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JPEG high jinks
Atari coder TXG reviews a new 8-bit graphic utility Here's a nice utility to convert graphics from other platforms to Atari 8-bit. In the past we had GIF convertors that worked great but some of them use some special non-standard graphics formats, like APAC. Then later the HIP format was developed followed by tools to convert BMP files to HIP. But making a HIP slide show is hard because each file takes up 16KB. But now we have A8JDPEG, a real JPEG decoder for the Atari 8-bit. A8JDPEG was first developed on the C64 as JUDDPEG v0.9182736 and the sources were released. Then I downloaded them and posted them on the Atari 8-I mailing list. Here was Raphael Espino and he managed a port to Atari 8-bit a few weeks later. This was already a nice program but only the old resolutions like 160x192 4 colors were supported, but the Atari XL can show HIP and RIP format now. Normally a screen is 8KB and non-interlaced but by using the interlace method you can have more colors. Normally you can have no more then 8 colors or shades at 160x192. HIP makes use of bug in the GTIA chip that allows 160x192 with 30 shades and RIP is the color version of HIP. The versions from 0.5 onwards support the HIP format. Raphael was talking about an Atari version that supports color JPEGs, maybe in the new release it will be supported.
| When you start A8JDPEG you can load the JPEG file. After the header of the JPEG you can select the graphics mode to display the decoded data. There is also a save option to several formats. Here are two screenshots of the cover of MyAtari magazine. Compare it to the original JPEG in greyscale, 8-bit resolution 160x192 30 shades. |
Useful contact You can find more info at: http://rjespino.webhop.org
Summary
Product | A8JDPEG 0.6 (256 greyscale JPEG decoder/viewer)
Author | Raphael Espino
Status | Open source
Pros | Great quality output
Cons | Speed and interface could be improved, no colour support (yet)
Score |
Picture format specifications HIP: Hard Interlace format Resolution 160x192 Size 16KB, 2x8KB screens 1 screen graphics mode 9 (8KB, 15 shades of grey), resolution 80x192 1 screen graphics mode 10 (8KB, 15-color mode programmed in grey shades) resolution 80x192 Due to a bug in the GTIA chip, it will shift a pixel half a pixel when changing two screens of different graphics modes (only for graphics mode 9 and 10). By using this effect a resolution of 160x192 can be shown without too much interlace effect seen in other programs. RIP: Same as HIP only the black and with colors used in graphics mode 10 are now real colors. A good example can be seen in the demo, BASE33.
MyAtari magazine - Review #1, May 2001
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