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From: rubywand@aol.com (RUBYWAND)
Newsgroups: comp.sys.apple2.programmer
Subject: Re: Looking for IIGS Image Format Info
Date: 13 Oct 1996 19:46:11 -0400
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In article <53gucv$bsh@solaris.cc.vt.edu>, exerda@vt.edu (John E. Nolley
II) writes:

>
>I'm looking for info on some of the common IIGS file formats for images,
>namely the $C9/$C1 formats (I know each has sub-formats as well, such
>as Paintworks Gold, etc.)
>
>I recall such info in an issue of Nibble, ....
>
>

     Right; this sounds like the Nibble article describing SuperPac.

     The format of a standard $C1 unpacked "screen image" is
straight-forward. You have 32000 (160 x 200) bytes of pic data followed by
200 Scanline Control bytes followed by 56 "reserved" bytes followed by 512
bytes for 16 32-byte Palettes. Each Palette uses 2 bytes to define each
color; so, there a 16 colors per palette.

     Pic data is arranged in memory starting with the upper left corner of
the image and moving left-right and down. For example, the 161st byte in
memory will have the pixels which are displayed at the start of the second
(horizontal) line of the pic.

     The upper part of each byte corresponds with the left-most pixel
displayed.  In 16-color 320-mode, each byte defines 2 pixels. Bits 4-7
define the left pixel; bits 0-3 define the right pixel.

     As to specifics on packed formats, perhaps Nathan, Tom, or someone
else will put up detailed docs on an ftp site. SuperPac, of course, was
thoroughly documented in Nibble.

     In terms of typical overall performance, the three current super-res
image formats benchmark as shown below:

Packing Density: 1-GIF   2-SuperPac   3-Apple Prefered

GIF is substantially denser for most pics. SP, generally, edges AP by one
or two sectors. AP usually does a bit better than SP on non-scenery
digitized images.


UnPack Speed: 1-SuperPac  2-Apple Preferred  3-GIF

Again, SP and AP are fairly close. Either is _much_  faster than GIF. 

   

Rubywand