Get Colormap Values Corresponding to Array Values

Question

Hannah_Mad 2021-8-13

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/897552-get-colormap-values-corresponding-to-array-values

评论： Hannah_Mad 2021-8-13

采纳的回答： Chunru

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Dear Matlab Community,

Currently I am trying to visualize neuroimaging data and have thus run into the following problem:

I have an array of 1990 values, which I want to plot in different colors on a continuous colorbar. So all I would require is the information on how I can get a matrix with RGB triplets corresponding to the data in my array. I have already tried the following:

c = jet(cvals)

Which yields in the following code:

Error using  / 
Matrix dimensions must agree.
Error in jet (line 23)
u = [(1:1:n)/n ones(1,n-1) (n:-1:1)/n]';

Any help would be greatly appreciated.

Thank you!

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Yazan 2021-8-13

What version of Matlab do you have? When run on 2021a, no errors were received.

Hannah_Mad 2021-8-13

I run R2021 a

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Answer 1

Chunru 2021-8-13

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https://ww2.mathworks.cn/matlabcentral/answers/897552-get-colormap-values-corresponding-to-array-values#answer_766197

在 MATLAB Online 中打开

% rand cvars
cvars = randi([10 450], [128, 1]);
% You need to specify the number of colors to represent these cvars
n = 512;
cmap = jet(n);
% cvars has a different range from cmap range (1:512), so you have to map
% it. (similar to imagesc)
cvars_map = (cvars - min(cvars))/(max(cvars)-min(cvars)) * (n-1) + 1;
% Now find the color of i-th cvars
i = 10;             
cvars(i)
ans = 136
cvars_map(i)            % mapped cvars
ans = 147
cmap(cvars_map(i), :)   % corresponding color
ans = 1×3
         0    0.6484    1.0000

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Chunru 2021-8-13

cvars is considered continuous (the code above just use the min and max of cvars). This continous values are then divided into n intervals. Each interval is then mapped into 1 of the n colors.

If you only have 70 unique values, then they correspond to 70 unique colors (out of n=512) colors. Some other colors will not really used.

If you do want to have each unique value correspond to a color, it can be also down. But you need to specify which color map you want to use.

Hannah_Mad 2021-8-13

Thank you very much! It works. Just one last question: if I have outliers (i.e. values are between 1 - 35) and one value is much higher (i.e. 70) is there any way I can change the colormap's limits? I only found caxis, but I do not think that it'll do the job here.

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