[stella] Optimized color reduction approaches

Subject: [stella] Optimized color reduction approaches
From: Glenn Saunders <mos6507@xxxxxxxxxxx>
Date: Tue, 11 Feb 2003 23:17:59 -0800
At 05:06 PM 2/12/2003 +1100, you wrote:
> Looks great.  I really like to weird look of the very wide pixels.  The
> interlacing looks nice and really reduces the flicker.  It just kinda

It's not actually interlaced - at least, it's not an interlaced TV frame.

I knew something didn't look quite right about it ;)

It's kind of double-interlaced in that each individual scanline
alternatively displays RGB, GBR, BRG... and the lines are out-of-synch with
each other, so consecutive lines display RGBRGBRGB etc....  That is, while
one line is displaying the red values for that line, the next line is
displaying it's green values, and the one after that displaying blue values.

I think this is how the COLRVIEW technique as used with GR8 on the Atari8-bit. Is that what you are trying to emulate? It just like a 1-bit version of COLRVIEW.

Another thing you might want to emulate is GED on the Atari8. GED involves blocking out zones of color on the horizontal and doing color register changes in mid screen almost like HAM on the Amiga, but obviously you can only change registers a few times. On the Atari you might only be able to change it once or twice per line. But this tends to work well for cartoon style artwork where you might have one character on one end that is mostly blue, let's say, and the other character on the right being mostly red. They could both use the same playfield color register if you changed it in mid screen over black.

The other thing you should do is come up with a routine that will optimize the RGB triad. Like let's say the top part of the screen was generally darker than the rest. Instead of relying on dithering alone (over black which is rather flickery to begin with) you could reduce the luminance of the red green and blue frames. And if the top of the screen is, let's say, a sky, you could optimize the RGB triad to be 3 shades of blue instead of R G and B. And as the sky gets generally lighter or darker, you can adjust the 3 shades of blue to approximate this and try to minimize the dithering.

This approach wouldn't work well unless the image naturally had zones where each zone strip had a somewhat dominant, monochromatic color scheme. I'd really like to see a landscape like a beach scene or something using this method, or a photo of a real sunset rather than the usual Activision one ;)

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