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Re: Simple programming query

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On 07/04/2018 12:50, David Feugey wrote:
> That's right. You have 256 colours, but based on a palette where you
> fix only 16 significative ones. So it's true to say that only 16
> colours are freely selectable. But you'll get a gradiant of 256 real &
> different colours.
> 
> "the VIDC1a had 16 hardware palette registers. This meant that in
> screen modes with sixteen colours or fewer, the colours could be
> mapped to any of the 4096 available. However, in 256 colour modes, 4
> bits of the colour data were hardware derived and could not be
> adjusted. The net result was 256 colours, but only 16 of them could be
> assigned as desired, covering a range of the 4096 available colours."
> 
> https://en.wikipedia.org/wiki/Acorn_Archimedes

That's not really a good description. Although the 16 pallet entries are 
used in 256 colour modes, they affect the bottom 4 bits of all colours 
in a completely un-useful way.

The only sensible action is to accept the default palette of 64 base 
colours (4x4x4 RGB) with 16 tint (white levels) variations.

> On the other hand, VIDC1 is really old technology

The VIDC20's (and later) true 256 colour modes with 256 palette entries, 
is far more useful, you can do some great effects.

---druck

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Simple programming query xltardy@gmail.com - 2018-01-11 03:05 -0800
  Re: Simple programming query Alan Adams <alan@adamshome.org.uk> - 2018-01-11 12:11 +0000
    Re: Simple programming query xltardy@gmail.com - 2018-01-11 06:01 -0800
    Re: Simple programming query jgh@mdfs.net - 2018-01-11 09:24 -0800
      Re: Simple programming query xltardy@gmail.com - 2018-01-11 10:15 -0800
        Re: Simple programming query Richard Ashbery <basura@invalid.addr.uk> - 2018-01-12 21:24 +0000
          Re: Simple programming query Rick Murray <Rick@bogus.email.address> - 2018-01-13 11:16 +0100
            Re: Simple programming query xltardy@gmail.com - 2018-03-01 23:09 -0800
              Re: Simple programming query Rick Murray <Rick@bogus.email.address> - 2018-03-02 22:45 +0100
                Re: Simple programming query xltardy@gmail.com - 2018-04-07 00:38 -0700
                Re: Simple programming query David Feugey <dfeugey@riscos.fr> - 2018-04-07 13:50 +0200
                Re: Simple programming query xltardy@gmail.com - 2018-04-09 11:40 -0700
                Re: Simple programming query David Feugey <dfeugey@riscos.fr> - 2018-04-10 08:31 +0200
                Re: Simple programming query druck <news@druck.org.uk> - 2018-04-09 21:05 +0100

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