image/jpeg: support 4:1:1 and 4:1:0 chroma subsampling.

The test data was generated by:
convert video-001.png tmp.tga
cjpeg -quality 50 -sample 4x2,1x1,1x1 tmp.tga > video-001.q50.410.jpeg
cjpeg -quality 50 -sample 4x1,1x1,1x1 tmp.tga > video-001.q50.411.jpeg
cjpeg -quality 50 -sample 4x2,1x1,1x1 -progressive tmp.tga > video-001.q50.410.progressive.jpeg
cjpeg -quality 50 -sample 4x1,1x1,1x1 -progressive tmp.tga > video-001.q50.411.progressive.jpeg
rm tmp.tga

Change-Id: I5570389c462360f98c3160f3c6963d9466d511de
Reviewed-on: https://go-review.googlesource.com/6041
Reviewed-by: Rob Pike <r@golang.org>

diff --git a/src/image/jpeg/reader.go b/src/image/jpeg/reader.go
index 5d7fefc6cd231b79cfafe2a3cc33d42884f69788..8fcb2e06c1168b3d4f90f1157525214ccacdfdf6 100644 (file)
--- a/src/image/jpeg/reader.go
+++ b/src/image/jpeg/reader.go
@@ -42,12 +42,6 @@ const (
        maxTq   = 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
-       // and 2 in the vertical direction.
-       maxH = 2
-       maxV = 2
 )
 
 const (
@@ -346,12 +340,13 @@ func (d *decoder) processSOF(n int) error {
                d.comp[i].v = int(hv & 0x0f)
                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).
+                       // 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
+                       // (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 {
+                               if hv != 0x11 && hv != 0x21 && hv != 0x22 && hv != 0x12 && hv != 0x41 && hv != 0x42 {
                                        return UnsupportedError("luma/chroma downsample ratio")
                                }
                        } else if hv != 0x11 {

diff --git a/src/image/jpeg/reader_test.go b/src/image/jpeg/reader_test.go
index 4de2e8ee7371585bdd625a7bb03c094845623ff9..c5a36cba21273e69d4064f9addcccf8d2fc51b9e 100644 (file)
--- a/src/image/jpeg/reader_test.go
+++ b/src/image/jpeg/reader_test.go
@@ -23,6 +23,8 @@ import (
 func TestDecodeProgressive(t *testing.T) {
        testCases := []string{
                "../testdata/video-001",
+               "../testdata/video-001.q50.410",
+               "../testdata/video-001.q50.411",
                "../testdata/video-001.q50.420",
                "../testdata/video-001.q50.422",
                "../testdata/video-001.q50.440",

diff --git a/src/image/jpeg/scan.go b/src/image/jpeg/scan.go
index 41689363125841365ece2ec75fe54925bd3ab03b..8fcf401dd836ea6a0c9ba589b9ebbd8c8d4d431f 100644 (file)
--- a/src/image/jpeg/scan.go
+++ b/src/image/jpeg/scan.go
@@ -26,6 +26,10 @@ func (d *decoder) makeImg(h0, v0, mxx, myy int) {
                subsampleRatio = image.YCbCrSubsampleRatio422
        case h0 == 2 && v0 == 2:
                subsampleRatio = image.YCbCrSubsampleRatio420
+       case h0 == 4 && v0 == 1:
+               subsampleRatio = image.YCbCrSubsampleRatio411
+       case h0 == 4 && v0 == 2:
+               subsampleRatio = image.YCbCrSubsampleRatio410
        default:
                panic("unreachable")
        }
@@ -175,13 +179,8 @@ func (d *decoder) processSOS(n int) error {
                                        //      0 1 2
                                        //      3 4 5
                                        if nComp != 1 {
-                                               bx, by = d.comp[compIndex].h*mx, d.comp[compIndex].v*my
-                                               if h0 == 1 {
-                                                       by += j
-                                               } else {
-                                                       bx += j % 2
-                                                       by += j / 2
-                                               }
+                                               bx = d.comp[compIndex].h*mx + j%h0
+                                               by = d.comp[compIndex].v*my + j/h0
                                        } else {
                                                q := mxx * d.comp[compIndex].h
                                                bx = blockCount % q

diff --git a/src/image/testdata/video-001.q50.410.jpeg b/src/image/testdata/video-001.q50.410.jpeg
new file mode 100644 (file)
index 0000000..4cebd1e
Binary files /dev/null and b/src/image/testdata/video-001.q50.410.jpeg differ

diff --git a/src/image/testdata/video-001.q50.410.progressive.jpeg b/src/image/testdata/video-001.q50.410.progressive.jpeg
new file mode 100644 (file)
index 0000000..fb71402
Binary files /dev/null and b/src/image/testdata/video-001.q50.410.progressive.jpeg differ

diff --git a/src/image/testdata/video-001.q50.411.jpeg b/src/image/testdata/video-001.q50.411.jpeg
new file mode 100644 (file)
index 0000000..b90de18
Binary files /dev/null and b/src/image/testdata/video-001.q50.411.jpeg differ

diff --git a/src/image/testdata/video-001.q50.411.progressive.jpeg b/src/image/testdata/video-001.q50.411.progressive.jpeg
new file mode 100644 (file)
index 0000000..1ddb22b
Binary files /dev/null and b/src/image/testdata/video-001.q50.411.progressive.jpeg differ