How to use bluewhitered function?

The bluewhitered function is a very used map plotting function. I want to know how to add limits, and how to set the center of the map. For example, if I want to plot a map with a range of [1,3], how to set the 2 to be the center and to be white?

[Walter Roberson]

caxis()

Answer 1

[Geoff Hayes]

Yandong - the bluewhitered code seems to have been intended to work under the assumption that it returns an M-by-3 matrix containing a blue to white to red colormap, with white corresponding to the CAXIS value closest to zero. In your case, you want :"white corresponding to the CAXIS value closes to two". I think that you can do this if you just ensure that the code corresponding to the first if statement is evaluated. Obviously you won't have positive and negative limits, so you could just replace the if-elseif-else block with

    ratio = 0.5; % abs(lims(1)) / (abs(lims(1)) + lims(2));
    neglen = round(m*ratio);
    poslen = m - neglen;
    
    % Just negative
    new = [bottom; botmiddle; middle];
    len = length(new);
    oldsteps = linspace(0, 1, len);
    newsteps = linspace(0, 1, neglen);
    newmap1 = zeros(neglen, 3);
    
    for i=1:3
        % Interpolate over RGB spaces of colormap
        newmap1(:,i) = min(max(interp1(oldsteps, new(:,i), newsteps)', 0), 1);
    end
    
    % Just positive
    new = [middle; topmiddle; top];
    len = length(new);
    oldsteps = linspace(0, 1, len);
    newsteps = linspace(0, 1, poslen);
    newmap = zeros(poslen, 3);
    
    for i=1:3
        % Interpolate over RGB spaces of colormap
        newmap(:,i) = min(max(interp1(oldsteps, new(:,i), newsteps)', 0), 1);
    end
    
    % And put 'em together
    newmap = [newmap1; newmap];

In the above, we set the ratio variable to be 0.5 since you want 2 to correspond to white and 2 is the middle value in the interval [1,3]. And that is it - there are no other code changes. Try it out and see what happens!

[Yandong Lang]

That makes sense, thank you so much!

Answer 2

[Yogesh Kumkar]

I have tested the function. The figure 1 is wrong because -10 is NaN (gray). The figure 2 is correct but when I save it, I get NaN as white. Please suggest how to fix it.

Z=randi(10,5);

Y=randi([-10 10],5);

Z([2,10,13,24])=nan;Y([3,12,23])=nan;

figure(2); % first method: wrong

ax11=subplot(1,2,1);imagesc(Z);caxis([-10 10]);

cmap11=colormap(ax11,bluewhitered(22));

cmap11(1,:) = [0.5 0.5 0.5];

colormap(ax11,cmap11); h11=(colorbar);

ax12=subplot(1,2,2);imagesc(Y);caxis([-10 10]);

cmap12=colormap(ax12,bluewhitered(22));

cmap12(1,:) = [0.5 0.5 0.5];

colormap(ax12,cmap12); h12=(colorbar);

sgtitle('Figure 1 (cmap(1,:)=[0.5 0.5 0.5])','fontweight','bold','fontsize',16);

saveas(gcf,'/Volumes/YKMac/PAPER_3/Figures_P3/zTestNaN1.png');

%$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

figure(3); % second method: correct

subplot(1,2,1);h3=imagesc(Z);caxis([-10 10]);

set(h3,'alphadata',~isnan(Z));

set(gca,'color', [0.5 0.5 0.5]);

colormap(bluewhitered(22)); colorbar; hold on;

subplot(1,2,2);h4=imagesc(Y);caxis([-10 10]);

set(h4,'alphadata',~isnan(Y));

set(gca,'color', [0.5 0.5 0.5]);

colormap(bluewhitered(22)); colorbar; hold on;

sgtitle('Figure 2 (set alphadata ~isnan(Y))','fontweight','bold','fontsize',16);

saveas(gcf,'/Volumes/YKMac/PAPER_3/Figures_P3/zTestNaN2.png');

[DGM]

This is a common problem when trying to rely on the axes background color. Make sure to unset the 'inverthardcopy' property of the figure.

Z=randi(10,5);
Y=randi([-10 10],5);
Z([2,10,13,24])=nan;Y([3,12,23])=nan;

% second method: correct
subplot(1,2,1);h3=imagesc(Z);caxis([-10 10]);
set(h3,'alphadata',~isnan(Z));
set(gca,'color', [0.5 0.5 0.5]);
colormap(bluewhitered(22)); colorbar; hold on;
subplot(1,2,2);h4=imagesc(Y);caxis([-10 10]);
set(h4,'alphadata',~isnan(Y));
set(gca,'color', [0.5 0.5 0.5]); 
colormap(bluewhitered(22)); colorbar; hold on;
sgtitle('Figure 2 (set alphadata ~isnan(Y))','fontweight','bold','fontsize',16); 

% write the figure as a png
set(gcf,'inverthardcopy',false)
fname = 'zTestNaN2.png';
saveas(gcf,fname);

% read it back and display it
A = imread(fname);
clf
imshow(A)

[Yogesh Kumkar]

set(gcf,'inverthardcopy',false)

works like a charm! Thanks.