// toYCbCr converts the 8x8 region of m whose top-left corner is p to its
// YCbCr values.
func toYCbCr(m image.Image, p image.Point, yBlock, cbBlock, crBlock *block) {
b := m.Bounds()
xmax := b.Max.X - 1
ymax := b.Max.Y - 1
for j := 0; j < 8; j++ {
for i := 0; i < 8; i++ {
r, g, b, _ := m.At(min(p.X+i, xmax), min(p.Y+j, ymax)).RGBA()
yy, cb, cr := ycbcr.RGBToYCbCr(uint8(r>>8), uint8(g>>8), uint8(b>>8))
yBlock[8*j+i] = int(yy)
cbBlock[8*j+i] = int(cb)
crBlock[8*j+i] = int(cr)
}
}
}
// rgbaToYCbCr is a specialized version of toYCbCr for image.RGBA images.
func rgbaToYCbCr(m *image.RGBA, p image.Point, yBlock, cbBlock, crBlock *block) {
b := m.Bounds()
xmax := b.Max.X - 1
ymax := b.Max.Y - 1
for j := 0; j < 8; j++ {
sj := p.Y + j
if sj > ymax {
sj = ymax
}
offset := (sj-b.Min.Y)*m.Stride - b.Min.X*4
for i := 0; i < 8; i++ {
sx := p.X + i
if sx > xmax {
sx = xmax
}
pix := m.Pix[offset+sx*4:]
yy, cb, cr := ycbcr.RGBToYCbCr(pix[0], pix[1], pix[2])
yBlock[8*j+i] = int(yy)
cbBlock[8*j+i] = int(cb)
crBlock[8*j+i] = int(cr)
}
}
}
// rgbaToYCbCr is a specialized version of toYCbCr for image.RGBA images.
func rgbaToYCbCr(m *image.RGBA, p image.Point, yBlock, cbBlock, crBlock *block) {
b := m.Bounds()
xmax := b.Max.X - 1
ymax := b.Max.Y - 1
for j := 0; j < 8; j++ {
sj := p.Y + j
if sj > ymax {
sj = ymax
}
yoff := sj * m.Stride
for i := 0; i < 8; i++ {
sx := p.X + i
if sx > xmax {
sx = xmax
}
col := &m.Pix[yoff+sx]
yy, cb, cr := ycbcr.RGBToYCbCr(col.R, col.G, col.B)
yBlock[8*j+i] = int(yy)
cbBlock[8*j+i] = int(cb)
crBlock[8*j+i] = int(cr)
}
}
}