88 lines
2.2 KiB
Go
88 lines
2.2 KiB
Go
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package image
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import (
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"image/color"
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)
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// YCbCrSubsampleRatio is the chroma subsample ratio used in a YCbCr image.
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type YCbCrSubsampleRatio int
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const (
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YCbCrSubsampleRatio444 YCbCrSubsampleRatio = iota
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YCbCrSubsampleRatio422
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YCbCrSubsampleRatio420
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)
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// YCbCr is an in-memory image of Y'CbCr colors. There is one Y sample per
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// pixel, but each Cb and Cr sample can span one or more pixels.
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// YStride is the Y slice index delta between vertically adjacent pixels.
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// CStride is the Cb and Cr slice index delta between vertically adjacent pixels
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// that map to separate chroma samples.
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// It is not an absolute requirement, but YStride and len(Y) are typically
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// multiples of 8, and:
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// For 4:4:4, CStride == YStride/1 && len(Cb) == len(Cr) == len(Y)/1.
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// For 4:2:2, CStride == YStride/2 && len(Cb) == len(Cr) == len(Y)/2.
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// For 4:2:0, CStride == YStride/2 && len(Cb) == len(Cr) == len(Y)/4.
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type YCbCr struct {
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Y []uint8
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Cb []uint8
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Cr []uint8
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YStride int
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CStride int
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SubsampleRatio YCbCrSubsampleRatio
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Rect Rectangle
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}
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func (p *YCbCr) ColorModel() color.Model {
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return color.YCbCrModel
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}
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func (p *YCbCr) Bounds() Rectangle {
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return p.Rect
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}
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func (p *YCbCr) At(x, y int) color.Color {
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if !(Point{x, y}.In(p.Rect)) {
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return color.YCbCr{}
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}
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switch p.SubsampleRatio {
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case YCbCrSubsampleRatio422:
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i := x / 2
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return color.YCbCr{
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p.Y[y*p.YStride+x],
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p.Cb[y*p.CStride+i],
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p.Cr[y*p.CStride+i],
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}
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case YCbCrSubsampleRatio420:
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i, j := x/2, y/2
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return color.YCbCr{
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p.Y[y*p.YStride+x],
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p.Cb[j*p.CStride+i],
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p.Cr[j*p.CStride+i],
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}
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}
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// Default to 4:4:4 subsampling.
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return color.YCbCr{
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p.Y[y*p.YStride+x],
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p.Cb[y*p.CStride+x],
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p.Cr[y*p.CStride+x],
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}
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}
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// SubImage returns an image representing the portion of the image p visible
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// through r. The returned value shares pixels with the original image.
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func (p *YCbCr) SubImage(r Rectangle) Image {
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q := new(YCbCr)
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*q = *p
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q.Rect = q.Rect.Intersect(r)
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return q
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}
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func (p *YCbCr) Opaque() bool {
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return true
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}
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