[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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