Posted: 4/1/2012 4:57 AM
Post subject: 9-Bit Color? What's up with that?
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Limne
Any
Joined: 2/24/2010
Posts: 153
So. It finally hit me how the PC Engine and Genesis used 9-bit color... How does that make sense with 16-bit PPUs? Why just discard those 5 other bits? Sure, having it divisible by 3 makes sense if it's in RGB, but why not 12 or 15 (like the SNES). What possible benefit could there have been?
Posted: 4/1/2012 6:01 AM
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Twelvepack
Joined: 5/2/2006
Posts: 1020
Location: Boulder, CO
I would be surprised if the bits were used for anything other than alpha. Then again, I honestly don't know anything about how color is handled in a genesis beyond what you just communicated, so your guess is as good as mine
Has never colored a dinosaur.
Posted: 4/1/2012 4:25 PM
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Derakon
Joined: 7/2/2007
Posts: 3960
To my knowledge alpha on the Genesis is strictly a binary affair; there's no alpha blending (it's faked using flicker or old-style TV's line blurring instead).
Pyrel - an open-source rewrite of the Angband roguelike game in Python.
Posted: 4/1/2012 6:08 PM
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marzojr
He/Him
Experienced player (761)
Joined: 9/29/2008
Posts: 964
Location: 🇫🇷 France
Sega TASer of 2014 Sega TAS of 2014 Sega TASer of 2010 Sega TAS of 2010
Lets see: fewer bits for color means fewer wires and simpler (thus cheaper) chips; it means less RAM needs to be used for palettes (and less color RAM), which means a cheaper console; and so on.
Marzo Junior
Posted: 4/1/2012 6:17 PM
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natt
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Joined: 5/11/2011
Posts: 1108
Location: Murka
the "9 bits" only comes into play when specifically storing palette colors. the individual graphics tiles themselves (in the case of the genesis) are all 4 bits per pixel, with 4 pixels combined into a 16 bit word and no wastage. accordingly, the only waste of space is in the palette ram itself; and it's likely there that the other 7 bits of each word just don't exist (since it's special purpose memory). the limiting design factor was likely the complexity of the video DAC rather than memory space, as even say, 24 bit color wouldn't have used up much more resources (so long as it was still a paletted mode and individual graphics tiles were still 4bpp).