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PostPosted: Sat May 25, 2019 2:30 pm 
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Random question here, were there any computer/console/arcade systems that used 3bpp for their graphics?
The NES used 2bpp and had four colors for its graphic tiles. The SMS used 4bpp and had sixteen colors for its graphic tiles. And as I think about it, using 3bpp to have eight colors sounds like it could have been theoretically possible. It would leave an extra bit or two hanging with no real purpose, so it really wouldn't be efficient, but it seems to me like it could have been technically possible.

Was it ever done? Was it even feasible?

And of course, I mean real-world examples, so the famicube doesn't count.


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PostPosted: Sat May 25, 2019 3:20 pm 
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In hardware, I don't think so, but some 4bpp platforms used 3bpp graphics to save space.


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PostPosted: Sat May 25, 2019 3:32 pm 
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tokumaru wrote:
In hardware, I don't think so, but some 4bpp platforms used 3bpp graphics to save space.

Like, as a legit way they were encoded and processed, or are we just talking about designing the graphics to use eight colors so that the other eight in the palette could be used by other tiles?


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PostPosted: Sat May 25, 2019 3:57 pm 
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I think they imposed a limit of 8 colors to the artists so the graphics could be encoded as 3bpp, saving some space. During decompression, a 4th bit would be added so they could be used by the video hardware normally. If I'm not mistaken, the most prominent example of this is Super Mario World on the SNES. I don't know if the game applied another layer of compression on top of that.

EDIT: my first post was poorly worded. I meant that certain games for 4bpp platforms would encode their graphics in 3bpp to save space.


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PostPosted: Sat May 25, 2019 8:05 pm 
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Most of the frame buffer of Missile Command is 2bpp, but the bottom few rows are 3bpp.

I remember reading an article within the past year or so about reverse engineering some arcade game with two 3bpp background planes. All I can remember is it had a pyramid in the background, and the title screen had to be split between the background and sprites because they were running out of space in the background side of the pattern table.

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PostPosted: Sat May 25, 2019 8:50 pm 
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On a system like Atari ST or Amiga where graphics were in a very planar format, it becomes reasonable to have arbitrary numbers of planes.

I can't think of any common 3-bit graphics mode, but there was a very standard 5-bit mode on the Amiga.

However, on both of those systems, I believe you probably could find examples of source/software data organized into 3-bpp for convenience. Sprite data that only needs 8 colours, despite the screen having 16 or 32 total, etc.

Similarly in YY-CHR and some graphics documents for the SNES you might find descriptions of 3-bpp graphics data as well, which despite not having an actual hardware function might have been convenient for storing data that doesn't need that extra bit.


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PostPosted: Sat May 25, 2019 10:04 pm 
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As far as I know, the original PC-8801 uses 3-bit(fixed RGB 111 palette).


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PostPosted: Sun May 26, 2019 4:18 am 
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The Amiga OCS supported 6 bitplanes plus sprites, and there were two fine scrolling registers each of those bitplanes could be assigned to. So 3+3 bitplanes were not infrequent.


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PostPosted: Sun May 26, 2019 9:47 am 
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tokumaru wrote:
In hardware, I don't think so, but some 4bpp platforms used 3bpp graphics to save space.


Many machines, including arcade boards, used eight colors with one bit each for R, G, B--not as a space issue, but because nobody thought it worthwhile to provide any finer control (even given a monitor that's limited to turning each guns on and off, a circuit to "dither" two bits each for R, G, and B would have required only two chips, but for whatever reason digital RGB without hardware dithering was very common.


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PostPosted: Sun May 26, 2019 12:18 pm 
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Marscaleb wrote:
Random question here, were there any computer/console/arcade systems that used 3bpp for their graphics?
The NES used 2bpp and had four colors for its graphic tiles. The SMS used 4bpp and had sixteen colors for its graphic tiles. And as I think about it, using 3bpp to have eight colors sounds like it could have been theoretically possible. It would leave an extra bit or two hanging with no real purpose, so it really wouldn't be efficient, but it seems to me like it could have been technically possible.

Was it ever done? Was it even feasible?

And of course, I mean real-world examples, so the famicube doesn't count.

It's fun you ask this now because I received no less than 3 new answers in the last 2 days here, but I don't have much time to review them right now.
Basically yes it was done, it is feasible but it wasn't common.


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PostPosted: Sun May 26, 2019 12:39 pm 
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lidnariq wrote:
The Amiga OCS supported 6 bitplanes plus sprites, and there were two fine scrolling registers each of those bitplanes could be assigned to. So 3+3 bitplanes were not infrequent.

Ah! I didn't realize it had two scrolling groups split by bitplane like that, but that makes a ton of sense. I knew I'd seen 3-bpp graphics in Amiga memory dumps when ripping graphics, but I didn't know it could occupy a layer in that way.


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PostPosted: Sun May 26, 2019 2:03 pm 
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rainwarrior wrote:
Ah! I didn't realize it had two scrolling groups split by bitplane like that, but that makes a ton of sense. I knew I'd seen 3-bpp graphics in Amiga memory dumps when ripping graphics, but I didn't know it could occupy a layer in that way.
I misremebered it as being more general than it actually is; indeed you could choose 1 to 6 bitplanes, and split them into two groups, but they automatically alternated which group they were part of ... so any Amiga game with multiple scrolling panes would always be 3bpp or less.


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