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PostPosted: Thu Dec 22, 2011 10:27 am 
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Well I'm pretty sure that for any effect that is simple in a color space, it can be done with a more complex (not mathematically complex but computationally complex) 3x3 matrix multiply.

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PostPosted: Mon Jan 09, 2012 8:49 am 
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tepples wrote:
But then EGA (16 colors out of 2bpc RGB) is not too far from the Master System.


This works only in 640x350. Due to IBM wanting compatibility of EGA in 200 lines modes with CGA monitors, only the 16 CGA text mode palette colors can be displayed in 200 line modes (640x200, 320x200 etc.). That is why most EGA graphics looks pretty bad.


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PostPosted: Mon Jan 09, 2012 9:13 am 
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Beeper wrote:
Due to IBM wanting compatibility of EGA in 200 lines modes with CGA monitors, only the 16 CGA text mode palette colors can be displayed in 200 line modes (640x200, 320x200 etc.). That is why most EGA graphics looks pretty bad.

Was it only BIOS that couldn't reprogram the palette in EGA modes, or did the card's hardware restrict the color palette whenever the dot clock was set below the frequency for 640x350? I seem to remember that a CGA would just use EGA green intensity for all three channels' intensity.


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PostPosted: Mon Jan 09, 2012 1:35 pm 
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No-one with the actual hardware has tested, but I strongly suspect that the color mapping (whether to treat secondary-green as secondary-all) is just a function of sync polarity.


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PostPosted: Tue Jan 10, 2012 4:35 am 
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Back when I used QBASIC, I remember being able to map any of the 262144 VGA colors to the 16 indexes of SCREEN 7 (I had to directly write to some ports instead of using the built in palette manipulation command though). I don't know if that was standard or not...


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PostPosted: Tue Jan 10, 2012 12:20 pm 
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I failed to read!
tepples wrote:
Was it only BIOS that couldn't reprogram the palette in EGA modes, or did the card's hardware restrict the color palette whenever the dot clock was set below the frequency for 640x350?
Neither! It's the monitor.

lidnariq wrote:
that the color mapping (whether to treat secondary-green as secondary-all) is just a function of sync polarity.
The question, however, is whether the EGA monitor's circuitry for hsync can self-sync to either 16kHz or 24kHz independent of sync polarity, or if the sync polarity determines both the mapping of digital values to colors as well as what hsync rate the monitor will not blow up on.

tokumaru wrote:
Back when I used QBASIC, I remember being able to map any of the 262144 VGA colors to the 16 indexes of SCREEN 7 (I had to directly write to some ports instead of using the built in palette manipulation command though). I don't know if that was standard or not...
Yeah, VGA cards, in order to be backwards compatible with EGA software, retained the EGA's hardware palette. I remember explicitly configuring the EGA palette (replacing brown, EGA palette 20, with dark yellow, palette 6) to simplify VGA palette wipes.


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