github.com/graybobo/golang.org-package-offline-cache@v0.0.0-20200626051047-6608995c132f/x/image/tiff/consts.go (about)

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