[Coco] Artifact purple/green wasRe: CoCo Monitor

[Fedor Steeman]

In fact, PAL had its own odd effects with the CoCo's B&W stripes
alltogether. I wonder if anyone has attempted to make a PAL mode in a (CoCo)
emulator showing its artifacts? It is actually what I grew up with, not knowing
any better, and it would be nice to be able to see this again in an
emulator system. If I had the skills, I would probably go in and build it
into MESS myself, just for fun!

Cheers,
Fedor

----- Original Message ----- 
From: "John Kowalski" <sock at axess.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Monday, June 28, 2004 5:50 PM
Subject: Re: [Coco] Artifact purple/green wasRe: CoCo Monitor


> At 10:24 PM 27/06/2004 -0500, CoCoList for Color Computer Enthusiasts
wrote:
> >Some of the emulators have an artifact mode, but now I wonder:  How far
> >do they go?  Do they just simply do the "odd is red, even is blue" or
> >vise versa colors, or did they actually try to emulate all the
> >artifacting in NTSC?  That would let our PAL friends see them.
> >
> > Allen
>
> Most emulators just do red,blue,white and black.
> MESS and Mocha, on the other hand simulate complex artifacting.
>
> What I did was hook up a CoCo to my PC's ATI All-In-Wonder video input,
and
> adjust all adjustments (color saturation,hue,etc..) until the display most
> closely duplicated how I remember seeing colors on an old TV.   In other
> words, adjusted until all the extra colors like purple,green,yellow and
cyan
> started appearing in PMODE4.  (New displays do a good job of eliminating
all
> these 'unwanted' colors.)
>
> Then, on another CoCo3, I loaded a sample PMODE4 bitmap into memory, and
> wrote a program to re-interpret the B&W image into 16 color 256x192
> resolution.   I chose a set of 16 colors that would be used to duplicate
all
> PMODE4 artifacting effects, then coded up a lookup table for the PMODE4
bit
> patterns.  The table was made to extend a few pixels before and after the
> 'target' pixel.  That is, the pattern of pixels extending to the left and
> right of any given pixel may have an effect on the appearance of the pixel
> in the center.
> Run the program, see what happens... adjust the tables... Run the program,
> see what happens... until eventually the simulated PMODE4 artifacting
looked
> just like the real thing.
>
> MESS and Mocha both use the resulting data and algorythm to simulate
> artifacting.  Mocha even simulates color artifacting in the green and
black
> PMODE4 screen! (You can get many hues of green, plus blue and
yellowish-green).
>
> And possibly, these CoCo emulators may be/have been the very first
emulators
> ever to simulate composite video color artifacting realistically.   As far
> as I know, not even Apple II (which relied heavily on artifact colors)
> emulators do this yet.
>
>                                          John Kowalski (Sock Master)
>
http://www.axess.com/twilight/sock/
>
>
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