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In 1992, Jeff D. Potter created a GIF decoder and image viewer for the Atari called APACView. APAC, or Any Point, Any Color, was a software-driven method of displaying an image using all 256 of the Atari's possible colors. By taking 80×192 mode lines that displayed 16 hues, and those that displayed 16 shades, and either interlacing rows of them, quickly alternating between rows of them, or both, a screen displaying 80×96 or 80×192 pixels in 256 colors could be perceived.
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Later, Potter created another GIF decoder, and later a JPEG decoder was created, which broke an image into the three red, green and blue channels. 16 shades of each, at 80×192 pixels, would be displayed in an interlaced and flickering fashion. The human eye's persistence of vision would allow the viewer to see 4096 colors (12 bpp) at 80×192, with slight 'rolling' artifacts in solid red, green or blue fields in the image. This was called ColrView mode. |
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In 1994, Clay Halliwell created a modem terminal program for the Atari (FlickerTerm80) which uses 40×24 text mode, combined with two character sets with an identical 4×8 font — one with the pixels on the left half of the 8×8 grid, the other on the right. By altering where in memory ANTIC looks for graphics, and which font to display, an 80×24 character screen can be displayed. It uses less memory (about 2 KiB) and can be more quickly manipulated, compared to rendering 80×24 characters using a 320×192 bitmap mode (which would require about 8 KiB). |
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In 1998, Bill Kendrick created a puzzle video game for the Atari (Gem Drop) which utilized a similar effect, but by using two alternating character sets (fonts) in colored text. (Each character is 4×8 pixels, each pixel being one of 4 colors.) No color palette changes occurred, and ANTIC's Display List wasn't altered — only a vertical blank interrupt was used to change the character set. This allowed for approximately 13 colors on the screen. Solid color fields that were based on two actual colors (e.g., dark red created by flickering between red and black) had less artifacting because they could be drawn in a checkerboard fashion. This mode was called SuperIRG. (Normal 4×8 multi-colored text on the Atari is called IRG.) |
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In 1996, Atari demo coders HARD Software from Hungary created HARD Interlacing Picture (HIP), which can display 160×192 pixels in 30 shades of grey. It interlaces two modes — 80×192 with 16 shades of grey, 80×192 with 9 paletted colors — and utilizes a bug in the GTIA chip that causes one of the modes to be shifted ½ pixel, allowing for a perceived 160 pixels across. |
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Later, other demo coders created RIP graphics mode, which is similar to HIP, but can display 160×192 pixels in color. |
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