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-rw-r--r--src/image/jpeg/reader.go812
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diff --git a/src/image/jpeg/reader.go b/src/image/jpeg/reader.go
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+// 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"
+)
+
+// 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 {
+ return nil
+ }
+ if err == io.EOF {
+ err = io.ErrUnexpectedEOF
+ }
+ 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 {
+ 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 {
+ 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)
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-30 01:20:45 +0000