Re: Explicit rgb colors [was Re: historysize]

[Theo H. <th...@ph...>]

Theo Hopman wrote:
> `set palette functions` would work well here. The following assumes 8 
> bits for each component, but can be modified to handle more. It also 
> assumes that the r,g,b components are specified in the data file as 
> integers from 0--255.
> 
>   rgb(r,g,b)=int(r*65536)+int(g*256)+int(b)
>   r(gray)=int(2.**24*gray)/65536/256.
>   g(gray)=int(2.**24*gray)%65536/256/256.
>   b(gray)=int(2.**24*gray)%256/256.
>   set palette color model RGB functions r(gray),g(gray),b(gray)
>   set cbrange [0:2.**24-1]
>   unset colorbox
>   splot 'colour-data.txt' using 1:2:3:(log($4)) \
>       with points pointtype 6 pointsize variable lc("black"), \
>     '' using 1:2:3:(rgb($1,$2,$3)) \
>       with points pointtype 7 palette

Grr. This works in theory, but not in practise, and the (wrong) results 
are different on different terminals. I suspect that the rapidly varying 
rgb() function is being sampled at a relatively low frequency to get a 
limited set of grey values. The binning of the rgb() values causes wrong 
(encoded) gravy values to be given to the r(), g() and b() functions, 
resulting in incorrect colours -- red is almost right, but green is 
wrong, and is useless.

THeo