func newAtFuncYCbCr(p *image.YCbCr) AtFunc {
return func(x, y int) (r, g, b, a uint32) {
yi := p.YOffset(x, y)
ci := p.COffset(x, y)
y1 := int32(p.Y[yi]) * 0x10100
cb1 := int32(p.Cb[ci]) - 128
cr1 := int32(p.Cr[ci]) - 128
r1 := (y1 + 91881*cr1) >> 8
g1 := (y1 - 22554*cb1 - 46802*cr1) >> 8
b1 := (y1 + 116130*cb1) >> 8
if r1 < 0 {
r1 = 0
} else if r1 > 0xffff {
r1 = 0xffff
}
if g1 < 0 {
g1 = 0
} else if g1 > 0xffff {
g1 = 0xffff
}
if b1 < 0 {
b1 = 0
} else if b1 > 0xffff {
b1 = 0xffff
}
return uint32(r1), uint32(g1), uint32(b1), 0xffff
}
}
// encodePGM encodes gotImage in the PGM format in the IMC4 layout.
func encodePGM(gotImage image.Image) ([]byte, error) {
var (
m *image.YCbCr
ma *nycbcra.Image
)
switch g := gotImage.(type) {
case *image.YCbCr:
m = g
case *nycbcra.Image:
m = &g.YCbCr
ma = g
default:
return nil, fmt.Errorf("lossy image did not decode to an *image.YCbCr")
}
if m.SubsampleRatio != image.YCbCrSubsampleRatio420 {
return nil, fmt.Errorf("lossy image did not decode to a 4:2:0 YCbCr")
}
b := m.Bounds()
w, h := b.Dx(), b.Dy()
w2, h2 := (w+1)/2, (h+1)/2
outW, outH := 2*w2, h+h2
if ma != nil {
outH += h
}
buf := new(bytes.Buffer)
fmt.Fprintf(buf, "P5\n%d %d\n255\n", outW, outH)
for y := b.Min.Y; y < b.Max.Y; y++ {
o := m.YOffset(b.Min.X, y)
buf.Write(m.Y[o : o+w])
if w&1 != 0 {
buf.WriteByte(0x00)
}
}
for y := b.Min.Y; y < b.Max.Y; y += 2 {
o := m.COffset(b.Min.X, y)
buf.Write(m.Cb[o : o+w2])
buf.Write(m.Cr[o : o+w2])
}
if ma != nil {
for y := b.Min.Y; y < b.Max.Y; y++ {
o := ma.AOffset(b.Min.X, y)
buf.Write(ma.A[o : o+w])
if w&1 != 0 {
buf.WriteByte(0x00)
}
}
}
return buf.Bytes(), nil
}
func convertYCbCr(dest *Image, src *image.YCbCr) {
var r, g, b uint8
var x, y, i, yi, ci int
for x = dest.Rect.Min.X; x < dest.Rect.Max.X; x++ {
for y = dest.Rect.Min.Y; y < dest.Rect.Max.Y; y++ {
yi, ci = src.YOffset(x, y), src.COffset(x, y)
r, g, b = color.YCbCrToRGB(src.Y[yi], src.Cb[ci], src.Cr[ci])
i = dest.PixOffset(x, y)
dest.Pix[i+0] = b
dest.Pix[i+1] = g
dest.Pix[i+2] = r
dest.Pix[i+3] = 0xff
}
}
}