Help Vectorizing For-Loop with Complex Statements

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% size of image
imageSize = 564;
% generate the color range used in the colormap
colormap_used_in_image = jet(256^3); % for perfect results use 256^3, 256^2 is good estimator
colormap_used_in_image = colormap_used_in_image * 255; % convert to actual RGB values
% example image where some of the data is in the jet colormap, some isn't
data = randi(255,564,564,3);
% convert data to doubles for math
data = double(data);
% empty array to be filled with our jet mapped data
jetmappedData = nan(imageSize,imageSize);
% this loop calculates which value from the colormap best fits the
% image
wb = waitbar(0,append('Colormapping Values for Image # ',string(1)));
for r = 1:imageSize % for each row in the image
    for c = 1:imageSize % for each column in the image
 
            diff1 = abs(data(r,c,1) - colormap_used_in_image(:,1)); % difference in R value
            diff2 = abs(data(r,c,2) - colormap_used_in_image(:,2)); % difference in G value
            diff3 = abs(data(r,c,3) - colormap_used_in_image(:,3)); % difference in B value
            diffTotal = diff1 + diff2 + diff3; % difference in all the values
            [val,loc] = min(diffTotal);
            if val <= 3 % if the value isn't found in jet
                jetmappedData(r,c) = loc;
            else
                jetmappedData(r,c) = NaN;
            end
    end
    waitbar(r/imageSize,wb,append('Colormapping Values for Image # ',string(1)));
end

I have a lossless image (564x564) generated from MATLAB with a jet-colorbar from a range of [0,1]. The original data is lost and I'm trying to recover it from the image. Here I am converting RGB values to their original datapoints. Over sixteen trillion operations need to be performed per photo... far too many. How can I vectorize this for loop to increase efficiency? (I also have a 3070ti GPU if it would help to utilize).

Thanks!

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Matt J 2022-4-24

Your code cannot be run. Input data has not been attached.

Parker McLeod 2022-4-24

Updated with sample data - good call :)

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Answer 1

Matt J 2022-4-24

在 MATLAB Online 中打开

0 个投票

Eliminating one of the loops should help.

cmap=reshape(colormap_used_in_image',1,3,[]);
for c = 1:imageSize % for each row in the image
    
   D= reshape(data(:,c,:),[],3);
   
   idx=circlePixels(:,c);
   
   D=sum( abs(D(idx,:)-cmap),2);
   
   [val,loc]=min(D,[],3);
   loc(val<120)=nan;
   
   jetmappedData(idx,c)=loc(:);
   
end

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Parker McLeod 2022-4-24

I'll look into those - thanks!

Matt J 2022-4-24

You're welcome, but if they work, please Accept-click the answer.

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