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    1 CHANGE LOG for Independent JPEG Group's JPEG software
    2 
    3 
    4 Version 6b  27-Mar-1998
    5 -----------------------
    6 
    7 jpegtran has new features for lossless image transformations (rotation
    8 and flipping) as well as "lossless" reduction to grayscale.
    9 
   10 jpegtran now copies comments by default; it has a -copy switch to enable
   11 copying all APPn blocks as well, or to suppress comments.  (Formerly it
   12 always suppressed comments and APPn blocks.)  jpegtran now also preserves
   13 JFIF version and resolution information.
   14 
   15 New decompressor library feature: COM and APPn markers found in the input
   16 file can be saved in memory for later use by the application.  (Before,
   17 you had to code this up yourself with a custom marker processor.)
   18 
   19 There is an unused field "void * client_data" now in compress and decompress
   20 parameter structs; this may be useful in some applications.
   21 
   22 JFIF version number information is now saved by the decoder and accepted by
   23 the encoder.  jpegtran uses this to copy the source file's version number,
   24 to ensure "jpegtran -copy all" won't create bogus files that contain JFXX
   25 extensions but claim to be version 1.01.  Applications that generate their
   26 own JFXX extension markers also (finally) have a supported way to cause the
   27 encoder to emit JFIF version number 1.02.
   28 
   29 djpeg's trace mode reports JFIF 1.02 thumbnail images as such, rather
   30 than as unknown APP0 markers.
   31 
   32 In -verbose mode, djpeg and rdjpgcom will try to print the contents of
   33 APP12 markers as text.  Some digital cameras store useful text information
   34 in APP12 markers.
   35 
   36 Handling of truncated data streams is more robust: blocks beyond the one in
   37 which the error occurs will be output as uniform gray, or left unchanged
   38 if decoding a progressive JPEG.  The appearance no longer depends on the
   39 Huffman tables being used.
   40 
   41 Huffman tables are checked for validity much more carefully than before.
   42 
   43 To avoid the Unisys LZW patent, djpeg's GIF output capability has been
   44 changed to produce "uncompressed GIFs", and cjpeg's GIF input capability
   45 has been removed altogether.  We're not happy about it either, but there
   46 seems to be no good alternative.
   47 
   48 The configure script now supports building libjpeg as a shared library
   49 on many flavors of Unix (all the ones that GNU libtool knows how to
   50 build shared libraries for).  Use "./configure --enable-shared" to
   51 try this out.
   52 
   53 New jconfig file and makefiles for Microsoft Visual C++ and Developer Studio.
   54 Also, a jconfig file and a build script for Metrowerks CodeWarrior
   55 on Apple Macintosh.  makefile.dj has been updated for DJGPP v2, and there
   56 are miscellaneous other minor improvements in the makefiles.
   57 
   58 jmemmac.c now knows how to create temporary files following Mac System 7
   59 conventions.
   60 
   61 djpeg's -map switch is now able to read raw-format PPM files reliably.
   62 
   63 cjpeg -progressive -restart no longer generates any unnecessary DRI markers.
   64 
   65 Multiple calls to jpeg_simple_progression for a single JPEG object
   66 no longer leak memory.
   67 
   68 
   69 Version 6a  7-Feb-96
   70 --------------------
   71 
   72 Library initialization sequence modified to detect version mismatches
   73 and struct field packing mismatches between library and calling application.
   74 This change requires applications to be recompiled, but does not require
   75 any application source code change.
   76 
   77 All routine declarations changed to the style "GLOBAL(type) name ...",
   78 that is, GLOBAL, LOCAL, METHODDEF, EXTERN are now macros taking the
   79 routine's return type as an argument.  This makes it possible to add
   80 Microsoft-style linkage keywords to all the routines by changing just
   81 these macros.  Note that any application code that was using these macros
   82 will have to be changed.
   83 
   84 DCT coefficient quantization tables are now stored in normal array order
   85 rather than zigzag order.  Application code that calls jpeg_add_quant_table,
   86 or otherwise manipulates quantization tables directly, will need to be
   87 changed.  If you need to make such code work with either older or newer
   88 versions of the library, a test like "#if JPEG_LIB_VERSION >= 61" is
   89 recommended.
   90 
   91 djpeg's trace capability now dumps DQT tables in natural order, not zigzag
   92 order.  This allows the trace output to be made into a "-qtables" file
   93 more easily.
   94 
   95 New system-dependent memory manager module for use on Apple Macintosh.
   96 
   97 Fix bug in cjpeg's -smooth option: last one or two scanlines would be
   98 duplicates of the prior line unless the image height mod 16 was 1 or 2.
   99 
  100 Repair minor problems in VMS, BCC, MC6 makefiles.
  101 
  102 New configure script based on latest GNU Autoconf.
  103 
  104 Correct the list of include files needed by MetroWerks C for ccommand().
  105 
  106 Numerous small documentation updates.
  107 
  108 
  109 Version 6  2-Aug-95
  110 -------------------
  111 
  112 Progressive JPEG support: library can read and write full progressive JPEG
  113 files.  A "buffered image" mode supports incremental decoding for on-the-fly
  114 display of progressive images.  Simply recompiling an existing IJG-v5-based
  115 decoder with v6 should allow it to read progressive files, though of course
  116 without any special progressive display.
  117 
  118 New "jpegtran" application performs lossless transcoding between different
  119 JPEG formats; primarily, it can be used to convert baseline to progressive
  120 JPEG and vice versa.  In support of jpegtran, the library now allows lossless
  121 reading and writing of JPEG files as DCT coefficient arrays.  This ability
  122 may be of use in other applications.
  123 
  124 Notes for programmers:
  125 * We changed jpeg_start_decompress() to be able to suspend; this makes all
  126 decoding modes available to suspending-input applications.  However,
  127 existing applications that use suspending input will need to be changed
  128 to check the return value from jpeg_start_decompress().  You don't need to
  129 do anything if you don't use a suspending data source.
  130 * We changed the interface to the virtual array routines: access_virt_array
  131 routines now take a count of the number of rows to access this time.  The
  132 last parameter to request_virt_array routines is now interpreted as the
  133 maximum number of rows that may be accessed at once, but not necessarily
  134 the height of every access.
  135 
  136 
  137 Version 5b  15-Mar-95
  138 ---------------------
  139 
  140 Correct bugs with grayscale images having v_samp_factor > 1.
  141 
  142 jpeg_write_raw_data() now supports output suspension.
  143 
  144 Correct bugs in "configure" script for case of compiling in
  145 a directory other than the one containing the source files.
  146 
  147 Repair bug in jquant1.c: sometimes didn't use as many colors as it could.
  148 
  149 Borland C makefile and jconfig file work under either MS-DOS or OS/2.
  150 
  151 Miscellaneous improvements to documentation.
  152 
  153 
  154 Version 5a  7-Dec-94
  155 --------------------
  156 
  157 Changed color conversion roundoff behavior so that grayscale values are
  158 represented exactly.  (This causes test image files to change.)
  159 
  160 Make ordered dither use 16x16 instead of 4x4 pattern for a small quality
  161 improvement.
  162 
  163 New configure script based on latest GNU Autoconf.
  164 Fix configure script to handle CFLAGS correctly.
  165 Rename *.auto files to *.cfg, so that configure script still works if
  166 file names have been truncated for DOS.
  167 
  168 Fix bug in rdbmp.c: didn't allow for extra data between header and image.
  169 
  170 Modify rdppm.c/wrppm.c to handle 2-byte raw PPM/PGM formats for 12-bit data.
  171 
  172 Fix several bugs in rdrle.c.
  173 
  174 NEED_SHORT_EXTERNAL_NAMES option was broken.
  175 
  176 Revise jerror.h/jerror.c for more flexibility in message table.
  177 
  178 Repair oversight in jmemname.c NO_MKTEMP case: file could be there
  179 but unreadable.
  180 
  181 
  182 Version 5  24-Sep-94
  183 --------------------
  184 
  185 Version 5 represents a nearly complete redesign and rewrite of the IJG
  186 software.  Major user-visible changes include:
  187   * Automatic configuration simplifies installation for most Unix systems.
  188   * A range of speed vs. image quality tradeoffs are supported.
  189     This includes resizing of an image during decompression: scaling down
  190     by a factor of 1/2, 1/4, or 1/8 is handled very efficiently.
  191   * New programs rdjpgcom and wrjpgcom allow insertion and extraction
  192     of text comments in a JPEG file.
  193 
  194 The application programmer's interface to the library has changed completely.
  195 Notable improvements include:
  196   * We have eliminated the use of callback routines for handling the
  197     uncompressed image data.  The application now sees the library as a
  198     set of routines that it calls to read or write image data on a
  199     scanline-by-scanline basis.
  200   * The application image data is represented in a conventional interleaved-
  201     pixel format, rather than as a separate array for each color channel.
  202     This can save a copying step in many programs.
  203   * The handling of compressed data has been cleaned up: the application can
  204     supply routines to source or sink the compressed data.  It is possible to
  205     suspend processing on source/sink buffer overrun, although this is not
  206     supported in all operating modes.
  207   * All static state has been eliminated from the library, so that multiple
  208     instances of compression or decompression can be active concurrently.
  209   * JPEG abbreviated datastream formats are supported, ie, quantization and
  210     Huffman tables can be stored separately from the image data.
  211   * And not only that, but the documentation of the library has improved
  212     considerably!
  213 
  214 
  215 The last widely used release before the version 5 rewrite was version 4A of
  216 18-Feb-93.  Change logs before that point have been discarded, since they
  217 are not of much interest after the rewrite.