INTRO

NAME
SYNOPSIS
DESCRIPTION
DATA TYPES
LIST OF ROUTINES
TAG USAGE
PSEUDO TAGS
DIAGNOSTICS
SEE ALSO
BUGS

NAME

libtiff − introduction to libtiff, a library for reading and writing TIFF files

SYNOPSIS

#include <tiffio.h>

cc file.c -ltiff

DESCRIPTION

libtiff is a library for reading and writing data files encoded with the Tag Image File format, Revision 6.0 (or revision 5.0 or revision 4.0). This file format is suitable for archiving multi-color and monochromatic image data.

The library supports several compression algorithms, as indicated by the Compression field, including: no compression (1), CCITT 1D Huffman compression (2), CCITT Group 3 Facsimile compression (3), CCITT Group 4 Facsimile compression (4), Lempel-Ziv & Welch compression (5), baseline JPEG compression (7), word-aligned 1D Huffman compression (32771), and PackBits compression (32773). In addition, several nonstandard compression algorithms are supported: the 4-bit compression algorithm used by the ThunderScan program (32809) (decompression only), NeXT’s 2-bit compression algorithm (32766) (decompression only), an experimental LZ-style algorithm known as Deflate (32946), and an experimental CIE LogLuv compression scheme designed for images with high dynamic range (32845 for LogL and 32845 for LogLuv). Directory information may be in either little- or big-endian byte order−byte swapping is automatically done by the library. Data bit ordering may be either Most Significant Bit ( MSB ) to Least Significant Bit ( LSB ) or LSB to MSB. Finally, the library does not support files in which the BitsPerSample, Compression, MinSampleValue, or MaxSampleValue fields are defined differently on a per-sample basis (in Rev. 6.0 the Compression tag is not defined on a per-sample basis, so this is immaterial).

DATA TYPES

The library makes extensive use of C typedefs to promote portability. Two sets of typedefs are used, one for communication with clients of the library and one for internal data structures and parsing of the TIFF format. The following typedefs are exposed to users either through function definitions or through parameters passed through the varargs interfaces.

	typedef unsigned short uint16;	16-bit unsigned integer
	typedef unsigned <thing> uint32;	32-bit unsigned integer
	typedef unsigned int ttag_t;	directory tag
	typedef uint16 tdir_t;	directory index
	typedef uint16 tsample_t;	sample number
	typedef uint32 tstrip_t;	strip number
	typedef uint32 ttile_t;	tile number
	typedef int32 tsize_t;	i/o size in bytes
	typedef void* tdata_t;	image data ref
	typedef void* thandle_t;	client data handle
	typedef int32 toff_t;	file offset

Note that tstrip_t, ttile_t, and tsize_t are constrained to be no more than 32-bit quantities by 32-bit fields they are stored in in the TIFF image. Likewise tsample_t is limited by the 16-bit field used to store the SamplesPerPixel tag. tdir_t constrains the maximum number of IFDs that may appear in an image and may be an arbitrary size (w/o penalty). ttag_t must be either int, unsigned int, pointer, or double because the library uses a varargs interface and ANSI C restricts the type of the parameter before an ellipsis to be a promoted type. toff_t is defined as int32 because TIFF file offsets are (unsigned) 32-bit quantities. A signed value is used because some interfaces return −1 on error. Finally, note that user-specified data references are passed as opaque handles and only cast at the lowest layers where their type is presumed.

LIST OF ROUTINES

The following routines are part of the library. Consult specific manual pages for details on their operation; on most systems doing ‘‘man function-name’’ will work.

Name Description

	TIFFCheckpointDirectory	writes the current state of the directory
	TIFFCheckTile	very x,y,z,sample is within image
	TIFFCIELabToRGBInit	initialize CIE Lab* 1976 to RGB conversion state
	TIFFCIELabToXYZ	perform CIE Lab* 1976 to CIE XYZ conversion
	TIFFClientOpen	open a file for reading or writing
	TIFFClose	close an open file
	TIFFComputeStrip	return strip containing y,sample
	TIFFComputeTile	return tile containing x,y,z,sample
	TIFFCurrentDirectory	return index of current directory
	TIFFCurrentRow	return index of current scanline
	TIFFCurrentStrip	return index of current strip
	TIFFCurrentTile	return index of current tile
	TIFFDataWidth	return the size of TIFF data types
	TIFFError	library error handler
	TIFFFdOpen	open a file for reading or writing
	TIFFFileName	return name of open file
	TIFFFileno	return open file descriptor
	TIFFFindCODEC	find standard codec for the specific scheme
	TIFFFlush	flush all pending writes
	TIFFFlushData	flush pending data writes
	TIFFGetBitRevTable	return bit reversal table
	TIFFGetField	return tag value in current directory
	TIFFGetFieldDefaulted	return tag value in current directory
	TIFFGetMode	return open file mode
	TIFFGetVersion	return library version string
	TIFFIsCODECConfigured	check, whether we have working codec
	TIFFIsMSB2LSB	return true if image data is being returned
		with bit 0 as the most significant bit
	TIFFIsTiled	return true if image data is tiled
	TIFFIsByteSwapped	return true if image data is byte-swapped
	TIFFNumberOfStrips	return number of strips in an image
	TIFFNumberOfTiles	return number of tiles in an image
	TIFFOpen	open a file for reading or writing
	TIFFPrintDirectory	print description of the current directory
	TIFFReadBufferSetup	specify i/o buffer for reading
	TIFFReadDirectory	read the next directory
	TIFFReadEncodedStrip	read and decode a strip of data
	TIFFReadEncodedTile	read and decode a tile of data
	TIFFReadRawStrip	read a raw strip of data
	TIFFReadRawTile	read a raw tile of data
	TIFFReadRGBAImage	read an image into a fixed format raster
	TIFFReadScanline	read and decode a row of data
	TIFFReadTile	read and decode a tile of data
	TIFFRegisterCODEC	override standard codec for the specific scheme
	TIFFReverseBits	reverse bits in an array of bytes
	TIFFRGBAImageBegin	setup decoder state for TIFFRGBAImageGet
	TIFFRGBAImageEnd	release TIFFRGBAImage decoder state
	TIFFRGBAImageGet	read and decode an image
	TIFFRGBAImageOK	is image readable by TIFFRGBAImageGet
	TIFFScanlineSize	return size of a scanline
	TIFFSetDirectory	set the current directory
	TIFFSetSubDirectory	set the current directory
	TIFFSetErrorHandler	set error handler function
	TIFFSetField	set a tag’s value in the current directory
	TIFFSetWarningHandler	set warning handler function
	TIFFStripSize	returns size of a strip
	TIFFRawStripSize	returns the number of bytes in a raw strip
	TIFFSwabShort	swap bytes of short
	TIFFSwabLong	swap bytes of long
	TIFFSwabArrayOfShort	swap bytes of an array of shorts
	TIFFSwabArrayOfLong	swap bytes of an array of longs
	TIFFTileRowSize	return size of a row in a tile
	TIFFTileSize	return size of a tile
	TIFFUnRegisterCODEC	unregisters the codec
	TIFFVGetField	return tag value in current directory
	TIFFVGetFieldDefaulted	return tag value in current directory
	TIFFVSetField	set a tag’s value in the current directory
	TIFFVStripSize	returns the number of bytes in a strip
	TIFFWarning	library warning handler
	TIFFWriteDirectory	write the current directory
	TIFFWriteEncodedStrip	compress and write a strip of data
	TIFFWriteEncodedTile	compress and write a tile of data
	TIFFWriteRawStrip	write a raw strip of data
	TIFFWriteRawTile	write a raw tile of data
	TIFFWriteScanline	write a scanline of data
	TIFFWriteTile	compress and write a tile of data
	TIFFXYZToRGB	perform CIE XYZ to RGB conversion
	TIFFYCbCrToRGBInit	initialize YCbCr to RGB conversion state
	TIFFYCbCrtoRGB	perform YCbCr to RGB conversion

Auxiliary functions:

	_TIFFfree	free memory buffer
	_TIFFmalloc	dynamically allocate memory buffer
	_TIFFmemcmp	compare contents of the memory buffers
	_TIFFmemcpy	copy contents of the one buffer to another
	_TIFFmemset	fill memory buffer with a constant byte
	_TIFFrealloc	dynamically reallocate memory buffer

TAG USAGE

The table below lists the TIFF tags that are recognized and handled by the library. If no use is indicated in the table, then the library reads and writes the tag, but does not use it internally. Note that some tags are meaningful only when a particular compression scheme is being used; e.g. Group3Options is only useful if Compression is set to CCITT Group 3 encoding. Tags of this sort are considered codec-specific tags and the library does not recognize them except when the Compression tag has been previously set to the relevant compression scheme.

Tag Name                Value  R/W  Library Use/Notes

Artist	315	R/W
BadFaxLines	326	R/W
BitsPerSample	258	R/W
		lots
CellLength	265
		parsed but ignored
CellWidth	264
		parsed but ignored
CleanFaxData	327	R/W
ColorMap	320	R/W
ColorResponseUnit	300
		parsed but ignored
Compression	259	R/W
		choosing codec
ConsecutiveBadFaxLines	328	R/W

DataType	32996	R
		obsoleted by SampleFormat tag
DateTime	306	R/W
DocumentName	269	R/W
DotRange	336	R/W
ExtraSamples	338	R/W
		lots
FaxRecvParams	34908	R/W
FaxSubAddress	34909	R/W
FaxRecvTime	34910	R/W
FillOrder	266	R/W
		control bit order
FreeByteCounts	289
		parsed but ignored
FreeOffsets	288
		parsed but ignored
GrayResponseCurve	291
		parsed but ignored
GrayResponseUnit	290
		parsed but ignored
Group3Options	292	R/W
		used by Group 3 codec
Group4Options	293	R/W
HostComputer	316	R/W
ImageDepth	32997	R/W
		tile/strip calculations
ImageDescription	270	R/W
ImageLength	257	R/W
		lots
ImageWidth	256	R/W
		lots
InkNames	333	R/W
InkSet	332	R/W
JPEGTables	347	R/W
		used by JPEG codec
Make	271	R/W
Matteing	32995	R
		obsoleted by ExtraSamples tag
MaxSampleValue	281	R/W
MinSampleValue	280	R/W
Model	272	R/W
NewSubFileType	254	R/W
		called SubFileType in spec
NumberOfInks	334	R/W
Orientation	274	R/W
PageName	285	R/W
PageNumber	297	R/W
PhotometricInterpretation		262
		R/Wused by Group 3 and JPEG codecs
PlanarConfiguration	284	R/W
		data i/o
Predictor	317	R/W
		used by LZW and Deflate codecs
PrimaryChromacities	319	R/W
ReferenceBlackWhite	532	R/W
ResolutionUnit	296	R/W
		used by Group 3 codec
RowsPerStrip	278	R/W
		data i/o
SampleFormat	339	R/W
SamplesPerPixel	277	R/W
		lots
SMinSampleValue	340	R/W
SMaxSampleValue	341	R/W
Software	305	R/W
StoNits	37439	R/W
StripByteCounts	279	R/W
		data i/o
StripOffsets	273	R/W
		data i/o
SubFileType	255	R/W
		called OSubFileType in spec
TargetPrinter	337	R/W
Thresholding	263	R/W

TileByteCounts	324	R/W
		data i/o
TileDepth	32998	R/W
		tile/strip calculations
TileLength	323	R/W
		data i/o
TileOffsets	324	R/W
		data i/o
TileWidth	322	R/W
		data i/o
TransferFunction	301	R/W
WhitePoint	318	R/W
XPosition	286	R/W
XResolution	282	R/W
YCbCrCoefficients	529	R/W
		used by TIFFRGBAImage support
YCbCrPositioning	531	R/W
		tile/strip size calulcations
YCbCrSubsampling	530	R/W
YPosition	286	R/W
YResolution	283	R/W
		used by Group 3 codec

PSEUDO TAGS

In addition to the normal TIFF tags the library supports a collection of tags whose values lie in a range outside the valid range of TIFF tags. These tags are termed pseud-tags and are used to control various codec-specific functions within the library. The table below summarizes the defined pseudo-tags.

Tag Name                Codec  R/W  Library Use/Notes

TIFFTAG_FAXMODE	G3	R/W
		general codec operation
TIFFTAG_FAXFILLFUNC	G3/G4	R/W
		bitmap fill function
TIFFTAG_JPEGQUALITY	JPEG	R/W
		compression quality control
TIFFTAG_JPEGCOLORMODE	JPEG	R/W
		control colorspace conversions
TIFFTAG_JPEGTABLESMODE	JPEG	R/W
		control contents of JPEGTables tag
TIFFTAG_ZIPQUALITY	Deflate	R/Wcompression quality level
TIFFTAG_PIXARLOGDATAFMT	PixarLog	R/Wuser data format
TIFFTAG_PIXARLOGQUALITY	PixarLog	R/Wcompression quality level
TIFFTAG_SGILOGDATAFMT	SGILog	R/W
		user data format

TIFFTAG_FAXMODE

Control the operation of the Group 3 codec. Possible values (independent bits that can be combined by or’ing them together) are: FAXMODE_CLASSIC (enable old-style format in which the RTC is written at the end of the last strip), FAXMODE_NORTC (opposite of FAXMODE_CLASSIC; also called FAXMODE_CLASSF), FAXMODE_NOEOL (do not write EOL codes at the start of each row of data), FAXMODE_BYTEALIGN (align each encoded row to an 8-bit boundary), FAXMODE_WORDALIGN (align each encoded row to an 16-bit boundary), The default value is dependent on the compression scheme; this pseudo-tag is used by the various G3 and G4 codecs to share code.

TIFFTAG_FAXFILLFUNC

Control the function used to convert arrays of black and white runs to packed bit arrays. This hook can be used to image decoded scanlines in multi-bit depth rasters (e.g. for display in colormap mode) or for other purposes. The default value is a pointer to a builtin function that images packed bilevel data.

TIFFTAG_IPTCNEWSPHOTO

Tag contaings image metadata per the IPTC newsphoto spec: Headline, captioning, credit, etc... Used by most wire services.

TIFFTAG_PHOTOSHOP

Tag contains Photoshop captioning information and metadata. Photoshop uses in parallel and redundantly alongside IPTCNEWSPHOTO information.

TIFFTAG_JPEGQUALITY

Control the compression quality level used in the baseline algorithm. Note that quality levels are in the range 0-100 with a default value of 75.

TIFFTAG_JPEGCOLORMODE

Control whether or not conversion is done between RGB and YCbCr colorspaces. Possible values are: JPEGCOLORMODE_RAW (do not convert), and JPEGCOLORMODE_RGB (convert to/from RGB) The default value is JPEGCOLORMODE_RAW.

TIFFTAG_JPEGTABLESMODE

Control the information written in the JPEGTables tag. Possible values (independent bits that can be combined by or’ing them together) are: JPEGTABLESMODE_QUANT (include quantization tables), and JPEGTABLESMODE_HUFF (include Huffman encoding tables). The default value is JPEGTABLESMODE_QUANT|JPEGTABLESMODE_HUFF.

TIFFTAG_ZIPQUALITY

Control the compression technique used by the Deflate codec. Quality levels are in the range 1-9 with larger numbers yielding better compression at the cost of more computation. The default quality level is 6 which yields a good time-space tradeoff.

TIFFTAG_PIXARLOGDATAFMT

Control the format of user data passed in to the PixarLog codec when encoding and passed out from when decoding. Possible values are: PIXARLOGDATAFMT_8BIT for 8-bit unsigned pixels, PIXARLOGDATAFMT_8BITABGR for 8-bit unsigned ABGR-ordered pixels, PIXARLOGDATAFMT_11BITLOG for 11-bit log-encoded raw data, PIXARLOGDATAFMT_12BITPICIO for 12-bit PICIO-compatible data, PIXARLOGDATAFMT_16BIT for 16-bit signed samples, and PIXARLOGDATAFMT_FLOAT for 32-bit IEEE floating point samples.

TIFFTAG_PIXARLOGQUALITY

Control the compression technique used by the PixarLog codec. This value is treated identically to TIFFTAG_ZIPQUALITY; see the above description.

TIFFTAG_SGILOGDATAFMT

Control the format of client data passed in to the SGILog codec when encoding and passed out from when decoding. Possible values are: SGILOGDATAFMT_FLTXYZ for converting between LogLuv and 32-bit IEEE floating valued XYZ pixels, SGILOGDATAFMT_16BITLUV for 16-bit encoded Luv pixels, SGILOGDATAFMT_32BITRAW and SGILOGDATAFMT_24BITRAW for no conversion of data, SGILOGDATAFMT_8BITRGB for returning 8-bit RGB data (valid only when decoding LogLuv-encoded data), SGILOGDATAFMT_FLTY for converting between LogL and 32-bit IEEE floating valued Y pixels, SGILOGDATAFMT_16BITL for 16-bit encoded L pixels, and SGILOGDATAFMT_8BITGRY for returning 8-bit greyscale data (valid only when decoding LogL-encoded data).

DIAGNOSTICS

All error messages are directed through the TIFFError routine. By default messages are directed to stderr in the form: module: message\n. Warning messages are likewise directed through the TIFFWarning routine.

BUGS

The library does not support multi-sample images where some samples have different bits/sample.

The library does not support random access to compressed data that is organized with more than one row per tile or strip. The library discards unknown tags. The library should do more validity checking of a directory’s contents.