johanels/photoprism
1
0
Fork 0
mirror of https://github.com/photoprism/photoprism.git synced 2025-12-11 16:24:11 +01:00
Code Issues Packages Projects Releases Wiki Activity
Files
19f083c7199b6237ec67aa65204edf1f9f73ca3c
photoprism/internal/thumb/README.md
Michael Mayer 19f083c719 Thumbs: Enhance embedding of ICC profiles based on InteropIndex #5178 
Signed-off-by: Michael Mayer <michael@photoprism.app>
2025-11-23 12:56:58 +01:00

3.0 KiB
Raw Blame History

PhotoPrism — Thumbnails Package

Last Updated: November 23, 2025

Overview

internal/thumb builds thumbnails with libvips, handling resize/crop options, color management, metadata stripping, and format export (JPEG/PNG). It is used by PhotoPrism’s workers and CLI to generate cached thumbs consistently.

Context & Constraints

  • Uses libvips via govips; initialization is centralized in VipsInit.
  • Works on files or in-memory buffers; writes outputs with fs.ModeFile.
  • ICC handling: if a JPEG lacks an embedded profile but sets EXIF InteroperabilityIndex (R03/Adobe RGB, R98/sRGB, THM/thumbnail), we embed an Adobe-compatible profile; otherwise we leave color untouched.
  • Metadata is removed from outputs to keep thumbs small.

Goals

  • Produce consistent thumbnails for all configured sizes and resample modes.
  • Preserve color fidelity when cameras signal color space through EXIF interop tags.
  • Keep error paths non-fatal: invalid sizes, missing files, or absent profiles should return errors (not panics).

Non-Goals

  • Serving or caching thumbnails (handled elsewhere).
  • Full ICC workflow management; only minimal embedding for interop-index cases.

Package Layout (Code Map)

  • vips.go — main Vips entry: load, resize/crop, strip metadata, export.
  • vips_icc.go — EXIF InteroperabilityIndex handling and ICC embedding.
  • icc.go — lists bundled ICC filenames (IccProfiles) and GetIccProfile helper.
  • resample.go, sizes.go — resample options and predefined sizes.
  • thumb.go and helpers — naming, caching, file info.
  • Tests live alongside sources (*_test.go, fixtures under testdata/).

ICC & Interop Handling

  • EXIF InteroperabilityIndex codes we honor (per EXIF TagNames and regex.info):
    • R03 → Adobe RGB (1998) compatible (a98.icc, etc.)
    • R98 → sRGB (assumed default; no embed)
    • THM → Thumbnail (treated as sRGB; no embed)
  • If an ICC profile already exists, we skip embedding.
  • Test Files:
    • testdata/interop_index.jpg — R03 interop tag, no ICC (expects Adobe profile embed).
    • testdata/interop_index_srgb_icc.jpg — R03 tag with embedded ICC (must remain unchanged).
    • testdata/interop_index_r98.jpg — R98 interop tag, no ICC (should stay sRGB without embedding).
    • testdata/interop_index_thm.jpg — THM interop tag, no ICC (thumbnail; should remain unchanged).
  • References:

Tests

  • Fast scoped: go test ./internal/thumb -run 'Icc|Vips' -count=1
  • Full: go test ./internal/thumb -count=1

Lint & Formatting

  • Format: make fmt-go
  • Lint: make lint-go or golangci-lint run ./internal/thumb/...

Notes

  • When adding ICC files, place them in assets/profiles/icc/ and append to IccProfiles.
  • Comments for exported identifiers must start with the identifier name (Go style).