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go.image/tiff: Support missing Compression tag

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no_compress.tiff is no_rps.tiff that was read in by go.image/tiff and written out again (with a hack to avoid creating the Compression tag on the way out).

$ tiffdump no_compress.tiff
no_compress.tiff:
Magic: 0x4949 <little-endian> Version: 0x2a
Directory 0: offset 968 (0x3c8) next 0 (0)
ImageWidth (256) SHORT (3) 1<16>
ImageLength (257) SHORT (3) 1<15>
BitsPerSample (258) SHORT (3) 4<8 8 8 8>
Photometric (262) SHORT (3) 1<2>
StripOffsets (273) LONG (4) 1<8>
SamplesPerPixel (277) SHORT (3) 1<4>
RowsPerStrip (278) SHORT (3) 1<15>
StripByteCounts (279) LONG (4) 1<960>
XResolution (282) RATIONAL (5) 1<72>
YResolution (283) RATIONAL (5) 1<72>
ResolutionUnit (296) SHORT (3) 1<2>
ExtraSamples (338) SHORT (3) 1<2>

LGTM=bsiegert, nigeltao
R=bsiegert, nigeltao
CC=golang-codereviews
https://golang.org/cl/95930044
This commit is contained in:
Patrick Riley 2014-05-12 16:41:44 +10:00 committed by Nigel Tao
parent f93749e6f2
commit 38c1f4ffe8
3 changed files with 16 additions and 2 deletions
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BIN
testdata/no_compress.tiff vendored Normal file
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Binary file not shown.

9
tiff/reader.go
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@ -11,6 +11,7 @@ import (
"compress/lzw"
"compress/zlib"
"encoding/binary"
"fmt"
"image"
"image/color"
"io"
@ -553,7 +554,11 @@ func Decode(r io.Reader) (img image.Image, err error) {
offset := int64(blockOffsets[j*blocksAcross+i])
n := int64(blockCounts[j*blocksAcross+i])
switch d.firstVal(tCompression) {
case cNone:
// According to the spec, Compression does not have a default value,
// but some tools interpret a missing Compression value as none so we do
// the same.
case cNone, 0:
if b, ok := d.r.(*buffer); ok {
d.buf, err = b.Slice(int(offset), int(n))
} else {
@ -574,7 +579,7 @@ func Decode(r io.Reader) (img image.Image, err error) {
case cPackBits:
d.buf, err = unpackBits(io.NewSectionReader(d.r, offset, n))
default:
err = UnsupportedError("compression")
err = UnsupportedError(fmt.Sprintf("compression value %d", d.firstVal(tCompression)))
}
if err != nil {
return nil, err

9
tiff/reader_test.go
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@ -44,6 +44,15 @@ func TestNoRPS(t *testing.T) {
}
}
// TestNoCompression tries to decode an images that has no Compression tag.
// This tag is mandatory, but most tools interpret a missing value as no compression.
func TestNoCompression(t *testing.T) {
_, err := load("no_compress.tiff")
if err != nil {
t.Fatal(err)
}
}
// TestUnpackBits tests the decoding of PackBits-encoded data.
func TestUnpackBits(t *testing.T) {
var unpackBitsTests = []struct {