Get Colormap Values Corresponding to Array Values

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!

[Yazan]

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

[Hannah_Mad]

I run R2021 a

Answer 1

[Chunru]

% 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

[Hannah_Mad]

Thank you for your quick reply. Unfortunately I forgot to mention that, while my array is 1990 x 1, it only has 70 unique values. That means, I only need 70 colors - right? So how do I match my 70 colors to the 1990 values that it corresponds to?

Thank you

[Chunru]

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]

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.