[Coco] The myth of the Coco3 256 color mode :)

Joel Ewy jcewy at swbell.net
Tue Apr 16 11:43:32 EDT 2013


On 04/16/2013 10:00 AM, Luis Antoniosi (CoCoDemus) wrote:
> Not only on CMP monitors but CMP CRT monitors. I tried once running the 256
> colors demo on my LCD screen (using composite input) and it sucks.
> Apparently all the fast switching screens don't work with lcd, at least my
> LCD.

Not just CRT monitors.  It may be that you are confusing the 8-bit 
artifact color 'mode' with a 'flicker' mode where you are switching 
between 2 or more images (time-domain multiplexing).  I was able to use 
a video capture card on a PC to make a video of a slideshow I cooked up 
using the method Robert Gault is referring to.  Though the conversion 
process resulted in pretty crummy video, the color artifacting worked 
like a charm, and the colors come out looking pretty much the same as 
they do on a monitor: http://www.youtube.com/watch?v=hjcUdoW0rrg

Also, I would add to Robert's original post that I see lots of cheap CRT 
TVs at thrift stores these days, many of which have composite video 
inputs.  $8 will get you a composite monitor.

JCE

>
> On Tue, Apr 16, 2013 at 10:55 AM, Robert Gault <robert.gault at att.net> wrote:
>
>> There have been several recent threads about generating multi-color
>> graphics screens on the Coco. One was for the Coco1 or 2, semigraphics was
>> mentioned, and also the 256 color mode on the Coco3 prototype board. Also
>> there is the flicker procedure where several different graphics screens are
>> rapidly switched to yield a blended image.
>>
>> While all the above are of interest, there is one Coco3 mode which
>> provides close to 256 colors at one time which may soon be lost to us
>> forever. It works on composite monitors only (which are a dying breed) and
>> is not supported by any emulator. The mode was discussed in a thread on
>> coco3.com and that site has been problematic of late and is frequently
>> off the air.
>> http://www.coco3.com/**community/2009/02/256-color-**mode-composite-mode-*
>> *artifacting/comment-page-1/#**comments<http://www.coco3.com/community/2009/02/256-color-mode-composite-mode-artifacting/comment-page-1/#comments>
>> There are 7 pages of comments.
>>
>> I don't want to see this mode lost in time and mythology as happened with
>> the supposed mode on the prototype board. :) So here is a short demo of the
>> technique for a Coco3 and CMP monitor.
>> 10 HSCREEN4:PALETTE0,0:PALETTE1,**16:PALETTE2,32:PALETTE3,48
>> 20 M=&H60000:POKE&HFFD9,0
>> 30 FOR Y=0TO3
>> 40 FOR X=315 TO 331 STEP 4
>> 50 FOR C=1TO3
>> 60 HCOLORC,0:HLINE(X+20*(C-1)-Y,**71+10*Y)-(X+20*(C-1)-Y,80+10***Y),PSET
>> 70 NEXTC,X,Y
>> 80 GOTO80
>>
>> By rights, the above should give just vertical gray lines on a CMP
>> monitor. Instead, you see four rows of three shaded colors, blue, purple,
>> red-orange, and green. It is possible to create a pattern that appears to
>> yield 256 colors, although depending on your CMP monitor some will seem
>> duplicates.
>>
>> I've written a Basic-ML pair of programs that will load a .bmp image that
>> displays perhaps 256 colors without any flickers associated with screen
>> swaps. The following restrictions apply.
>>
>> * This works only on a TV/composite monitor. It will not work with an
>> emulator or RGB monitor.
>> * BMP images are limited to 256 colors. The width
>> * must be 256 pixels or less.
>> * With a 128K Coco3, the total image must be 65K bytes or less. With a
>> * 512K Coco3, the total must be 458K bytes or less.
>> * The screens used are 640x225x4.
>>
>> You need to use a PC graphics program to convert an image to the above
>> conditions and place the image on a .dsk or real Coco disk. The program
>> will work nicely with Drivewire.
>> I can send a program disk on request but this list does not like
>> "attachments".
>>
>> All of the above resulted from a discussion started by Potatohead (who are
>> you?) and a Coco program called GrafExpress.
>>
>> Robert
>>
>> --
>> Coco mailing list
>> Coco at maltedmedia.com
>> http://five.pairlist.net/**mailman/listinfo/coco<http://five.pairlist.net/mailman/listinfo/coco>
>>
>
>




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