change.log

CHANGE LOG for Independent JPEG Group's JPEG software


Version 5a  7-Dec-94
--------------------

Changed color conversion roundoff behavior so that grayscale values are
represented exactly.  (This causes test image files to change.)

Make ordered dither use 16x16 instead of 4x4 pattern for a small quality
improvement.

New configure script based on latest GNU Autoconf.
Fix configure script to handle CFLAGS correctly.
Rename *.auto files to *.cfg, so that configure script still works if
file names have been truncated for DOS.

Fix bug in rdbmp.c: didn't allow for extra data between header and image.

Modify rdppm.c/wrppm.c to handle 2-byte raw PPM/PGM formats for 12-bit data.

Fix several bugs in rdrle.c.

NEED_SHORT_EXTERNAL_NAMES option was broken.

Revise jerror.h/jerror.c for more flexibility in message table.

Repair oversight in jmemname.c NO_MKTEMP case: file could be there
but unreadable.


Version 5  24-Sep-94
--------------------

Version 5 represents a nearly complete redesign and rewrite of the IJG
software.  Major user-visible changes include:
  * Automatic configuration simplifies installation for most Unix systems.
  * A range of speed vs. image quality tradeoffs are supported.
    This includes resizing of an image during decompression: scaling down
    by a factor of 1/2, 1/4, or 1/8 is handled very efficiently.
  * New programs rdjpgcom and wrjpgcom allow insertion and extraction
    of text comments in a JPEG file.

The application programmer's interface to the library has changed completely.
Notable improvements include:
  * We have eliminated the use of callback routines for handling the
    uncompressed image data.  The application now sees the library as a
    set of routines that it calls to read or write image data on a
    scanline-by-scanline basis.
  * The application image data is represented in a conventional interleaved-
    pixel format, rather than as a separate array for each color channel.
    This can save a copying step in many programs.
  * The handling of compressed data has been cleaned up: the application can
    supply routines to source or sink the compressed data.  It is possible to
    suspend processing on source/sink buffer overrun, although this is not
    supported in all operating modes.
  * All static state has been eliminated from the library, so that multiple
    instances of compression or decompression can be active concurrently.
  * JPEG abbreviated datastream formats are supported, ie, quantization and
    Huffman tables can be stored separately from the image data.
  * And not only that, but the documentation of the library has improved
    considerably!


The last widely used release before the version 5 rewrite was version 4A of
18-Feb-93.  Change logs before that point have been discarded, since they
are not of much interest after the rewrite.