JFIFdt44 44.19

Short:        fastest JPEG picture datatype
Author:       Henryk Richter, gni@gecko.de (Gunther Nikl)
Uploader:     henryk richter gmx net (Henryk Richter)
Type:         util/dtype
Version:      44.19
Architecture: m68k-amigaos >= 3.0.0
Distribution: NoCD

This datatype contains a highly optimized 68020+ JPEG
decoder core, aiming for maximum speed without compromising 
accuracy.

Changes in this release:
- This release fixes a rare issue in the optimized Entropy
  decoder. At extremely high bitrates (quality setting 
  100%) and high noise levels, minor localized block errors
  could have resulted. (Thanks to P. "flype" Carpentier)
- Smaller JPEG files up to 1 MB in size are now loaded
  directly instead of double buffered streaming on systems
  with plenty (>= 32MB) of RAM.

A performance comparison is shown below. (on A3000 with 
BFG9060@100 MHz, 3.2+ ROM, CyberVision64 in HiColor, 
picture.datatype 47.15 from OS3.2.1, all datatypes at 
default settings; times in seconds measured as median over 
5 iterations with "visage nojpeg time test"):

Name                                |akjfif  |jfif    |warpjpeg|os32jpeg|
Version                             |45.95   |44.19   |45.17   |47.8    |
------------------------------------|--------|--------|--------|--------|
AnalogPac640x480_70_seq.jpg         |0.484   |0.305   |0.461   |0.372   |
BGA1024x1024_gray.jpg               |1.583   |1.386   |1.545   |1.534   |
CasaDeCampo_2592x1728_70_seq_420.jpg|4.593   |2.988   |3.969   |3.650   |
CasaDeCampo_2592x1728_90_seq_444.jpg|8.232   |5.405   |7.760   |6.565   |
Goose1024x768_12_baselineopt.jpg    |1.971   |1.417   |1.861   |1.797   |
Molli512x384_9_seq.jpg              |0.374   |0.255   |0.351   |0.310   |
Peacock800x600_10_baseline.jpg      |0.923   |0.605   |0.891   |0.739   |
Sail768x576_9_seq.jpg               |0.680   |0.423   |0.627   |0.511   |
Wnmde1152x768_70_422v_prog.jpg      |1.788   |1.457   |1.637   |1.633   |
Wnmde1536x1024_90_422h_seq.jpg      |1.834   |1.183   |1.686   |1.432   |
jordan199b.jpg                      |1.185   |0.717   |1.045   |0.871   |


The test images, benchmarking scripts, system details and 
raw results are available at:
http://bax.comlab.uni-rostock.de/fileadmin/downloads/jpegbench.zip

The datatype is an all-in-one binary for any 68020+ Amiga.
A fallback 68000 version (without assembly optimizations) is 
provided as well.


Changes in this release
 44.19:
 - workaround for potential Huffman decoder glitch at 
   extremely high bitrates (SAFERESTART option)
 - smaller JPEG files are loaded in one step now instead 
   of streaming
 44.18:
 - added installer script
 - overhauled YCC to RGB conversion by avoiding 
   multiplications such that it runs much faster 
   on MC68030/68040
 - updated both HQ and fast integer iDCT algorithms with 
   faster paths for some special cases that are computed as
   more efficient 2D iDCT instead of the customary 1D 
   separated row/column approach
 44.17:
 - fixed V42 mode (3.0/3.1 without updated picture.datatype)
 - added CPU check to 020+ version to exit cleanly 
   on 68000/10
 - removed FPU requirement (FPU iDCT is still optionally 
   available on FPU equipped systems)
 - added minimum CPU type to version string
 44.16:
 - fixed occasionally missing rows of pixels in cases where
   the SCALE or MAXLENGTH options are active
 - prepared for additional speedup on OS3.2.1 (about 100ms 
   per megapixel on 060/50 with picture.datatype 47.15)
 44.15:
 - fixed incompatibility with picture.datatype 45.17 
   (OS3.9BB2)
 44.14:
 - enabled arithmetic residual coding (not part of the 
   JPEG standard last I checked, but there are some pictures
   on the internet using this mode)
 - improvements to Huffman decoding functions
 - leverage V47 picture.datatype features for more speed
 - improvements to grayscale image handling


Feature overview

 - supports normal and progressive JFIFs with all their
   flavours
 - supports HAM output (HAM6 as well as HAM8)
 - switches to V43 mode if a picture.datatype V43+ is present
 - asynchronous file I/O to speedup image loading and decoding
 - utilizes WritePixelLine8() for chunky-to-planar in V42 mode
 - automatic colour quantizing of true-colour data for V42
 - can be configured to suit personal preferences
 - OS 3.5 and later support (minimum OS3.0)
 - FBlit tolerance
 - based on libjpeg-turbo
 - ASM optimizations to Huffman decoding, iDCT and color 
   transform (68020+)
 - 30 bit internal resolution for color transform functions
 - Highly accurate and fast default inverse cosine transform
   function (stock libjpeg methods still available as options)
 - AMMX optimization for Apollo Core Gold 2.7 and later
 - FPU and AMMX availability is checked before use at runtime
 - support for XMP JFIF files
 - all-in-one binary for 68020+


Tuning (see also the guide file for additional options):

 Classic 68k based Amigas
 - The old fast iDCT is still about 10% faster than the default
   on 68030/68040.
   If you care more for speed than accuracy, just type 
    makedir envarc:classes
    makedir envarc:classes/datatypes
    echo "DCT=FAST" >envarc:classes/datatypes/jfif44.prefs
   in a shell window. Alternatively, a single commandline
   call is also possible:
    setenv envarc:classes/datatypes/jfif44.prefs DCT=FAST
   
 Vampire Amigas
 - On Vampire, the default iDCT is the AMMX fast, less accurate iDCT. 
   If you'd like to have the better accuracy of the new iDCT, type 
   the following lines in a shell window:
    makedir envarc:classes
    makedir envarc:classes/datatypes
    echo "DCT=FASTGOOD" >envarc:classes/datatypes/jfif44.prefs
  alternative:
    setenv envarc:classes/datatypes/jfif44.prefs DCT=FASTGOOD