[Coco] screencast presentation re: NTSC 8-bit Color on the Color Computer 3

[Joel Ewy]

On 04/29/2014 06:23 PM, John W. Linville wrote:
> I made a screencast version of the presentation I gave at the 23rd
> Annual "Last" Chicago CoCoFEST! about the CoCo3's NTSC-only 8-bit
> color mode.  If you didn't get to see it (or want to see it again),
> then now is your chance -- enjoy!
>
> 	https://www.youtube.com/watch?v=gc6Eu7IansE
>
> John
Thanks for posting this, John.  This was helpful in understanding 
artifact colors a little better.  In addition to emulator support (which 
would really encourage the wider use of 8-bit artifacts), being able to 
calculate artifact colors programmatically would be useful for, say, GIF 
display programs on the CoCo 3, though a look-up table would probably be 
faster.  But if 16 palette registers and the 'A' bits yield different 
palettes than just the 'S' bits alone, then you could select the most 
representative palette for a given image algorithmically, assuming all 
that can eventually be worked out.

One thing I'm still not clear on is this business of 160 color 
transitions per line.  If that is inherent to the NTSC signal, then the 
effective horizontal resolution of all NTSC video is only the analog 
equivalent of 160 "pixels" (plus overscan?).  Somehow my video cassettes 
look better than that, even as low-def as they are. Is it just that the 
Luma can vary quicker and is more visually important?  Or am I 
misunderstanding something.

Regarding the relative importance of luma over chroma, I have considered 
combining 4-color 640 pixel wide grayscale images derived from the Y 
component with 160 pixel color images mapped to one of the artifact 
palettes in order to get more visual detail in these 8-bit artifact 
color images.  Undoubtedly because of the artifacting there would be 
some additional color error, but I think it's worth trying.

JCE