vidc20 palette control
Robert Black
Does anyone know how to control the vidc20 palette in 16bpp modes?
I'm posting this here because I DON'T want the RiscOS answer. You
can assume knowledge of controlling the palette in 8bpp modes.
Cheers
Rob Black
Owen Smith
As far as I recall, there is no palette in 16bpp modes. You get 5 bits of
each of red, green and blue and that's it. (I can't remember if the spare bit
is used for anything.)
--
Owen (owen....@net-tel.co.uk)
If you choose to attribute my words to NET-TEL that's your problem.........77
Matthias Seifert
>Robert Black <rbl...@ic.ac.uk> wrote:
>
>>Does anyone know how to control the vidc20 palette in 16bpp modes?
>>I'm posting this here because I DON'T want the RiscOS answer. You
>>can assume knowledge of controlling the palette in 8bpp modes.
>
>As far as I recall, there is no palette in 16bpp modes. You get 5 bits of
>each of red, green and blue and that's it. (I can't remember if the spare bit
>is used for anything.)
That's not the full truth. In fact you can even program the palette in 16
and 32 bpp modes. But this is not very easy. You could for example define
a 16 bpp palette with 64k colours instead of the 32k colours.
The spare bit is not used in the default definition of the 16 bpp mode.
Bye
M. Seifert
Andreas Joos
OS> As far as I recall, there is no palette in 16bpp modes. You get 5 bits of
OS> each of red, green and blue and that's it. (I can't remember if the spare
OS> bit is used for anything.)
AFAIK you can split the bits for red/green/blue, as you like. Say 2 bits red,
8 bits green and 5 blue.
Bye, Andreas Joos
=== Acorn A3000 - you can't beat the feeling...
Keith Clarke
>Robert Black <rbl...@ic.ac.uk> wrote:
>>Does anyone know how to control the vidc20 palette in 16bpp modes?
>>I'm posting this here because I DON'T want the RiscOS answer. You
>>can assume knowledge of controlling the palette in 8bpp modes.
>As far as I recall, there is no palette in 16bpp modes. You get 5 bits of
>each of red, green and blue and that's it. (I can't remember if the spare bit
>is used for anything.)
Unfortunately you are off the mark by some way. In fact vidc20 uses a
special patented technique in this mode to allow a wide variety of
options.
Within the 16bits of the pixel the number of bits used for each of the
colours can vary from 4 to 8 at the extremes, for example the
following splits between Red, Green and Blue are all valid: 5-5-5,
5-6-5, 4-8-4, 7-3-6.
There are effectively three RAMs of 256 entries for each of the
colours. In the 16bpp mode, bits 0 to 7 are used to look up
into the Red palette RAM, bits 4 to 11 for the Green palette RAM and
bits 0 to 7 for the Blue palette RAM.
If a 4-8-4 mode was being used then the 16 translated colours for red
would be stored in locations 0 to 15, then again in 16 to 31 and so
on. The 16 translated blue colors would be stored at 0, 16, 32, 48,
64, etc and repeated at 1, 17, 33, 49, 65 and so on.
I hope this helps,
Keith
DISCLAIMER: I speak for me only, not my company.