image: add YCbCrSubsampleRatio411 and YCbCrSubsampleRatio410.

Some real world JPEG images are in 4:1:1 and 4:1:0 formats.

See also http://en.wikipedia.org/wiki/Chroma_subsampling

Change-Id: I2d51a41944f581cf11f4ab975046b1737271842f
Reviewed-on: https://go-review.googlesource.com/5838
Reviewed-by: Rob Pike <r@golang.org>

diff --git a/src/image/ycbcr.go b/src/image/ycbcr.go
index 0126060d00c1bae82e590fa6ae4112c6f66057fe..93c354b33b41c04eaf2b2dd45c9cbc14b4704c6e 100644 (file)
--- a/src/image/ycbcr.go
+++ b/src/image/ycbcr.go
@@ -16,6 +16,8 @@ const (
        YCbCrSubsampleRatio422
        YCbCrSubsampleRatio420
        YCbCrSubsampleRatio440
+       YCbCrSubsampleRatio411
+       YCbCrSubsampleRatio410
 )
 
 func (s YCbCrSubsampleRatio) String() string {
@@ -28,6 +30,10 @@ func (s YCbCrSubsampleRatio) String() string {
                return "YCbCrSubsampleRatio420"
        case YCbCrSubsampleRatio440:
                return "YCbCrSubsampleRatio440"
+       case YCbCrSubsampleRatio411:
+               return "YCbCrSubsampleRatio411"
+       case YCbCrSubsampleRatio410:
+               return "YCbCrSubsampleRatio410"
        }
        return "YCbCrSubsampleRatioUnknown"
 }
@@ -43,6 +49,8 @@ func (s YCbCrSubsampleRatio) String() string {
 //     For 4:2:2, CStride == YStride/2 && len(Cb) == len(Cr) == len(Y)/2.
 //     For 4:2:0, CStride == YStride/2 && len(Cb) == len(Cr) == len(Y)/4.
 //     For 4:4:0, CStride == YStride/1 && len(Cb) == len(Cr) == len(Y)/2.
+//     For 4:1:1, CStride == YStride/4 && len(Cb) == len(Cr) == len(Y)/4.
+//     For 4:1:0, CStride == YStride/4 && len(Cb) == len(Cr) == len(Y)/8.
 type YCbCr struct {
        Y, Cb, Cr      []uint8
        YStride        int
@@ -92,6 +100,10 @@ func (p *YCbCr) COffset(x, y int) int {
                return (y/2-p.Rect.Min.Y/2)*p.CStride + (x/2 - p.Rect.Min.X/2)
        case YCbCrSubsampleRatio440:
                return (y/2-p.Rect.Min.Y/2)*p.CStride + (x - p.Rect.Min.X)
+       case YCbCrSubsampleRatio411:
+               return (y-p.Rect.Min.Y)*p.CStride + (x/4 - p.Rect.Min.X/4)
+       case YCbCrSubsampleRatio410:
+               return (y/2-p.Rect.Min.Y/2)*p.CStride + (x/4 - p.Rect.Min.X/4)
        }
        // Default to 4:4:4 subsampling.
        return (y-p.Rect.Min.Y)*p.CStride + (x - p.Rect.Min.X)
@@ -139,6 +151,12 @@ func NewYCbCr(r Rectangle, subsampleRatio YCbCrSubsampleRatio) *YCbCr {
        case YCbCrSubsampleRatio440:
                cw = w
                ch = (r.Max.Y+1)/2 - r.Min.Y/2
+       case YCbCrSubsampleRatio411:
+               cw = (r.Max.X+3)/4 - r.Min.X/4
+               ch = h
+       case YCbCrSubsampleRatio410:
+               cw = (r.Max.X+3)/4 - r.Min.X/4
+               ch = (r.Max.Y+1)/2 - r.Min.Y/2
        default:
                // Default to 4:4:4 subsampling.
                cw = w

diff --git a/src/image/ycbcr_test.go b/src/image/ycbcr_test.go
index 5ab4fc3fea44cb1f5615e67ff4dff9ab3a2c45a7..4996bc8dcaeeb1d67b5adbdcbf58aa4723179c6e 100644 (file)
--- a/src/image/ycbcr_test.go
+++ b/src/image/ycbcr_test.go
@@ -37,6 +37,8 @@ func TestYCbCr(t *testing.T) {
                YCbCrSubsampleRatio422,
                YCbCrSubsampleRatio420,
                YCbCrSubsampleRatio440,
+               YCbCrSubsampleRatio411,
+               YCbCrSubsampleRatio410,
        }
        deltas := []Point{
                Pt(0, 0),