# problem with calculation of percentage of colormap

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joanna on 10 Jan 2013
i want to calculate the percentage of high amount of "red" in an image of a colormap. what should be the equation i should input? 'stress' is a colormap image.
[image_1x image_1y] = size(stress);
for x = 1:image_1x
for y = 1:image_1y
if(stress(x,y) <=250) || (stress(x,y) >=255)
//???
end
end
end

Teja Muppirala on 10 Jan 2013
You don't need to loop over every element one by one to do this. MATLAB is very good at doing operations on entire matrices in one command. You can simply write
L = 55; % Pick a level
percent_over = 100 * nnz(I > L) / numel(I)
This is basically counting the number of elements greater than L, and dividing it by the total number of elements in the image.
You can replace L with whatever value you would like to use (from your picture, "red" seems to be anything above about 50).
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Image Analyst on 10 Jan 2013
caption = sprintf('The number = %.3f', theNumber);
set(handleToStaticTextControl, 'String', caption);