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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package image
import (
"image/color"
)
// YCbCrSubsampleRatio is the chroma subsample ratio used in a YCbCr image.
type YCbCrSubsampleRatio int
const (
YCbCrSubsampleRatio444 YCbCrSubsampleRatio = iota
YCbCrSubsampleRatio422
YCbCrSubsampleRatio420
)
// YCbCr is an in-memory image of Y'CbCr colors. There is one Y sample per
// pixel, but each Cb and Cr sample can span one or more pixels.
// YStride is the Y slice index delta between vertically adjacent pixels.
// CStride is the Cb and Cr slice index delta between vertically adjacent pixels
// that map to separate chroma samples.
// It is not an absolute requirement, but YStride and len(Y) are typically
// multiples of 8, and:
// For 4:4:4, CStride == YStride/1 && len(Cb) == len(Cr) == len(Y)/1.
// 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.
type YCbCr struct {
Y []uint8
Cb []uint8
Cr []uint8
YStride int
CStride int
SubsampleRatio YCbCrSubsampleRatio
Rect Rectangle
}
func (p *YCbCr) ColorModel() color.Model {
return color.YCbCrModel
}
func (p *YCbCr) Bounds() Rectangle {
return p.Rect
}
func (p *YCbCr) At(x, y int) color.Color {
if !(Point{x, y}.In(p.Rect)) {
return color.YCbCr{}
}
switch p.SubsampleRatio {
case YCbCrSubsampleRatio422:
i := x / 2
return color.YCbCr{
p.Y[y*p.YStride+x],
p.Cb[y*p.CStride+i],
p.Cr[y*p.CStride+i],
}
case YCbCrSubsampleRatio420:
i, j := x/2, y/2
return color.YCbCr{
p.Y[y*p.YStride+x],
p.Cb[j*p.CStride+i],
p.Cr[j*p.CStride+i],
}
}
// Default to 4:4:4 subsampling.
return color.YCbCr{
p.Y[y*p.YStride+x],
p.Cb[y*p.CStride+x],
p.Cr[y*p.CStride+x],
}
}
// SubImage returns an image representing the portion of the image p visible
// through r. The returned value shares pixels with the original image.
func (p *YCbCr) SubImage(r Rectangle) Image {
q := new(YCbCr)
*q = *p
q.Rect = q.Rect.Intersect(r)
return q
}
func (p *YCbCr) Opaque() bool {
return true
}
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