[Coco] Coco3 CMP color swatches

John Kowalski sock at axess.com
Thu Sep 1 08:54:54 EDT 2005

At 09:37 AM 31/08/2005 -0400, Robert Gault wrote:
>In fact, I can't remember any Coco articles where the 
>monochrome bit was in use to enable 64 levels of gray. Do you know of 
>any public use of the 64 gray scale mode?

There's no such mode.  Not 64 gray scale anyway - If you set the monochrome
bit, all you get is 4 levels of grey.  Colors 0-15 are black, 16-31 are dark
grey, 32-47 are light grey and 48-63 are white.
Except for colors 1-15 (which really shouldn't ever simply display as just
black), this roughly corresponds to the luminance values of the composite

Also, there is no relation between the composite color set and the RGB color
set.  They're generated by different ciruits.  Except for 0 (black) and 63
(white), they are different color sets.  This is why composite has two
whites - the 2nd one was added simply to retain black & white compatibility
between RGB and CMP displays.
Luckily a few other colors (like 18 (green)) also happen to generate similar
colors in both RGB and composite, but it's a very small list.  In the case
of green, it may be deliberate - they may have adjusted the composite
chrominance phase so the RGB value for green also generated a greenish
chroma in composite video.

                                         John Kowalski (Sock Master)

More information about the Coco mailing list