func drawYCbCr(dst *image.RGBA, r image.Rectangle, src *ycbcr.YCbCr, sp image.Point) {
// A YCbCr image is always fully opaque, and so if the mask is implicitly nil
// (i.e. fully opaque) then the op is effectively always Src.
var (
yy, cb, cr uint8
)
x0 := (r.Min.X - dst.Rect.Min.X) * 4
x1 := (r.Max.X - dst.Rect.Min.X) * 4
y0 := r.Min.Y - dst.Rect.Min.Y
y1 := r.Max.Y - dst.Rect.Min.Y
switch src.SubsampleRatio {
case ycbcr.SubsampleRatio422:
for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
dpix := dst.Pix[y*dst.Stride:]
for x, sx := x0, sp.X; x != x1; x, sx = x+4, sx+1 {
i := sx / 2
yy = src.Y[sy*src.YStride+sx]
cb = src.Cb[sy*src.CStride+i]
cr = src.Cr[sy*src.CStride+i]
rr, gg, bb := ycbcr.YCbCrToRGB(yy, cb, cr)
dpix[x+0] = rr
dpix[x+1] = gg
dpix[x+2] = bb
dpix[x+3] = 255
}
}
case ycbcr.SubsampleRatio420:
for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
dpix := dst.Pix[y*dst.Stride:]
for x, sx := x0, sp.X; x != x1; x, sx = x+4, sx+1 {
i, j := sx/2, sy/2
yy = src.Y[sy*src.YStride+sx]
cb = src.Cb[j*src.CStride+i]
cr = src.Cr[j*src.CStride+i]
rr, gg, bb := ycbcr.YCbCrToRGB(yy, cb, cr)
dpix[x+0] = rr
dpix[x+1] = gg
dpix[x+2] = bb
dpix[x+3] = 255
}
}
default:
// Default to 4:4:4 subsampling.
for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
dpix := dst.Pix[y*dst.Stride:]
for x, sx := x0, sp.X; x != x1; x, sx = x+4, sx+1 {
yy = src.Y[sy*src.YStride+sx]
cb = src.Cb[sy*src.CStride+sx]
cr = src.Cr[sy*src.CStride+sx]
rr, gg, bb := ycbcr.YCbCrToRGB(yy, cb, cr)
dpix[x+0] = rr
dpix[x+1] = gg
dpix[x+2] = bb
dpix[x+3] = 255
}
}
}
}
func drawYCbCr(dst *image.RGBA, r image.Rectangle, src *ycbcr.YCbCr, sp image.Point) {
// A YCbCr image is always fully opaque, and so if the mask is implicitly nil
// (i.e. fully opaque) then the op is effectively always Src.
var (
yy, cb, cr uint8
rr, gg, bb uint8
)
switch src.SubsampleRatio {
case ycbcr.SubsampleRatio422:
for y, sy := r.Min.Y, sp.Y; y != r.Max.Y; y, sy = y+1, sy+1 {
dpix := dst.Pix[y*dst.Stride : (y+1)*dst.Stride]
for x, sx := r.Min.X, sp.X; x != r.Max.X; x, sx = x+1, sx+1 {
i := sx / 2
yy = src.Y[sy*src.YStride+sx]
cb = src.Cb[sy*src.CStride+i]
cr = src.Cr[sy*src.CStride+i]
rr, gg, bb = ycbcr.YCbCrToRGB(yy, cb, cr)
dpix[x] = image.RGBAColor{rr, gg, bb, 255}
}
}
case ycbcr.SubsampleRatio420:
for y, sy := r.Min.Y, sp.Y; y != r.Max.Y; y, sy = y+1, sy+1 {
dpix := dst.Pix[y*dst.Stride : (y+1)*dst.Stride]
for x, sx := r.Min.X, sp.X; x != r.Max.X; x, sx = x+1, sx+1 {
i, j := sx/2, sy/2
yy = src.Y[sy*src.YStride+sx]
cb = src.Cb[j*src.CStride+i]
cr = src.Cr[j*src.CStride+i]
rr, gg, bb = ycbcr.YCbCrToRGB(yy, cb, cr)
dpix[x] = image.RGBAColor{rr, gg, bb, 255}
}
}
default:
// Default to 4:4:4 subsampling.
for y, sy := r.Min.Y, sp.Y; y != r.Max.Y; y, sy = y+1, sy+1 {
dpix := dst.Pix[y*dst.Stride : (y+1)*dst.Stride]
for x, sx := r.Min.X, sp.X; x != r.Max.X; x, sx = x+1, sx+1 {
yy = src.Y[sy*src.YStride+sx]
cb = src.Cb[sy*src.CStride+sx]
cr = src.Cr[sy*src.CStride+sx]
rr, gg, bb = ycbcr.YCbCrToRGB(yy, cb, cr)
dpix[x] = image.RGBAColor{rr, gg, bb, 255}
}
}
}
}
// resizeYCbCr returns a scaled copy of the YCbCr image slice r of m.
// The returned image has width w and height h.
func resizeYCbCr(m *ycbcr.YCbCr, r image.Rectangle, w, h int) (image.Image, bool) {
var verticalRes int
switch m.SubsampleRatio {
case ycbcr.SubsampleRatio420:
verticalRes = 2
case ycbcr.SubsampleRatio422:
verticalRes = 1
default:
return nil, false
}
ww, hh := uint64(w), uint64(h)
dx, dy := uint64(r.Dx()), uint64(r.Dy())
// See comment in Resize.
n, sum := dx*dy, make([]uint64, 4*w*h)
for y := r.Min.Y; y < r.Max.Y; y++ {
Y := m.Y[y*m.YStride:]
Cb := m.Cb[y/verticalRes*m.CStride:]
Cr := m.Cr[y/verticalRes*m.CStride:]
for x := r.Min.X; x < r.Max.X; x++ {
// Get the source pixel.
r8, g8, b8 := ycbcr.YCbCrToRGB(Y[x], Cb[x/2], Cr[x/2])
r64 := uint64(r8)
g64 := uint64(g8)
b64 := uint64(b8)
// Spread the source pixel over 1 or more destination rows.
py := uint64(y) * hh
for remy := hh; remy > 0; {
qy := dy - (py % dy)
if qy > remy {
qy = remy
}
// Spread the source pixel over 1 or more destination columns.
px := uint64(x) * ww
index := 4 * ((py/dy)*ww + (px / dx))
for remx := ww; remx > 0; {
qx := dx - (px % dx)
if qx > remx {
qx = remx
}
qxy := qx * qy
sum[index+0] += r64 * qxy
sum[index+1] += g64 * qxy
sum[index+2] += b64 * qxy
sum[index+3] += 0xFFFF * qxy
index += 4
px += qx
remx -= qx
}
py += qy
remy -= qy
}
}
}
return average(sum, w, h, n), true
}