function [ r , g , b ] = clrmap( num_colors )

% black-red-yellow-white colormap

third_num_colors = floor( num_colors / 3 );

r = ones(num_colors,1);

r(1:third_num_colors+1) = [ 0 : 1/(third_num_colors) : 1 ]';

r = round( r * 255 );

g = r >> third_num_colors;
b = g >> third_num_colors;