Problem bluewhitered function colormap

Question

Jonas Neu 2022-6-14

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1740055-problem-bluewhitered-function-colormap

评论： DGM 2022-6-15

Hello,

I have a problem using the bluewhitered function. I want to create a average image of a sequence (works) and change the colormap to bluewhitered, where I can see all 3 colors. This doesn't work as planed, because the final picture is just red and white. How can I change that?

pwd=uigetdir('Choose folder with pictures');
savepath=uigetdir('SavePath');
savename='averageIm';
cd (pwd)
DirFiles = dir([pwd '/*.tif']); 
jpg_average = 0;
for i = 1:numel(DirFiles)
      im=double(imread(DirFiles(i).name));
      jpg_average = im + jpg_average;
end
average= double(jpg_average/numel(DirFiles));
figure(1);
colormap(bluewhitered(256));
im = imagesc(average);
cd(savepath);
saveas(figure(1), (strcat('Case_',strcat(savename),'.png')) )

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Answer 1

DGM 2022-6-14

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1740055-problem-bluewhitered-function-colormap#answer_985330

编辑：DGM 2022-6-14

在 MATLAB Online 中打开

bluewhitered.m

bluewhitered() doesn't work like normal colormap tools. It actually queries the current axes 'clim' property and the map is truncated such that white corresponds to zero -- no matter what the actual data range is. The default axes 'clim' is [0 1], and the data range is [23 250] (all >0), so the entire colormap returned by bluewhitered() is white-red.

This tool is intended to be used with data that's roughly centered around zero. If you're going to try to apply it to data with some arbitrary range, you can try something like this

savepath = './';

savename = 'asdf';

% i'm just going to kludge this to make it run

jpg_average = 0;

for k = 1:10

im=double(imread(sprintf('AT3_1m4_%02d.tif',k)));

jpg_average = im + jpg_average;

end

average = double(jpg_average/10);

caxis([-1 1]) % force symmetric limits

cm = bluewhitered(256); % get a full map

colormap(cm); % use it

im = imagesc(average); % display the image

% save the actual image instead of saving a screenshot of the image.

% specify the path instead of changing the working directory

outpict = im2uint8(mat2gray(average));

outpict = ind2rgb(outpict,cm);

imwrite(outpict,fullfile(savepath,[savename '.png']))

but bear in mind that the center will just correspond to the midpoint of the data range.

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Jonas Neu 2022-6-15

It worked. Thank you very much for your help.

DGM 2022-6-15

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