diff options
Diffstat (limited to 'tiff/html/internals.html')
| -rwxr-xr-x | tiff/html/internals.html | 572 |
1 files changed, 0 insertions, 572 deletions
diff --git a/tiff/html/internals.html b/tiff/html/internals.html deleted file mode 100755 index 83d53b0..0000000 --- a/tiff/html/internals.html +++ /dev/null @@ -1,572 +0,0 @@ -<HTML> -<HEAD> -<TITLE> -Modifying The TIFF Library -</TITLE> -</HEAD> -<BODY BGCOLOR=white> -<FONT FACE="Arial, Helvetica, Sans"> -<H1> -<IMG SRC=images/dave.gif WIDTH=107 HEIGHT=148 BORDER=2 ALIGN=left HSPACE=6> -Modifying The TIFF Library -</H1> - - -<P> -This chapter provides information about the internal structure of -the library, how to control the configuration when building it, and -how to add new support to the library. -The following sections are found in this chapter: - -<UL> -<LI><A HREF=#Config>Library Configuration</A> -<LI><A HREF=#Portability>General Portability Comments</A> -<LI><A HREF="#Types">Types and Portability</A> -<LI><A HREF="addingtags.html">Adding New Tags</A> -<LI><A HREF=#AddingCODECS>Adding New Builtin Codecs</A> -<LI><A HREF="addingtags.html#AddingCODECTags">Adding New Codec-private Tags</A> -<LI><A HREF=#Other>Other Comments</A> -</UL> - - -<A NAME="Config"><P><HR WIDTH=65% ALIGN=right><H3>Library Configuration</H3></A> - -Information on compiling the library is given -<A HREF=build.html>elsewhere in this documentation</A>. -This section describes the low-level mechanisms used to control -the optional parts of the library that are configured at build -time. Control is based on -a collection of C defines that are specified either on the compiler -command line or in a configuration file such as <TT>port.h</TT> -(as generated by the <TT>configure</TT> script for UNIX systems) -or <B>tiffconf.h</B>. - -<P> -Configuration defines are split into three areas: -<UL> -<LI>those that control which compression schemes are - configured as part of the builtin codecs, -<LI>those that control support for groups of tags that - are considered optional, and -<LI>those that control operating system or machine-specific support. -</UL> - -<P> -If the define <TT>COMPRESSION_SUPPORT</TT> is <STRONG>not defined</STRONG> -then a default set of compression schemes is automatically -configured: -<UL> -<LI>CCITT Group 3 and 4 algorithms (compression codes 2, 3, 4, and 32771), -<LI>the Macintosh PackBits algorithm (compression 32773), -<LI>a 4-bit run-length encoding scheme from ThunderScan (compression 32809), -<LI>a 2-bit encoding scheme used by NeXT (compression 32766), and -<LI>two experimental schemes intended for images with high dynamic range -(compression 34676 and 34677). -</UL> - -<P> - -To override the default compression behaviour define -<TT>COMPRESSION_SUPPORT</TT> and then one or more additional defines -to enable configuration of the appropriate codecs (see the table -below); e.g. - -<UL><PRE> -#define COMPRESSION_SUPPORT -#define CCITT_SUPPORT -#define PACKBITS_SUPPORT -</PRE></UL> - -Several other compression schemes are configured separately from -the default set because they depend on ancillary software -packages that are not distributed with <TT>libtiff</TT>. - -<P> -Support for JPEG compression is controlled by <TT>JPEG_SUPPORT</TT>. -The JPEG codec that comes with <TT>libtiff</TT> is designed for -use with release 5 or later of the Independent JPEG Group's freely -available software distribution. -This software can be retrieved from the directory -<A HREF=ftp://ftp.uu.net/graphics/jpeg>ftp.uu.net:/graphics/jpeg/</A>. - - -<P> -<IMG SRC="images/info.gif" ALT="NOTE: " ALIGN=left HSPACE=8> -<EM>Enabling JPEG support automatically enables support for -the TIFF 6.0 colorimetry and YCbCr-related tags.</EM> - -<P> -Experimental support for the deflate algorithm is controlled by -<TT>DEFLATE_SUPPORT</TT>. -The deflate codec that comes with <TT>libtiff</TT> is designed -for use with version 0.99 or later of the freely available -<TT>libz</TT> library written by Jean-loup Gailly and Mark Adler. -The data format used by this library is described -in the files -<A HREF=ftp://ftp.uu.net/pub/archiving/zip/doc/zlib-3.1.doc>zlib-3.1.doc</A>, -and -<A HREF=ftp://ftp.uu.net/pub/archiving/zip/doc/deflate-1.1.doc>deflate-1.1.doc</A>, -available in the directory -<A HREF=ftp://ftp.uu.net/pub/archiving/zip/doc>ftp.uu.net:/pub/archiving/zip/doc</A>.</EM> -The library can be retried from the directory -<A HREF=ftp://ftp.uu.net/pub/archiving/zip/zlib/>ftp.uu.net:/pub/archiving/zip/zlib/</A> -(or try <A HREF=ftp://quest.jpl.nasa.gov/beta/zlib/>quest.jpl.nasa.gov:/beta/zlib/</A>). - -<P> -<IMG SRC="images/warning.gif" ALT="NOTE: " ALIGN=left HSPACE=8 VSPACE=6> -<EM>The deflate algorithm is experimental. Do not expect -to exchange files using this compression scheme; -it is included only because the similar, and more common, -LZW algorithm is claimed to be governed by licensing restrictions.</EM> - - -<P> -By default <B>tiffconf.h</B> defines -<TT>COLORIMETRY_SUPPORT</TT>, -<TT>YCBCR_SUPPORT</TT>, -and -<TT>CMYK_SUPPORT</TT>. - -<P> -<TABLE BORDER CELLPADDING=3> - -<TR><TH ALIGN=left>Define</TH><TH ALIGN=left>Description</TH></TR> - -<TR> -<TD VALIGN=top><TT>CCITT_SUPPORT</TT></TD> -<TD>CCITT Group 3 and 4 algorithms (compression codes 2, 3, 4, - and 32771)</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>PACKBITS_SUPPORT</TT></TD> -<TD>Macintosh PackBits algorithm (compression 32773)</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>LZW_SUPPORT</TT></TD> -<TD>Lempel-Ziv & Welch (LZW) algorithm (compression 5)</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>THUNDER_SUPPORT</TT></TD> -<TD>4-bit -run-length encoding scheme from ThunderScan (compression 32809)</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>NEXT_SUPPORT</TT></TD> -<TD>2-bit encoding scheme used by NeXT (compression 32766)</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>OJPEG_SUPPORT</TT></TD> -<TD>obsolete JPEG scheme defined in the 6.0 spec (compression 6)</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>JPEG_SUPPORT</TT></TD> -<TD>current JPEG scheme defined in TTN2 (compression 7)</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>ZIP_SUPPORT</TT></TD> -<TD>experimental Deflate scheme (compression 32946)</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>PIXARLOG_SUPPORT</TT></TD> -<TD>Pixar's compression scheme for high-resolution color images (compression 32909)</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>SGILOG_SUPPORT</TT></TD> -<TD>SGI's compression scheme for high-resolution color images (compression 34676 and 34677)</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>COLORIMETRY_SUPPORT</TT></TD> -<TD>support for the TIFF 6.0 colorimetry tags</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>YCBCR_SUPPORT</TT></TD> -<TD>support for the TIFF 6.0 YCbCr-related tags</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>CMYK_SUPPORT</TT></TD> -<TD>support for the TIFF 6.0 CMYK-related tags</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>ICC_SUPPORT</TT></TD> -<TD>support for the ICC Profile tag; see -<I>The ICC Profile Format Specification</I>, -Annex B.3 "Embedding ICC Profiles in TIFF Files"; -available at -<A HREF=http://www.color.org>http://www.color.org</A> -</TD> -</TR> - -</TABLE> - - -<A NAME="Portability"><P><HR WIDTH=65% ALIGN=right><H3>General Portability Comments</H3></A> - -This software is developed on Silicon Graphics UNIX -systems (big-endian, MIPS CPU, 32-bit ints, -IEEE floating point). -The <TT>configure</TT> shell script generates the appropriate -include files and make files for UNIX systems. -Makefiles exist for non-UNIX platforms that the -code runs on -- this work has mostly been done by other people. - -<P> -In general, the code is guaranteed to work only on SGI machines. -In practice it is highly portable to any 32-bit or 64-bit system and much -work has been done to insure portability to 16-bit systems. -If you encounter portability problems please return fixes so -that future distributions can be improved. - -<P> -The software is written to assume an ANSI C compilation environment. -If your compiler does not support ANSI function prototypes, <TT>const</TT>, -and <TT><stdarg.h></TT> then you will have to make modifications to the -software. In the past I have tried to support compilers without <TT>const</TT> -and systems without <TT><stdarg.h></TT>, but I am -<EM>no longer interested in these -antiquated environments</EM>. With the general availability of -the freely available GCC compiler, I -see no reason to incorporate modifications to the software for these -purposes. - -<P> -An effort has been made to isolate as many of the -operating system-dependencies -as possible in two files: <B>tiffcomp.h</B> and -<B>libtiff/tif_<os>.c</B>. The latter file contains -operating system-specific routines to do I/O and I/O-related operations. -The UNIX (<B>tif_unix.c</B>), -Macintosh (<B>tif_apple.c</B>), -and VMS (<B>tif_vms.c</B>) -code has had the most use; -the MS/DOS support (<B>tif_msdos.c</B>) assumes -some level of UNIX system call emulation (i.e. -<TT>open</TT>, -<TT>read</TT>, -<TT>write</TT>, -<TT>fstat</TT>, -<TT>malloc</TT>, -<TT>free</TT>). - -<P> -Native CPU byte order is determined on the fly by -the library and does not need to be specified. -The <TT>HOST_FILLORDER</TT> and <TT>HOST_BIGENDIAN</TT> -definitions are not currently used, but may be employed by -codecs for optimization purposes. - -<P> -The following defines control general portability: - -<P> -<TABLE BORDER CELLPADDING=3 WIDTH=100%> - -<TR> -<TD VALIGN=top><TT>BSDTYPES</TT></TD> -<TD>Define this if your system does NOT define the - usual BSD typedefs: <TT>u_char</TT>, - <TT>u_short</TT>, <TT>u_int</TT>, <TT>u_long</TT>.</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>HAVE_IEEEFP</TT></TD> -<TD>Define this as 0 or 1 according to the floating point - format suported by the machine. If your machine does - not support IEEE floating point then you will need to - add support to tif_machdep.c to convert between the - native format and IEEE format.</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>HAVE_MMAP</TT></TD> -<TD>Define this if there is <I>mmap-style</I> support for -mapping files into memory (used only to read data).</TD> -</TR> - -<TR> -<TD VALIGN=top><TT>HOST_FILLORDER</TT></TD> -<TD>Define the native CPU bit order: one of <TT>FILLORDER_MSB2LSB</TT> - or <TT>FILLORDER_LSB2MSB</TT></TD> -</TR> - -<TR> -<TD VALIGN=top><TT>HOST_BIGENDIAN</TT></TD> -<TD>Define the native CPU byte order: 1 if big-endian (Motorola) - or 0 if little-endian (Intel); this may be used - in codecs to optimize code</TD> -</TR> -</TABLE> - -<P> -On UNIX systems <TT>HAVE_MMAP</TT> is defined through the running of -the <TT>configure</TT> script; otherwise support for memory-mapped -files is disabled. -Note that <B>tiffcomp.h</B> defines <TT>HAVE_IEEEFP</TT> to be -1 (<TT>BSDTYPES</TT> is not defined). - - -<A NAME="Types"><P><HR WIDTH=65% ALIGN=right><H3>Types and Portability</H3></A> - -The software 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. There are interactions between these two to be careful -of, but for the most part you should be able to deal with portability -purely by fiddling with the following machine-dependent typedefs: - - -<P> -<TABLE BORDER CELLPADDING=3 WIDTH=100%> - -<TR> -<TD>uint8</TD> -<TD>8-bit unsigned integer</TD> -<TD>tiff.h</TD> -</TR> - -<TR> -<TD>int8</TD> -<TD>8-bit signed integer</TD> -<TD>tiff.h</TD> -</TR> - -<TR> -<TD>uint16</TD> -<TD>16-bit unsigned integer</TD> -<TD>tiff.h</TD> -</TR> - -<TR> -<TD>int16</TD> -<TD>16-bit signed integer</TD> -<TD>tiff.h</TD> -</TR> - -<TR> -<TD>uint32</TD> -<TD>32-bit unsigned integer</TD> -<TD>tiff.h</TD> -</TR> - -<TR> -<TD>int32</TD> -<TD>32-bit signed integer</TD> -<TD>tiff.h</TD> -</TR> - -<TR> -<TD>dblparam_t</TD> -<TD>promoted type for floats</TD> -<TD>tiffcomp.h</TD> -</TR> - -</TABLE> - -<P> -(to clarify <TT>dblparam_t</TT>, it is the type that float parameters are -promoted to when passed by value in a function call.) - -<P> -The following typedefs are used throughout the library and interfaces -to refer to certain objects whose size is dependent on the TIFF image -structure: - - -<P> -<TABLE BORDER CELLPADDING=3 WIDTH=100%> - -<TR> -<TD WIDTH=25%>typedef unsigned int ttag_t;</TD> <TD>directory tag</TD> -</TR> - -<TR> -<TD>typedef uint16 tdir_t;</TD> <TD>directory index</TD> -</TR> - -<TR> -<TD>typedef uint16 tsample_t;</TD> <TD>sample number</TD> -</TR> - -<TR> -<TD>typedef uint32 tstrip_t;</TD> <TD>strip number</TD> -</TR> - -<TR> -<TD>typedef uint32 ttile_t;</TD> <TD>tile number</TD> -</TR> - -<TR> -<TD>typedef int32 tsize_t;</TD> <TD>i/o size in bytes</TD> -</TR> - -<TR> -<TD>typedef void* tdata_t;</TD> <TD>image data ref</TD> -</TR> - -<TR> -<TD>typedef void* thandle_t;</TD> <TD>client data handle</TD> -</TR> - -<TR> -<TD>typedef int32 toff_t;</TD> <TD>file offset (should be off_t)</TD> -</TR> - -<TR> -<TD>typedef unsigned char* tidata_t;</TD> <TD>internal image data</TD> -</TR> - -</TABLE> - -<P> -Note that <TT>tstrip_t</TT>, <TT>ttile_t</TT>, and <TT>tsize_t</TT> -are constrained to be -no more than 32-bit quantities by 32-bit fields they are stored -in in the TIFF image. Likewise <TT>tsample_t</TT> is limited by the 16-bit -field used to store the <TT>SamplesPerPixel</TT> tag. <TT>tdir_t</TT> -constrains -the maximum number of IFDs that may appear in an image and may -be an arbitrary size (without penalty). <TT>ttag_t</TT> must be either -<TT>int</TT>, <TT>unsigned int</TT>, pointer, or <TT>double</TT> -because the library uses a varargs -interface and ANSI C restricts the type of the parameter before an -ellipsis to be a promoted type. <TT>toff_t</TT> is defined as -<TT>int32</TT> because -TIFF file offsets are (unsigned) 32-bit quantities. A signed -value is used because some interfaces return -1 on error (sigh). -Finally, note that <TT>tidata_t</TT> is used internally to the library to -manipulate internal data. User-specified data references are -passed as opaque handles and only cast at the lowest layers where -their type is presumed. - - -<P><HR WIDTH=65% ALIGN=right><H3>General Comments</H3></A> - -The library is designed to hide as much of the details of TIFF from -applications as -possible. In particular, TIFF directories are read in their entirety -into an internal format. Only the tags known by the library are -available to a user and certain tag data may be maintained that a user -does not care about (e.g. transfer function tables). - -<A NAME=AddingCODECS><P><HR WIDTH=65% ALIGN=right><H3>Adding New Builtin Codecs</H3></A> - -To add builtin support for a new compression algorithm, you can either -use the "tag-extension" trick to override the handling of the -TIFF Compression tag (see <A HREF=addingtags.html>Adding New Tags</A>), -or do the following to add support directly to the core library: - -<OL> -<LI>Define the tag value in <B>tiff.h</B>. -<LI>Edit the file <B>tif_codec.c</B> to add an entry to the - _TIFFBuiltinCODECS array (see how other algorithms are handled). -<LI>Add the appropriate function prototype declaration to - <B>tiffiop.h</B> (close to the bottom). -<LI>Create a file with the compression scheme code, by convention files - are named <B>tif_*.c</B> (except perhaps on some systems where the - tif_ prefix pushes some filenames over 14 chars. -<LI>Edit <B>Makefile.in</B> (and any other Makefiles) - to include the new source file. -</OL> - -<P> -A codec, say <TT>foo</TT>, can have many different entry points: - -<PRE> -TIFFInitfoo(tif, scheme)/* initialize scheme and setup entry points in tif */ -fooSetupDecode(tif) /* called once per IFD after tags has been frozen */ -fooPreDecode(tif, sample)/* called once per strip/tile, after data is read, - but before the first row is decoded */ -fooDecode*(tif, bp, cc, sample)/* decode cc bytes of data into the buffer */ - fooDecodeRow(...) /* called to decode a single scanline */ - fooDecodeStrip(...) /* called to decode an entire strip */ - fooDecodeTile(...) /* called to decode an entire tile */ -fooSetupEncode(tif) /* called once per IFD after tags has been frozen */ -fooPreEncode(tif, sample)/* called once per strip/tile, before the first row in - a strip/tile is encoded */ -fooEncode*(tif, bp, cc, sample)/* encode cc bytes of user data (bp) */ - fooEncodeRow(...) /* called to decode a single scanline */ - fooEncodeStrip(...) /* called to decode an entire strip */ - fooEncodeTile(...) /* called to decode an entire tile */ -fooPostEncode(tif) /* called once per strip/tile, just before data is written */ -fooSeek(tif, row) /* seek forwards row scanlines from the beginning - of a strip (row will always be >0 and <rows/strip */ -fooCleanup(tif) /* called when compression scheme is replaced by user */ -</PRE> - -<P> -Note that the encoding and decoding variants are only needed when -a compression algorithm is dependent on the structure of the data. -For example, Group 3 2D encoding and decoding maintains a reference -scanline. The sample parameter identifies which sample is to be -encoded or decoded if the image is organized with <TT>PlanarConfig</TT>=2 -(separate planes). This is important for algorithms such as JPEG. -If <TT>PlanarConfig</TT>=1 (interleaved), then sample will always be 0. - -<A NAME=Other><P><HR WIDTH=65% ALIGN=right><H3>Other Comments</H3></A> - -The library handles most I/O buffering. There are two data buffers -when decoding data: a raw data buffer that holds all the data in a -strip, and a user-supplied scanline buffer that compression schemes -place decoded data into. When encoding data the data in the -user-supplied scanline buffer is encoded into the raw data buffer (from -where it is written). Decoding routines should never have to explicitly -read data -- a full strip/tile's worth of raw data is read and scanlines -never cross strip boundaries. Encoding routines must be cognizant of -the raw data buffer size and call <TT>TIFFFlushData1()</TT> when necessary. -Note that any pending data is automatically flushed when a new strip/tile is -started, so there's no need do that in the tif_postencode routine (if -one exists). Bit order is automatically handled by the library when -a raw strip or tile is filled. If the decoded samples are interpreted -by the decoding routine before they are passed back to the user, then -the decoding logic must handle byte-swapping by overriding the -<TT>tif_postdecode</TT> -routine (set it to <TT>TIFFNoPostDecode</TT>) and doing the required work -internally. For an example of doing this look at the horizontal -differencing code in the routines in <B>tif_predict.c</B>. - -<P> -The variables <TT>tif_rawcc</TT>, <TT>tif_rawdata</TT>, and -<TT>tif_rawcp</TT> in a <TT>TIFF</TT> structure -are associated with the raw data buffer. <TT>tif_rawcc</TT> must be non-zero -for the library to automatically flush data. The variable -<TT>tif_scanlinesize</TT> is the size a user's scanline buffer should be. The -variable <TT>tif_tilesize</TT> is the size of a tile for tiled images. This -should not normally be used by compression routines, except where it -relates to the compression algorithm. That is, the <TT>cc</TT> parameter to the -<TT>tif_decode*</TT> and <TT>tif_encode*</TT> -routines should be used in terminating -decompression/compression. This ensures these routines can be used, -for example, to decode/encode entire strips of data. - -<P> -In general, if you have a new compression algorithm to add, work from -the code for an existing routine. In particular, -<B>tif_dumpmode.c</B> -has the trivial code for the "nil" compression scheme, -<B>tif_packbits.c</B> is a -simple byte-oriented scheme that has to watch out for buffer -boundaries, and <B>tif_lzw.c</B> has the LZW scheme that has the most -complexity -- it tracks the buffer boundary at a bit level. -Of course, using a private compression scheme (or private tags) limits -the portability of your TIFF files. - -<P> -<HR> - -Last updated: $Date: 2004-09-10 14:47:31 $ - -</BODY> - -</HTML> |