// Copyright 2009 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 jpeg implements a JPEG image decoder and encoder.
//
// JPEG is defined in ITU-T T.81: https://www.w3.org/Graphics/JPEG/itu-t81.pdf.
package jpeg
import (
"image"
"image/color"
"image/internal/imageutil"
"io"
)
// TODO(nigeltao): fix up the doc comment style so that sentences start with
// the name of the type or function that they annotate.
// A FormatError reports that the input is not a valid JPEG.
type FormatError string
func (e FormatError) Error() string { return "invalid JPEG format: " + string(e) }
// An UnsupportedError reports that the input uses a valid but unimplemented JPEG feature.
type UnsupportedError string
func (e UnsupportedError) Error() string { return "unsupported JPEG feature: " + string(e) }
var errUnsupportedSubsamplingRatio = UnsupportedError("luma/chroma subsampling ratio")
// Component specification, specified in section B.2.2.
type component struct {
h int // Horizontal sampling factor.
v int // Vertical sampling factor.
c uint8 // Component identifier.
tq uint8 // Quantization table destination selector.
}
const (
dcTable = 0
acTable = 1
maxTc = 1
maxTh = 3
maxTq = 3
maxComponents = 4
)
const (
sof0Marker = 0xc0 // Start Of Frame (Baseline Sequential).
sof1Marker = 0xc1 // Start Of Frame (Extended Sequential).
sof2Marker = 0xc2 // Start Of Frame (Progressive).
dhtMarker = 0xc4 // Define Huffman Table.
rst0Marker = 0xd0 // ReSTart (0).
rst7Marker = 0xd7 // ReSTart (7).
soiMarker = 0xd8 // Start Of Image.
eoiMarker = 0xd9 // End Of Image.
sosMarker = 0xda // Start Of Scan.
dqtMarker = 0xdb // Define Quantization Table.
driMarker = 0xdd // Define Restart Interval.
comMarker = 0xfe // COMment.
// "APPlication specific" markers aren't part of the JPEG spec per se,
// but in practice, their use is described at
// https://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/JPEG.html
app0Marker = 0xe0
app14Marker = 0xee
app15Marker = 0xef
)
// See https://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/JPEG.html#Adobe
const (
adobeTransformUnknown = 0
adobeTransformYCbCr = 1
adobeTransformYCbCrK = 2
)
// unzig maps from the zig-zag ordering to the natural ordering. For example,
// unzig[3] is the column and row of the fourth element in zig-zag order. The
// value is 16, which means first column (16%8 == 0) and third row (16/8 == 2).
var unzig = [blockSize]int{
0, 1, 8, 16, 9, 2, 3, 10,
17, 24, 32, 25, 18, 11, 4, 5,
12, 19, 26, 33, 40, 48, 41, 34,
27, 20, 13, 6, 7, 14, 21, 28,
35, 42, 49, 56, 57, 50, 43, 36,
29, 22, 15, 23, 30, 37, 44, 51,
58, 59, 52, 45, 38, 31, 39, 46,
53, 60, 61, 54, 47, 55, 62, 63,
}
// Deprecated: Reader is not used by the image/jpeg package and should
// not be used by others. It is kept for compatibility.
type Reader interface {
io.ByteReader
io.Reader
}
// bits holds the unprocessed bits that have been taken from the byte-stream.
// The n least significant bits of a form the unread bits, to be read in MSB to
// LSB order.
type bits struct {
a uint32 // accumulator.
m uint32 // mask. m==1<<(n-1) when n>0, with m==0 when n==0.
n int32 // the number of unread bits in a.
}
type decoder struct {
r io.Reader
bits bits
// bytes is a byte buffer, similar to a bufio.Reader, except that it
// has to be able to unread more than 1 byte, due to byte stuffing.
// Byte stuffing is specified in section F.1.2.3.
bytes struct {
// buf[i:j] are the buffered bytes read from the underlying
// io.Reader that haven't yet been passed further on.
buf [4096]byte
i, j int
// nUnreadable is the number of bytes to back up i after
// overshooting. It can be 0, 1 or 2.
nUnreadable int
}
width, height int
img1 *image.Gray
img3 *image.YCbCr
blackPix []byte
blackStride int
ri int // Restart Interval.
nComp int
// As per section 4.5, there are four modes of operation (selected by the
// SOF? markers): sequential DCT, progressive DCT, lossless and
// hierarchical, although this implementation does not support the latter
// two non-DCT modes. Sequential DCT is further split into baseline and
// extended, as per section 4.11.
baseline bool
progressive bool
jfif bool
adobeTransformValid bool
adobeTransform uint8
eobRun uint16 // End-of-Band run, specified in section G.1.2.2.
comp [maxComponents]component
progCoeffs [maxComponents][]block // Saved state between progressive-mode scans.
huff [maxTc + 1][maxTh + 1]huffman
quant [maxTq + 1]block // Quantization tables, in zig-zag order.
tmp [2 * blockSize]byte
}
// fill fills up the d.bytes.buf buffer from the underlying io.Reader. It
// should only be called when there are no unread bytes in d.bytes.
func (d *decoder) fill() error {
if d.bytes.i != d.bytes.j {
panic("jpeg: fill called when unread bytes exist")
}
// Move the last 2 bytes to the start of the buffer, in case we need
// to call unreadByteStuffedByte.
if d.bytes.j > 2 {
d.bytes.buf[0] = d.bytes.buf[d.bytes.j-2]
d.bytes.buf[1] = d.bytes.buf[d.bytes.j-1]
d.bytes.i, d.bytes.j = 2, 2
}
// Fill in the rest of the buffer.
n, err := d.r.Read(d.bytes.buf[d.bytes.j:])
d.bytes.j += n
if n > 0 {
err = nil
}
return err
}
// unreadByteStuffedByte undoes the most recent readByteStuffedByte call,
// giving a byte of data back from d.bits to d.bytes. The Huffman look-up table
// requires at least 8 bits for look-up, which means that Huffman decoding can
// sometimes overshoot and read one or two too many bytes. Two-byte overshoot
// can happen when expecting to read a 0xff 0x00 byte-stuffed byte.
func (d *decoder) unreadByteStuffedByte() {
d.bytes.i -= d.bytes.nUnreadable
d.bytes.nUnreadable = 0
if d.bits.n >= 8 {
d.bits.a >>= 8
d.bits.n -= 8
d.bits.m >>= 8
}
}
// readByte returns the next byte, whether buffered or not buffered. It does
// not care about byte stuffing.
func (d *decoder) readByte() (x byte, err error) {
for d.bytes.i == d.bytes.j {
if err = d.fill(); err != nil {
return 0, err
}
}
x = d.bytes.buf[d.bytes.i]
d.bytes.i++
d.bytes.nUnreadable = 0
return x, nil
}
// errMissingFF00 means that readByteStuffedByte encountered an 0xff byte (a
// marker byte) that wasn't the expected byte-stuffed sequence 0xff, 0x00.
var errMissingFF00 = FormatError("missing 0xff00 sequence")
// readByteStuffedByte is like readByte but is for byte-stuffed Huffman data.
func (d *decoder) readByteStuffedByte() (x byte, err error) {
// Take the fast path if d.bytes.buf contains at least two bytes.
if d.bytes.i+2 <= d.bytes.j {
x = d.bytes.buf[d.bytes.i]
d.bytes.i++
d.bytes.nUnreadable = 1
if x != 0xff {
return x, err
}
if d.bytes.buf[d.bytes.i] != 0x00 {
return 0, errMissingFF00
}
d.bytes.i++
d.bytes.nUnreadable = 2
return 0xff, nil
}
d.bytes.nUnreadable = 0
x, err = d.readByte()
if err != nil {
return 0, err
}
d.bytes.nUnreadable = 1
if x != 0xff {
return x, nil
}
x, err = d.readByte()
if err != nil {
return 0, err
}
d.bytes.nUnreadable = 2
if x != 0x00 {
return 0, errMissingFF00
}
return 0xff, nil
}
// readFull reads exactly len(p) bytes into p. It does not care about byte
// stuffing.
func (d *decoder) readFull(p []byte) error {
// Unread the overshot bytes, if any.
if d.bytes.nUnreadable != 0 {
if d.bits.n >= 8 {
d.unreadByteStuffedByte()
}
d.bytes.nUnreadable = 0
}
for {
n := copy(p, d.bytes.buf[d.bytes.i:d.bytes.j])
p = p[n:]
d.bytes.i += n
if len(p) == 0 {
break
}
if err := d.fill(); err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return err
}
}
return nil
}
// ignore ignores the next n bytes.
func (d *decoder) ignore(n int) error {
// Unread the overshot bytes, if any.
if d.bytes.nUnreadable != 0 {
if d.bits.n >= 8 {
d.unreadByteStuffedByte()
}
d.bytes.nUnreadable = 0
}
for {
m := d.bytes.j - d.bytes.i
if m > n {
m = n
}
d.bytes.i += m
n -= m
if n == 0 {
break
}
if err := d.fill(); err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return err
}
}
return nil
}
// Specified in section B.2.2.
func (d *decoder) processSOF(n int) error {
if d.nComp != 0 {
return FormatError("multiple SOF markers")
}
switch n {
case 6 + 3*1: // Grayscale image.
d.nComp = 1
case 6 + 3*3: // YCbCr or RGB image.
d.nComp = 3
case 6 + 3*4: // YCbCrK or CMYK image.
d.nComp = 4
default:
return UnsupportedError("number of components")
}
if err := d.readFull(d.tmp[:n]); err != nil {
return err
}
// We only support 8-bit precision.
if d.tmp[0] != 8 {
return UnsupportedError("precision")
}
d.height = int(d.tmp[1])<<8 + int(d.tmp[2])
d.width = int(d.tmp[3])<<8 + int(d.tmp[4])
if int(d.tmp[5]) != d.nComp {
return FormatError("SOF has wrong length")
}
for i := 0; i < d.nComp; i++ {
d.comp[i].c = d.tmp[6+3*i]
// Section B.2.2 states that "the value of C_i shall be different from
// the values of C_1 through C_(i-1)".
for j := 0; j < i; j++ {
if d.comp[i].c == d.comp[j].c {
return FormatError("repeated component identifier")
}
}
d.comp[i].tq = d.tmp[8+3*i]
if d.comp[i].tq > maxTq {
return FormatError("bad Tq value")
}
hv := d.tmp[7+3*i]
h, v := int(hv>>4), int(hv&0x0f)
if h < 1 || 4 < h || v < 1 || 4 < v {
return FormatError("luma/chroma subsampling ratio")
}
if h == 3 || v == 3 {
return errUnsupportedSubsamplingRatio
}
switch d.nComp {
case 1:
// If a JPEG image has only one component, section A.2 says "this data
// is non-interleaved by definition" and section A.2.2 says "[in this
// case...] the order of data units within a scan shall be left-to-right
// and top-to-bottom... regardless of the values of H_1 and V_1". Section
// 4.8.2 also says "[for non-interleaved data], the MCU is defined to be
// one data unit". Similarly, section A.1.1 explains that it is the ratio
// of H_i to max_j(H_j) that matters, and similarly for V. For grayscale
// images, H_1 is the maximum H_j for all components j, so that ratio is
// always 1. The component's (h, v) is effectively always (1, 1): even if
// the nominal (h, v) is (2, 1), a 20x5 image is encoded in three 8x8
// MCUs, not two 16x8 MCUs.
h, v = 1, 1
case 3:
// For YCbCr images, we only support 4:4:4, 4:4:0, 4:2:2, 4:2:0,
// 4:1:1 or 4:1:0 chroma subsampling ratios. This implies that the
// (h, v) values for the Y component are either (1, 1), (1, 2),
// (2, 1), (2, 2), (4, 1) or (4, 2), and the Y component's values
// must be a multiple of the Cb and Cr component's values. We also
// assume that the two chroma components have the same subsampling
// ratio.
switch i {
case 0: // Y.
// We have already verified, above, that h and v are both
// either 1, 2 or 4, so invalid (h, v) combinations are those
// with v == 4.
if v == 4 {
return errUnsupportedSubsamplingRatio
}
case 1: // Cb.
if d.comp[0].h%h != 0 || d.comp[0].v%v != 0 {
return errUnsupportedSubsamplingRatio
}
case 2: // Cr.
if d.comp[1].h != h || d.comp[1].v != v {
return errUnsupportedSubsamplingRatio
}
}
case 4:
// For 4-component images (either CMYK or YCbCrK), we only support two
// hv vectors: [0x11 0x11 0x11 0x11] and [0x22 0x11 0x11 0x22].
// Theoretically, 4-component JPEG images could mix and match hv values
// but in practice, those two combinations are the only ones in use,
// and it simplifies the applyBlack code below if we can assume that:
// - for CMYK, the C and K channels have full samples, and if the M
// and Y channels subsample, they subsample both horizontally and
// vertically.
// - for YCbCrK, the Y and K channels have full samples.
switch i {
case 0:
if hv != 0x11 && hv != 0x22 {
return errUnsupportedSubsamplingRatio
}
case 1, 2:
if hv != 0x11 {
return errUnsupportedSubsamplingRatio
}
case 3:
if d.comp[0].h != h || d.comp[0].v != v {
return errUnsupportedSubsamplingRatio
}
}
}
d.comp[i].h = h
d.comp[i].v = v
}
return nil
}
// Specified in section B.2.4.1.
func (d *decoder) processDQT(n int) error {
loop:
for n > 0 {
n--
x, err := d.readByte()
if err != nil {
return err
}
tq := x & 0x0f
if tq > maxTq {
return FormatError("bad Tq value")
}
switch x >> 4 {
default:
return FormatError("bad Pq value")
case 0:
if n < blockSize {
break loop
}
n -= blockSize
if err := d.readFull(d.tmp[:blockSize]); err != nil {
return err
}
for i := range d.quant[tq] {
d.quant[tq][i] = int32(d.tmp[i])
}
case 1:
if n < 2*blockSize {
break loop
}
n -= 2 * blockSize
if err := d.readFull(d.tmp[:2*blockSize]); err != nil {
return err
}
for i := range d.quant[tq] {
d.quant[tq][i] = int32(d.tmp[2*i])<<8 | int32(d.tmp[2*i+1])
}
}
}
if n != 0 {
return FormatError("DQT has wrong length")
}
return nil
}
// Specified in section B.2.4.4.
func (d *decoder) processDRI(n int) error {
if n != 2 {
return FormatError("DRI has wrong length")
}
if err := d.readFull(d.tmp[:2]); err != nil {
return err
}
d.ri = int(d.tmp[0])<<8 + int(d.tmp[1])
return nil
}
func (d *decoder) processApp0Marker(n int) error {
if n < 5 {
return d.ignore(n)
}
if err := d.readFull(d.tmp[:5]); err != nil {
return err
}
n -= 5
d.jfif = d.tmp[0] == 'J' && d.tmp[1] == 'F' && d.tmp[2] == 'I' && d.tmp[3] == 'F' && d.tmp[4] == '\x00'
if n > 0 {
return d.ignore(n)
}
return nil
}
func (d *decoder) processApp14Marker(n int) error {
if n < 12 {
return d.ignore(n)
}
if err := d.readFull(d.tmp[:12]); err != nil {
return err
}
n -= 12
if d.tmp[0] == 'A' && d.tmp[1] == 'd' && d.tmp[2] == 'o' && d.tmp[3] == 'b' && d.tmp[4] == 'e' {
d.adobeTransformValid = true
d.adobeTransform = d.tmp[11]
}
if n > 0 {
return d.ignore(n)
}
return nil
}
// decode reads a JPEG image from r and returns it as an image.Image.
func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, error) {
d.r = r
// Check for the Start Of Image marker.
if err := d.readFull(d.tmp[:2]); err != nil {
return nil, err
}
if d.tmp[0] != 0xff || d.tmp[1] != soiMarker {
return nil, FormatError("missing SOI marker")
}
// Process the remaining segments until the End Of Image marker.
for {
err := d.readFull(d.tmp[:2])
if err != nil {
return nil, err
}
for d.tmp[0] != 0xff {
// Strictly speaking, this is a format error. However, libjpeg is
// liberal in what it accepts. As of version 9, next_marker in
// jdmarker.c treats this as a warning (JWRN_EXTRANEOUS_DATA) and
// continues to decode the stream. Even before next_marker sees
// extraneous data, jpeg_fill_bit_buffer in jdhuff.c reads as many
// bytes as it can, possibly past the end of a scan's data. It
// effectively puts back any markers that it overscanned (e.g. an
// "\xff\xd9" EOI marker), but it does not put back non-marker data,
// and thus it can silently ignore a small number of extraneous
// non-marker bytes before next_marker has a chance to see them (and
// print a warning).
//
// We are therefore also liberal in what we accept. Extraneous data
// is silently ignored.
//
// This is similar to, but not exactly the same as, the restart
// mechanism within a scan (the RST[0-7] markers).
//
// Note that extraneous 0xff bytes in e.g. SOS data are escaped as
// "\xff\x00", and so are detected a little further down below.
d.tmp[0] = d.tmp[1]
d.tmp[1], err = d.readByte()
if err != nil {
return nil, err
}
}
marker := d.tmp[1]
if marker == 0 {
// Treat "\xff\x00" as extraneous data.
continue
}
for marker == 0xff {
// Section B.1.1.2 says, "Any marker may optionally be preceded by any
// number of fill bytes, which are bytes assigned code X'FF'".
marker, err = d.readByte()
if err != nil {
return nil, err
}
}
if marker == eoiMarker { // End Of Image.
break
}
if rst0Marker <= marker && marker <= rst7Marker {
// Figures B.2 and B.16 of the specification suggest that restart markers should
// only occur between Entropy Coded Segments and not after the final ECS.
// However, some encoders may generate incorrect JPEGs with a final restart
// marker. That restart marker will be seen here instead of inside the processSOS
// method, and is ignored as a harmless error. Restart markers have no extra data,
// so we check for this before we read the 16-bit length of the segment.
continue
}
// Read the 16-bit length of the segment. The value includes the 2 bytes for the
// length itself, so we subtract 2 to get the number of remaining bytes.
if err = d.readFull(d.tmp[:2]); err != nil {
return nil, err
}
n := int(d.tmp[0])<<8 + int(d.tmp[1]) - 2
if n < 0 {
return nil, FormatError("short segment length")
}
switch marker {
case sof0Marker, sof1Marker, sof2Marker:
d.baseline = marker == sof0Marker
d.progressive = marker == sof2Marker
err = d.processSOF(n)
if configOnly && d.jfif {
return nil, err
}
case dhtMarker:
if configOnly {
err = d.ignore(n)
} else {
err = d.processDHT(n)
}
case dqtMarker:
if configOnly {
err = d.ignore(n)
} else {
err = d.processDQT(n)
}
case sosMarker:
if configOnly {
return nil, nil
}
err = d.processSOS(n)
case driMarker:
if configOnly {
err = d.ignore(n)
} else {
err = d.processDRI(n)
}
case app0Marker:
err = d.processApp0Marker(n)
case app14Marker:
err = d.processApp14Marker(n)
default:
if app0Marker <= marker && marker <= app15Marker || marker == comMarker {
err = d.ignore(n)
} else if marker < 0xc0 { // See Table B.1 "Marker code assignments".
err = FormatError("unknown marker")
} else {
err = UnsupportedError("unknown marker")
}
}
if err != nil {
return nil, err
}
}
if d.progressive {
if err := d.reconstructProgressiveImage(); err != nil {
return nil, err
}
}
if d.img1 != nil {
return d.img1, nil
}
if d.img3 != nil {
if d.blackPix != nil {
return d.applyBlack()
} else if d.isRGB() {
return d.convertToRGB()
}
return d.img3, nil
}
return nil, FormatError("missing SOS marker")
}
// applyBlack combines d.img3 and d.blackPix into a CMYK image. The formula
// used depends on whether the JPEG image is stored as CMYK or YCbCrK,
// indicated by the APP14 (Adobe) metadata.
//
// Adobe CMYK JPEG images are inverted, where 255 means no ink instead of full
// ink, so we apply "v = 255 - v" at various points. Note that a double
// inversion is a no-op, so inversions might be implicit in the code below.
func (d *decoder) applyBlack() (image.Image, error) {
if !d.adobeTransformValid {
return nil, UnsupportedError("unknown color model: 4-component JPEG doesn't have Adobe APP14 metadata")
}
// If the 4-component JPEG image isn't explicitly marked as "Unknown (RGB
// or CMYK)" as per
// https://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/JPEG.html#Adobe
// we assume that it is YCbCrK. This matches libjpeg's jdapimin.c.
if d.adobeTransform != adobeTransformUnknown {
// Convert the YCbCr part of the YCbCrK to RGB, invert the RGB to get
// CMY, and patch in the original K. The RGB to CMY inversion cancels
// out the 'Adobe inversion' described in the applyBlack doc comment
// above, so in practice, only the fourth channel (black) is inverted.
bounds := d.img3.Bounds()
img := image.NewRGBA(bounds)
imageutil.DrawYCbCr(img, bounds, d.img3, bounds.Min)
for iBase, y := 0, bounds.Min.Y; y < bounds.Max.Y; iBase, y = iBase+img.Stride, y+1 {
for i, x := iBase+3, bounds.Min.X; x < bounds.Max.X; i, x = i+4, x+1 {
img.Pix[i] = 255 - d.blackPix[(y-bounds.Min.Y)*d.blackStride+(x-bounds.Min.X)]
}
}
return &image.CMYK{
Pix: img.Pix,
Stride: img.Stride,
Rect: img.Rect,
}, nil
}
// The first three channels (cyan, magenta, yellow) of the CMYK
// were decoded into d.img3, but each channel was decoded into a separate
// []byte slice, and some channels may be subsampled. We interleave the
// separate channels into an image.CMYK's single []byte slice containing 4
// contiguous bytes per pixel.
bounds := d.img3.Bounds()
img := image.NewCMYK(bounds)
translations := [4]struct {
src []byte
stride int
}{
{d.img3.Y, d.img3.YStride},
{d.img3.Cb, d.img3.CStride},
{d.img3.Cr, d.img3.CStride},
{d.blackPix, d.blackStride},
}
for t, translation := range translations {
subsample := d.comp[t].h != d.comp[0].h || d.comp[t].v != d.comp[0].v
for iBase, y := 0, bounds.Min.Y; y < bounds.Max.Y; iBase, y = iBase+img.Stride, y+1 {
sy := y - bounds.Min.Y
if subsample {
sy /= 2
}
for i, x := iBase+t, bounds.Min.X; x < bounds.Max.X; i, x = i+4, x+1 {
sx := x - bounds.Min.X
if subsample {
sx /= 2
}
img.Pix[i] = 255 - translation.src[sy*translation.stride+sx]
}
}
}
return img, nil
}
func (d *decoder) isRGB() bool {
if d.jfif {
return false
}
if d.adobeTransformValid && d.adobeTransform == adobeTransformUnknown {
// https://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/JPEG.html#Adobe
// says that 0 means Unknown (and in practice RGB) and 1 means YCbCr.
return true
}
return d.comp[0].c == 'R' && d.comp[1].c == 'G' && d.comp[2].c == 'B'
}
func (d *decoder) convertToRGB() (image.Image, error) {
cScale := d.comp[0].h / d.comp[1].h
bounds := d.img3.Bounds()
img := image.NewRGBA(bounds)
for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
po := img.PixOffset(bounds.Min.X, y)
yo := d.img3.YOffset(bounds.Min.X, y)
co := d.img3.COffset(bounds.Min.X, y)
for i, iMax := 0, bounds.Max.X-bounds.Min.X; i < iMax; i++ {
img.Pix[po+4*i+0] = d.img3.Y[yo+i]
img.Pix[po+4*i+1] = d.img3.Cb[co+i/cScale]
img.Pix[po+4*i+2] = d.img3.Cr[co+i/cScale]
img.Pix[po+4*i+3] = 255
}
}
return img, nil
}
// Decode reads a JPEG image from r and returns it as an image.Image.
func Decode(r io.Reader) (image.Image, error) {
var d decoder
return d.decode(r, false)
}
// DecodeConfig returns the color model and dimensions of a JPEG image without
// decoding the entire image.
func DecodeConfig(r io.Reader) (image.Config, error) {
var d decoder
if _, err := d.decode(r, true); err != nil {
return image.Config{}, err
}
switch d.nComp {
case 1:
return image.Config{
ColorModel: color.GrayModel,
Width: d.width,
Height: d.height,
}, nil
case 3:
cm := color.YCbCrModel
if d.isRGB() {
cm = color.RGBAModel
}
return image.Config{
ColorModel: cm,
Width: d.width,
Height: d.height,
}, nil
case 4:
return image.Config{
ColorModel: color.CMYKModel,
Width: d.width,
Height: d.height,
}, nil
}
return image.Config{}, FormatError("missing SOF marker")
}
func init() {
image.RegisterFormat("jpeg", "\xff\xd8", Decode, DecodeConfig)
}
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