blob: 3c51a70befbd92153bad23616ef9057849d85c79 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
|
// Copyright 2011 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 tiff
// A tiff image file contains one or more images. The metadata
// of each image is contained in an Image File Directory (IFD),
// which contains entries of 12 bytes each and is described
// on page 14-16 of the specification. An IFD entry consists of
//
// - a tag, which describes the signification of the entry,
// - the data type and length of the entry,
// - the data itself or a pointer to it if it is more than 4 bytes.
//
// The presence of a length means that each IFD is effectively an array.
const (
leHeader = "II\x2A\x00" // Header for little-endian files.
beHeader = "MM\x00\x2A" // Header for big-endian files.
ifdLen = 12 // Length of an IFD entry in bytes.
)
// Data types (p. 14-16 of the spec).
const (
dtByte = 1
dtASCII = 2
dtShort = 3
dtLong = 4
dtRational = 5
)
// The length of one instance of each data type in bytes.
var lengths = [...]uint32{0, 1, 1, 2, 4, 8}
// Tags (see p. 28-41 of the spec).
const (
tImageWidth = 256
tImageLength = 257
tBitsPerSample = 258
tCompression = 259
tPhotometricInterpretation = 262
tStripOffsets = 273
tSamplesPerPixel = 277
tRowsPerStrip = 278
tStripByteCounts = 279
tTileWidth = 322
tTileLength = 323
tTileOffsets = 324
tTileByteCounts = 325
tXResolution = 282
tYResolution = 283
tResolutionUnit = 296
tPredictor = 317
tColorMap = 320
tExtraSamples = 338
tSampleFormat = 339
)
// Compression types (defined in various places in the spec and supplements).
const (
cNone = 1
cCCITT = 2
cG3 = 3 // Group 3 Fax.
cG4 = 4 // Group 4 Fax.
cLZW = 5
cJPEGOld = 6 // Superseded by cJPEG.
cJPEG = 7
cDeflate = 8 // zlib compression.
cPackBits = 32773
cDeflateOld = 32946 // Superseded by cDeflate.
)
// Photometric interpretation values (see p. 37 of the spec).
const (
pWhiteIsZero = 0
pBlackIsZero = 1
pRGB = 2
pPaletted = 3
pTransMask = 4 // transparency mask
pCMYK = 5
pYCbCr = 6
pCIELab = 8
)
// Values for the tPredictor tag (page 64-65 of the spec).
const (
prNone = 1
prHorizontal = 2
)
// Values for the tResolutionUnit tag (page 18).
const (
resNone = 1
resPerInch = 2 // Dots per inch.
resPerCM = 3 // Dots per centimeter.
)
// imageMode represents the mode of the image.
type imageMode int
const (
mBilevel imageMode = iota
mPaletted
mGray
mGrayInvert
mRGB
mRGBA
mNRGBA
)
// CompressionType describes the type of compression used in Options.
type CompressionType int
const (
Uncompressed CompressionType = iota
Deflate
)
// specValue returns the compression type constant from the TIFF spec that
// is equivalent to c.
func (c CompressionType) specValue() uint32 {
switch c {
case Deflate:
return cDeflate
}
return cNone
}
|
