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Old 13 June 2018, 11:12   #1
Foebane
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Is it true the Amiga nearly DIDN'T use RGB for colour?

I've got a video of Jay Miner giving a speech about Amiga specs and development, and he says at one point that they only decided on using RGB for the Amiga palette at the last minute, as well as bitplanes as we know them.

For 16-bit computers and onwards, RGB is the most comprehensive, versatile, "natural" and compatible colour space for colour palettes for use on RGB CRT displays (which is the standard) and I can't imagine what other colour space could be used in place of it (AFAIK, Atari 8-Bits used HSV, which was more limited for certain types of colours).
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Old 13 June 2018, 11:20   #2
Hewitson
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I wouldn't be surprised. Remember that the Amiga was created in the US, where RGB compatible TV's don't exist.
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Old 13 June 2018, 11:29   #3
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I'm not sure about the main question, but from memories of my old 800XL, the Atari 8-bits were a little more primitive than proper HSV/HSL, which can still produce a wide palette. Instead they used a partial version, where you had 16 colours to choose from (H) and 16 levels of brightness (L) for a total of 256 possible colours. Special tricks were needed to show them all on screen though, similar to copper tricks on the Amiga. Typically you'd only have 16 of them on screen at any one time.
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Old 13 June 2018, 13:32   #4
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I'm sure I remember reading somewhere that HAM mode was originally intended to work in some kind of YUV-like mode instead of RGB, and it was nearly removed when the decision was made to go RGB. (Of course I can't find any such reference now!)
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Old 13 June 2018, 18:55   #5
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Composite YUV was probably the most used way for a A1000.
But the signal was generated by the Vidiot from the RGB signals (a more sophisticated colour-version of the later A500 b/w signal)

So it would have made sense to stay in the YUV realm during the whole signal chain.
So instead of 12bit RGB values you could simply use 12bit YUV in the registers - bitplanes and blitter-operations would stay the same.

A "reverse-vidiot" could than generate a RGB signal from the YUV values....
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Old 14 June 2018, 13:12   #6
robinsonb5
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So it would have made sense to stay in the YUV realm during the whole signal chain.
So instead of 12bit RGB values you could simply use 12bit YUV in the registers - bitplanes and blitter-operations would stay the same.
Interesting - it does make sense, so much so that I'm now wondering if any computers were actually designed and built that dealt with colour in this way? (In the 80s / very early 90s, at least -I'm not counting YUV video overlays on modern PC graphics cards)
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Old 14 June 2018, 13:54   #7
Toni Wilen
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Yes, HAM was designed because original design used YUV color space where HAM makes much more sense and it was going to be removed after design was changed to RGB.

I think it was mentioned in some old interviews, also in Ron Nicholson and Joe Decuir at Amiga 30th anniversary presentation few years ago and Amiga Years book.

I have never heard of bitplanes being late change. It probably is a misunderstanding because <some other gfx design> to bitplanes would have been very big change. YUV to RGB was easy, no Agnus or Denise changes needed, only needed to rename signal lines coming Denise
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Old 14 June 2018, 17:05   #8
Gorf
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Interesting - it does make sense, so much so that I'm now wondering if any computers were actually designed and built that dealt with colour in this way? (In the 80s / very early 90s, at least -I'm not counting YUV video overlays on modern PC graphics cards)
The Atari Jaguar did. The colour-format its labeled CRY there.
It allows easier shading and lighting since only the Y component needs to change...
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Old 14 June 2018, 18:40   #9
Bruce Abbott
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I'm now wondering if any computers were actually designed and built that dealt with colour in this way? (In the 80s / very early 90s, at least -I'm not counting YUV video overlays on modern PC graphics cards)
Many 80's home computers produced YUV internally, because that was easier to convert to NTSC/PAL. Of course due to limited graphics memory and bandwidth they mapped a small number of colors into the YUV space. Then the TV had to convert the YUV to RGB to drive the tube!

The MC6847 (used in the Acorn Atom, Tandy Color Computer. Lazer 200/VZ200...) and TI9928/9 (Ti-99/4a, Sega SC3000, Spectravideo, MSX...) were two popular graphics chips that had YUV outputs. Also the original ZX Spectrum ULA produced a form of YUV.

For those of us who wanted sharp displays this was a pain because the analog circuitry required to convert YUV to RGB was quite complex and tricky to set up. RGB was much preferred due to its simplicity and ease of obtaining a sharp picture, but you needed an RGB monitor to get the best out of it (a standard TV could be modified to take RGB in, but the video amplifiers had low bandwaidth and the tube had a coarse shadow mask so the result was usually unsatisfactory).

Having sharp RGB outputs and a matching monitor made the Amiga much more desirable than other home computers which only had crappy composite/rf outputs! That it nearly didn't get it is another example of how lucky we are.
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