694 lines
17 KiB
Go
694 lines
17 KiB
Go
// Copyright 2009 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 png implements a PNG image decoder and encoder.
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//
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// The PNG specification is at http://www.w3.org/TR/PNG/.
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package png
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import (
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"compress/zlib"
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"encoding/binary"
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"fmt"
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"hash"
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"hash/crc32"
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"image"
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"image/color"
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"io"
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)
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// Color type, as per the PNG spec.
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const (
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ctGrayscale = 0
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ctTrueColor = 2
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ctPaletted = 3
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ctGrayscaleAlpha = 4
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ctTrueColorAlpha = 6
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)
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// A cb is a combination of color type and bit depth.
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const (
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cbInvalid = iota
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cbG1
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cbG2
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cbG4
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cbG8
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cbGA8
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cbTC8
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cbP1
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cbP2
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cbP4
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cbP8
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cbTCA8
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cbG16
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cbGA16
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cbTC16
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cbTCA16
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)
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// Filter type, as per the PNG spec.
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const (
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ftNone = 0
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ftSub = 1
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ftUp = 2
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ftAverage = 3
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ftPaeth = 4
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nFilter = 5
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)
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// Decoding stage.
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// The PNG specification says that the IHDR, PLTE (if present), IDAT and IEND
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// chunks must appear in that order. There may be multiple IDAT chunks, and
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// IDAT chunks must be sequential (i.e. they may not have any other chunks
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// between them).
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// http://www.w3.org/TR/PNG/#5ChunkOrdering
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const (
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dsStart = iota
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dsSeenIHDR
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dsSeenPLTE
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dsSeenIDAT
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dsSeenIEND
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)
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const pngHeader = "\x89PNG\r\n\x1a\n"
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type decoder struct {
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r io.Reader
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img image.Image
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crc hash.Hash32
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width, height int
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depth int
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palette color.Palette
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cb int
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stage int
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idatLength uint32
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tmp [3 * 256]byte
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}
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// A FormatError reports that the input is not a valid PNG.
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type FormatError string
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func (e FormatError) Error() string { return "png: invalid format: " + string(e) }
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var chunkOrderError = FormatError("chunk out of order")
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// An UnsupportedError reports that the input uses a valid but unimplemented PNG feature.
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type UnsupportedError string
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func (e UnsupportedError) Error() string { return "png: unsupported feature: " + string(e) }
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func min(a, b int) int {
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if a < b {
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return a
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}
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return b
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}
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func (d *decoder) parseIHDR(length uint32) error {
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if length != 13 {
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return FormatError("bad IHDR length")
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}
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if _, err := io.ReadFull(d.r, d.tmp[:13]); err != nil {
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return err
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}
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d.crc.Write(d.tmp[:13])
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if d.tmp[10] != 0 || d.tmp[11] != 0 || d.tmp[12] != 0 {
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return UnsupportedError("compression, filter or interlace method")
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}
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w := int32(binary.BigEndian.Uint32(d.tmp[0:4]))
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h := int32(binary.BigEndian.Uint32(d.tmp[4:8]))
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if w < 0 || h < 0 {
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return FormatError("negative dimension")
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}
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nPixels := int64(w) * int64(h)
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if nPixels != int64(int(nPixels)) {
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return UnsupportedError("dimension overflow")
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}
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d.cb = cbInvalid
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d.depth = int(d.tmp[8])
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switch d.depth {
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case 1:
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switch d.tmp[9] {
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case ctGrayscale:
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d.cb = cbG1
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case ctPaletted:
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d.cb = cbP1
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}
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case 2:
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switch d.tmp[9] {
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case ctGrayscale:
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d.cb = cbG2
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case ctPaletted:
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d.cb = cbP2
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}
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case 4:
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switch d.tmp[9] {
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case ctGrayscale:
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d.cb = cbG4
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case ctPaletted:
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d.cb = cbP4
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}
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case 8:
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switch d.tmp[9] {
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case ctGrayscale:
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d.cb = cbG8
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case ctTrueColor:
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d.cb = cbTC8
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case ctPaletted:
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d.cb = cbP8
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case ctGrayscaleAlpha:
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d.cb = cbGA8
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case ctTrueColorAlpha:
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d.cb = cbTCA8
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}
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case 16:
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switch d.tmp[9] {
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case ctGrayscale:
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d.cb = cbG16
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case ctTrueColor:
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d.cb = cbTC16
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case ctGrayscaleAlpha:
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d.cb = cbGA16
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case ctTrueColorAlpha:
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d.cb = cbTCA16
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}
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}
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if d.cb == cbInvalid {
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return UnsupportedError(fmt.Sprintf("bit depth %d, color type %d", d.tmp[8], d.tmp[9]))
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}
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d.width, d.height = int(w), int(h)
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return d.verifyChecksum()
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}
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func (d *decoder) parsePLTE(length uint32) error {
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np := int(length / 3) // The number of palette entries.
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if length%3 != 0 || np <= 0 || np > 256 || np > 1<<uint(d.depth) {
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return FormatError("bad PLTE length")
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}
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n, err := io.ReadFull(d.r, d.tmp[:3*np])
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if err != nil {
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return err
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}
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d.crc.Write(d.tmp[:n])
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switch d.cb {
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case cbP1, cbP2, cbP4, cbP8:
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d.palette = make(color.Palette, 256)
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for i := 0; i < np; i++ {
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d.palette[i] = color.RGBA{d.tmp[3*i+0], d.tmp[3*i+1], d.tmp[3*i+2], 0xff}
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}
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for i := np; i < 256; i++ {
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// Initialize the rest of the palette to opaque black. The spec (section
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// 11.2.3) says that "any out-of-range pixel value found in the image data
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// is an error", but some real-world PNG files have out-of-range pixel
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// values. We fall back to opaque black, the same as libpng 1.5.13;
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// ImageMagick 6.5.7 returns an error.
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d.palette[i] = color.RGBA{0x00, 0x00, 0x00, 0xff}
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}
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d.palette = d.palette[:np]
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case cbTC8, cbTCA8, cbTC16, cbTCA16:
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// As per the PNG spec, a PLTE chunk is optional (and for practical purposes,
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// ignorable) for the ctTrueColor and ctTrueColorAlpha color types (section 4.1.2).
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default:
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return FormatError("PLTE, color type mismatch")
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}
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return d.verifyChecksum()
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}
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func (d *decoder) parsetRNS(length uint32) error {
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if length > 256 {
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return FormatError("bad tRNS length")
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}
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n, err := io.ReadFull(d.r, d.tmp[:length])
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if err != nil {
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return err
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}
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d.crc.Write(d.tmp[:n])
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switch d.cb {
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case cbG8, cbG16:
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return UnsupportedError("grayscale transparency")
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case cbTC8, cbTC16:
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return UnsupportedError("truecolor transparency")
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case cbP1, cbP2, cbP4, cbP8:
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if len(d.palette) < n {
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d.palette = d.palette[:n]
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}
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for i := 0; i < n; i++ {
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rgba := d.palette[i].(color.RGBA)
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d.palette[i] = color.NRGBA{rgba.R, rgba.G, rgba.B, d.tmp[i]}
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}
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case cbGA8, cbGA16, cbTCA8, cbTCA16:
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return FormatError("tRNS, color type mismatch")
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}
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return d.verifyChecksum()
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}
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// Read presents one or more IDAT chunks as one continuous stream (minus the
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// intermediate chunk headers and footers). If the PNG data looked like:
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// ... len0 IDAT xxx crc0 len1 IDAT yy crc1 len2 IEND crc2
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// then this reader presents xxxyy. For well-formed PNG data, the decoder state
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// immediately before the first Read call is that d.r is positioned between the
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// first IDAT and xxx, and the decoder state immediately after the last Read
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// call is that d.r is positioned between yy and crc1.
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func (d *decoder) Read(p []byte) (int, error) {
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if len(p) == 0 {
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return 0, nil
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}
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for d.idatLength == 0 {
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// We have exhausted an IDAT chunk. Verify the checksum of that chunk.
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if err := d.verifyChecksum(); err != nil {
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return 0, err
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}
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// Read the length and chunk type of the next chunk, and check that
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// it is an IDAT chunk.
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if _, err := io.ReadFull(d.r, d.tmp[:8]); err != nil {
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return 0, err
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}
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d.idatLength = binary.BigEndian.Uint32(d.tmp[:4])
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if string(d.tmp[4:8]) != "IDAT" {
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return 0, FormatError("not enough pixel data")
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}
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d.crc.Reset()
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d.crc.Write(d.tmp[4:8])
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}
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if int(d.idatLength) < 0 {
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return 0, UnsupportedError("IDAT chunk length overflow")
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}
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n, err := d.r.Read(p[:min(len(p), int(d.idatLength))])
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d.crc.Write(p[:n])
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d.idatLength -= uint32(n)
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return n, err
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}
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// decode decodes the IDAT data into an image.
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func (d *decoder) decode() (image.Image, error) {
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r, err := zlib.NewReader(d)
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if err != nil {
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return nil, err
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}
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defer r.Close()
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bitsPerPixel := 0
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pixOffset := 0
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var (
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gray *image.Gray
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rgba *image.RGBA
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paletted *image.Paletted
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nrgba *image.NRGBA
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gray16 *image.Gray16
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rgba64 *image.RGBA64
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nrgba64 *image.NRGBA64
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img image.Image
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)
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switch d.cb {
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case cbG1, cbG2, cbG4, cbG8:
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bitsPerPixel = d.depth
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gray = image.NewGray(image.Rect(0, 0, d.width, d.height))
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img = gray
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case cbGA8:
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bitsPerPixel = 16
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nrgba = image.NewNRGBA(image.Rect(0, 0, d.width, d.height))
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img = nrgba
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case cbTC8:
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bitsPerPixel = 24
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rgba = image.NewRGBA(image.Rect(0, 0, d.width, d.height))
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img = rgba
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case cbP1, cbP2, cbP4, cbP8:
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bitsPerPixel = d.depth
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paletted = image.NewPaletted(image.Rect(0, 0, d.width, d.height), d.palette)
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img = paletted
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case cbTCA8:
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bitsPerPixel = 32
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nrgba = image.NewNRGBA(image.Rect(0, 0, d.width, d.height))
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img = nrgba
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case cbG16:
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bitsPerPixel = 16
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gray16 = image.NewGray16(image.Rect(0, 0, d.width, d.height))
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img = gray16
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case cbGA16:
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bitsPerPixel = 32
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nrgba64 = image.NewNRGBA64(image.Rect(0, 0, d.width, d.height))
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img = nrgba64
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case cbTC16:
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bitsPerPixel = 48
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rgba64 = image.NewRGBA64(image.Rect(0, 0, d.width, d.height))
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img = rgba64
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case cbTCA16:
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bitsPerPixel = 64
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nrgba64 = image.NewNRGBA64(image.Rect(0, 0, d.width, d.height))
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img = nrgba64
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}
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bytesPerPixel := (bitsPerPixel + 7) / 8
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// cr and pr are the bytes for the current and previous row.
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// The +1 is for the per-row filter type, which is at cr[0].
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cr := make([]uint8, 1+(bitsPerPixel*d.width+7)/8)
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pr := make([]uint8, 1+(bitsPerPixel*d.width+7)/8)
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for y := 0; y < d.height; y++ {
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// Read the decompressed bytes.
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_, err := io.ReadFull(r, cr)
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if err != nil {
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return nil, err
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}
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// Apply the filter.
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cdat := cr[1:]
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pdat := pr[1:]
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switch cr[0] {
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case ftNone:
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// No-op.
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case ftSub:
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for i := bytesPerPixel; i < len(cdat); i++ {
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cdat[i] += cdat[i-bytesPerPixel]
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}
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case ftUp:
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for i, p := range pdat {
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cdat[i] += p
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}
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case ftAverage:
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for i := 0; i < bytesPerPixel; i++ {
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cdat[i] += pdat[i] / 2
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}
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for i := bytesPerPixel; i < len(cdat); i++ {
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cdat[i] += uint8((int(cdat[i-bytesPerPixel]) + int(pdat[i])) / 2)
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}
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case ftPaeth:
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filterPaeth(cdat, pdat, bytesPerPixel)
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default:
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return nil, FormatError("bad filter type")
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}
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// Convert from bytes to colors.
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switch d.cb {
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case cbG1:
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for x := 0; x < d.width; x += 8 {
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b := cdat[x/8]
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for x2 := 0; x2 < 8 && x+x2 < d.width; x2++ {
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gray.SetGray(x+x2, y, color.Gray{(b >> 7) * 0xff})
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b <<= 1
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}
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}
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case cbG2:
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for x := 0; x < d.width; x += 4 {
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b := cdat[x/4]
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for x2 := 0; x2 < 4 && x+x2 < d.width; x2++ {
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gray.SetGray(x+x2, y, color.Gray{(b >> 6) * 0x55})
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b <<= 2
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}
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}
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case cbG4:
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for x := 0; x < d.width; x += 2 {
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b := cdat[x/2]
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for x2 := 0; x2 < 2 && x+x2 < d.width; x2++ {
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gray.SetGray(x+x2, y, color.Gray{(b >> 4) * 0x11})
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b <<= 4
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}
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}
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case cbG8:
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copy(gray.Pix[pixOffset:], cdat)
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pixOffset += gray.Stride
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case cbGA8:
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for x := 0; x < d.width; x++ {
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ycol := cdat[2*x+0]
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nrgba.SetNRGBA(x, y, color.NRGBA{ycol, ycol, ycol, cdat[2*x+1]})
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}
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case cbTC8:
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pix, i, j := rgba.Pix, pixOffset, 0
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for x := 0; x < d.width; x++ {
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pix[i+0] = cdat[j+0]
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pix[i+1] = cdat[j+1]
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pix[i+2] = cdat[j+2]
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pix[i+3] = 0xff
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i += 4
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j += 3
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}
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pixOffset += rgba.Stride
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case cbP1:
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for x := 0; x < d.width; x += 8 {
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b := cdat[x/8]
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for x2 := 0; x2 < 8 && x+x2 < d.width; x2++ {
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idx := b >> 7
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if len(paletted.Palette) <= int(idx) {
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paletted.Palette = paletted.Palette[:int(idx)+1]
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}
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paletted.SetColorIndex(x+x2, y, idx)
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b <<= 1
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}
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}
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case cbP2:
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for x := 0; x < d.width; x += 4 {
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b := cdat[x/4]
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for x2 := 0; x2 < 4 && x+x2 < d.width; x2++ {
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idx := b >> 6
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if len(paletted.Palette) <= int(idx) {
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paletted.Palette = paletted.Palette[:int(idx)+1]
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}
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paletted.SetColorIndex(x+x2, y, idx)
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b <<= 2
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}
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}
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case cbP4:
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for x := 0; x < d.width; x += 2 {
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b := cdat[x/2]
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for x2 := 0; x2 < 2 && x+x2 < d.width; x2++ {
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idx := b >> 4
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if len(paletted.Palette) <= int(idx) {
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paletted.Palette = paletted.Palette[:int(idx)+1]
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}
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paletted.SetColorIndex(x+x2, y, idx)
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b <<= 4
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}
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}
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case cbP8:
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if len(paletted.Palette) != 255 {
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for x := 0; x < d.width; x++ {
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if len(paletted.Palette) <= int(cdat[x]) {
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paletted.Palette = paletted.Palette[:int(cdat[x])+1]
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}
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}
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}
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copy(paletted.Pix[pixOffset:], cdat)
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pixOffset += paletted.Stride
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case cbTCA8:
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copy(nrgba.Pix[pixOffset:], cdat)
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pixOffset += nrgba.Stride
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case cbG16:
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for x := 0; x < d.width; x++ {
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ycol := uint16(cdat[2*x+0])<<8 | uint16(cdat[2*x+1])
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gray16.SetGray16(x, y, color.Gray16{ycol})
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}
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case cbGA16:
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for x := 0; x < d.width; x++ {
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ycol := uint16(cdat[4*x+0])<<8 | uint16(cdat[4*x+1])
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acol := uint16(cdat[4*x+2])<<8 | uint16(cdat[4*x+3])
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nrgba64.SetNRGBA64(x, y, color.NRGBA64{ycol, ycol, ycol, acol})
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}
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case cbTC16:
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for x := 0; x < d.width; x++ {
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rcol := uint16(cdat[6*x+0])<<8 | uint16(cdat[6*x+1])
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gcol := uint16(cdat[6*x+2])<<8 | uint16(cdat[6*x+3])
|
|
bcol := uint16(cdat[6*x+4])<<8 | uint16(cdat[6*x+5])
|
|
rgba64.SetRGBA64(x, y, color.RGBA64{rcol, gcol, bcol, 0xffff})
|
|
}
|
|
case cbTCA16:
|
|
for x := 0; x < d.width; x++ {
|
|
rcol := uint16(cdat[8*x+0])<<8 | uint16(cdat[8*x+1])
|
|
gcol := uint16(cdat[8*x+2])<<8 | uint16(cdat[8*x+3])
|
|
bcol := uint16(cdat[8*x+4])<<8 | uint16(cdat[8*x+5])
|
|
acol := uint16(cdat[8*x+6])<<8 | uint16(cdat[8*x+7])
|
|
nrgba64.SetNRGBA64(x, y, color.NRGBA64{rcol, gcol, bcol, acol})
|
|
}
|
|
}
|
|
|
|
// The current row for y is the previous row for y+1.
|
|
pr, cr = cr, pr
|
|
}
|
|
|
|
// Check for EOF, to verify the zlib checksum.
|
|
n, err := r.Read(pr[:1])
|
|
if err != io.EOF {
|
|
return nil, FormatError(err.Error())
|
|
}
|
|
if n != 0 || d.idatLength != 0 {
|
|
return nil, FormatError("too much pixel data")
|
|
}
|
|
|
|
return img, nil
|
|
}
|
|
|
|
func (d *decoder) parseIDAT(length uint32) (err error) {
|
|
d.idatLength = length
|
|
d.img, err = d.decode()
|
|
if err != nil {
|
|
return err
|
|
}
|
|
return d.verifyChecksum()
|
|
}
|
|
|
|
func (d *decoder) parseIEND(length uint32) error {
|
|
if length != 0 {
|
|
return FormatError("bad IEND length")
|
|
}
|
|
return d.verifyChecksum()
|
|
}
|
|
|
|
func (d *decoder) parseChunk() error {
|
|
// Read the length and chunk type.
|
|
n, err := io.ReadFull(d.r, d.tmp[:8])
|
|
if err != nil {
|
|
return err
|
|
}
|
|
length := binary.BigEndian.Uint32(d.tmp[:4])
|
|
d.crc.Reset()
|
|
d.crc.Write(d.tmp[4:8])
|
|
|
|
// Read the chunk data.
|
|
switch string(d.tmp[4:8]) {
|
|
case "IHDR":
|
|
if d.stage != dsStart {
|
|
return chunkOrderError
|
|
}
|
|
d.stage = dsSeenIHDR
|
|
return d.parseIHDR(length)
|
|
case "PLTE":
|
|
if d.stage != dsSeenIHDR {
|
|
return chunkOrderError
|
|
}
|
|
d.stage = dsSeenPLTE
|
|
return d.parsePLTE(length)
|
|
case "tRNS":
|
|
if d.stage != dsSeenPLTE {
|
|
return chunkOrderError
|
|
}
|
|
return d.parsetRNS(length)
|
|
case "IDAT":
|
|
if d.stage < dsSeenIHDR || d.stage > dsSeenIDAT || (d.cb == cbP8 && d.stage == dsSeenIHDR) {
|
|
return chunkOrderError
|
|
}
|
|
d.stage = dsSeenIDAT
|
|
return d.parseIDAT(length)
|
|
case "IEND":
|
|
if d.stage != dsSeenIDAT {
|
|
return chunkOrderError
|
|
}
|
|
d.stage = dsSeenIEND
|
|
return d.parseIEND(length)
|
|
}
|
|
// Ignore this chunk (of a known length).
|
|
var ignored [4096]byte
|
|
for length > 0 {
|
|
n, err = io.ReadFull(d.r, ignored[:min(len(ignored), int(length))])
|
|
if err != nil {
|
|
return err
|
|
}
|
|
d.crc.Write(ignored[:n])
|
|
length -= uint32(n)
|
|
}
|
|
return d.verifyChecksum()
|
|
}
|
|
|
|
func (d *decoder) verifyChecksum() error {
|
|
if _, err := io.ReadFull(d.r, d.tmp[:4]); err != nil {
|
|
return err
|
|
}
|
|
if binary.BigEndian.Uint32(d.tmp[:4]) != d.crc.Sum32() {
|
|
return FormatError("invalid checksum")
|
|
}
|
|
return nil
|
|
}
|
|
|
|
func (d *decoder) checkHeader() error {
|
|
_, err := io.ReadFull(d.r, d.tmp[:len(pngHeader)])
|
|
if err != nil {
|
|
return err
|
|
}
|
|
if string(d.tmp[:len(pngHeader)]) != pngHeader {
|
|
return FormatError("not a PNG file")
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// Decode reads a PNG image from r and returns it as an image.Image.
|
|
// The type of Image returned depends on the PNG contents.
|
|
func Decode(r io.Reader) (image.Image, error) {
|
|
d := &decoder{
|
|
r: r,
|
|
crc: crc32.NewIEEE(),
|
|
}
|
|
if err := d.checkHeader(); err != nil {
|
|
if err == io.EOF {
|
|
err = io.ErrUnexpectedEOF
|
|
}
|
|
return nil, err
|
|
}
|
|
for d.stage != dsSeenIEND {
|
|
if err := d.parseChunk(); err != nil {
|
|
if err == io.EOF {
|
|
err = io.ErrUnexpectedEOF
|
|
}
|
|
return nil, err
|
|
}
|
|
}
|
|
return d.img, nil
|
|
}
|
|
|
|
// DecodeConfig returns the color model and dimensions of a PNG image without
|
|
// decoding the entire image.
|
|
func DecodeConfig(r io.Reader) (image.Config, error) {
|
|
d := &decoder{
|
|
r: r,
|
|
crc: crc32.NewIEEE(),
|
|
}
|
|
if err := d.checkHeader(); err != nil {
|
|
if err == io.EOF {
|
|
err = io.ErrUnexpectedEOF
|
|
}
|
|
return image.Config{}, err
|
|
}
|
|
for {
|
|
if err := d.parseChunk(); err != nil {
|
|
if err == io.EOF {
|
|
err = io.ErrUnexpectedEOF
|
|
}
|
|
return image.Config{}, err
|
|
}
|
|
paletted := d.cb == cbP8 || d.cb == cbP4 || d.cb == cbP2 || d.cb == cbP1
|
|
if d.stage == dsSeenIHDR && !paletted {
|
|
break
|
|
}
|
|
if d.stage == dsSeenPLTE && paletted {
|
|
break
|
|
}
|
|
}
|
|
var cm color.Model
|
|
switch d.cb {
|
|
case cbG1, cbG2, cbG4, cbG8:
|
|
cm = color.GrayModel
|
|
case cbGA8:
|
|
cm = color.NRGBAModel
|
|
case cbTC8:
|
|
cm = color.RGBAModel
|
|
case cbP1, cbP2, cbP4, cbP8:
|
|
cm = d.palette
|
|
case cbTCA8:
|
|
cm = color.NRGBAModel
|
|
case cbG16:
|
|
cm = color.Gray16Model
|
|
case cbGA16:
|
|
cm = color.NRGBA64Model
|
|
case cbTC16:
|
|
cm = color.RGBA64Model
|
|
case cbTCA16:
|
|
cm = color.NRGBA64Model
|
|
}
|
|
return image.Config{
|
|
ColorModel: cm,
|
|
Width: d.width,
|
|
Height: d.height,
|
|
}, nil
|
|
}
|
|
|
|
func init() {
|
|
image.RegisterFormat("png", pngHeader, Decode, DecodeConfig)
|
|
}
|