Skip to content

Commit

Permalink
image/jpeg: support chroma hv values other than 0x11.
Browse files Browse the repository at this point in the history 
The testdata was generated by:
convert video-001.png tmp1.tga
cjpeg -quality 100 -sample 2x2,1x2,1x2 tmp1.tga > video-001.221212.jpeg
djpeg -nosmooth -targa video-001.221212.jpeg > tmp2.tga
convert tmp2.tga video-001.221212.png
rm tmp1.tga tmp2.tga

Change-Id: Ica241dfc19b3eb47ade150bf0432373c6006c38a
Reviewed-on: https://go-review.googlesource.com/7264
Reviewed-by: Rob Pike <[email protected]>
  • Loading branch information
@nigeltao
nigeltao committed Mar 11, 2015
1 parent 532bc5f commit 782db7f
Show file tree
Hide file tree
Showing 5 changed files with 78 additions and 45 deletions.
12 changes: 10 additions & 2 deletions src/image/decode_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ package image_test

import (
"bufio"
"fmt"
"image"
"image/color"
"os"
Expand All @@ -32,6 +33,7 @@ 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-001.221212.png", "testdata/video-001.221212.jpeg", 8 << 8},
{"testdata/video-001.cmyk.png", "testdata/video-001.cmyk.jpeg", 8 << 8},
{"testdata/video-001.rgb.png", "testdata/video-001.rgb.jpeg", 8 << 8},
// Grayscale images.
Expand Down Expand Up @@ -76,6 +78,11 @@ func withinTolerance(c0, c1 color.Color, tolerance int) bool {
}

func TestDecode(t *testing.T) {
rgba := func(c color.Color) string {
r, g, b, a := c.RGBA()
return fmt.Sprintf("rgba = 0x%04x, 0x%04x, 0x%04x, 0x%04x for %T%v", r, g, b, a, c, c)
}

golden := make(map[string]image.Image)
loop:
for _, it := range imageTests {
Expand All @@ -96,13 +103,14 @@ loop:
}
b := g.Bounds()
if !b.Eq(m.Bounds()) {
t.Errorf("%s: want bounds %v got %v", it.filename, b, m.Bounds())
t.Errorf("%s: got bounds %v want %v", it.filename, m.Bounds(), b)
continue loop
}
for y := b.Min.Y; y < b.Max.Y; y++ {
for x := b.Min.X; x < b.Max.X; x++ {
if !withinTolerance(g.At(x, y), m.At(x, y), it.tolerance) {
t.Errorf("%s: at (%d, %d), want %v got %v", it.filename, x, y, g.At(x, y), m.At(x, y))
t.Errorf("%s: at (%d, %d):\ngot %v\nwant %v",
it.filename, x, y, rgba(m.At(x, y)), rgba(g.At(x, y)))
continue loop
}
}
Expand Down
69 changes: 45 additions & 24 deletions src/image/jpeg/reader.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,8 @@ type UnsupportedError string

func (e UnsupportedError) Error() string { return "unsupported JPEG feature: " + string(e) }

var errUnsupportedSubsamplingRatio = UnsupportedError("luma/chroma subsampling ratio")

// Component specification, specified in section B.2.2.
type component struct {
h int // Horizontal sampling factor.
Expand Down Expand Up @@ -303,7 +305,7 @@ func (d *decoder) processSOF(n int) error {
case 6 + 3*4: // YCbCrK or CMYK image.
d.nComp = 4
default:
return UnsupportedError("SOF has wrong length")
return UnsupportedError("number of components")
}
if err := d.readFull(d.tmp[:n]); err != nil {
return err
Expand All @@ -315,8 +317,9 @@ func (d *decoder) processSOF(n int) error {
d.height = int(d.tmp[1])<<8 + int(d.tmp[2])
d.width = int(d.tmp[3])<<8 + int(d.tmp[4])
if int(d.tmp[5]) != d.nComp {
return UnsupportedError("SOF has wrong number of image components")
return FormatError("SOF has wrong length")
}

for i := 0; i < d.nComp; i++ {
d.comp[i].c = d.tmp[6+3*i]
// Section B.2.2 states that "the value of C_i shall be different from
Expand All @@ -328,8 +331,16 @@ func (d *decoder) processSOF(n int) error {
}

d.comp[i].tq = d.tmp[8+3*i]

if d.nComp == 1 {
hv := d.tmp[7+3*i]
h, v := int(hv>>4), int(hv&0x0f)
if h < 1 || 4 < h || v < 1 || 4 < v {
return FormatError("luma/chroma subsampling ratio")
}
if h == 3 || v == 3 {
return errUnsupportedSubsamplingRatio
}
switch d.nComp {
case 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
Expand All @@ -341,27 +352,34 @@ func (d *decoder) processSOF(n int) error {
// always 1. The component's (h, v) is effectively always (1, 1): even if
// the nominal (h, v) is (2, 1), a 20x5 image is encoded in three 8x8
// MCUs, not two 16x8 MCUs.
d.comp[i].h = 1
d.comp[i].v = 1
continue
}
hv := d.tmp[7+3*i]
d.comp[i].h = int(hv >> 4)
d.comp[i].v = int(hv & 0x0f)
switch d.nComp {
h, v = 1, 1

case 3:
// For YCbCr images, we only support 4:4:4, 4:4:0, 4:2:2, 4:2:0,
// 4:1:1 or 4:1:0 chroma downsampling ratios. This implies that the
// 4:1:1 or 4:1:0 chroma subsampling ratios. This implies that the
// (h, v) values for the Y component are either (1, 1), (1, 2),
// (2, 1), (2, 2), (4, 1) or (4, 2), and the (h, v) values for the Cr
// and Cb components must be (1, 1).
if i == 0 {
if hv != 0x11 && hv != 0x21 && hv != 0x22 && hv != 0x12 && hv != 0x41 && hv != 0x42 {
return UnsupportedError("luma/chroma downsample ratio")
// (2, 1), (2, 2), (4, 1) or (4, 2), and the Y component's values
// must be a multiple of the Cb and Cr component's values. We also
// assume that the two chroma components have the same subsampling
// ratio.
switch i {
case 0: // Y.
// We have already verified, above, that h and v are both
// either 1, 2 or 4, so invalid (h, v) combinations are those
// with v == 4.
if v == 4 {
return errUnsupportedSubsamplingRatio
}
case 1: // Cb.
if d.comp[0].h%h != 0 || d.comp[0].v%v != 0 {
return errUnsupportedSubsamplingRatio
}
case 2: // Cr.
if d.comp[1].h != h || d.comp[1].v != v {
return errUnsupportedSubsamplingRatio
}
} 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].
Expand All @@ -375,18 +393,21 @@ func (d *decoder) processSOF(n int) error {
switch i {
case 0:
if hv != 0x11 && hv != 0x22 {
return UnsupportedError("luma/chroma downsample ratio")
return errUnsupportedSubsamplingRatio
}
case 1, 2:
if hv != 0x11 {
return UnsupportedError("luma/chroma downsample ratio")
return errUnsupportedSubsamplingRatio
}
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")
if d.comp[0].h != h || d.comp[0].v != v {
return errUnsupportedSubsamplingRatio
}
}
}

d.comp[i].h = h
d.comp[i].v = v
}
return nil
}
Expand Down
42 changes: 23 additions & 19 deletions src/image/jpeg/scan.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -9,26 +9,30 @@ import (
)

// makeImg allocates and initializes the destination image.
func (d *decoder) makeImg(h0, v0, mxx, myy int) {
func (d *decoder) makeImg(mxx, myy int) {
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
}

h0 := d.comp[0].h
v0 := d.comp[0].v
hRatio := h0 / d.comp[1].h
vRatio := v0 / d.comp[1].v
var subsampleRatio image.YCbCrSubsampleRatio
switch {
case h0 == 1 && v0 == 1:
switch hRatio<<4 | vRatio {
case 0x11:
subsampleRatio = image.YCbCrSubsampleRatio444
case h0 == 1 && v0 == 2:
case 0x12:
subsampleRatio = image.YCbCrSubsampleRatio440
case h0 == 2 && v0 == 1:
case 0x21:
subsampleRatio = image.YCbCrSubsampleRatio422
case h0 == 2 && v0 == 2:
case 0x22:
subsampleRatio = image.YCbCrSubsampleRatio420
case h0 == 4 && v0 == 1:
case 0x41:
subsampleRatio = image.YCbCrSubsampleRatio411
case h0 == 4 && v0 == 2:
case 0x42:
subsampleRatio = image.YCbCrSubsampleRatio410
default:
panic("unreachable")
Expand Down Expand Up @@ -141,7 +145,7 @@ func (d *decoder) processSOS(n int) error {
mxx := (d.width + 8*h0 - 1) / (8 * h0)
myy := (d.height + 8*v0 - 1) / (8 * v0)
if d.img1 == nil && d.img3 == nil {
d.makeImg(h0, v0, mxx, myy)
d.makeImg(mxx, myy)
}
if d.progressive {
for i := 0; i < nComp; i++ {
Expand All @@ -158,19 +162,19 @@ func (d *decoder) processSOS(n int) error {
// b is the decoded coefficients, in natural (not zig-zag) order.
b block
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:
// bx is 2 and by is 0, even though the pixel is in the second MCU.
// bx and by are the location of the current block, in units of 8x8
// blocks: the third block in the first row has (bx, by) = (2, 0).
bx, by int
blockCount int
)
for my := 0; my < myy; my++ {
for mx := 0; mx < mxx; mx++ {
for i := 0; i < nComp; i++ {
compIndex := scan[i].compIndex
hi := d.comp[compIndex].h
vi := d.comp[compIndex].v
qt := &d.quant[d.comp[compIndex].tq]
for j := 0; j < d.comp[compIndex].h*d.comp[compIndex].v; j++ {
for j := 0; j < hi*vi; j++ {
// The blocks are traversed one MCU at a time. For 4:2:0 chroma
// subsampling, there are four Y 8x8 blocks in every 16x16 MCU.
//
Expand All @@ -197,10 +201,10 @@ func (d *decoder) processSOS(n int) error {
// 0 1 2
// 3 4 5
if nComp != 1 {
bx = d.comp[compIndex].h*mx + j%h0
by = d.comp[compIndex].v*my + j/h0
bx = hi*mx + j%hi
by = vi*my + j/hi
} else {
q := mxx * d.comp[compIndex].h
q := mxx * hi
bx = blockCount % q
by = blockCount / q
blockCount++
Expand All @@ -211,7 +215,7 @@ func (d *decoder) processSOS(n int) error {

// Load the previous partially decoded coefficients, if applicable.
if d.progressive {
b = d.progCoeffs[compIndex][by*mxx*d.comp[compIndex].h+bx]
b = d.progCoeffs[compIndex][by*mxx*hi+bx]
} else {
b = block{}
}
Expand Down Expand Up @@ -284,7 +288,7 @@ func (d *decoder) processSOS(n int) error {
if d.progressive {
if zigEnd != blockSize-1 || al != 0 {
// We haven't completely decoded this 8x8 block. Save the coefficients.
d.progCoeffs[compIndex][by*mxx*d.comp[compIndex].h+bx] = b
d.progCoeffs[compIndex][by*mxx*hi+bx] = b
// At this point, we could execute the rest of the loop body to dequantize and
// perform the inverse DCT, to save early stages of a progressive image to the
// *image.YCbCr buffers (the whole point of progressive encoding), but in Go,
Expand Down
Binary file added src/image/testdata/video-001.221212.jpeg
View file
Loading
Sorry, something went wrong. Reload?
Sorry, we cannot display this file.
Sorry, this file is invalid so it cannot be displayed.
Binary file added src/image/testdata/video-001.221212.png
View file
Loading
Sorry, something went wrong. Reload?
Sorry, we cannot display this file.
Sorry, this file is invalid so it cannot be displayed.

0 comments on commit 782db7f

Please sign in to comment.