------------------------------------- JagPeg Conversion Tools version 1.5 PC Version Release 1.2 Release Date: 9/24/94 CONFIDENTIAL INFORMATION ------------------------------------- Copyright 1993 Atari Corp. All Rights Reserved. Author: Mike Pooler, Atari Corp. Update: Mike Fulton, Atari Corp. Introduction ------------ This describes how to use TGAJAG, a group of utility programs that convert a Targa file (.TGA) to a JagPeg file (.JAG). Background: JagPeg is Atari's version of JPEG. A JagPeg file has a .JAG extension, and it contains one compressed 24-bit true color bitmap. It is uncompressed by a program called DEJAG, which runs in the Jaguar's GPU. DEJAG is described seperatly (see DEJAG.DOC). The main utility for performing the conversion process is named TGAJAG. On MS-DOS, TGAJAG is an executable program named TGAJAG.EXE. Input Files ----------- TGAJAG takes the filename of a Targa file as its first argument. The Targa file must be: - Uncompressed (Image type 2) - 24-bits per pixel - A multiple of 8 pixels in width (If HALF or QUAD subsampling, a multiple of 16 pixels in width) (Subsampling is explained below) - A multiple of 8 pixels in height (If QUAD subsampling, a multiple of 16 pixels in height) Some Targa files which meet the above requirements are stored from bottom-up, (with the first screen-line at the end of the file), others from top-down. Both types are supported by TGAJAG. Output Files ------------ TGAJAG writes two files as output. The first is a JagPeg file (.JAG), which has this format: [Word 0] JagPeg version number (currently 1) [Word 1] Picture format code 1: YCrCb with no subsampling 2: YCrCb with HALF subsampling 3: YCrCb with QUAD subsampling [Word 2] Width in 8-pixel blocks (e.g. 40 == 320 pixels) [Word 3] Height in 8-pixel blocks [Data...] The second output file from TGAJAG is a file containing a dequantization table for the requested compression quality, which is required by the JPEG decoding routines. This file will named 'DQ??.DAT' (where the ?? is the quality percentage). Using TGAJAG ------------ TGAJAG for MSDOS takes a command line of the form: TGAJAG [-quality n] [-quiet] [-o outputfile] [-quad | -half] inputfile The command line options may be used in any order, but only one input file may be specified, or else an error is generated. -quality n Sets the JPEG compression quality/compression ratio percentage. The value 'n' must be between 1-100. The higher the value, the higher the image quality and the less the image is compressed. -quiet Supresses status messages from being shown on screen during the conversion process. -o outputfile Allows you to specify the desired filename of the converted picture file that will be output. -quad or -half Specify either QUAD or HALF subsampling. The default is to use neither QUAD or HALF subsampling. See below for more information. inputfile This parameter is the filename of the .TGA Targa picture file to be converted. You may leave off the ".TGA" extension if you want. The resulting .JAG file will be placed into the same directory as the inputfile, but the DQ??.DAT file will be placed into the current directory. Examples: tgajag -quality 60 cat will convert CAT.TGA to CAT.JAG with quality setting of 60. tgajag -half -quality 75 ship will convert SHIP.TGA to SHIP.JAG, using HALF subsampling, and a quality setting of 75. Image Quality ------------- For most purposes, an image quality setting between 60 and 80 will provide the best balance between compression ratio and quality. High quality settings give less lossy compression, thus larger .JAG file sizes. Lower numbers get you better compression and smaller files, but if the number is too low you will get a visable degradation in visual quality (this will appear as fuzzyness and/or blockiness). The goal is to find a quality setting that gives you acceptable compression and a picture that is is nearly indistinguishable from the original .TGA, visually. This "ideal" setting is different for different pictures, so it's a matter of trial and error. The default quality setting is 75, which is usually a good starting point. If you go much above 75 you lose more and more compression without a significant gain in image quality. TGAJAG produces a unique "dequantize" table for each quality setting, which is used during the decompression process (see DEJAG.DOC). SUBSAMPLING ----------- You also have the option of using HALF subsampling or QUAD subsampling. HALF subsampling means that the picture's color components are cut to half their horizontal size before processing by CJPEG. (The luminance component is left as is). While this is quite lossy, it often produces little visable change in the final output, while getting a good reduction in size. We recommend that you use HALF subsampling as your default starting point. QUAD subsampling means that the picture's color components are cut to one quarter the original size (half vertical, half horizontal) before processing. Size reductions over HALF are less dramatic, visual differences are more dramatic. It may be worth a try, but we recommend HALF as your best option. Remember if you use HALF or QUAD, picture width must be a multiple of 16 pixels (instead of 8). If you use QUAD, picture height must be a mulitple of 16 pixels. Decompression speed is DIRECTLY related to .JAG size. A .JAG file that is 30% smaller than another will usually decompress in about 30% less time. Notes ----- Free disk space requirements for TGAJAG are such that you should have at least double the size of your TGA file, to be safe, before running TGAJAG (e.g. for a 200K TGA file, have 400K free). Note that the utilities do not all detect disk-full conditions, and they will probably do a whole lot of nothing once disk space runs out (even if they look like they're working). If the final JAG file is larger than you expect, try using HALF subsampling and/or a lower quality setting. There is little error checking - if you feed it an illegal Targa picture (see above), or a bad filename, it may do ungraceful things. v1.2 Release Notes: ------------------- The MSDOS version formerly used the batch files TGAJAG.BAT, TGAJAGH.BAT, and TGAJAGQ.BAT to run the various steps of the conversion process. They have been replaced by TGAJAG.EXE, which performs the same operation, but with better control over the various options and with better error checking. Note also that the archive setup has been changed so that the tools install into the JAGUAR\BIN directory instead of JAGUAR\BIN\TGAJAG. This was done so that you can call the conversion utilities directly from your project's directory, rather than changing to the utilities directory. Please note that the JAGUAR\BIN\TGAJAG directory is no longer used by the archives at all. To avoid filename conflicts with other utilities, the filenames of the JAGPEG compression utilities have been changed. Basically, a "j" was added to the beginning of the filename. The old names and new names are shown below. Old Name New Name -------- -------- STRIP JSTRIP QUAD JQUAD MERGE JMERGE MERGEH JMERGEH MERGEQ JMERGEQ SPLIT JSPLIT SPLITH JSPLITH SPLITQ JSPLITQ MAKEQ JMAKEQ CJPEG JCJPEG Normally you don't call these programs yourself directly; they are called by the TGAJAG program. If you have old versions of these files, please delete them. v1.1 Release Notes: ------------------- Earlier versions of the PC version of the MAKEQ tool (one of the utilities called by TGAJAG) did not work correctly, but this has now been fixed. Earlier versions of the TGAJAG tools used an .ABS extension for the DQ??.ABS files they created. This has been changed to create a DQ??.DAT file instead, to avoid confusion with the .ABS files created by the ALN linker.