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Re: [offtopic][retro] 16 color palette definition

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On 31/03/2020 19:56, Eli the Bearded wrote:
> In comp.lang.c, Bart  <bc@freeuk.com> wrote:
>> If stuck with 4 bits, and able to use a palette, then there is no clear
>> way of using RGB, as you use 1 bit for each of R, G, B, but then what
>> purpose is the 4th bit?
> 
> Wasn't it traditionally a brightness?
> 
> R G B br	->  modern RGB
> 0 0 0 0		->  000000
> 0 0 0 1		->  505050
> 1 1 1 0		->  A0A0A0
> 1 1 1 1		->  FFFFFF
> 1 0 0 0		->  800000
> 1 0 0 1		->  FF0000
> 0 1 0 0		->  008000
> 0 1 0 1		->  00FF00
> 0 0 1 0		->  000080
> 0 0 1 1		->  0000FF
> 
> (etc)
> 
> But I wouldn't call that a "palette". To me that term is when your
> color is an index into a lookup table, not an attempt to make each
> bit meaningful.

A palette can be involved, even if the bits directly correspond to RGB 
with one spare. For example, if generating a 4-bit/16-colour BMP file, 
that required a palette. And I think Windows' display also made use of a 
palette, but I forget all the details.

>> So I think it might be worth looking at using CMYK instead. C,M,Y,K are
>> used in printing, as either on or off. So such 4-bit colour pixels could
>> be used to show photos, given enough pixels and using dithering or
>> half-tone patterns.
> 
> I think using CMYK for screens, and 4 bit CMYK at that, is foolish. Too
> many colors in the CMYK space have redundant representations and it's
> not a close match for display hardware. There are technical reasons
> due to ink opacity and drying time to choose between 30% K or 50% K
> which make no sense for a photon driven output.

Thinking CMYK would give you 16 different colours was misguided.

But CMYK /is/ fundamentally 4-bit: each ink is either present or not 
present on the paper.

When I was writing drivers for colour dot matrix in the 80s, each colour 
was either on or off. However for the sorts of reason you say, solid 
colours (all dots coloured for an area of solid Magenta, say), would be 
too intense (the paper would become saturated with ink).

So only a proportion of dots would be coloured, according to some 
scheme. (Another thing was, if doing separate passes of the print head 
for each primary, you did the lighter colours last.)

I think, with an original image of 24/32 bits, you might sometimes use 
CMYK over RGB, but for specialist work.

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[offtopic][retro] 16 color palette definition fir <profesor.fir@gmail.com> - 2020-03-28 03:54 -0700
  Re: [offtopic][retro] 16 color palette definition felix@palmen-it.de (Felix Palmen) - 2020-03-28 12:11 +0100
    Re: [offtopic][retro] 16 color palette definition fir <profesor.fir@gmail.com> - 2020-03-28 05:45 -0700
      Re: [offtopic][retro] 16 color palette definition felix@palmen-it.de (Felix Palmen) - 2020-03-28 15:41 +0100
        Re: [offtopic][retro] 16 color palette definition BGB <cr88192@gmail.com> - 2020-03-30 08:05 -0500
          Re: [offtopic][retro] 16 color palette definition felix@palmen-it.de (Felix Palmen) - 2020-03-30 17:43 +0200
            Re: [offtopic][retro] 16 color palette definition BGB <cr88192@gmail.com> - 2020-03-30 12:04 -0500
  Re: [offtopic][retro] 16 color palette definition fir <profesor.fir@gmail.com> - 2020-03-28 04:16 -0700
    Re: [offtopic][retro] 16 color palette definition fir <profesor.fir@gmail.com> - 2020-03-28 05:32 -0700
  Re: [offtopic][retro] 16 color palette definition bert <bert.hutchings@btinternet.com> - 2020-03-28 07:05 -0700
    Re: [offtopic][retro] 16 color palette definition Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-03-28 08:13 -0700
      Re: [offtopic][retro] 16 color palette definition Bart <bc@freeuk.com> - 2020-03-28 15:33 +0000
        Re: [offtopic][retro] 16 color palette definition Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-03-28 08:40 -0700
          Re: [offtopic][retro] 16 color palette definition fir <profesor.fir@gmail.com> - 2020-03-28 08:58 -0700
            Re: [offtopic][retro] 16 color palette definition Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-03-28 09:08 -0700
              Re: [offtopic][retro] 16 color palette definition fir <profesor.fir@gmail.com> - 2020-03-28 09:31 -0700
                Re: [offtopic][retro] 16 color palette definition Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-03-28 10:51 -0700
                Re: [offtopic][retro] 16 color palette definition fir <profesor.fir@gmail.com> - 2020-03-28 11:03 -0700
                Re: [offtopic][retro] 16 color palette definition fir <profesor.fir@gmail.com> - 2020-03-28 11:10 -0700
        Re: [offtopic][retro] 16 color palette definition Bart <bc@freeuk.com> - 2020-03-30 18:31 +0100
          Re: [offtopic][retro] 16 color palette definition Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-03-30 11:26 -0700
            Re: [offtopic][retro] 16 color palette definition Bart <bc@freeuk.com> - 2020-03-30 21:09 +0100
          Re: [offtopic][retro] 16 color palette definition BGB <cr88192@gmail.com> - 2020-03-30 13:45 -0500
          Re: [offtopic][retro] 16 color palette definition Eli the Bearded <*@eli.users.panix.com> - 2020-03-31 18:56 +0000
            Re: [offtopic][retro] 16 color palette definition Bart <bc@freeuk.com> - 2020-03-31 20:32 +0100
              Re: [offtopic][retro] 16 color palette definition Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2020-03-31 13:51 -0700
      Re: [offtopic][retro] 16 color palette definition BGB <cr88192@gmail.com> - 2020-03-29 22:40 -0500
  Re: [offtopic][retro] 16 color palette definition Bonita Montero <Bonita.Montero@gmail.com> - 2020-03-28 16:09 +0100
  Re: [offtopic][retro] 16 color palette definition Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-03-28 14:10 -0400
    Re: [offtopic][retro] 16 color palette definition fir <profesor.fir@gmail.com> - 2020-03-28 11:59 -0700
      Re: [offtopic][retro] 16 color palette definition fir <profesor.fir@gmail.com> - 2020-03-28 12:02 -0700
        Re: [offtopic][retro] 16 color palette definition fir <profesor.fir@gmail.com> - 2020-03-28 12:49 -0700
    Re: [offtopic][retro] 16 color palette definition Jorgen Grahn <grahn+nntp@snipabacken.se> - 2020-03-28 20:57 +0000

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