[Coco] Re: CoCo Monitor

Robert Gault robert.gault at worldnet.att.net
Sat Jun 26 22:24:49 EDT 2004

KnudsenMJ at aol.com wrote:
> In a message dated 6/26/04 6:28:27 PM Eastern Daylight Time, 
> rtaylor at bayou.com writes:
>>The most famous 
>> dithering pattern we've seen on the CoCo is the "every other pixel" 
> pattern 
>> which will produce red or blue.  In other words, if you plot the colors 
>> from left to right and fill the entire screen with 
>> black/white/black/white/black/white.... and so on, the resulting image 
>> would appear to be solid blue (or red). 
> I'm wondering what happens if you change the "phase" between alternate lines:
> B W B W ...
> W B W B ...
> B W B W ...
> Do you get purple?  Hard to believe I never tried that one -- Mike K.

You will get from top to bottom alternating red and blue lines. From a 
distance, the screen may look purple. It does not from normal viewing 

Here is a simple program to generate the needed pattern.
12 COLOR3,0
20 FOR I=0TO191STEP2
30 LINE(0,I)-(255,I),PSET
42 COLOR2,0
50 FOR I=1TO191STEP2
60 LINE(0,I)-(255,I),PSET
90 GOTO90

A better purple would need a more complex pattern so that red and blue 
alternated horizontally as well as vertically.

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