JPEG: Embed Adobe RGB ICC profile with an InteropIndex tag #5178

Signed-off-by: Michael Mayer <michael@photoprism.app>

internal/thumb/icc.go

@@ -0,0 +1,21 @@
+package thumb
+
+import (
+	"os"
+	"path"
+)
+
+/*
+Possible TODO: move this into a shared pkg/ so non-thumb
+consumers can also use it. However, it looks fiddly to hook that
+up to `assets`, so I'm punting on that for now.
+*/
+
+func MustGetAdobeRGB1998Path() string {
+	p := path.Join(IccProfilesPath, "adobe_rgb_compat.icc")
+	_, err := os.Stat(p)
+	if err != nil {
+		panic(err)
+	}
+	return p
+}

internal/thumb/vips.go

@@ -77,6 +77,10 @@ func Vips(imageName string, imageBuffer []byte, hash, thumbPath string, width, h
 		size = vips.SizeBoth
 	}
 
+	if err = vipsSetIccProfileForInteropIndex(img, clean.Log(filepath.Base(imageName))); err != nil {
+		log.Debugf("vips: %s in %s (set icc profile for interop index tag)", err, clean.Log(filepath.Base(imageName)))
+	}
+
 	// Create thumbnail image.
 	if err = img.ThumbnailWithSize(width, height, crop, size); err != nil {
 		log.Debugf("vips: %s in %s (create thumbnail)", err, clean.Log(filepath.Base(imageName)))
@@ -157,3 +161,47 @@ func VipsJpegExportParams(width, height int) *vips.JpegExportParams {
 
 	return params
 }
+
+func vipsSetIccProfileForInteropIndex(img *vips.ImageRef, logName string) error {
+
+	// Many cameras will define a JPEG's colour space by setting the InteroperabilityIndex
+	// tag instead of embedding an inline ICC profile.
+	// We detect this and embed explicit icc profiles for thumbs of such images, for the benefit of Vips
+	// and web browsers, none of which pay any attention to the InteropIndex tag.
+	iiFull := img.GetString("exif-ifd4-InteroperabilityIndex")
+	if iiFull == "" {
+		return nil
+	}
+
+	// according to my reading, I think [:4] should be e.g. "R98\x00".
+	// However, vips always returns [:4] = "R98 ", e.g. space instead of null.
+	// I'm pulling [:3] instead to paper over this - the exif spec says "4 bytes
+	// incl null terminator" so I think this is safe.
+	ii := iiFull[:3]
+	log.Tracef("interopindex: %s read exif and got interopindex %s, %s", logName, ii, iiFull)
+
+	if img.HasICCProfile() {
+		log.Debugf("interopindex: %s has both an interop index tag and an embedded ICC profile. ignoring.", logName)
+		return nil
+	}
+
+	fallbackProfile := ""
+	switch ii {
+	case "R03":
+		// adobe rgb
+		fallbackProfile = MustGetAdobeRGB1998Path()
+	case "R98":
+		// srgb
+		// we could logically embed an srgb profile in the image here, but
+		// there's no value in doing so; everything assumes srgb anyway.
+	case "THM":
+		// a thumbnail file. I can't find a ref on what colour space
+		// this is, so I'm assuming without evidence that they are also srgb.
+	default:
+		log.Debugf("interopindex: %s has unknown interop index %s", logName, ii)
+	}
+	if fallbackProfile == "" {
+		return nil
+	}
+	return img.TransformICCProfileWithFallback(fallbackProfile, fallbackProfile) // icc profile gets embedded here
+}

internal/thumb/vips_test.go

@@ -25,6 +25,28 @@ func TestVips(t *testing.T) {
 		assert.True(t, strings.HasSuffix(fileName, dst))
 		assert.FileExists(t, dst)
 	})
+	t.Run("InteropIndexColors", func(t *testing.T) {
+		thumb := Sizes[Tile500]
+		src := "testdata/interop_index.jpg"
+		dst := "testdata/vips/1/3/3/133456789098765432_500x500_center.jpg"
+
+		assert.FileExists(t, src)
+
+		fileName, _, err := Vips(src, nil, "133456789098765432", "testdata/vips", thumb.Width, thumb.Height, thumb.Options...)
+
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		assert.True(t, strings.HasSuffix(fileName, dst))
+		assert.Equal(t, fileName, dst)
+		assert.FileExists(t, dst)
+
+		dstimg, err := vips.LoadImageFromFile(dst, vips.NewImportParams())
+		assert.NoError(t, err)
+		assert.True(t, dstimg.HasICCProfile())
+		assert.True(t, dstimg.IsColorSpaceSupported())
+	})
 	t.Run("Left224", func(t *testing.T) {
 		thumb := SizeLeft224
 		src := "testdata/fixed.jpg"