Re: Apple IIgs video modes?

[jmk3@crux3.cit.cornell.edu (Jay Krell)]

>        640 mode has 4 pure colors per line, 64 per screen with
>multiple palette and 800 using the equivalent of 3200 color mode in
>640 mode.  That's pure colors though.
 
I beg to differ Steve. It is completely impractical for drawing, but you could
give each line's palette 16 different colors. Each pixel has a choice of 4 of
these, but all 16 could appear on the line.
 
You could also mix 640 and 320 modes, using the practical 4 colors per line for
640 mode, giving 4m + 16n colors, where there are m 640 lines and n 320 lines.
:)
 
In case people don't know the IIGS video (and for the person that asked in
email):
 
        Each line is individually selectable between 640 and 320 modes. Each
line selects one of 16 16-color palettes (or its own 16 color palette if
swapping palettes for 3200 colors). In 640 mode, "The 16 colors in the palette
are divided into four groups of 4 colors each. The first pixel in each
horizontal line can select one of 4 colors from the third group of 4 in the
palette. The second pixel selects from the fourth group of 4 colors in the
palette. The third pixel selects from the first group of 4 colors, and the
fourth pixel selects from the second group, as shown in Table 4-21. The process
repeats for each successive group of 4 pixels in a horizontal line. Thus, even
though a given pixel can be one of 4 colors, different pixels in a line can
take on any of the 16 colors in a palette." (IIGS Hardware Ref, 2nd ed, p. 96)
 

--
  --Jay, jay.krell@cornell.edu