Serve and accept JPEG XL as an image format (part of #222)

A JPEG XL source is accepted, and orig of one is JPEG XL. The format
jxl works in plain and encrypted URLs and on the generator page,
served as image/jxl; auto chooses it first when Accept names
image/jxl.

govips sends libvips a JPEG XL distance, which overrides the quality,
so q is turned into a distance, keeping 100 lossy. govips cannot have
libvips strip metadata from JPEG XL, so it is removed from the image
before saving; libvips 8.16 and later still add an EXIF block of their
own, with nothing from the source. The conversion to sRGB moved ahead
of the format switch, and a CMYK image with no ICC profile is
converted to sRGB too, as libvips cannot save CMYK as JPEG XL.

Model: opus-5-5

README.md

@@ -253,8 +253,9 @@ once, is refused with 400.
   both optional (values under Signature Specification). Both are part of what is
   cached, so each value of either is a separate cached image.
 
-The source image may be JPEG, PNG, GIF, WebP, AVIF or JPEG XL. The upstream's
+The source image may be JPEG, PNG, GIF, WebP, AVIF, JPEG XL or SVG. The
-`Content-Type` must name its format, and the image's first bytes must match it.
+upstream's `Content-Type` must name its format, and the image's first bytes must
+match it.
 
 With the format `auto`, pixa chooses the format for each request from its
 `Accept` header, in this order:
@@ -355,10 +356,10 @@ turned off.
 - An image with an ICC profile is converted to sRGB first, since clients show an
   image with no profile as sRGB. Colours outside sRGB, such as the most
   saturated ones in a Display P3 photo, are clipped.
-- The one exception is JPEG XL: a JPEG XL image carries an EXIF block that
+- The one exception is JPEG XL with libvips 8.16 and later: libvips then writes
-  libvips writes itself, with the image's orientation, resolution, size and
+  an EXIF block of its own into the image, with its orientation, resolution,
-  colour space and fixed defaults, but nothing from the source's EXIF, as govips
+  size and colour space and fixed defaults, but nothing from the source's EXIF,
-  cannot ask libvips to leave it out.
+  as govips cannot ask libvips to leave it out.
 
 ### Source Hosts
 

TODO.md

@@ -39,10 +39,13 @@ P2: security: per-IP rate limiting on the image routes
   `image/jxl`. govips sends libvips a JPEG XL distance with every save, so
   libvips ignores the quality: pixa turns `q` into a distance with libvips' own
   formula, keeping 100 lossy, and removes the metadata from the image before
-  saving, as govips cannot have libvips strip it from JPEG XL. libvips still
+  saving, as govips cannot have libvips strip it from JPEG XL. libvips 8.16 and
-  writes an EXIF block of its own into JPEG XL (orientation, resolution, size,
+  later still write an EXIF block of their own into JPEG XL (orientation,
-  colour space, fixed defaults), with nothing from the source. libvips' default
+  resolution, size, colour space, fixed defaults), with nothing from the source.
-  effort, 7, is kept. JPEG XL is not yet the default output.
+  An image with an ICC profile is converted to sRGB before the JPEG XL save too,
+  and a CMYK image with none is converted to sRGB, as libvips cannot save CMYK
+  as JPEG XL. libvips' default effort, 7, is kept. JPEG XL is not yet the
+  default output.
 - 2026-10-08 requests no longer wait behind eviction queries that read a whole
   table (closes #227): the new `cache_usage` table holds the total cache usage,
   kept up to date by triggers on `source_content` and `variant_content` in the

internal/imageprocessor/imageprocessor.go

@@ -562,6 +562,16 @@ func (p *ImageProcessor) encode(
 // encoder's own measure of quality, along with the quality, and libvips then
 // uses the distance alone, so the quality is also given as a distance.
 func exportJXL(img *vips.ImageRef, quality int) ([]byte, error) {
+	// libvips converts a CMYK image to sRGB before it saves WebP, AVIF or
+	// PNG, but cannot save one as JPEG XL. encode has already converted
+	// any image with an ICC profile to sRGB, so this is CMYK with none.
+	if img.Interpretation() == vips.InterpretationCMYK {
+		err := img.ToColorSpace(vips.InterpretationSRGB)
+		if err != nil {
+			return nil, fmt.Errorf("failed to convert CMYK to sRGB: %w", err)
+		}
+	}
+
 	// govips cannot make libvips strip metadata from JPEG XL, so it is
 	// removed from the image itself. RemoveMetadata removes EXIF, XMP and
 	// IPTC but keeps the ICC profile. libvips 8.16 and later still write an

internal/imageprocessor/jpegxl_internal_test.go

@@ -1,10 +1,6 @@
 package imageprocessor
 
 import (
-	"bytes"
-	"io"
-	"math"
-	"os"
 	"testing"
 
 	"github.com/davidbyttow/govips/v2/vips"
@@ -54,118 +50,3 @@ func TestLibvipsSavesAndLoadsJPEGXL(t *testing.T) {
 		t.Errorf("loaded size = %dx%d, want 64x48", loaded.Width(), loaded.Height())
 	}
 }
-
-// TestImageProcessor_EncodeJPEGXL converts a JPEG to a smaller JPEG XL and
-// checks the content type, and the format and size the output loads as.
-func TestImageProcessor_EncodeJPEGXL(t *testing.T) {
-	t.Parallel()
-
-	req := &Request{Size: Size{Width: 100, Height: 75}, Format: FormatJXL}
-
-	result, err := New(Params{}).Process(
-		t.Context(), bytes.NewReader(createTestJPEG(t, 200, 150)), req,
-	)
-	if err != nil {
-		t.Fatalf("Process() error = %v", err)
-	}
-
-	defer func() { _ = result.Content.Close() }()
-
-	if result.ContentType != "image/jxl" {
-		t.Errorf("ContentType = %q, want image/jxl", result.ContentType)
-	}
-
-	data, err := io.ReadAll(result.Content)
-	if err != nil {
-		t.Fatalf("failed to read result: %v", err)
-	}
-
-	output, err := vips.NewImageFromBuffer(data)
-	if err != nil {
-		t.Fatalf("failed to load the output: %v", err)
-	}
-
-	defer output.Close()
-
-	if output.Format() != vips.ImageTypeJXL {
-		t.Errorf("output format = %s, want jxl", vips.ImageTypes[output.Format()])
-	}
-
-	if output.Width() != 100 || output.Height() != 75 {
-		t.Errorf("output size = %dx%d, want 100x75", output.Width(), output.Height())
-	}
-}
-
-// TestImageProcessor_JPEGXLQuality verifies that the quality reaches the JPEG
-// XL encoder: the same image comes out smaller at quality 30 than at 90.
-func TestImageProcessor_JPEGXLQuality(t *testing.T) {
-	t.Parallel()
-
-	input := createTestJPEG(t, 400, 300)
-	outputBytes := make(map[int]int64)
-
-	for _, quality := range []int{30, 90} {
-		result, err := New(Params{}).Process(t.Context(),
-			bytes.NewReader(input), &Request{Format: FormatJXL, Quality: quality})
-		if err != nil {
-			t.Fatalf("Process() at quality %d error = %v", quality, err)
-		}
-
-		_ = result.Content.Close()
-		outputBytes[quality] = result.ContentLength
-	}
-
-	if outputBytes[30] >= outputBytes[90] {
-		t.Errorf("%d bytes at quality 30, %d at 90, want fewer at 30",
-			outputBytes[30], outputBytes[90])
-	}
-}
-
-// TestImageProcessor_JPEGXLDropsSourceEXIF verifies that none of the source's
-// EXIF reaches a JPEG XL output. libvips 8.16 and later write an EXIF block of
-// their own into JPEG XL (orientation, resolution, size, colour space and
-// fixed defaults), and govips cannot ask them to leave it out, so the test
-// looks for the source's fields rather than for no EXIF at all.
-func TestImageProcessor_JPEGXLDropsSourceEXIF(t *testing.T) {
-	t.Parallel()
-
-	input, err := os.ReadFile("testdata/gps-exif.jpg")
-	if err != nil {
-		t.Fatalf("failed to read test JPEG: %v", err)
-	}
-
-	exif := processAndDecode(t, input, &Request{Format: FormatJXL}).GetExif()
-
-	for _, field := range []string{
-		"exif-ifd0-Make", "exif-ifd0-Model", "exif-ifd2-BodySerialNumber",
-		"exif-ifd2-DateTimeOriginal", "exif-ifd3-GPSLatitude",
-		"exif-ifd3-GPSLongitude",
-	} {
-		if value, found := exif[field]; found {
-			t.Errorf("output has %s: %s", field, value)
-		}
-	}
-}
-
-// TestJXLDistance verifies the JPEG XL distance for a few qualities: 90 is
-// distance 1, the encoder's own default, and 100 stays lossy.
-func TestJXLDistance(t *testing.T) {
-	t.Parallel()
-
-	tests := []struct {
-		quality int
-		want    float64
-	}{
-		{quality: 100, want: 0.1},
-		{quality: 90, want: 1},
-		{quality: 30, want: 6.4},
-		{quality: 20, want: 9.0667},
-	}
-
-	for _, tt := range tests {
-		got := jxlDistance(tt.quality)
-		if math.Abs(got-tt.want) > 0.0001 {
-			t.Errorf("jxlDistance(%d) = %v, want %v", tt.quality, got, tt.want)
-		}
-	}
-}

internal/imageprocessor/jpegxl_output_internal_test.go

@@ -0,0 +1,220 @@
+package imageprocessor
+
+import (
+	"bytes"
+	"io"
+	"math"
+	"os"
+	"testing"
+
+	"github.com/davidbyttow/govips/v2/vips"
+)
+
+// TestImageProcessor_EncodeJPEGXL converts a JPEG to a smaller JPEG XL and
+// checks the content type, and the format and size the output loads as.
+func TestImageProcessor_EncodeJPEGXL(t *testing.T) {
+	t.Parallel()
+
+	req := &Request{Size: Size{Width: 100, Height: 75}, Format: FormatJXL}
+
+	result, err := New(Params{}).Process(
+		t.Context(), bytes.NewReader(createTestJPEG(t, 200, 150)), req,
+	)
+	if err != nil {
+		t.Fatalf("Process() error = %v", err)
+	}
+
+	defer func() { _ = result.Content.Close() }()
+
+	if result.ContentType != "image/jxl" {
+		t.Errorf("ContentType = %q, want image/jxl", result.ContentType)
+	}
+
+	data, err := io.ReadAll(result.Content)
+	if err != nil {
+		t.Fatalf("failed to read result: %v", err)
+	}
+
+	output, err := vips.NewImageFromBuffer(data)
+	if err != nil {
+		t.Fatalf("failed to load the output: %v", err)
+	}
+
+	defer output.Close()
+
+	if output.Format() != vips.ImageTypeJXL {
+		t.Errorf("output format = %s, want jxl", vips.ImageTypes[output.Format()])
+	}
+
+	if output.Width() != 100 || output.Height() != 75 {
+		t.Errorf("output size = %dx%d, want 100x75", output.Width(), output.Height())
+	}
+}
+
+// TestImageProcessor_JPEGXLQuality verifies that the quality reaches the JPEG
+// XL encoder: the same image comes out smaller at quality 30 than at 90.
+func TestImageProcessor_JPEGXLQuality(t *testing.T) {
+	t.Parallel()
+
+	input := createTestJPEG(t, 400, 300)
+	outputBytes := make(map[int]int64)
+
+	for _, quality := range []int{30, 90} {
+		result, err := New(Params{}).Process(t.Context(),
+			bytes.NewReader(input), &Request{Format: FormatJXL, Quality: quality})
+		if err != nil {
+			t.Fatalf("Process() at quality %d error = %v", quality, err)
+		}
+
+		_ = result.Content.Close()
+		outputBytes[quality] = result.ContentLength
+	}
+
+	if outputBytes[30] >= outputBytes[90] {
+		t.Errorf("%d bytes at quality 30, %d at 90, want fewer at 30",
+			outputBytes[30], outputBytes[90])
+	}
+}
+
+// TestImageProcessor_JPEGXLDropsSourceEXIF verifies that none of the source's
+// EXIF reaches a JPEG XL output. libvips 8.16 and later write an EXIF block of
+// their own into JPEG XL (orientation, resolution, size, colour space and
+// fixed defaults), and govips cannot ask them to leave it out, so the test
+// looks for the source's fields rather than for no EXIF at all.
+func TestImageProcessor_JPEGXLDropsSourceEXIF(t *testing.T) {
+	t.Parallel()
+
+	input, err := os.ReadFile("testdata/gps-exif.jpg")
+	if err != nil {
+		t.Fatalf("failed to read test JPEG: %v", err)
+	}
+
+	exif := processAndDecode(t, input, &Request{Format: FormatJXL}).GetExif()
+
+	for _, field := range []string{
+		"exif-ifd0-Make", "exif-ifd0-Model", "exif-ifd2-BodySerialNumber",
+		"exif-ifd2-DateTimeOriginal", "exif-ifd3-GPSLatitude",
+		"exif-ifd3-GPSLongitude",
+	} {
+		if value, found := exif[field]; found {
+			t.Errorf("output has %s: %s", field, value)
+		}
+	}
+}
+
+// TestImageProcessor_JPEGXLAppliesEXIFOrientation verifies that a JPEG XL
+// output is turned upright, as TestImageProcessor_AppliesEXIFOrientation does
+// for PNG.
+func TestImageProcessor_JPEGXLAppliesEXIFOrientation(t *testing.T) {
+	t.Parallel()
+
+	// orientation-6.jpg is stored 16x8, red on the left and blue on the
+	// right, with EXIF orientation 6 (turn 90 degrees clockwise to view).
+	// Upright it is 8x16, red on top and blue below.
+	input, err := os.ReadFile("testdata/orientation-6.jpg")
+	if err != nil {
+		t.Fatalf("failed to read test JPEG: %v", err)
+	}
+
+	output := processAndDecode(t, input, &Request{Format: FormatJXL})
+
+	if output.Width() != 8 || output.Height() != 16 {
+		t.Fatalf("output is %dx%d, want 8x16", output.Width(), output.Height())
+	}
+
+	top, err := output.GetPoint(4, 0)
+	if err != nil {
+		t.Fatalf("GetPoint() error = %v", err)
+	}
+
+	bottom, err := output.GetPoint(4, 15)
+	if err != nil {
+		t.Fatalf("GetPoint() error = %v", err)
+	}
+
+	if top[0] <= top[2] || bottom[2] <= bottom[0] {
+		t.Errorf("top pixel = %v, bottom pixel = %v, want red above blue",
+			top, bottom)
+	}
+}
+
+// TestImageProcessor_JPEGXLConvertsWideGamutToSRGB verifies that a JPEG XL
+// output is converted to sRGB, as TestImageProcessor_ConvertsWideGamutToSRGB
+// does for PNG. It does not check for an ICC profile, as libvips reports one
+// for every JPEG XL image it loads.
+func TestImageProcessor_JPEGXLConvertsWideGamutToSRGB(t *testing.T) {
+	t.Parallel()
+
+	// display-p3.jpg is a flat 8x8 image with the Display P3 profile
+	// embedded, filled with Display P3 (234, 51, 35), which is sRGB red.
+	input, err := os.ReadFile("testdata/display-p3.jpg")
+	if err != nil {
+		t.Fatalf("failed to read test JPEG: %v", err)
+	}
+
+	output := processAndDecode(t, input, &Request{Format: FormatJXL})
+
+	pixel, err := output.GetPoint(4, 4)
+	if err != nil {
+		t.Fatalf("GetPoint() error = %v", err)
+	}
+
+	want := []float64{255, 0, 0}
+	for i := range want {
+		if math.Abs(pixel[i]-want[i]) > 5 {
+			t.Fatalf("pixel = %v, want within 5 of %v", pixel, want)
+		}
+	}
+}
+
+// TestImageProcessor_JPEGXLFromCMYK verifies that a CMYK JPEG with no ICC
+// profile can be served as JPEG XL, in sRGB.
+func TestImageProcessor_JPEGXLFromCMYK(t *testing.T) {
+	t.Parallel()
+
+	// cmyk.jpg is a flat 8x8 CMYK image with no ICC profile, filled with
+	// full cyan and no magenta, yellow or black.
+	input, err := os.ReadFile("testdata/cmyk.jpg")
+	if err != nil {
+		t.Fatalf("failed to read test JPEG: %v", err)
+	}
+
+	output := processAndDecode(t, input, &Request{Format: FormatJXL})
+
+	if output.Bands() != 3 {
+		t.Fatalf("output has %d bands, want 3", output.Bands())
+	}
+
+	pixel, err := output.GetPoint(4, 4)
+	if err != nil {
+		t.Fatalf("GetPoint() error = %v", err)
+	}
+
+	// Cyan in sRGB: little red, much green and blue.
+	if pixel[0] > 50 || pixel[1] < 100 || pixel[2] < 200 {
+		t.Errorf("pixel = %v, want cyan", pixel)
+	}
+}
+
+// TestJXLDistance verifies the JPEG XL distance for a few qualities: 90 is
+// distance 1, the encoder's own default, and 100 stays lossy.
+func TestJXLDistance(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		quality int
+		want    float64
+	}{
+		{quality: 100, want: 0.1},
+		{quality: 90, want: 1},
+		{quality: 30, want: 6.4},
+		{quality: 20, want: 9.0667},
+	}
+
+	for _, tt := range tests {
+		got := jxlDistance(tt.quality)
+		if math.Abs(got-tt.want) > 0.0001 {
+			t.Errorf("jxlDistance(%d) = %v, want %v", tt.quality, got, tt.want)
+		}
+	}
+}