Red to blue color map, with while for zero.

b2r.m

function newmap = b2r(cmin_input,cmax_input)
%BLUEWHITERED   Blue, white, and red color map.
%   this matlab file is designed to draw anomaly figures, the color of
%   the colorbar is from blue to white and then to red, corresponding to 
%   the anomaly values from negative to zero to positive, respectively. 
%   The color white always correspondes to value zero. 
%   
%   You should input two values like caxis in matlab, that is the min and
%   the max value of color values designed.  e.g. colormap(b2r(-3,5))
%   
%   the brightness of blue and red will change according to your setting,
%   so that the brightness of the color corresponded to the color of his
%   opposite number
%   e.g. colormap(b2r(-3,6))   is from light blue to deep red
%   e.g. colormap(b2r(-3,3))   is from deep blue to deep red
%
%   I'd advise you to use colorbar first to make sure the caxis' cmax and cmin
%
%   by Cunjie Zhang
%   2011-3-14
%   find bugs ====> email : daisy19880411@126.com
%  
%   Examples:
%   ------------------------------
%   figure
%   peaks;
%   colormap(b2r(-6,8)), colorbar, title('b2r')
%   


%% check the input
if nargin ~= 2 ;
   disp('input error');
   disp('input two variables, the range of caxis , for example : colormap(b2r(-3,3))')
end

if cmin_input >= cmax_input
    disp('input error')
    disp('the color range must be from a smaller one to a larger one')
end

%% control the figure caxis 
lims = get(gca, 'CLim');   % get figure caxis formation
caxis([cmin_input cmax_input])

%% color configuration : from blue to light blue to white untill to red

red_top     = [1 0 0];
white_middle= [1 1 1];
blue_bottom = [0 0 1];

%% color interpolation 

color_num = 250;   
color_input = [blue_bottom;  white_middle;  red_top];
oldsteps = linspace(-1, 1, length(color_input));
newsteps = linspace(-1, 1, color_num);  

%% Category Discussion according to the cmin and cmax input

%  the color data will be remaped to color range from -max(abs(cmin_input,abs(cmax_input)))
%  to max(abs(cmin_input,abs(cmax_input))) , and then squeeze the color
%  data in order to make suere the blue and red color selected corresponded
%  to their math values

%  for example :
%  if b2r(-3,6) ,the color range is from light blue to deep red ,
%  so that the color at -3 is light blue while the color at 3 is light red
%  corresponded

%% Category Discussion according to the cmin and cmax input
% first : from negative to positive
% then  : from positive to positive
% last  : from negative to negative

newmap_all = NaN(size(newsteps,2),3);
if (cmin_input < 0)  &&  (cmax_input > 0) ;  
    
    
    if abs(cmin_input) < cmax_input 
         
        % |--------|---------|--------------------|    
      % -cmax      cmin       0                  cmax         [cmin,cmax]
      %    squeeze(colormap(round((cmin+cmax)/2/cmax),size(colormap)))
 
       for j=1:3
           newmap_all(:,j) = min(max(transpose(interp1(oldsteps, color_input(:,j), newsteps)), 0), 1);
       end
       start_point = round((cmin_input+cmax_input)/2/cmax_input*color_num);
       newmap = squeeze(newmap_all(start_point:color_num,:));
       
    elseif abs(cmin_input) >= cmax_input
        
         % |------------------|------|--------------|    
       %  cmin                0     cmax          -cmin         [cmin,cmax]
       %    squeeze(colormap(round((cmin+cmax)/2/cmax),size(colormap)))       
       
       for j=1:3
           newmap_all(:,j) = min(max(transpose(interp1(oldsteps, color_input(:,j), newsteps)), 0), 1);
       end
       end_point = round((cmax_input-cmin_input)/2/abs(cmin_input)*color_num);
       newmap = squeeze(newmap_all(1:end_point,:));
    end
    
       
elseif cmin_input >= 0

       if lims(1) < 0 
           disp('caution:')
           disp('there are still values smaller than 0, but cmin is larger than 0.')
           disp('some area will be in red color while it should be in blue color')
       end
        % |-----------------|-------|-------------|    
      % -cmax               0      cmin          cmax         [cmin,cmax]
      %    squeeze(colormap(round((cmin+cmax)/2/cmax),size(colormap)))
 
       for j=1:3
           newmap_all(:,j) = min(max(transpose(interp1(oldsteps, color_input(:,j), newsteps)), 0), 1);
       end
       start_point = round((cmin_input+cmax_input)/2/cmax_input*color_num);
       newmap = squeeze(newmap_all(start_point:color_num,:));

elseif cmax_input <= 0

       if lims(2) > 0 
           disp('caution:')
           disp('there are still values larger than 0, but cmax is smaller than 0.')
           disp('some area will be in blue color while it should be in red color')
       end
       
         % |------------|------|--------------------|    
       %  cmin         cmax    0                  -cmin         [cmin,cmax]
       %    squeeze(colormap(round((cmin+cmax)/2/cmax),size(colormap)))       

       for j=1:3
           newmap_all(:,j) = min(max(transpose(interp1(oldsteps, color_input(:,j), newsteps)), 0), 1);
       end
       end_point = round((cmax_input-cmin_input)/2/abs(cmin_input)*color_num);
       newmap = squeeze(newmap_all(1:end_point,:));
end