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79 lines
2.7 KiB
Go
79 lines
2.7 KiB
Go
package thumb
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import (
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"fmt"
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"github.com/davidbyttow/govips/v2/vips"
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)
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// InteroperabilityIndex EXIF codes used by some cameras to hint at the color space.
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// Sources: EXIF TagNames (R03=Adobe RGB, R98=sRGB, THM=thumbnail)
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// https://unpkg.com/exiftool-vendored.pl@10.50.0/bin/html/TagNames/EXIF.html
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// Additional context: https://regex.info/blog/photo-tech/color-spaces-page7
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const (
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// InteropIndexAdobeRGB is the EXIF code for Adobe RGB (1998) ("R03").
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InteropIndexAdobeRGB = "R03"
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// InteropIndexSRGB is the EXIF code for sRGB ("R98").
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InteropIndexSRGB = "R98"
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// InteropIndexThumb marks a thumbnail image; treated as sRGB ("THM").
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InteropIndexThumb = "THM"
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)
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// vipsSetIccProfileForInteropIndex embeds an ICC profile when a JPEG declares
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// its color space via the EXIF InteroperabilityIndex tag (e.g., "R03"/Adobe RGB)
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// but lacks an embedded profile. If an ICC profile is already present, it
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// leaves the image untouched.
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func vipsSetIccProfileForInteropIndex(img *vips.ImageRef, logName string) (err error) {
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// Some cameras signal color space via EXIF InteroperabilityIndex instead of
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// embedding an ICC profile. Browsers and libvips ignore this tag, so we
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// inject a matching ICC profile to produce correct thumbnails.
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iiFull := img.GetString("exif-ifd4-InteroperabilityIndex")
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if iiFull == "" {
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return nil
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}
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// EXIF InteroperabilityIndex is 4 bytes including null; libvips returns
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// a string with a trailing space. Using the first three bytes covers the
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// meaningful code (e.g., "R03", "R98").
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if len(iiFull) < 3 {
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log.Debugf("interopindex: %s has unexpected interop index %q", logName, iiFull)
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return nil
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}
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ii := iiFull[:3]
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log.Tracef("interopindex: %s read exif and got interopindex %s, %s", logName, ii, iiFull)
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if img.HasICCProfile() {
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log.Debugf("interopindex: %s already has an embedded ICC profile; skipping fallback.", logName)
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return nil
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}
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profilePath := ""
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switch ii {
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case InteropIndexAdobeRGB:
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// Use Adobe RGB 1998 compatible profile.
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profilePath, err = GetIccProfile(IccAdobeRGBCompat, IccAdobeRGBCompatV2, IccAdobeRGBCompatV4)
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if err != nil {
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return fmt.Errorf("interopindex %s: %w", ii, err)
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}
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case InteropIndexSRGB:
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// sRGB: browsers and libvips assume sRGB by default, so no embed needed.
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case InteropIndexThumb:
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// Thumbnail file; specification unclear—treat as sRGB and do nothing.
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default:
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log.Debugf("interopindex: %s has unknown interop index %s", logName, ii)
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}
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if profilePath == "" {
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return nil
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}
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// Embed ICC profile. govips expects both an input (fallback) and output
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// profile; using the same path injects the chosen profile when none is
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// embedded and keeps colors consistent otherwise.
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return img.TransformICCProfileWithFallback(profilePath, profilePath)
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}
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