Guilherme S., Atari ST 16-color mode, Floyd-Steinberg [PIC]

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Posted by Yadgar (other posts) on September 18, 2017 at 08:38:20 Previous Next

In Reply to: Re: Can someone with curly hair post on this website? posted by Guilherme S. on September 18, 2017 at 03:15:29:


This version is in the Atari ST 16-color mode; the full-screen resolution is 320 by 200 pixels, scaled to double size here. The Atari ST uses a 9-bit RGB palette, thus consisting of 512 colors. Each channel can have eight different intensities as it uses three bits, on the PC this equals the 8-bit values 0, 36, 72, 109, 145, 182, 218 and 255.

When converting 24-bit color into this depth, I first create a 16-color palette out the 16,777,216 colors a modern-day graphics card is able to display; when assigning the Atari ST colors afterwards, in many cases, two or even more 24-bit palette colors are converted to the same 9-bit RGB values, so de facto the resulting picture contains less than 16 colors. This is especially true for grayscale images; in 9-bit RGB of course there can only be 8 grayscales, and due to the closeness of the original colors it mostly even boils down to only 6 or 7 grayscales.

Towards the end of the 1980s, Atari improved the ST by giving it a more advanced 12-bit RGB palette (4,096 colors, similar to the Commodore Amiga) for more differentiated coloring. This "extended" ST was marketed as the Atari STE.

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