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640 x 200 x 2 color mode discussion

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The ones up-thread, where the screen capture zoom work well.


An alternative is to send the composite signal into the luma of an S-video display. That's not extinct, and is the method I use on my capture card to see this kind of thing.


Been on the hunt for an 800 XL. That is the machine I used way back when.


There are two projects like this that I am chipping away on. One is ~256 colors on a CoCo 3, using artifacting on composite. I've got that machine coming soon. The other is a quick and dirty demo of this technique. Both are kind of waiting on hardware. If an XL takes too long, I might mod the 400. It's just iffy and will freeze from time to time. I don't do much with it, because of that. :( It will play Star Raiders all day long. Will freeze on something like Ms PacMan though.


Given your results from before, I'm wondering if some displays either compensate for this, or the masking on the CRT renders it difficult to see.


My larger SONY WEGA will display it nicely enough. Had the Propeller and modded VCS hooked up to it's S-video. Both displayed the long vertical lines clearly enough. Color cycling on the VCS, showed the shifting that occurs too. I've not tried the Propeller, but the VCS also displays the lines on the newer HDTV plasma. I found that varying the chroma level (I did the Ben Heck mod with three pots) significantly impacted this. Best results for me was a dark background luma, and a brighter foreground one.


Was looking at the video mod thread Longhorn Engineer has going. It may be that some machines filter this out too. His mods do not display the color pixels, and that's intended, of course. Some machines then, might vary in how well they will display this stuff.


Given the state of hardware, I'm going to work through the CoCo project first. That machine is going to be here this week, and it's fairly straightforward to knock up a demo showing 160xsomethingx256 colors. On that machine, the 160x96 works best, but it will do 192 and 200 vertically also.


On the 800 XL are both composite video and separate luma available? Are you using the luma only?


If so, that's the trouble as the luma doesn't exhibit the shift.




I see separate luma signal on Atari 800, XL, and XE but it did not show any shifts. Composite output also did not show any shifts using Amiga monitor.


I hooked up via RF signal on TV and there are shifts but thickness of color of line varies as well so you end up dealing with another obstacle toward a clear display.


What are they doing with VCS with color shifting-- 320*200 mode vs. 160*200?


>The Propeller one is going to have to wait, but here is one from the Flashback II title screen. That's baseband composite running into the luma input of an S-video capable display. In this case, it's my capture card. The stripes are associated with each color displayed. If you don't see those stripes, there won't be any shift.


I'll have to hook up one of those to see what it looks like.

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If each pixel is subdivided into 15 sub-pixels, then for hue values other than $00, about half of those will be lighter than the other half. For one hue value, the light ones would be first; for the next hue value there would be one dark, then half light, then the rest dark. There is thus some control over where to place the brightest part of the pixel.


If it were possible to set the hue for a single 320-mode pixel, such ability could be used to achieve high resolution when viewing stuff on a monochrome screen (on a color screen, chroma artifacts would make it impossible to see fractional pixels). Unfortunately, the hue is set for a pair of 320-mode pixels; consequently, while one could make the left half of a pixel lighter and the right half darker, or vice versa, or the center two quarters lighter and the left and right quarters lighter, or vice versa, there is no way to make the left quarter lighter without also making the right quarter lighter. I thus don't see any strong prospects of showing a usable 640x200 screen.

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