go.image/bmp: add Encode
R=nigeltao CC=golang-dev https://golang.org/cl/13407045
This commit is contained in:
ChaiShushan
Nigel Tao
parent
de306d5329
commit
864256f267
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@ -2,7 +2,7 @@
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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 bmp implements a BMP image decoder.
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// Package bmp implements a BMP image decoder and encoder.
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//
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// The BMP specification is at http://www.digicamsoft.com/bmp/bmp.html.
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package bmp
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158
bmp/writer.go
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158
bmp/writer.go
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@ -0,0 +1,158 @@
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// Copyright 2013 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 bmp
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import (
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"encoding/binary"
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"image"
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"io"
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)
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type header struct {
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sigBM [2]byte
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fileSize uint32
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resverved [2]uint16
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pixOffset uint32
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dibHeaderSize uint32
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width uint32
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height uint32
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colorPlane uint16
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bpp uint16
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compression uint32
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imageSize uint32
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xPixelsPerMeter uint32
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yPixelsPerMeter uint32
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colorUse uint32
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colorImportant uint32
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}
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func encodePaletted(w io.Writer, pix []uint8, dx, dy, stride, step int) error {
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var padding []byte
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if dx < step {
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padding = make([]byte, step-dx)
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}
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for y := dy - 1; y >= 0; y-- {
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min := y*stride + 0
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max := y*stride + dx
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if _, err := w.Write(pix[min:max]); err != nil {
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return err
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}
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if padding != nil {
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if _, err := w.Write(padding); err != nil {
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return err
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}
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}
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}
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return nil
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}
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func encodeRGBA(w io.Writer, pix []uint8, dx, dy, stride, step int) error {
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buf := make([]byte, step)
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for y := dy - 1; y >= 0; y-- {
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min := y*stride + 0
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max := y*stride + dx*4
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off := 0
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for i := min; i < max; i += 4 {
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buf[off+2] = pix[i+0]
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buf[off+1] = pix[i+1]
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buf[off+0] = pix[i+2]
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off += 3
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}
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if _, err := w.Write(buf); err != nil {
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return err
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}
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}
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return nil
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}
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func encode(w io.Writer, m image.Image, step int) error {
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b := m.Bounds()
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buf := make([]byte, step)
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for y := b.Max.Y - 1; y >= b.Min.Y; y-- {
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off := 0
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for x := b.Min.X; x < b.Max.X; x++ {
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r, g, b, _ := m.At(x, y).RGBA()
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buf[off+2] = byte(r >> 8)
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buf[off+1] = byte(g >> 8)
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buf[off+0] = byte(b >> 8)
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off += 3
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}
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if _, err := w.Write(buf); err != nil {
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return err
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}
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}
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return nil
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}
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// Encode writes the image m to w in BMP format.
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func Encode(w io.Writer, m image.Image) error {
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d := m.Bounds().Size()
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h := &header{
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sigBM: [2]byte{'B', 'M'},
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fileSize: 14 + 40,
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pixOffset: 14 + 40,
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dibHeaderSize: 40,
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width: uint32(d.X),
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height: uint32(d.Y),
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colorPlane: 1,
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}
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var step int
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var palette []byte
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switch m := m.(type) {
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case *image.Gray:
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step = (d.X + 3) &^ 3
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palette = make([]byte, 1024)
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for i := 0; i < 256; i++ {
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palette[i*4+0] = uint8(i)
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palette[i*4+1] = uint8(i)
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palette[i*4+2] = uint8(i)
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palette[i*4+3] = 0xFF
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}
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h.imageSize = uint32(d.Y * step)
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h.fileSize += uint32(len(palette)) + h.imageSize
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h.pixOffset += uint32(len(palette))
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h.bpp = 8
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case *image.Paletted:
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step = (d.X + 3) &^ 3
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palette = make([]byte, 1024)
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for i := 0; i < len(m.Palette) && i < 256; i++ {
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r, g, b, _ := m.Palette[i].RGBA()
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palette[i*4+0] = uint8(b >> 8)
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palette[i*4+1] = uint8(g >> 8)
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palette[i*4+2] = uint8(r >> 8)
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palette[i*4+3] = 0xFF
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}
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h.imageSize = uint32(d.Y * step)
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h.fileSize += uint32(len(palette)) + h.imageSize
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h.pixOffset += uint32(len(palette))
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h.bpp = 8
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default:
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step = (3*d.X + 3) &^ 3
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h.imageSize = uint32(d.Y * step)
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h.fileSize += h.imageSize
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h.bpp = 24
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}
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if err := binary.Write(w, binary.LittleEndian, h); err != nil {
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return err
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}
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if palette != nil {
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if err := binary.Write(w, binary.LittleEndian, palette); err != nil {
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return err
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}
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}
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switch m := m.(type) {
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case *image.Gray:
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return encodePaletted(w, m.Pix, d.X, d.Y, m.Stride, step)
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case *image.Paletted:
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return encodePaletted(w, m.Pix, d.X, d.Y, m.Stride, step)
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case *image.RGBA:
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return encodeRGBA(w, m.Pix, d.X, d.Y, m.Stride, step)
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}
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return encode(w, m, step)
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}
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56
bmp/writer_test.go
Normal file
56
bmp/writer_test.go
Normal file
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@ -0,0 +1,56 @@
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// Copyright 2013 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 bmp
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import (
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"bytes"
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"image"
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"io/ioutil"
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"os"
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"testing"
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)
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func openImage(filename string) (image.Image, error) {
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f, err := os.Open(testdataDir + filename)
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if err != nil {
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return nil, err
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}
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defer f.Close()
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return Decode(f)
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}
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func TestEncode(t *testing.T) {
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img0, err := openImage("video-001.bmp")
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if err != nil {
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t.Fatal(err)
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}
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buf := new(bytes.Buffer)
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err = Encode(buf, img0)
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if err != nil {
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t.Fatal(err)
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}
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img1, err := Decode(buf)
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if err != nil {
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t.Fatal(err)
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}
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compare(t, img0, img1)
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}
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// BenchmarkEncode benchmarks the encoding of an image.
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func BenchmarkEncode(b *testing.B) {
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img, err := openImage("video-001.bmp")
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if err != nil {
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b.Fatal(err)
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}
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s := img.Bounds().Size()
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b.SetBytes(int64(s.X * s.Y * 4))
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b.ResetTimer()
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for i := 0; i < b.N; i++ {
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Encode(ioutil.Discard, img)
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}
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}
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