, on the render workers): thumbnails, cached view previews, embedded camera JPEGs and merge previews.
What stays sRGB: the histogram (of the same sampled pixels, converted back to sRGB), the rendered-thumbnail and view-preview caches (a profile change doesn't invalidate them), exports, and the UI itself.
Soft proofing: the blue "display" gamut warning shows what the monitor can't show, from its profile.
Conversions are relative colorimetric: the display's white is the image's white.

Cost

Measured on a 2-core cloud VM, 2560 × 1707 preview: the tone-curve tables take about 5 ms (single-threaded); converting the sampled histogram pixels a few ms; the sRGB copy for the view-preview cache (full-quality renders only) about 30 ms; a LUT-based profile's correction about 65 ms. Drafts during slider drags skip the full sRGB copy.

Not yet

Picking up the profile the operating system assigns (X11 _ICC_PROFILE, colord, ColorSync, WCS) and following the window across monitors with different profiles.

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