golang-image/webp/decode.go

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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 webp implements a decoder for WEBP images.
//
// WEBP is defined at:
// https://developers.google.com/speed/webp/docs/riff_container
package webp
import (
"errors"
"image"
"image/color"
"io"
"code.google.com/p/go.image/vp8"
"code.google.com/p/go.image/vp8l"
)
const (
formatVP8 = 1
formatVP8L = 2
)
func decode(r io.Reader, configOnly bool) (image.Image, image.Config, error) {
var b [20]byte
if _, err := io.ReadFull(r, b[:]); err != nil {
return nil, image.Config{}, err
}
format := 0
switch string(b[8:16]) {
case "WEBPVP8 ":
format = formatVP8
case "WEBPVP8L":
format = formatVP8L
}
if string(b[:4]) != "RIFF" || format == 0 {
return nil, image.Config{}, errors.New("webp: invalid format")
}
riffLen := uint32(b[4]) | uint32(b[5])<<8 | uint32(b[6])<<16 | uint32(b[7])<<24
dataLen := uint32(b[16]) | uint32(b[17])<<8 | uint32(b[18])<<16 | uint32(b[19])<<24
if riffLen < dataLen+12 {
return nil, image.Config{}, errors.New("webp: invalid format")
}
if dataLen >= 1<<31 {
return nil, image.Config{}, errors.New("webp: invalid format")
}
if format == formatVP8 {
d := vp8.NewDecoder()
d.Init(r, int(dataLen))
fh, err := d.DecodeFrameHeader()
if err != nil {
return nil, image.Config{}, err
}
if configOnly {
return nil, image.Config{
ColorModel: color.YCbCrModel,
Width: fh.Width,
Height: fh.Height,
}, nil
}
m, err := d.DecodeFrame()
return m, image.Config{}, nil
}
vp8: skip filtering for all-zero-DC macroblock residuals. This makes the Go code match the libwebp C code's output on blue-purple-pink-large.*-filter.lossy.webp Also make the various WEBP benchmarks all decode a similar image, the image at http://blog.golang.org/gophercon/image01.jpg, to make it more meaningful to e.g. compare the simple filter's numbers with the normal filter's numbers. Also fix a "go vet" warning in webp/decode.go. The test data was generated by: wget http://blog.golang.org/gophercon/image01.jpg -O blue-purple-pink-large.jpeg convert blue-purple-pink-large.jpeg blue-purple-pink-large.png cwebp -lossless blue-purple-pink-large.png -o blue-purple-pink-large.lossless.webp cwebp -q 80 -f 0 blue-purple-pink-large.png -o blue-purple-pink-large.no-filter.lossy.webp cwebp -q 80 -strong blue-purple-pink-large.png -o blue-purple-pink-large.normal-filter.lossy.webp cwebp -q 80 -nostrong blue-purple-pink-large.png -o blue-purple-pink-large.simple-filter.lossy.webp dwebp -pgm blue-purple-pink-large.no-filter.lossy.webp -o tmp.pgm && convert tmp.pgm blue-purple-pink-large.no-filter.lossy.webp.ycbcr.png && rm tmp.pgm dwebp -pgm blue-purple-pink-large.normal-filter.lossy.webp -o tmp.pgm && convert tmp.pgm blue-purple-pink-large.normal-filter.lossy.webp.ycbcr.png && rm tmp.pgm dwebp -pgm blue-purple-pink-large.simple-filter.lossy.webp -o tmp.pgm && convert tmp.pgm blue-purple-pink-large.simple-filter.lossy.webp.ycbcr.png && rm tmp.pgm LGTM=r R=r CC=golang-codereviews https://golang.org/cl/106230044
2014-06-30 02:36:25 +02:00
r = &io.LimitedReader{R: r, N: int64(dataLen)}
if configOnly {
c, err := vp8l.DecodeConfig(r)
return nil, c, err
}
m, err := vp8l.Decode(r)
return m, image.Config{}, err
}
// Decode reads a WEBP image from r and returns it as an image.Image.
func Decode(r io.Reader) (image.Image, error) {
m, _, err := decode(r, false)
if err != nil {
return nil, err
}
return m, err
}
// DecodeConfig returns the color model and dimensions of a WEBP image without
// decoding the entire image.
func DecodeConfig(r io.Reader) (image.Config, error) {
_, c, err := decode(r, true)
return c, err
}
func init() {
image.RegisterFormat("webp", "RIFF????WEBPVP8", Decode, DecodeConfig)
}