image/jpeg: support decoding CMYK and YCbCrK images.

The new testdata was created by:

convert video-001.png -colorspace cmyk video-001.cmyk.jpeg

video-001.cmyk.jpeg was then converted back to video-001.cmyk.png via
the GIMP. ImageMagick (convert) wasn't used for this second conversion
because IM's default color profiles complicates things.

Fixes #4500.

Change-Id: Ibf533f6a6c7e76883acc493ce3a4289d7875df3f
Reviewed-on: https://go-review.googlesource.com/4801Reviewed-by: Rob Pike <r@golang.org>

src/image/decode_test.go

@@ -32,6 +32,7 @@ var imageTests = []imageTest{
 	// JPEG is a lossy format and hence needs a non-zero tolerance.
 	{"testdata/video-001.png", "testdata/video-001.jpeg", 8 << 8},
 	{"testdata/video-001.png", "testdata/video-001.progressive.jpeg", 8 << 8},
+	{"testdata/video-001.cmyk.png", "testdata/video-001.cmyk.jpeg", 8 << 8},
 	// Grayscale images.
 	{"testdata/video-005.gray.png", "testdata/video-005.gray.jpeg", 8 << 8},
 	{"testdata/video-005.gray.png", "testdata/video-005.gray.png", 0},

src/image/jpeg/reader.go

@@ -10,6 +10,7 @@ package jpeg
 import (
 	"image"
 	"image/color"
+	"image/draw"
 	"io"
 )
 
@@ -41,10 +42,7 @@ const (
 	maxTh   = 3
 	maxTq   = 3
 
-	// A grayscale JPEG image has only a Y component.
-	nGrayComponent = 1
-	// A color JPEG image has Y, Cb and Cr components.
-	nColorComponent = 3
+	maxComponents = 4
 
 	// We only support 4:4:4, 4:4:0, 4:2:2 and 4:2:0 downsampling, and therefore the
 	// number of luma samples per chroma sample is at most 2 in the horizontal
@@ -64,9 +62,20 @@ const (
 	driMarker  = 0xdd // Define Restart Interval.
 	rst0Marker = 0xd0 // ReSTart (0).
 	rst7Marker = 0xd7 // ReSTart (7).
-	app0Marker  = 0xe0 // APPlication specific (0).
-	app15Marker = 0xef // APPlication specific (15).
 	comMarker  = 0xfe // COMment.
+	// "APPlication specific" markers aren't part of the JPEG spec per se,
+	// but in practice, their use is described at
+	// http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/JPEG.html
+	app0Marker  = 0xe0
+	app14Marker = 0xee
+	app15Marker = 0xef
+)
+
+// See http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/JPEG.html#Adobe
+const (
+	adobeTransformUnknown = 0
+	adobeTransformYCbCr   = 1
+	adobeTransformYCbCrK  = 2
 )
 
 // unzig maps from the zig-zag ordering to the natural ordering. For example,
@@ -114,14 +123,21 @@ type decoder struct {
 		nUnreadable int
 	}
 	width, height int
+
 	img1        *image.Gray
 	img3        *image.YCbCr
+	blackPix    []byte
+	blackStride int
+
 	ri                  int // Restart Interval.
 	nComp               int
 	progressive         bool
+	adobeTransformValid bool
+	adobeTransform      uint8
 	eobRun              uint16 // End-of-Band run, specified in section G.1.2.2.
-	comp          [nColorComponent]component
-	progCoeffs    [nColorComponent][]block // Saved state between progressive-mode scans.
+
+	comp       [maxComponents]component
+	progCoeffs [maxComponents][]block // Saved state between progressive-mode scans.
 	huff       [maxTc + 1][maxTh + 1]huffman
 	quant      [maxTq + 1]block // Quantization tables, in zig-zag order.
 	tmp        [blockSize + 1]byte
@@ -285,10 +301,12 @@ func (d *decoder) ignore(n int) error {
 // Specified in section B.2.2.
 func (d *decoder) processSOF(n int) error {
 	switch n {
-	case 6 + 3*nGrayComponent:
-		d.nComp = nGrayComponent
-	case 6 + 3*nColorComponent:
-		d.nComp = nColorComponent
+	case 6 + 3*1: // Grayscale image.
+		d.nComp = 1
+	case 6 + 3*3: // YCbCr image. (TODO(nigeltao): or RGB image.)
+		d.nComp = 3
+	case 6 + 3*4: // YCbCrK or CMYK image.
+		d.nComp = 4
 	default:
 		return UnsupportedError("SOF has wrong length")
 	}
@@ -307,7 +325,7 @@ func (d *decoder) processSOF(n int) error {
 	for i := 0; i < d.nComp; i++ {
 		d.comp[i].c = d.tmp[6+3*i]
 		d.comp[i].tq = d.tmp[8+3*i]
-		if d.nComp == nGrayComponent {
+		if d.nComp == 1 {
 			// If a JPEG image has only one component, section A.2 says "this data
 			// is non-interleaved by definition" and section A.2.2 says "[in this
 			// case...] the order of data units within a scan shall be left-to-right
@@ -326,7 +344,9 @@ func (d *decoder) processSOF(n int) error {
 		hv := d.tmp[7+3*i]
 		d.comp[i].h = int(hv >> 4)
 		d.comp[i].v = int(hv & 0x0f)
-		// For color images, we only support 4:4:4, 4:4:0, 4:2:2 or 4:2:0 chroma
+		switch d.nComp {
+		case 3:
+			// For YCbCr images, we only support 4:4:4, 4:4:0, 4:2:2 or 4:2:0 chroma
 			// downsampling ratios. This implies that the (h, v) values for the Y
 			// component are either (1, 1), (1, 2), (2, 1) or (2, 2), and the (h, v)
 			// values for the Cr and Cb components must be (1, 1).
@@ -337,6 +357,31 @@ func (d *decoder) processSOF(n int) error {
 			} else if hv != 0x11 {
 				return UnsupportedError("luma/chroma downsample ratio")
 			}
+		case 4:
+			// For 4-component images (either CMYK or YCbCrK), we only support two
+			// hv vectors: [0x11 0x11 0x11 0x11] and [0x22 0x11 0x11 0x22].
+			// Theoretically, 4-component JPEG images could mix and match hv values
+			// but in practice, those two combinations are the only ones in use,
+			// and it simplifies the applyBlack code below if we can assume that:
+			//	- for CMYK, the C and K channels have full samples, and if the M
+			//	  and Y channels subsample, they subsample both horizontally and
+			//	  vertically.
+			//	- for YCbCrK, the Y and K channels have full samples.
+			switch i {
+			case 0:
+				if hv != 0x11 && hv != 0x22 {
+					return UnsupportedError("luma/chroma downsample ratio")
+				}
+			case 1, 2:
+				if hv != 0x11 {
+					return UnsupportedError("luma/chroma downsample ratio")
+				}
+			case 3:
+				if d.comp[0].h != d.comp[3].h || d.comp[0].v != d.comp[3].v {
+					return UnsupportedError("luma/chroma downsample ratio")
+				}
+			}
+		}
 	}
 	return nil
 }
@@ -378,6 +423,26 @@ func (d *decoder) processDRI(n int) error {
 	return nil
 }
 
+func (d *decoder) processApp14Marker(n int) error {
+	if n < 12 {
+		return d.ignore(n)
+	}
+	if err := d.readFull(d.tmp[:12]); err != nil {
+		return err
+	}
+	n -= 12
+
+	if d.tmp[0] == 'A' && d.tmp[1] == 'd' && d.tmp[2] == 'o' && d.tmp[3] == 'b' && d.tmp[4] == 'e' {
+		d.adobeTransformValid = true
+		d.adobeTransform = d.tmp[11]
+	}
+
+	if n > 0 {
+		return d.ignore(n)
+	}
+	return nil
+}
+
 // decode reads a JPEG image from r and returns it as an image.Image.
 func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, error) {
 	d.r = r
@@ -459,26 +524,30 @@ func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, error) {
 			return nil, FormatError("short segment length")
 		}
 
-		switch {
-		case marker == sof0Marker || marker == sof2Marker: // Start Of Frame.
+		switch marker {
+		case sof0Marker, sof2Marker:
 			d.progressive = marker == sof2Marker
 			err = d.processSOF(n)
 			if configOnly {
 				return nil, err
 			}
-		case marker == dhtMarker: // Define Huffman Table.
+		case dhtMarker:
 			err = d.processDHT(n)
-		case marker == dqtMarker: // Define Quantization Table.
+		case dqtMarker:
 			err = d.processDQT(n)
-		case marker == sosMarker: // Start Of Scan.
+		case sosMarker:
 			err = d.processSOS(n)
-		case marker == driMarker: // Define Restart Interval.
+		case driMarker:
 			err = d.processDRI(n)
-		case app0Marker <= marker && marker <= app15Marker || marker == comMarker: // APPlication specific, or COMment.
-			err = d.ignore(n)
+		case app14Marker:
+			err = d.processApp14Marker(n)
 		default:
+			if app0Marker <= marker && marker <= app15Marker || marker == comMarker {
+				err = d.ignore(n)
+			} else {
 				err = UnsupportedError("unknown marker")
 			}
+		}
 		if err != nil {
 			return nil, err
 		}
@@ -487,11 +556,89 @@ func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, error) {
 		return d.img1, nil
 	}
 	if d.img3 != nil {
+		if d.blackPix != nil {
+			return d.applyBlack()
+		}
 		return d.img3, nil
 	}
 	return nil, FormatError("missing SOS marker")
 }
 
+// applyBlack combines d.img3 and d.blackPix into a CMYK image. The formula
+// used depends on whether the JPEG image is stored as CMYK or YCbCrK,
+// indicated by the APP14 (Adobe) metadata.
+//
+// Adobe CMYK JPEG images are inverted, where 255 means no ink instead of full
+// ink, so we apply "v = 255 - v" at various points. Note that a double
+// inversion is a no-op, so inversions might be implicit in the code below.
+func (d *decoder) applyBlack() (image.Image, error) {
+	if !d.adobeTransformValid {
+		return nil, UnsupportedError("unknown color model: 4-component JPEG doesn't have Adobe APP14 metadata")
+	}
+
+	// If the 4-component JPEG image isn't explicitly marked as "Unknown (RGB
+	// or CMYK)" as per
+	// http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/JPEG.html#Adobe
+	// we assume that it is YCbCrK. This matches libjpeg's jdapimin.c.
+	if d.adobeTransform != adobeTransformUnknown {
+		// Convert the YCbCr part of the YCbCrK to RGB, invert the RGB to get
+		// CMY, and patch in the original K. The RGB to CMY inversion cancels
+		// out the 'Adobe inversion' described in the applyBlack doc comment
+		// above, so in practice, only the fourth channel (black) is inverted.
+		bounds := d.img3.Bounds()
+		img := image.NewRGBA(bounds)
+		// TODO(nigeltao): do the draw.Draw YCbCr -> RGB conversion directly,
+		// instead of having the image/jpeg package depend on the image/draw
+		// package.
+		draw.Draw(img, bounds, d.img3, bounds.Min, draw.Src)
+		for iBase, y := 0, bounds.Min.Y; y < bounds.Max.Y; iBase, y = iBase+img.Stride, y+1 {
+			for i, x := iBase+3, bounds.Min.X; x < bounds.Max.X; i, x = i+4, x+1 {
+				img.Pix[i] = 255 - d.blackPix[(y-bounds.Min.Y)*d.blackStride+(x-bounds.Min.X)]
+			}
+		}
+		return &image.CMYK{
+			Pix:    img.Pix,
+			Stride: img.Stride,
+			Rect:   img.Rect,
+		}, nil
+	}
+
+	// The first three channels (cyan, magenta, yellow) of the CMYK
+	// were decoded into d.img3, but each channel was decoded into a separate
+	// []byte slice, and some channels may be subsampled. We interleave the
+	// separate channels into an image.CMYK's single []byte slice containing 4
+	// contiguous bytes per pixel.
+	bounds := d.img3.Bounds()
+	img := image.NewCMYK(bounds)
+
+	translations := [4]struct {
+		src    []byte
+		stride int
+	}{
+		{d.img3.Y, d.img3.YStride},
+		{d.img3.Cb, d.img3.CStride},
+		{d.img3.Cr, d.img3.CStride},
+		{d.blackPix, d.blackStride},
+	}
+	for t, translation := range translations {
+		subsample := d.comp[t].h != d.comp[0].h || d.comp[t].v != d.comp[0].v
+		for iBase, y := 0, bounds.Min.Y; y < bounds.Max.Y; iBase, y = iBase+img.Stride, y+1 {
+			sy := y - bounds.Min.Y
+			if subsample {
+				sy /= 2
+			}
+			for i, x := iBase+t, bounds.Min.X; x < bounds.Max.X; i, x = i+4, x+1 {
+				sx := x - bounds.Min.X
+				if subsample {
+					sx /= 2
+				}
+				img.Pix[i] = 255 - translation.src[sy*translation.stride+sx]
+			}
+		}
+	}
+	return img, nil
+}
+
 // Decode reads a JPEG image from r and returns it as an image.Image.
 func Decode(r io.Reader) (image.Image, error) {
 	var d decoder
@@ -506,15 +653,21 @@ func DecodeConfig(r io.Reader) (image.Config, error) {
 		return image.Config{}, err
 	}
 	switch d.nComp {
-	case nGrayComponent:
+	case 1:
 		return image.Config{
 			ColorModel: color.GrayModel,
 			Width:      d.width,
 			Height:     d.height,
 		}, nil
-	case nColorComponent:
+	case 3:
+		return image.Config{
+			ColorModel: color.YCbCrModel, // TODO(nigeltao): support RGB JPEGs.
+			Width:      d.width,
+			Height:     d.height,
+		}, nil
+	case 4:
 		return image.Config{
-			ColorModel: color.YCbCrModel,
+			ColorModel: color.CMYKModel,
 			Width:      d.width,
 			Height:     d.height,
 		}, nil

src/image/jpeg/scan.go

@@ -10,11 +10,12 @@ import (
 
 // makeImg allocates and initializes the destination image.
 func (d *decoder) makeImg(h0, v0, mxx, myy int) {
-	if d.nComp == nGrayComponent {
+	if d.nComp == 1 {
 		m := image.NewGray(image.Rect(0, 0, 8*mxx, 8*myy))
 		d.img1 = m.SubImage(image.Rect(0, 0, d.width, d.height)).(*image.Gray)
 		return
 	}
+
 	var subsampleRatio image.YCbCrSubsampleRatio
 	switch {
 	case h0 == 1 && v0 == 1:
@@ -30,6 +31,12 @@ func (d *decoder) makeImg(h0, v0, mxx, myy int) {
 	}
 	m := image.NewYCbCr(image.Rect(0, 0, 8*h0*mxx, 8*v0*myy), subsampleRatio)
 	d.img3 = m.SubImage(image.Rect(0, 0, d.width, d.height)).(*image.YCbCr)
+
+	if d.nComp == 4 {
+		h3, v3 := d.comp[3].h, d.comp[3].v
+		d.blackPix = make([]byte, 8*h3*mxx*8*v3*myy)
+		d.blackStride = 8 * h3 * mxx
+	}
 }
 
 // Specified in section B.2.3.
@@ -47,7 +54,7 @@ func (d *decoder) processSOS(n int) error {
 	if n != 4+2*nComp {
 		return FormatError("SOS length inconsistent with number of components")
 	}
-	var scan [nColorComponent]struct {
+	var scan [maxComponents]struct {
 		compIndex uint8
 		td        uint8 // DC table selector.
 		ta        uint8 // AC table selector.
@@ -128,7 +135,7 @@ func (d *decoder) processSOS(n int) error {
 	var (
 		// b is the decoded coefficients, in natural (not zig-zag) order.
 		b  block
-		dc [nColorComponent]int32
+		dc [maxComponents]int32
 		// bx and by are the location of the current (in terms of 8x8 blocks).
 		// For example, with 4:2:0 chroma subsampling, the block whose top left
 		// pixel co-ordinates are (16, 8) is the third block in the first row:
@@ -276,7 +283,7 @@ func (d *decoder) processSOS(n int) error {
 					}
 					idct(&b)
 					dst, stride := []byte(nil), 0
-					if d.nComp == nGrayComponent {
+					if d.nComp == 1 {
 						dst, stride = d.img1.Pix[8*(by*d.img1.Stride+bx):], d.img1.Stride
 					} else {
 						switch compIndex {
@@ -286,6 +293,8 @@ func (d *decoder) processSOS(n int) error {
 							dst, stride = d.img3.Cb[8*(by*d.img3.CStride+bx):], d.img3.CStride
 						case 2:
 							dst, stride = d.img3.Cr[8*(by*d.img3.CStride+bx):], d.img3.CStride
+						case 3:
+							dst, stride = d.blackPix[8*(by*d.blackStride+bx):], d.blackStride
 						default:
 							return UnsupportedError("too many components")
 						}
@@ -325,7 +334,7 @@ func (d *decoder) processSOS(n int) error {
 				// Reset the Huffman decoder.
 				d.bits = bits{}
 				// Reset the DC components, as per section F.2.1.3.1.
-				dc = [nColorComponent]int32{}
+				dc = [maxComponents]int32{}
 				// Reset the progressive decoder state, as per section G.1.2.2.
 				d.eobRun = 0
 			}