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Atari 8-bit

JPEG

Viewers

Gallery    Usage    History    Report a Bug    Technical Details    Pipeline    Thanks    Home   

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Want to view JPEG images on your Atari 8-bit? Then you've come to the right place. The programs on this page are based on Juddpeg, the JPEG decoder and viewer for the C=64, written by Stephen L. Judd and Adrian Gonzalez. The Atari 8-bit versions use a modified version of Stephen L. Judd's decoder along with 3 new viewers.

a8jdpeg 0.8 (14Sep02)

The original Atari 8-bit interface.

JpegView 0.9 (17Oct03)

A friendlier menu oriented version of a8jdpeg

JpegShow 0.1 (07Aug01)

A slideshow version


Colour JPEG Viewer new

The colour version of the JPEG Viewer

All source files as a ZIP file (131821 bytes)


The executables are in Atari DOS binary format (the .bin extension is to make sure the file gets downloaded as a binary), you should be able to save it on a disk and run it straight from your Atari 8-bit (or emulator).

NOTE: The display modes marked as 64K really really do need 64K! This includes using the RAM under the OS. Most versions of SpartaDOS also use this area and your machine WILL crash if you use a 64K display mode with one of these SpartaDOS versions. The 48K modes should work though. If you do want to use a 64K display mode with a SpartaDOS disk, then either give BEWEDOS a try, or take a look at PgmView.

a8jdpeg and JpegView can both convert JPEGs to the Atari 8-bit Micropainter and HIP formats. If these don't suit you, or if you want access to the uncompressed image data for whatever reason, then they can also convert to PGM (Portable Greymap) format. This format can easily be read on the Atari 8-bit (and many other machines) and converted to whatever format suits you. An example BASIC program for reading the PGMs produced by a8jdpeg is available.


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a8jdpeg Changes

Version 0.8 (14Sep02) replaces the release dated 07Aug01, and includes the following changes:

JpegView Changes

Version 0.9 of JpegView replaces the release dated 07Aug01, this includes all the improvements made in a8jdpeg 0.8 (as listed above) as well as the following:


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Bugs

Have you found a bug? Do you have an idea for further improvements? If so, send me an e-mail.

This version should work fine on most baseline JPEGs out there. It will not work on progressive JPEGs. Progressive JPEGs are designed for viewing over a slow connection. When viewing a progressive JPEG over a slow connection, it starts out as a low quality fuzzy image which becomes clearer as more data is downloaded. The way progressive JPEGs are implemented makes then harder (although not impossible) to handle in 48/64K of RAM.

Progressive JPEGs can be converted to baseline JPEGs using the jpegtran program provided by the IJG (The Independent JPEG Group):

jpegtran input.jpg > output.jpg

Then try displaying the new image. This may also fix other problems with images too. The jpegtran program is available for many systems, although not (unfortunately) for the Atari 8-bit. If you do not already have this program you can download it from ftp://ftp.uu.net/graphics/jpeg

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Screenshot Gallery

Want to see some screenshots? Take a look at the Gallery

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Usage

First boot up into your favourite DOS, without BASIC (hold down the OPTION key when booting XL/XE models, remove all cartridges on 400/800 models) then load a8jdpeg, JpegView or JpegShow (use the L option under DOS 2.0/2.5/MyDOS or equivalent).

JpegView

Once loaded, JpegView will display all files with a .JPG extender on drive 1. To load a file, press the letter displayed next to the file name. To view the files on a different drive, or redisplay the files on the current drive, press the appropriate drive number (1 for D1:, 2 for D2:, etc.). Pressing the Tab key will allow you to change the files listed. Change the mask to *.* to view all files and subdirectories on the current drive.

JpegShow

JpegShow will start displaying all files with a .JPG extender on drive 1, pausing between each one. To change any of the parameters used press the Esc key. To make these options permanent use the save option, this will create a D:JPEGSHOW.CFG file on the disk in drive 1.

a8jdpeg

a8jdpeg will first prompt you for a file name. The device or drive number displayed can be changed by backspacing and replacing them with the new ones. Pressing the Tab key will display the previous file name used. If no extension is added to the file name ".JPG" will be added automatically. To stop this from happening, add a dot at the end of the file name:
D:ATARI.JPG load a file called ATARI.JPG from D:
D:ATARI load a file called ATARI.JPG from D:, .JPG is added automatically
D:ATARI. load a file called ATARI from D:, .JPG is not added automatically

Files can also be loaded from the directory list by pressing the corresponding letter on the keyboard after displaying the directory. To display a directory type in a directory mask using the '*' and '?' wildcards and place an extra ':' at the end. The above rules for file names also apply:
D:*.*: display contents of D:
D:*.JPG: display all files with a .JPG extension on D:
D2:*: display all files with a .JPG extension on D2:, .JPG is added automatically
D2:: display all files with a .JPG extension on D2:, *.JPG is added automatically
D2:PIC??: display all files that start with "PIC" followed by 2 characters and have a .JPG extension on D2:, this will match PIC01.JPG, PICEL.JPG, PIC75.JPG, etc.
D2:PICS:: display all files with a .JPG extension in the PICS directory on D2:, this assumes your DOS supports subdirectories
D8:PICS:PIC??: display all files that start with "PIC" followed by 2 characters and have a .JPG extension in the PICS subdirectory on D8:, this will match PIC01.JPG, PICEL.JPG, PIC75.JPG, etc. This assumes your DOS supports subdirectories

To return to DOS press the RETURN key, leaving the file name empty. The file name can be up to about 60 characters long (if your DOS supports this). An error here probably means you mistyped the file name. If successful the image size will be displayed and you will be asked for the row and column offsets, these default to'C' meaning centre the image, and you can just press RETURN. Since JPEG images can be (much) bigger than 320x200, you can specify here at what row and column you want a8jdpeg to start displaying the image. Each unit for the row and column values equates to 8 pixels, so giving values of 4 for the row and 6 for the column would display pixel 48(6*8), 32(4*8) at the top left hand corner of the screen. Then you will be asked for the graphics mode you want to view the image in, select one of the options from the menu.  If this mode supports dithering you will also be asked if you want the image dithered or not.  Dithering will provide better image quality but will slow things down a little.

The screen will then start to flash as the image is decoded and displayed. While the image is being decoded you can press the S key to toggle the screen, speeding up image decoding. Pressing the Esc key while the screen is flashing will abort everything and take you back to the file name prompt, pressing the C key will abort and allow you to change the display parameters for the image. Once the image has been decoded the screen will stop flashing, and you should be looking at your JPEG. Pressing the X key will take you back to DOS, pressing the ESC key will take you back to the a8jdpeg menu. Pressing the Space bar will display the image information/help screen.  The + and - keys will allow you to cycle through different colour values.  The S key will save the displayed image in modes that support this (2, 3, D and E).
 

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Technical details

On a 48K machine, there are 3 display modes available:

  • 320x200 in 2 levels of grey (Graphics 8)
  • 160x200 in 4 levels of grey (Graphics 15)
  • 80x200 in 16 levels of grey (Graphics 9)

  • Plus 3 options in a8jdpeg for reducing the image horizontaly (JpegView will automatically reduce images).

    64K and greater XL/XE machines have another 4 modes available:

  • 320x200 in 4 levels of grey (Graphics 8 flicker mode)
  • 160x200 in 9 levels of grey (Graphics 15 flicker mode)
  • 80x200 in 31 levels of grey (Graphics 9 flicker mode)
  • 160x200 in 30 levels of grey (HIP flicker mode)

  • Plus another 4 options in a8jdpeg for reducing the image horizontaly (JpegView will automatically reduce images).

    All modes (except the GR.9 flicker and HIP modes in a8jdpeg) also support dithering. Since JPEG images can contain up to 255 different levels of grey, these will have to be reduced to the number of levels supported by the mode selected. Without dithering this extra information will be discarded. Dithering finds the closest available grey to the one used in the image and displays that. The difference between the requested grey and the one actually used is then calculated, this "error" is then distributed over 4 surrounding pixels, and modifies their values. This can provide better quality images at the expense of speed.

    JpegView and a8jdpeg can convert the images to Micropainter (62 sector), HIP and PGM formats. This is the same PGM (Portable Greymap) raw format as found in the Unix world and beyond.  This is the best format to use if you want to extract the image information for your own use. Take a look at the PGM page for more details, a PGM viewer and sample code.

    This version should work with any 48K or more 8-bit Atari computer. To get the Graphics 9 and HIP modes you do need a GTIA chip though. Since it doesn't use any memory below $2000 (except for pages 4 to 6 and the top half of page 0) it should also work with most DOSes. The 64K modes also use the RAM hidden under the OS, so will crash any DOSes that use that area (i.e. most versions of SpartaDOS). If you do have any trouble with it on your system, then let me know along with details of your set up.

    Source code

    The source code comes in two parts, the decoder and the viewers. The decoder is a port of Stephen L. Judd's jpy1223-8 file, and is greyscale only.  The viewers have been written from scratch for the Atari.  New viewers can be written by replacing the viewer code with you own. No modification of the decoder is needed. Details of how to do this are in the decoder and the viewers source code.

    The source code is in ca65 format, part of the cc65 cross compiler package. It should be possible to modify this to work on native Atari assemblers too (MAC/65, AMAC, etc.).
     

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    History

    a8jdpeg

    JpegView

    JpegShow


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    In the pipeline

    Here is the current development plan:


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    Any problems, suggestions, comments, bugs, feedback? Let me know

    Thanks to:
    Stephen L. Judd - for writing the original C=64 version and making the source available


    Also thanks to:
    René de Bie, Mathy van Nisselroy, TJ Edmister, Marco Antonio Checa Funcke, James Bradford, Chris Martin, Andreas Magenheimer, Piotr Fusik, Daniel Miller, Andrew Floyd - for comments, suggestions, ideas, feedback and other help.

    Enjoy!


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