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

[Joel Ewy]

On 04/16/2013 07:38 PM, Stephen H. Fischer wrote:
> Hi,
>
> Not only was it too long, I kept looking for some sign that it was 256 
> colors and perhaps missed it. I watched the start and the end.
>
> The static 64 color demo did show that ~ 64 colors were used, all 64 
> on the screen at once.
>
> The demo could actually be using only 64 colors, but I think not as 
> the 64 color mode only allows 16 colors per line.
>
> Some of the pictures appear to be using much less than 256 colors.
>

This has been discussed extensively elsewhere, if not on this list.

1 byte is used to represent a pixel.  There are 256 different patterns 
possible using 1 byte.  It is possible that some of the artifact colors 
that result from this are indistinguishable from others.  But the total 
possible number of colors is 256.  But a real palette of 256 actual 
colors was selected by several guys a few years back (I credited Jason 
Law, Briza, Robert Gault and Potatohead at the end of the slideshow for 
those with the fortitude to watch it all the way through) and the photos 
were mapped to this palette in GIMP.

Now, if you map an arbitrary digital photo to a fixed palette of 256 
colors, there are likely to be colors in the palette that aren't used in 
the photo, and colors in the photo that aren't represented in the 
palette.  Keep in mind that when you look at a 256 color image displayed 
on a VGA board, for example, the video display can show 256 out of a 
total of ~262,000 (for original VGA) or 16,777,216 (for most modern 
SVGA).  When you take a JPEG photo and convert it to a 256 color .GIF, a 
program like GIMP or Photoshop will select the best 256 colors out of 24 
bits of color to represent that image.  So if you're accustomed to 
looking at 256 color images that can make use of a 24-bit DAC, you may 
be expecting a color fidelity that exceeds what is possible using a 
fixed palette of approximately 256 artifact colors on the CoCo 3.

So yes, the color count is approximate, and results will vary, 
especially if you are looking at these pictures on a color TV where the 
hue and saturation can be (mal)adjusted.  I noticed that two of my TVs 
displayed these artifact colors somewhat differently, until I adjusted 
the saturation on one.

And yes, any given photo isn't likely to be using all 256 colors.

It puts a lot more colors on screen than normal 16 out of 64, and does 
so without involving the CPU or any flicker.
>> I also included one picture that was not a photo but a computer 
>> generated graphic.
>
> Time code for that please.
>

4:37.  I don't think it's an especially good example myself, but I've 
definitely seen worse stuff on the CoCo.

>> 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.
>
> How much of the poor quality is due to that.
>
> I actually looked at it with no glasses, $4,400 well spent.
>
> Somewhere on http://www.tandycoco.com/forum/index.php
>
> there is a 256 color display suggesting what a FPGA could do, but I 
> cannot find it.
>
> (Not actual screen capture.)
>
> SHF
>
>
> ----- Original Message ----- From: "Joel Ewy" <jcewy at swbell.net>
> To: <coco at maltedmedia.com>
> Sent: Tuesday, April 16, 2013 5:02 PM
> Subject: Re: [Coco] The myth of the Coco3 256 color mode :)
>
>
>> On 04/16/2013 04:49 PM, Stephen H. Fischer wrote:
>>>
>>> ----- Original Message ----- From: "Joel Ewy" <jcewy at swbell.net>
>>> To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
>>> Sent: Tuesday, April 16, 2013 8:56 AM
>>> Subject: Re: [Coco] The myth of the Coco3 256 color mode :)
>>>
>>>
>>> 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
>>>>>
>>>> FWIW, I think the above URL might be an abridged version of the 
>>>> slideshow. Not sure what that's about.  The whole thing seems to be 
>>>> here: 
>>>> http://www.youtube.com/watch?feature=player_detailpage&v=hjcUdoW0rrg
>>>>
>>>> JCE
>>>
>>> If it has been shortened, thanks.
>>>
>>> It was like watching a friends vacation slides without your glasses 
>>> and wanting to go home.
>>>
>>> SHF
>>>
>>
>> Sorry if you found the subject matter boring and the resolution low, 
>> Stephen.  I chose photos that were Creative Commons licensed, so I 
>> could legally include them in a derivative work, and that would 
>> demonstrate what digital photos would look like using this method of 
>> display.  I tried to pick a variety of subjects.  I wanted to show 
>> people, both close up and at a little distance.  I wanted to show 
>> things that one might see in an adventure game.  I also included one 
>> picture that was not a photo but a computer generated graphic.
>>
>> Personally, watching the slideshow again, I am surprised at how good 
>> the images look, aside from the messiness of the video capture.  Use 
>> 'view' in NitrOS-9 to display a 256 color .gif and tell me how you 
>> think it looks compared to the images I put in that slideshow. 
>> Remember, this is an unmodified CoCo 3, and this uses no palette 
>> switching or screen flipping, so it can be used in games, or anywhere 
>> else you can display a 640x200x4 image, as long as you have a 
>> composite monitor or TV.  The effective resolution is low: 160x200.  
>> But the added colors can make it well worth the trade-off for some 
>> purposes.  If you want to see the best quality representation of a 
>> digital photo the CoCo 3 can produce, try Sockmaster's Hi-color 
>> program.  It's fantastic, though it still does have a little 
>> glitchiness when the palette registers are updated, and some flicker, 
>> though much less than most.  The problem is, that doesn't work in 
>> OS-9, and it doesn't work as a slideshow, and it can't easily be used 
>> inside other programs.
>>
>> One thing I've been playing with is the possibility of making a 
>> hybrid image that superimposes high detail areas as a 4 gray 640x200 
>> image on top of the 160x200 artifact color image.  I remember from 
>> CoCo Max that while you might get some unwanted artifacts (color 
>> error), you could still put a lot of detail in a 256x192 image by 
>> treating it as a full-resolution B/W bitmap, but use the red/blue 
>> artifacts to add color in larger areas. From what I understand, the 
>> human eye is more sensitive to shades of gray than color, so 
>> rendering areas of detail in gray should make for a more recognizable 
>> image, even if there are some unwanted color artifacts.  My initial 
>> experiments are promising, but I don't have anything to show quite yet.
>>
>> JCE
>>
>
>
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