28+ colors on coco II /DRAGON (NO FLICKER)

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28+ colors on coco II /DRAGON (NO FLICKER)

Postby simon » Sat Nov 21, 2015 8:59 pm

Hey guys...

i finally pulled and programmed an idea i have had in my head for a long time:

how to artifact on PAL to provide extra colors (sorry guys no NTSC)...

this trick relies on the way PAL works...

what PAL does is average the color on 2 consecutive scanlines....
so what happens if we do this:
red
blue
red
blue

we gain a new color....

what we have to watch out for though is that the colors we combine have the same LUMA value or else it's *stipes*
today i programmed this concept in sg24 and got 28 (30 if i do something else) colors out of a coco II

the picture does NOT do it justice and i will provide a better picture later when my 40" lcd isn't being occupied by tv watchers (wife & mum)

XROAR WILL NOT SHOW THIS ! IT WILL SHOW YOU STRIPES

here is real HW (BAD PHOTO)

Image


XROAR WILL ONLY SHOW YOU STRIPES:

Image

the luma values that match can be gleaned from the VDG doc:

Image


the following combinations work (alternate lines):

blue/red
magenta/red
cyan/green
orange/green
yellow/white
orange/cyan
magenta/orange
magenta/green
magenta/cyan
dark green/black
dark orange/black

this can also be reversed tp provide other shades

the .asm file is here

http://www.roust-it.dk/coco/colours/colmix.asm

ENJOY....

I will try to provide a better image of the real hw doing it's thing later on

/SIMON :ugeek: :ugeek:
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Re: 28+ colors on coco II /DRAGON (NO FLICKER)

Postby Bosco » Mon Nov 23, 2015 8:58 pm

Glad to see you're still tinkering Simon.

Of course all this stuff goes straight over my head. :)
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Re: 28+ colors on coco II /DRAGON (NO FLICKER)

Postby sorchard » Mon Nov 23, 2015 9:47 pm

Nicely illustrated Simon! What I like about this is that it's been sitting under our noses all this time but is not common knowledge. i.e. it's easy to dismiss the mixed colours as the result of an inferior quality display but in fact PAL decoders do generally mix the colour info from two lines to reduce the appearance of transmission errors.
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