| // 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| cJPEGOld = 6 // Superseded by cJPEG.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| cDeflateOld = 32946 // Superseded by cDeflate.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 |
| } |