From 9491825ddff7a294d1f49061bae7044e426aeb2e Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?J=C3=B6rg=20Frings-F=C3=BCrst?= Date: Fri, 6 Nov 2015 05:38:49 +0100 Subject: Imported Upstream version 1.8.3 --- tiff/html/libtiff.html | 747 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 747 insertions(+) create mode 100755 tiff/html/libtiff.html (limited to 'tiff/html/libtiff.html') diff --git a/tiff/html/libtiff.html b/tiff/html/libtiff.html new file mode 100755 index 0000000..16355ad --- /dev/null +++ b/tiff/html/libtiff.html @@ -0,0 +1,747 @@ + + + + Using The TIFF Library + + + + + + + + + + +

Using The TIFF Library

+ libtiff is a set of C functions (a library) that support + the manipulation of TIFF image files. + The library requires an ANSI C compilation environment for building + and presumes an ANSI C environment for use. +

+
+

+ libtiff + provides interfaces to image data at several layers of abstraction (and cost). + At the highest level image data can be read into an 8-bit/sample, + ABGR pixel raster format without regard for the underlying data organization, + colorspace, or compression scheme. Below this high-level interface + the library provides scanline-, strip-, and tile-oriented interfaces that + return data decompressed but otherwise untransformed. These interfaces + require that the application first identify the organization of stored + data and select either a strip-based or tile-based API for manipulating + data. At the lowest level the library + provides access to the raw uncompressed strips or tiles, + returning the data exactly as it appears in the file. +

+ The material presented in this chapter is a basic introduction + to the capabilities of the library; it is not an attempt to describe + everything a developer needs to know about the library or about TIFF. + Detailed information on the interfaces to the library are given in + the UNIX + manual pages that accompany this software. +

+ Michael Still has also written a useful introduction to libtiff for the + IBM DeveloperWorks site available at + http://www.ibm.com/developerworks/linux/library/l-libtiff. +

+ The following sections are found in this chapter: +

How to tell which version you have
Library Datatypes
Memory Management
Error Handling
Basic File Handling
TIFF Directories
TIFF Tags
TIFF Compression Schemes
Byte Order
Data Placement
TIFFRGBAImage Support
Scanline-based Image I/O
Strip-oriented Image I/O
Tile-oriented Image I/O
Other Stuff

How to tell which version you have

+ The software version can be found by looking at the file named + VERSION + that is located at the top of the source tree; the precise alpha number + is given in the file dist/tiff.alpha. + If you have need to refer to this + specific software, you should identify it as: +

+ TIFF <version> <alpha> +

+ where <version> is whatever you get from + "cat VERSION" and <alpha> is + what you get from "cat dist/tiff.alpha". +

+ Within an application that uses libtiff the TIFFGetVersion + routine will return a pointer to a string that contains software version + information. + The library include file <tiffio.h> contains a C pre-processor + define TIFFLIB_VERSION that can be used to check library + version compatiblity at compile time. +

Library Datatypes

+ libtiff defines a portable programming interface through the + use of a set of C type definitions. + These definitions, defined in in the files tiff.h and + tiffio.h, + isolate the libtiff API from the characteristics + of the underlying machine. + To insure portable code and correct operation, applications that use + libtiff should use the typedefs and follow the function + prototypes for the library API. +

Memory Management

+ libtiff uses a machine-specific set of routines for managing + dynamically allocated memory. + _TIFFmalloc, _TIFFrealloc, and _TIFFfree + mimic the normal ANSI C routines. + Any dynamically allocated memory that is to be passed into the library + should be allocated using these interfaces in order to insure pointer + compatibility on machines with a segmented architecture. + (On 32-bit UNIX systems these routines just call the normal malloc, + realloc, and free routines in the C library.) +

+ To deal with segmented pointer issues libtiff also provides + _TIFFmemcpy, _TIFFmemset, and _TIFFmemmove + routines that mimic the equivalent ANSI C routines, but that are + intended for use with memory allocated through _TIFFmalloc + and _TIFFrealloc. +

Error Handling

+ libtiff handles most errors by returning an invalid/erroneous + value when returning from a function call. + Various diagnostic messages may also be generated by the library. + All error messages are directed to a single global error handler + routine that can be specified with a call to TIFFSetErrorHandler. + Likewise warning messages are directed to a single handler routine + that can be specified with a call to TIFFSetWarningHandler +

Basic File Handling

+ The library is modeled after the normal UNIX stdio library. + For example, to read from an existing TIFF image the + file must first be opened: +

+ #include "tiffio.h" + main() + { + TIFF* tif = TIFFOpen("foo.tif", "r"); + ... do stuff ... + TIFFClose(tif); + } +

+ The handle returned by TIFFOpen is opaque, that is + the application is not permitted to know about its contents. + All subsequent library calls for this file must pass the handle + as an argument. +

+ To create or overwrite a TIFF image the file is also opened, but with + a "w" argument: +

+ #include "tiffio.h" + main() + { + TIFF* tif = TIFFOpen("foo.tif", "w"); + ... do stuff ... + TIFFClose(tif); + } +

+ If the file already exists it is first truncated to zero length. +

+ + + + + +

Note that unlike the stdio library TIFF image files may not be + opened for both reading and writing; + there is no support for altering the contents of a TIFF file.

+ libtiff buffers much information associated with writing a + valid TIFF image. Consequently, when writing a TIFF image it is necessary + to always call TIFFClose or TIFFFlush to flush any + buffered information to a file. Note that if you call TIFFClose + you do not need to call TIFFFlush. +

TIFF Directories

+ TIFF supports the storage of multiple images in a single file. + Each image has an associated data structure termed a directory + that houses all the information about the format and content of the + image data. + Images in a file are usually related but they do not need to be; it + is perfectly alright to store a color image together with a black and + white image. + Note however that while images may be related their directories are + not. + That is, each directory stands on its own; their is no need to read + an unrelated directory in order to properly interpret the contents + of an image. +

+ libtiff provides several routines for reading and writing + directories. In normal use there is no need to explicitly + read or write a directory: the library automatically reads the first + directory in a file when opened for reading, and directory information + to be written is automatically accumulated and written when writing + (assuming TIFFClose or TIFFFlush are called). +

+ For a file open for reading the TIFFSetDirectory routine can + be used to select an arbitrary directory; directories are referenced by + number with the numbering starting at 0. Otherwise the + TIFFReadDirectory and TIFFWriteDirectory routines can + be used for sequential access to directories. + For example, to count the number of directories in a file the following + code might be used: +

+ #include "tiffio.h" + main(int argc, char* argv[]) + { + TIFF* tif = TIFFOpen(argv[1], "r"); + if (tif) { + int dircount = 0; + do { + dircount++; + } while (TIFFReadDirectory(tif)); + printf("%d directories in %s\n", dircount, argv[1]); + TIFFClose(tif); + } + exit(0); + } +

+ Finally, note that there are several routines for querying the + directory status of an open file: + TIFFCurrentDirectory returns the index of the current + directory and + TIFFLastDirectory returns an indication of whether the + current directory is the last directory in a file. + There is also a routine, TIFFPrintDirectory, that can + be called to print a formatted description of the contents of + the current directory; consult the manual page for complete details. +

TIFF Tags

+ Image-related information such as the image width and height, number + of samples, orientation, colorimetric information, etc. + are stored in each image + directory in fields or tags. + Tags are identified by a number that is usually a value registered + with the Aldus (now Adobe) Corporation. + Beware however that some vendors write + TIFF images with tags that are unregistered; in this case interpreting + their contents is usually a waste of time. +

+ libtiff reads the contents of a directory all at once + and converts the on-disk information to an appropriate in-memory + form. While the TIFF specification permits an arbitrary set of + tags to be defined and used in a file, the library only understands + a limited set of tags. + Any unknown tags that are encountered in a file are ignored. + There is a mechanism to extend the set of tags the library handles + without modifying the library itself; + this is described elsewhere. +

+ libtiff provides two interfaces for getting and setting tag + values: TIFFGetField and TIFFSetField. + These routines use a variable argument list-style interface to pass + parameters of different type through a single function interface. + The get interface takes one or more pointers to memory locations + where the tag values are to be returned and also returns one or + zero according to whether the requested tag is defined in the directory. + The set interface takes the tag values either by-reference or + by-value. + The TIFF specification defines + default values for some tags. + To get the value of a tag, or its default value if it is undefined, + the TIFFGetFieldDefaulted interface may be used. +

+ The manual pages for the tag get and set routines specifiy the exact data types + and calling conventions required for each tag supported by the library. +

TIFF Compression Schemes

+ libtiff includes support for a wide variety of + data compression schemes. + In normal operation a compression scheme is automatically used when + the TIFF Compression tag is set, either by opening a file + for reading, or by setting the tag when writing. +

+ Compression schemes are implemented by software modules termed codecs + that implement decoder and encoder routines that hook into the + core library i/o support. + Codecs other than those bundled with the library can be registered + for use with the TIFFRegisterCODEC routine. + This interface can also be used to override the core-library + implementation for a compression scheme. +

Byte Order

+ The TIFF specification says, and has always said, that + a correct TIFF + reader must handle images in big-endian and little-endian byte order. + libtiff conforms in this respect. + Consequently there is no means to force a specific + byte order for the data written to a TIFF image file (data is + written in the native order of the host CPU unless appending to + an existing file, in which case it is written in the byte order + specified in the file). +

Data Placement

+ The TIFF specification requires that all information except an + 8-byte header can be placed anywhere in a file. + In particular, it is perfectly legitimate for directory information + to be written after the image data itself. + Consequently TIFF is inherently not suitable for passing through a + stream-oriented mechanism such as UNIX pipes. + Software that require that data be organized in a file in a particular + order (e.g. directory information before image data) does not + correctly support TIFF. + libtiff provides no mechanism for controlling the placement + of data in a file; image data is typically written before directory + information. +

TIFFRGBAImage Support

+ libtiff provides a high-level interface for reading image + data from a TIFF file. This interface handles the details of + data organization and format for a wide variety of TIFF files; + at least the large majority of those files that one would normally + encounter. Image data is, by default, returned as ABGR + pixels packed into 32-bit words (8 bits per sample). Rectangular + rasters can be read or data can be intercepted at an intermediate + level and packed into memory in a format more suitable to the + application. + The library handles all the details of the format of data stored on + disk and, in most cases, if any colorspace conversions are required: + bilevel to RGB, greyscale to RGB, CMYK to RGB, YCbCr to RGB, 16-bit + samples to 8-bit samples, associated/unassociated alpha, etc. +

+ There are two ways to read image data using this interface. If + all the data is to be stored in memory and manipulated at once, + then the routine TIFFReadRGBAImage can be used: +

+ #include "tiffio.h" + main(int argc, char* argv[]) + { + TIFF* tif = TIFFOpen(argv[1], "r"); + if (tif) { + uint32 w, h; + size_t npixels; + uint32* raster; + + TIFFGetField(tif, TIFFTAG_IMAGEWIDTH, &w); + TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &h); + npixels = w * h; + raster = (uint32*) _TIFFmalloc(npixels * sizeof (uint32)); + if (raster != NULL) { + if (TIFFReadRGBAImage(tif, w, h, raster, 0)) { + ...process raster data... + } + _TIFFfree(raster); + } + TIFFClose(tif); + } + exit(0); + } +

+ Note above that _TIFFmalloc is used to allocate memory for + the raster passed to TIFFReadRGBAImage; this is important + to insure the ``appropriate type of memory'' is passed on machines + with segmented architectures. +

+ Alternatively, TIFFReadRGBAImage can be replaced with a + more low-level interface that permits an application to have more + control over this reading procedure. The equivalent to the above + is: +

+ #include "tiffio.h" + main(int argc, char* argv[]) + { + TIFF* tif = TIFFOpen(argv[1], "r"); + if (tif) { + TIFFRGBAImage img; + char emsg[1024]; + + if (TIFFRGBAImageBegin(&img, tif, 0, emsg)) { + size_t npixels; + uint32* raster; + + npixels = img.width * img.height; + raster = (uint32*) _TIFFmalloc(npixels * sizeof (uint32)); + if (raster != NULL) { + if (TIFFRGBAImageGet(&img, raster, img.width, img.height)) { + ...process raster data... + } + _TIFFfree(raster); + } + TIFFRGBAImageEnd(&img); + } else + TIFFError(argv[1], emsg); + TIFFClose(tif); + } + exit(0); + } +

+ However this usage does not take advantage of the more fine-grained + control that's possible. That is, by using this interface it is + possible to: +

repeatedly fetch (and manipulate) an image without opening + and closing the file
interpose a method for packing raster pixel data according to + application-specific needs (or write the data at all)
interpose methods that handle TIFF formats that are not already + handled by the core library

+ The first item means that, for example, image viewers that want to + handle multiple files can cache decoding information in order to + speedup the work required to display a TIFF image. +

+ The second item is the main reason for this interface. By interposing + a "put method" (the routine that is called to pack pixel data in + the raster) it is possible share the core logic that understands how + to deal with TIFF while packing the resultant pixels in a format that + is optimized for the application. This alternate format might be very + different than the 8-bit per sample ABGR format the library writes by + default. For example, if the application is going to display the image + on an 8-bit colormap display the put routine might take the data and + convert it on-the-fly to the best colormap indices for display. +

+ The last item permits an application to extend the library + without modifying the core code. + By overriding the code provided an application might add support + for some esoteric flavor of TIFF that it needs, or it might + substitute a packing routine that is able to do optimizations + using application/environment-specific information. +

+ The TIFF image viewer found in tools/sgigt.c is an example + of an application that makes use of the TIFFRGBAImage + support. +

Scanline-based Image I/O

+ The simplest interface provided by libtiff is a + scanline-oriented interface that can be used to read TIFF + images that have their image data organized in strips + (trying to use this interface to read data written in tiles + will produce errors.) + A scanline is a one pixel high row of image data whose width + is the width of the image. + Data is returned packed if the image data is stored with samples + packed together, or as arrays of separate samples if the data + is stored with samples separated. + The major limitation of the scanline-oriented interface, other + than the need to first identify an existing file as having a + suitable organization, is that random access to individual + scanlines can only be provided when data is not stored in a + compressed format, or when the number of rows in a strip + of image data is set to one (RowsPerStrip is one). +

+ Two routines are provided for scanline-based i/o: + TIFFReadScanline + and + TIFFWriteScanline. + For example, to read the contents of a file that + is assumed to be organized in strips, the following might be used: +

+ #include "tiffio.h" + main() + { + TIFF* tif = TIFFOpen("myfile.tif", "r"); + if (tif) { + uint32 imagelength; + tdata_t buf; + uint32 row; + + TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imagelength); + buf = _TIFFmalloc(TIFFScanlineSize(tif)); + for (row = 0; row < imagelength; row++) + tiffreadscanline(tif, buf, row); + _tifffree(buf); + tiffclose(tif); + } + } +

+ TIFFScanlineSize returns the number of bytes in + a decoded scanline, as returned by TIFFReadScanline. + Note however that if the file had been create with samples + written in separate planes, then the above code would only + read data that contained the first sample of each pixel; + to handle either case one might use the following instead: +

+ #include "tiffio.h" + main() + { + TIFF* tif = TIFFOpen("myfile.tif", "r"); + if (tif) { + uint32 imagelength; + tdata_t buf; + uint32 row; + + TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imagelength); + TIFFGetField(tif, TIFFTAG_PLANARCONFIG, &config); + buf = _TIFFmalloc(TIFFScanlineSize(tif)); + if (config == PLANARCONFIG_CONTIG) { + for (row = 0; row < imagelength; row++) + tiffreadscanline(tif, buf, row); + } else if (config == planarconfig_separate) { + uint16 s, nsamples; + + tiffgetfield(tif, tifftag_samplesperpixel, &nsamples); + for (s = 0; s < nsamples; s++) + for (row = 0; row < imagelength; row++) + tiffreadscanline(tif, buf, row, s); + } + _tifffree(buf); + tiffclose(tif); + } + } +

+ Beware however that if the following code were used instead to + read data in the case PLANARCONFIG_SEPARATE,... +

+ for (row = 0; row < imagelength; row++) + for (s = 0; s < nsamples; s++) + tiffreadscanline(tif, buf, row, s); +

+ ...then problems would arise if RowsPerStrip was not one + because the order in which scanlines are requested would require + random access to data within strips (something that is not supported + by the library when strips are compressed). +

Strip-oriented Image I/O

+ The strip-oriented interfaces provided by the library provide + access to entire strips of data. Unlike the scanline-oriented + calls, data can be read or written compressed or uncompressed. + Accessing data at a strip (or tile) level is often desirable + because there are no complications with regard to random access + to data within strips. +

+ A simple example of reading an image by strips is: +

+ #include "tiffio.h" + main() + { + TIFF* tif = TIFFOpen("myfile.tif", "r"); + if (tif) { + tdata_t buf; + tstrip_t strip; + + buf = _TIFFmalloc(TIFFStripSize(tif)); + for (strip = 0; strip < tiffnumberofstrips(tif); strip++) + tiffreadencodedstrip(tif, strip, buf, (tsize_t) -1); + _tifffree(buf); + tiffclose(tif); + } + } +

+ Notice how a strip size of -1 is used; TIFFReadEncodedStrip + will calculate the appropriate size in this case. +

+ The above code reads strips in the order in which the + data is physically stored in the file. If multiple samples + are present and data is stored with PLANARCONFIG_SEPARATE + then all the strips of data holding the first sample will be + read, followed by strips for the second sample, etc. +

+ Finally, note that the last strip of data in an image may have fewer + rows in it than specified by the RowsPerStrip tag. A + reader should not assume that each decoded strip contains a full + set of rows in it. +

+ The following is an example of how to read raw strips of data from + a file: +

+ #include "tiffio.h" + main() + { + TIFF* tif = TIFFOpen("myfile.tif", "r"); + if (tif) { + tdata_t buf; + tstrip_t strip; + uint32* bc; + uint32 stripsize; + + TIFFGetField(tif, TIFFTAG_STRIPBYTECOUNTS, &bc); + stripsize = bc[0]; + buf = _TIFFmalloc(stripsize); + for (strip = 0; strip < tiffnumberofstrips(tif); strip++) { + if (bc[strip] > stripsize) { + buf = _TIFFrealloc(buf, bc[strip]); + stripsize = bc[strip]; + } + TIFFReadRawStrip(tif, strip, buf, bc[strip]); + } + _TIFFfree(buf); + TIFFClose(tif); + } + } +

+ As above the strips are read in the order in which they are + physically stored in the file; this may be different from the + logical ordering expected by an application. +

Tile-oriented Image I/O

+ Tiles of data may be read and written in a manner similar to strips. + With this interface, an image is + broken up into a set of rectangular areas that may have dimensions + less than the image width and height. All the tiles + in an image have the same size, and the tile width and length must each + be a multiple of 16 pixels. Tiles are ordered left-to-right and + top-to-bottom in an image. As for scanlines, samples can be packed + contiguously or separately. When separated, all the tiles for a sample + are colocated in the file. That is, all the tiles for sample 0 appear + before the tiles for sample 1, etc. +

+ Tiles and strips may also be extended in a z dimension to form + volumes. Data volumes are organized as "slices". That is, all the + data for a slice is colocated. Volumes whose data is organized in + tiles can also have a tile depth so that data can be organized in + cubes. +

+ There are actually two interfaces for tiles. + One interface is similar to scanlines, to read a tiled image, + code of the following sort might be used: +

+ main() + { + TIFF* tif = TIFFOpen("myfile.tif", "r"); + if (tif) { + uint32 imageWidth, imageLength; + uint32 tileWidth, tileLength; + uint32 x, y; + tdata_t buf; + + TIFFGetField(tif, TIFFTAG_IMAGEWIDTH, &imageWidth); + TIFFGetField(tif, TIFFTAG_IMAGELENGTH, &imageLength); + TIFFGetField(tif, TIFFTAG_TILEWIDTH, &tileWidth); + TIFFGetField(tif, TIFFTAG_TILELENGTH, &tileLength); + buf = _TIFFmalloc(TIFFTileSize(tif)); + for (y = 0; y < imagelength; y += tilelength) + for (x = 0; x < imagewidth; x += tilewidth) + tiffreadtile(tif, buf, x, y, 0); + _tifffree(buf); + tiffclose(tif); + } + } +

+ (once again, we assume samples are packed contiguously.) +

+ Alternatively a direct interface to the low-level data is provided + a la strips. Tiles can be read with + TIFFReadEncodedTile or TIFFReadRawTile, + and written with TIFFWriteEncodedTile or + TIFFWriteRawTile. For example, to read all the tiles in an image: +

+ #include "tiffio.h" + main() + { + TIFF* tif = TIFFOpen("myfile.tif", "r"); + if (tif) { + tdata_t buf; + ttile_t tile; + + buf = _TIFFmalloc(TIFFTileSize(tif)); + for (tile = 0; tile < tiffnumberoftiles(tif); tile++) + tiffreadencodedtile(tif, tile, buf, (tsize_t) -1); + _tifffree(buf); + tiffclose(tif); + } + } +

Other Stuff

+ Some other stuff will almost certainly go here... +

+ Last updated: $Date: 2005-12-28 06:53:18 $ +

+ + -- cgit v1.2.3