134 lines
3.0 KiB
Go
134 lines
3.0 KiB
Go
|
// 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cJPEGOld = 6 // Superseded by cJPEG.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
|
||
|
|
}
|