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convert.go
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convert.go
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package video
import (
"fmt"
"image"
"image/color"
"sync"
)
// imageToYCbCr converts src to *image.YCbCr and store it to dst
// Note: conversion can be lossy
func imageToYCbCr(dst *image.YCbCr, src image.Image) {
if dst == nil {
panic("dst can't be nil")
}
yuvImg, ok := src.(*image.YCbCr)
if ok {
*dst = *yuvImg
return
}
bounds := src.Bounds()
dy := bounds.Dy()
dx := bounds.Dx()
flat := dy * dx
if len(dst.Y)+len(dst.Cb)+len(dst.Cr) < 3*flat {
i0 := 1 * flat
i1 := 2 * flat
i2 := 3 * flat
if cap(dst.Y) < i2 {
dst.Y = make([]uint8, i2)
}
dst.Y = dst.Y[:i0]
dst.Cb = dst.Y[i0:i1]
dst.Cr = dst.Y[i1:i2]
}
dst.SubsampleRatio = image.YCbCrSubsampleRatio444
dst.YStride = dx
dst.CStride = dx
dst.Rect = bounds
switch s := src.(type) {
case *image.RGBA:
rgbaToI444(dst, s)
default:
i := 0
for yi := 0; yi < dy; yi++ {
for xi := 0; xi < dx; xi++ {
// TODO: probably try to get the alpha value with something like
// https://en.wikipedia.org/wiki/Alpha_compositing
r, g, b, _ := src.At(xi, yi).RGBA()
yy, cb, cr := color.RGBToYCbCr(uint8(r/256), uint8(g/256), uint8(b/256))
dst.Y[i] = yy
dst.Cb[i] = cb
dst.Cr[i] = cr
i++
}
}
}
}
// bytePool stores slices to be reused
// New method is not set as the slice size
// should be allocated according to subsample ratio
var bytesPool sync.Pool
// ToI420 converts r to a new reader that will output images in I420 format
func ToI420(r Reader) Reader {
var yuvImg image.YCbCr
getSlice := func(cLen int) []uint8 {
// Retrieve slice from pool
dst, ok := bytesPool.Get().([]byte)
// Compare value or capacity of retrieved object
// If less than expected, reallocate new object
if !ok || cap(dst) < 2*cLen {
// Allocating memory for Cb and Cr
dst = make([]byte, 2*cLen, 2*cLen)
}
return dst
}
return ReaderFunc(func() (image.Image, func(), error) {
img, _, err := r.Read()
if err != nil {
return nil, func() {}, err
}
var releaseFunc func() = func() {}
imageToYCbCr(&yuvImg, img)
// Covert pixel format to I420
switch yuvImg.SubsampleRatio {
case image.YCbCrSubsampleRatio420:
case image.YCbCrSubsampleRatio444:
cLen := yuvImg.CStride * yuvImg.Rect.Dy() / 4
dst := getSlice(cLen)
yuvImg = i444ToI420(yuvImg, dst)
releaseFunc = func() {
bytesPool.Put(dst)
}
case image.YCbCrSubsampleRatio422:
cLen := yuvImg.CStride * (yuvImg.Rect.Dy() / 2)
dst := getSlice(cLen)
yuvImg = i422ToI420(yuvImg, dst)
releaseFunc = func() {
bytesPool.Put(dst)
}
default:
return nil, releaseFunc, fmt.Errorf("unsupported pixel format: %s", yuvImg.SubsampleRatio)
}
return &yuvImg, releaseFunc, nil
})
}
// imageToRGBA converts src to *image.RGBA and store it to dst
func imageToRGBA(dst *image.RGBA, src image.Image) {
if dst == nil {
panic("dst can't be nil")
}
if srcRGBA, ok := src.(*image.RGBA); ok {
*dst = *srcRGBA
return
}
bounds := src.Bounds()
dy := bounds.Dy()
dx := bounds.Dx()
if len(dst.Pix) < 4*dx*dy {
dst.Pix = make([]uint8, 4*dx*dy)
}
dst.Stride = 4 * dx
dst.Rect = bounds
if srcYCbCr, ok := src.(*image.YCbCr); ok &&
srcYCbCr.SubsampleRatio == image.YCbCrSubsampleRatio444 {
i444ToRGBA(dst, srcYCbCr)
return
}
i := 0
for yi := 0; yi < dy; yi++ {
for xi := 0; xi < dx; xi++ {
r, g, b, a := src.At(xi, yi).RGBA()
dst.Pix[i+0] = uint8(r / 0x100)
dst.Pix[i+1] = uint8(g / 0x100)
dst.Pix[i+2] = uint8(b / 0x100)
dst.Pix[i+3] = uint8(a / 0x100)
i += 4
}
}
}
// ToRGBA converts r to a new reader that will output images in RGBA format
func ToRGBA(r Reader) Reader {
var dst image.RGBA
return ReaderFunc(func() (image.Image, func(), error) {
img, _, err := r.Read()
if err != nil {
return nil, func() {}, err
}
imageToRGBA(&dst, img)
return &dst, func() {}, nil
})
}