| <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> |