diff options
Diffstat (limited to 'libgo/go/image/color/ycbcr.go')
| -rw-r--r-- | libgo/go/image/color/ycbcr.go | 110 |
1 files changed, 70 insertions, 40 deletions
diff --git a/libgo/go/image/color/ycbcr.go b/libgo/go/image/color/ycbcr.go index 904434f6a3d..3df5d3675d6 100644 --- a/libgo/go/image/color/ycbcr.go +++ b/libgo/go/image/color/ycbcr.go @@ -15,24 +15,37 @@ func RGBToYCbCr(r, g, b uint8) (uint8, uint8, uint8) { r1 := int32(r) g1 := int32(g) b1 := int32(b) + + // yy is in range [0,0xff]. yy := (19595*r1 + 38470*g1 + 7471*b1 + 1<<15) >> 16 - cb := (-11056*r1 - 21712*g1 + 32768*b1 + 257<<15) >> 16 - cr := (32768*r1 - 27440*g1 - 5328*b1 + 257<<15) >> 16 - if yy < 0 { - yy = 0 - } else if yy > 0xff { - yy = 0xff - } - if cb < 0 { - cb = 0 - } else if cb > 0xff { - cb = 0xff + + // The bit twiddling below is equivalent to + // + // cb := (-11056*r1 - 21712*g1 + 32768*b1 + 257<<15) >> 16 + // if cb < 0 { + // cb = 0 + // } else if cb > 0xff { + // cb = ^int32(0) + // } + // + // but uses fewer branches and is faster. + // Note that the uint8 type conversion in the return + // statement will convert ^int32(0) to 0xff. + // The code below to compute cr uses a similar pattern. + cb := -11056*r1 - 21712*g1 + 32768*b1 + 257<<15 + if uint32(cb)&0xff000000 == 0 { + cb >>= 16 + } else { + cb = ^(cb >> 31) } - if cr < 0 { - cr = 0 - } else if cr > 0xff { - cr = 0xff + + cr := 32768*r1 - 27440*g1 - 5328*b1 + 257<<15 + if uint32(cr)&0xff000000 == 0 { + cr >>= 16 + } else { + cr = ^(cr >> 31) } + return uint8(yy), uint8(cb), uint8(cr) } @@ -44,27 +57,44 @@ func YCbCrToRGB(y, cb, cr uint8) (uint8, uint8, uint8) { // B = Y' + 1.77200*(Cb-128) // http://www.w3.org/Graphics/JPEG/jfif3.pdf says Y but means Y'. - yy1 := int32(y) * 0x10100 // Convert 0x12 to 0x121200. + yy1 := int32(y) * 0x010100 // Convert 0x12 to 0x121200. cb1 := int32(cb) - 128 cr1 := int32(cr) - 128 - r := (yy1 + 91881*cr1) >> 16 - g := (yy1 - 22554*cb1 - 46802*cr1) >> 16 - b := (yy1 + 116130*cb1) >> 16 - if r < 0 { - r = 0 - } else if r > 0xff { - r = 0xff + + // The bit twiddling below is equivalent to + // + // r := (yy1 + 91881*cr1) >> 16 + // if r < 0 { + // r = 0 + // } else if r > 0xff { + // r = ^int32(0) + // } + // + // but uses fewer branches and is faster. + // Note that the uint8 type conversion in the return + // statement will convert ^int32(0) to 0xff. + // The code below to compute g and b uses a similar pattern. + r := yy1 + 91881*cr1 + if uint32(r)&0xff000000 == 0 { + r >>= 16 + } else { + r = ^(r >> 31) } - if g < 0 { - g = 0 - } else if g > 0xff { - g = 0xff + + g := yy1 - 22554*cb1 - 46802*cr1 + if uint32(g)&0xff000000 == 0 { + g >>= 16 + } else { + g = ^(g >> 31) } - if b < 0 { - b = 0 - } else if b > 0xff { - b = 0xff + + b := yy1 + 116130*cb1 + if uint32(b)&0xff000000 == 0 { + b >>= 16 + } else { + b = ^(b >> 31) } + return uint8(r), uint8(g), uint8(b) } @@ -220,10 +250,10 @@ func RGBToCMYK(r, g, b uint8) (uint8, uint8, uint8, uint8) { // CMYKToRGB converts a CMYK quadruple to an RGB triple. func CMYKToRGB(c, m, y, k uint8) (uint8, uint8, uint8) { - w := uint32(0xffff - uint32(k)*0x101) - r := uint32(0xffff-uint32(c)*0x101) * w / 0xffff - g := uint32(0xffff-uint32(m)*0x101) * w / 0xffff - b := uint32(0xffff-uint32(y)*0x101) * w / 0xffff + w := 0xffff - uint32(k)*0x101 + r := (0xffff - uint32(c)*0x101) * w / 0xffff + g := (0xffff - uint32(m)*0x101) * w / 0xffff + b := (0xffff - uint32(y)*0x101) * w / 0xffff return uint8(r >> 8), uint8(g >> 8), uint8(b >> 8) } @@ -239,11 +269,11 @@ func (c CMYK) RGBA() (uint32, uint32, uint32, uint32) { // This code is a copy of the CMYKToRGB function above, except that it // returns values in the range [0, 0xffff] instead of [0, 0xff]. - w := uint32(0xffff - uint32(c.K)*0x101) - r := uint32(0xffff-uint32(c.C)*0x101) * w / 0xffff - g := uint32(0xffff-uint32(c.M)*0x101) * w / 0xffff - b := uint32(0xffff-uint32(c.Y)*0x101) * w / 0xffff - return uint32(r), uint32(g), uint32(b), 0xffff + w := 0xffff - uint32(c.K)*0x101 + r := (0xffff - uint32(c.C)*0x101) * w / 0xffff + g := (0xffff - uint32(c.M)*0x101) * w / 0xffff + b := (0xffff - uint32(c.Y)*0x101) * w / 0xffff + return r, g, b, 0xffff } // CMYKModel is the Model for CMYK colors. |