readme.txt

DELPHI版的JPEG文件解码源程序

_____________________________________________________________________________

PASJPEG 1.1                                                   May 29th, 1999

Based on the Independent JPEG Group's JPEG software release 6b

Copyright (C) 1996,1998,1999 by NOMSSI NZALI Jacques H. C.
[kn&n DES]         See "Legal issues" for conditions of distribution and use.
_____________________________________________________________________________


Information in this file
========================

  o Introduction
  o Notes
  o File list
  o Translation
  o Legal issues
  o Archive Locations

Introduction
============

PASJPEG is a port of the sixth public release of the IJG C source (release
6b of 27-Mar-98) [3], that implements JPEG baseline, extended-sequential, and
progressive compression processes to Turbo Pascal 7.0 for DOS (TP). The code
has been tested under Delphi 3.0, it can be ported to other Pascal
environments, since many compilers try to be compatible to TP.

JPEG (pronounced "jay-peg") is a standardized familly of algorithms for
compression of continous tone still images. Most JPEG processes are lossy,
the output image is not exactly identical to the input image. However, on
typical photographic images, very good compression levels can be obtained
with no visible change, and remarkably high compression levels are possible
if you can tolerate a low-quality image [1],[2]. The Independent JPEG Group
(IJG) has created a free, portable C library for JPEG compression and
decompression of JPEG images.

The IJG documentation (system architecture, using the IJG JPEG library,
usage and file list) is a must read. The files DEMO.PAS, TEST.PAS, CJPEG.PAS,
DJPEG.PAS and EXAMPLE.PAS demonstrate the usage of the JPEG decompression
and compression library. The RDJPGCOM application shows how to parse a JFIF
file.

Notes:
======

* Please report any errors/problems you may find in code and in the
  documentation (e.g. this README.TXT file).

* The sample applications (CJPEG, DJPEG) doesn't support all the options
  of the original C code. WRJPGCOM is not ported.

* Environment variable JPEGMEM syntax changed;

* You can modify the jpeg.pas unit from the Delphi 3 distribution to
  use PasJPEG.

Change log
==========

1. bugs fixed: 
   * in procedure read_gif_map(), unit RDCOLMAP.PAS (used by DJPEG sample 
     application). Davie Lee Reed <[e-mail]>
   * -dct int and -dct fast now bytewise equal to the IJG output.
   * -dct float produced large files

2. Support for scripts

3. BASM version of JIDCTINT.PAS for Delphi 2 and 3.

4. images with integral sampling ratios were not decoded correctly.
   Create a jpeg file with cjpeg and the option "-sample 4x1" and try to decode 
   it with any software that uses PasJpeg. Thanks to Jannie Gerber for reporting
   this with a fix: In JDSAMPLE.PAS, procedure int_upsample(), 
         
    for h := pred(h_expand) downto 0 do
    begin
      outptr^ := invalue;
 +=>  inc(outptr);   { this is the culprit that was left out!!! }
      Dec(outcount);
    end;

File list
=========

Here is a road map to the files in the PasJPEG distribution.  The
distribution includes the JPEG library proper, plus two application
programs ("cjpeg" and "djpeg") which use the library to convert JPEG
files to and from some other popular image formats.  A third application
"jpegtran" uses the library to do lossless conversion between different
variants of JPEG.  There is also the stand-alone applications "rdjpgcom".

Documentation(see README for a guide to the documentation files):

readme.txt      Introduction, Documentation

Additional files

demo.pas        Demo program, uses example.pas
example.pas     Sample code for calling JPEG library.
test.pas        Sample application code for demo.pas

Configuration/installation files and programs (see install.doc for more info):

jconfig.inc     Configuration declarations.

*.ijg           script files

Pascal source code files:

jinclude.pas    Central include file used by all IJG .c files to reference
		system include files.
jpeglib.pas     JPEG library's internal data structures, exported data
                and function declarations.
jmorecfg.pas    Additional configuration declarations; need not be changed
                for a standard installation.
jdeferr.pas     defines the error and message text.
jerror.pas      Declares JPEG library's error and trace message codes.
jinclude.pas    the place to specify system depedent input/output code.
jdct.pas        Private declarations for forward & reverse DCT subsystems.

These files contain most of the functions intended to be called directly by
an application program:

jcapimin.pas    Application program interface: core routines for compression.
jcapistd.pas    Application program interface: standard compression.
jdapimin.pas    Application program interface: core routines for decompression.
jdapistd.pas    Application program interface: standard decompression.
jcomapi.pas     Application program interface routines common to compression
                and decompression.
jcparam.pas     Compression parameter setting helper routines.
jctrans.pas     API and library routines for transcoding compression.
jdtrans.pas     API and library routines for transcoding decompression.

Compression side of the library:

jcinit.pas      Initialization: determines which other modules to use.
jcmaster.pas    Master control: setup and inter-pass sequencing logic.
jcmainct.pas    Main buffer controller (preprocessor => JPEG compressor).
jcprepct.pas    Preprocessor buffer controller.
jccoefct.pas    Buffer controller for DCT coefficient buffer.
jccolor.pas     Color space conversion.
jcsample.pas    Downsampling.
jcdctmgr.pas    DCT manager (DCT implementation selection & control).
jfdctint.pas    Forward DCT using slow-but-accurate integer method.
jfdctfst.pas    Forward DCT using faster, less accurate integer method.
jfdctflt.pas    Forward DCT using floating-point arithmetic.
jchuff.pas      Huffman entropy coding for sequential JPEG.
jcphuff.pas     Huffman entropy coding for progressive JPEG.
jcmarker.pas    JPEG marker writing.
jdatadst.pas    Data destination manager for stdio output.

Decompression side of the library:

jdmaster.pas    Master control: determines which other modules to use.
jdinput.pas     Input controller: controls input processing modules.
jdmainct.pas    Main buffer controller (JPEG decompressor => postprocessor).
jdcoefct.pas    Buffer controller for DCT coefficient buffer.
jdpostct.pas    Postprocessor buffer controller.
jdmarker.pas    JPEG marker reading.
jdhuff.pas      Huffman entropy decoding for sequential JPEG.
jdphuff.pas     Huffman entropy decoding for progressive JPEG.
jddctmgr.pas    IDCT manager (IDCT implementation selection & control).
jidctint.pas    Inverse DCT using slow-but-accurate integer method.
jidctasm.pas    BASM specific version of jidctint.pas for 32bit Delphi.
jidctfst.pas    Inverse DCT using faster, less accurate integer method.
jidctflt.pas    Inverse DCT using floating-point arithmetic.
jidctred.pas    Inverse DCTs with reduced-size outputs.
jidct2d.pas     How to for a direct 2D Inverse DCT - not used
jdsample.pas    Upsampling.
jdcolor.pas     Color space conversion.
jdmerge.pas     Merged upsampling/color conversion (faster, lower quality).
jquant1.pas     One-pass color quantization using a fixed-spacing colormap.
jquant2.pas     Two-pass color quantization using a custom-generated colormap.
		Also handles one-pass quantization to an externally given map.
jdatasrc.pas    Data source manager for stdio input.

Support files for both compression and decompression:

jerror.pas      Standard error handling routines (application replaceable).
jmemmgr.pas     System-independent (more or less) memory management code.
jutils.pas      Miscellaneous utility routines.

jmemmgr.pas relies on a system-dependent memory management module.  The
PASJPEG distribution includes the following implementations of the system-
dependent module:

jmemnobs.pas    "No backing store": assumes adequate virtual memory exists.
jmemdos.pas     Custom implementation for MS-DOS (16-bit environment only):