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

A place to discuss everything Dragon related that doesn't fall into the other categories.
Post Reply
simon
Posts: 163
Joined: Wed Nov 27, 2013 8:56 pm

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

Post by simon »

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:
User avatar
Bosco
Posts: 330
Joined: Tue Mar 04, 2014 11:49 pm
Location: Nottingham, UK

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

Post by Bosco »

Glad to see you're still tinkering Simon.

Of course all this stuff goes straight over my head. :)
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

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

Post by sorchard »

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.
Stew
Post Reply