439 lines
12 KiB
Go
439 lines
12 KiB
Go
// Copyright 2012 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 tiff
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import (
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"bytes"
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"compress/zlib"
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"encoding/binary"
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"image"
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"io"
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"sort"
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)
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// The TIFF format allows to choose the order of the different elements freely.
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// The basic structure of a TIFF file written by this package is:
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//
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// 1. Header (8 bytes).
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// 2. Image data.
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// 3. Image File Directory (IFD).
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// 4. "Pointer area" for larger entries in the IFD.
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// We only write little-endian TIFF files.
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var enc = binary.LittleEndian
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// An ifdEntry is a single entry in an Image File Directory.
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// A value of type dtRational is composed of two 32-bit values,
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// thus data contains two uints (numerator and denominator) for a single number.
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type ifdEntry struct {
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tag int
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datatype int
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data []uint32
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}
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func (e ifdEntry) putData(p []byte) {
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for _, d := range e.data {
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switch e.datatype {
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case dtByte, dtASCII:
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p[0] = byte(d)
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p = p[1:]
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case dtShort:
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enc.PutUint16(p, uint16(d))
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p = p[2:]
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case dtLong, dtRational:
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enc.PutUint32(p, uint32(d))
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p = p[4:]
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}
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}
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}
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type byTag []ifdEntry
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func (d byTag) Len() int { return len(d) }
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func (d byTag) Less(i, j int) bool { return d[i].tag < d[j].tag }
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func (d byTag) Swap(i, j int) { d[i], d[j] = d[j], d[i] }
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func encodeGray(w io.Writer, pix []uint8, dx, dy, stride int, predictor bool) error {
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if !predictor {
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return writePix(w, pix, dy, dx, stride)
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}
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buf := make([]byte, dx)
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for y := 0; y < dy; y++ {
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min := y*stride + 0
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max := y*stride + dx
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off := 0
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var v0 uint8
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for i := min; i < max; i++ {
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v1 := pix[i]
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buf[off] = v1 - v0
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v0 = v1
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off++
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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 encodeGray16(w io.Writer, pix []uint8, dx, dy, stride int, predictor bool) error {
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buf := make([]byte, dx*2)
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for y := 0; y < dy; y++ {
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min := y*stride + 0
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max := y*stride + dx*2
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off := 0
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var v0 uint16
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for i := min; i < max; i += 2 {
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// An image.Gray16's Pix is in big-endian order.
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v1 := uint16(pix[i])<<8 | uint16(pix[i+1])
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if predictor {
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v0, v1 = v1, v1-v0
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}
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// We only write little-endian TIFF files.
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buf[off+0] = byte(v1)
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buf[off+1] = byte(v1 >> 8)
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off += 2
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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 encodeRGBA(w io.Writer, pix []uint8, dx, dy, stride int, predictor bool) error {
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if !predictor {
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return writePix(w, pix, dy, dx*4, stride)
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}
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buf := make([]byte, dx*4)
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for y := 0; y < dy; 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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var r0, g0, b0, a0 uint8
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for i := min; i < max; i += 4 {
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r1, g1, b1, a1 := pix[i+0], pix[i+1], pix[i+2], pix[i+3]
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buf[off+0] = r1 - r0
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buf[off+1] = g1 - g0
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buf[off+2] = b1 - b0
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buf[off+3] = a1 - a0
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off += 4
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r0, g0, b0, a0 = r1, g1, b1, a1
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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 encodeRGBA64(w io.Writer, pix []uint8, dx, dy, stride int, predictor bool) error {
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buf := make([]byte, dx*8)
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for y := 0; y < dy; y++ {
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min := y*stride + 0
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max := y*stride + dx*8
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off := 0
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var r0, g0, b0, a0 uint16
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for i := min; i < max; i += 8 {
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// An image.RGBA64's Pix is in big-endian order.
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r1 := uint16(pix[i+0])<<8 | uint16(pix[i+1])
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g1 := uint16(pix[i+2])<<8 | uint16(pix[i+3])
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b1 := uint16(pix[i+4])<<8 | uint16(pix[i+5])
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a1 := uint16(pix[i+6])<<8 | uint16(pix[i+7])
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if predictor {
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r0, r1 = r1, r1-r0
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g0, g1 = g1, g1-g0
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b0, b1 = b1, b1-b0
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a0, a1 = a1, a1-a0
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}
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// We only write little-endian TIFF files.
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buf[off+0] = byte(r1)
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buf[off+1] = byte(r1 >> 8)
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buf[off+2] = byte(g1)
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buf[off+3] = byte(g1 >> 8)
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buf[off+4] = byte(b1)
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buf[off+5] = byte(b1 >> 8)
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buf[off+6] = byte(a1)
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buf[off+7] = byte(a1 >> 8)
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off += 8
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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, predictor bool) error {
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bounds := m.Bounds()
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buf := make([]byte, 4*bounds.Dx())
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for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
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off := 0
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if predictor {
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var r0, g0, b0, a0 uint8
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for x := bounds.Min.X; x < bounds.Max.X; x++ {
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r, g, b, a := m.At(x, y).RGBA()
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r1 := uint8(r >> 8)
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g1 := uint8(g >> 8)
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b1 := uint8(b >> 8)
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a1 := uint8(a >> 8)
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buf[off+0] = r1 - r0
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buf[off+1] = g1 - g0
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buf[off+2] = b1 - b0
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buf[off+3] = a1 - a0
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off += 4
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r0, g0, b0, a0 = r1, g1, b1, a1
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}
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} else {
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for x := bounds.Min.X; x < bounds.Max.X; x++ {
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r, g, b, a := m.At(x, y).RGBA()
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buf[off+0] = uint8(r >> 8)
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buf[off+1] = uint8(g >> 8)
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buf[off+2] = uint8(b >> 8)
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buf[off+3] = uint8(a >> 8)
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off += 4
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}
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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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// writePix writes the internal byte array of an image to w. It is less general
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// but much faster then encode. writePix is used when pix directly
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// corresponds to one of the TIFF image types.
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func writePix(w io.Writer, pix []byte, nrows, length, stride int) error {
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if length == stride {
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_, err := w.Write(pix[:nrows*length])
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return err
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}
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for ; nrows > 0; nrows-- {
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if _, err := w.Write(pix[:length]); err != nil {
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return err
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}
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pix = pix[stride:]
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}
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return nil
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}
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func writeIFD(w io.Writer, ifdOffset int, d []ifdEntry) error {
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var buf [ifdLen]byte
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// Make space for "pointer area" containing IFD entry data
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// longer than 4 bytes.
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parea := make([]byte, 1024)
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pstart := ifdOffset + ifdLen*len(d) + 6
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var o int // Current offset in parea.
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// The IFD has to be written with the tags in ascending order.
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sort.Sort(byTag(d))
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// Write the number of entries in this IFD.
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if err := binary.Write(w, enc, uint16(len(d))); err != nil {
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return err
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}
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for _, ent := range d {
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enc.PutUint16(buf[0:2], uint16(ent.tag))
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enc.PutUint16(buf[2:4], uint16(ent.datatype))
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count := uint32(len(ent.data))
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if ent.datatype == dtRational {
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count /= 2
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}
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enc.PutUint32(buf[4:8], count)
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datalen := int(count * lengths[ent.datatype])
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if datalen <= 4 {
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ent.putData(buf[8:12])
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} else {
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if (o + datalen) > len(parea) {
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newlen := len(parea) + 1024
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for (o + datalen) > newlen {
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newlen += 1024
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}
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newarea := make([]byte, newlen)
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copy(newarea, parea)
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parea = newarea
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}
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ent.putData(parea[o : o+datalen])
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enc.PutUint32(buf[8:12], uint32(pstart+o))
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o += datalen
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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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// The IFD ends with the offset of the next IFD in the file,
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// or zero if it is the last one (page 14).
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if err := binary.Write(w, enc, uint32(0)); err != nil {
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return err
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}
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_, err := w.Write(parea[:o])
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return err
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}
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// Options are the encoding parameters.
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type Options struct {
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// Compression is the type of compression used.
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Compression CompressionType
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// Predictor determines whether a differencing predictor is used;
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// if true, instead of each pixel's color, the color difference to the
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// preceding one is saved. This improves the compression for certain
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// types of images and compressors. For example, it works well for
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// photos with Deflate compression.
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Predictor bool
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}
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// Encode writes the image m to w. opt determines the options used for
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// encoding, such as the compression type. If opt is nil, an uncompressed
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// image is written.
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func Encode(w io.Writer, m image.Image, opt *Options) error {
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d := m.Bounds().Size()
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compression := uint32(cNone)
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predictor := false
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if opt != nil {
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compression = opt.Compression.specValue()
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// The predictor field is only used with LZW. See page 64 of the spec.
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predictor = opt.Predictor && compression == cLZW
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}
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_, err := io.WriteString(w, leHeader)
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if err != nil {
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return err
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}
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// Compressed data is written into a buffer first, so that we
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// know the compressed size.
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var buf bytes.Buffer
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// dst holds the destination for the pixel data of the image --
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// either w or a writer to buf.
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var dst io.Writer
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// imageLen is the length of the pixel data in bytes.
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// The offset of the IFD is imageLen + 8 header bytes.
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var imageLen int
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switch compression {
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case cNone:
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dst = w
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// Write IFD offset before outputting pixel data.
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switch m.(type) {
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case *image.Paletted:
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imageLen = d.X * d.Y * 1
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case *image.Gray:
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imageLen = d.X * d.Y * 1
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case *image.Gray16:
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imageLen = d.X * d.Y * 2
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case *image.RGBA64:
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imageLen = d.X * d.Y * 8
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case *image.NRGBA64:
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imageLen = d.X * d.Y * 8
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default:
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imageLen = d.X * d.Y * 4
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}
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err = binary.Write(w, enc, uint32(imageLen+8))
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if err != nil {
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return err
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}
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case cDeflate:
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dst = zlib.NewWriter(&buf)
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}
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pr := uint32(prNone)
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photometricInterpretation := uint32(pRGB)
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samplesPerPixel := uint32(4)
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bitsPerSample := []uint32{8, 8, 8, 8}
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extraSamples := uint32(0)
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colorMap := []uint32{}
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if predictor {
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pr = prHorizontal
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}
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switch m := m.(type) {
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case *image.Paletted:
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photometricInterpretation = pPaletted
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samplesPerPixel = 1
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bitsPerSample = []uint32{8}
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colorMap = make([]uint32, 256*3)
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for i := 0; i < 256 && i < len(m.Palette); i++ {
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r, g, b, _ := m.Palette[i].RGBA()
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colorMap[i+0*256] = uint32(r)
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colorMap[i+1*256] = uint32(g)
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colorMap[i+2*256] = uint32(b)
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}
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err = encodeGray(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
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case *image.Gray:
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photometricInterpretation = pBlackIsZero
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samplesPerPixel = 1
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bitsPerSample = []uint32{8}
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err = encodeGray(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
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case *image.Gray16:
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photometricInterpretation = pBlackIsZero
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samplesPerPixel = 1
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bitsPerSample = []uint32{16}
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err = encodeGray16(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
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case *image.NRGBA:
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extraSamples = 2 // Unassociated alpha.
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err = encodeRGBA(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
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case *image.NRGBA64:
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extraSamples = 2 // Unassociated alpha.
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bitsPerSample = []uint32{16, 16, 16, 16}
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err = encodeRGBA64(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
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case *image.RGBA:
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extraSamples = 1 // Associated alpha.
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err = encodeRGBA(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
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case *image.RGBA64:
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extraSamples = 1 // Associated alpha.
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bitsPerSample = []uint32{16, 16, 16, 16}
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err = encodeRGBA64(dst, m.Pix, d.X, d.Y, m.Stride, predictor)
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default:
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extraSamples = 1 // Associated alpha.
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err = encode(dst, m, predictor)
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}
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if err != nil {
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return err
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}
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if compression != cNone {
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if err = dst.(io.Closer).Close(); err != nil {
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return err
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}
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imageLen = buf.Len()
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if err = binary.Write(w, enc, uint32(imageLen+8)); err != nil {
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return err
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}
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if _, err = buf.WriteTo(w); err != nil {
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return err
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}
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}
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ifd := []ifdEntry{
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{tImageWidth, dtShort, []uint32{uint32(d.X)}},
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{tImageLength, dtShort, []uint32{uint32(d.Y)}},
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{tBitsPerSample, dtShort, bitsPerSample},
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{tCompression, dtShort, []uint32{compression}},
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{tPhotometricInterpretation, dtShort, []uint32{photometricInterpretation}},
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{tStripOffsets, dtLong, []uint32{8}},
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{tSamplesPerPixel, dtShort, []uint32{samplesPerPixel}},
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{tRowsPerStrip, dtShort, []uint32{uint32(d.Y)}},
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{tStripByteCounts, dtLong, []uint32{uint32(imageLen)}},
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// There is currently no support for storing the image
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// resolution, so give a bogus value of 72x72 dpi.
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{tXResolution, dtRational, []uint32{72, 1}},
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{tYResolution, dtRational, []uint32{72, 1}},
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{tResolutionUnit, dtShort, []uint32{resPerInch}},
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}
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if pr != prNone {
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ifd = append(ifd, ifdEntry{tPredictor, dtShort, []uint32{pr}})
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}
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if len(colorMap) != 0 {
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ifd = append(ifd, ifdEntry{tColorMap, dtShort, colorMap})
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}
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if extraSamples > 0 {
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ifd = append(ifd, ifdEntry{tExtraSamples, dtShort, []uint32{extraSamples}})
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}
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return writeIFD(w, imageLen+8, ifd)
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}
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