MATLAB: How to calculate the proportion of the color in Lab coordinate

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I wish to calculate the proportion of the color in an image in the L*a *b space, but I don't how to implement in Matlab code.
The idea is as follow:
  1. load a png file and convert the RGB space to Lab space via "rgb2lab";
  2. divide the L vector into three section: [0, 30], [31, 61], [62, 100], divide the a vector into three sections: [-128, -44], [-43, 41], [42, 127], divide the b vector into three sections: [-128, -44], [-43, 41], [42, 127]. After dividing, we now have 3*3*3=27 sub-sapces in the L*a*b space;
  3. calculate the amount of pixel each L*a*b sub-space contains and the proportion of pixel in each L*a*b sub-space.
Could anyone tell me how to implement the idea above?

Best Answer

Try this example
im = imread('peacock.jpg');
im_lab = rgb2lab(im);
L = round(im_lab(:,:,1));
a = round(im_lab(:,:,2));
b = round(im_lab(:,:,3));
L_partition = {[0, 30], [31, 61], [62, 100]};
a_partition = {[-128, -44], [-43, 41], [42, 127]};
b_partition = {[-128, -44], [-43, 41], [42, 127]};
combs = combvec(1:3,1:3,1:3).';
in_range = @(frame, range) (frame >= range(1)) & (frame <= range(2));
result = cell(size(combs,1), 4);
for i=1:size(combs,1)
    comb = combs(i,:);
    l_part = L_partition{comb(1)};
    a_part = a_partition{comb(2)};
    b_part = b_partition{comb(3)};
    
    pxlSum = sum(in_range(L,l_part).*in_range(a,a_part).*in_range(b,b_part), 'all');
    
    result(i,:) = [{l_part} {a_part} {b_part} {pxlSum}];
end
T = cell2table(result, 'VariableNames', {'L range', 'a range', 'b range', 'pixel count'});
disp(T)
Result:
     L range       a range         b range       pixel count
    _________    ____________    ____________    ___________
     0     30    -128     -44    -128     -44           0   
    31     61    -128     -44    -128     -44           0   
    62    100    -128     -44    -128     -44           0   
     0     30     -43      41    -128     -44        1008   
    31     61     -43      41    -128     -44        6352   
    62    100     -43      41    -128     -44         364   
     0     30      42     127    -128     -44           0   
    31     61      42     127    -128     -44           1   
    62    100      42     127    -128     -44           0   
     0     30    -128     -44     -43      41           0   
    31     61    -128     -44     -43      41           0   
    62    100    -128     -44     -43      41           0   
     0     30     -43      41     -43      41      103521   
    31     61     -43      41     -43      41      518927   
    62    100     -43      41     -43      41      204572   
     0     30      42     127     -43      41           0   
    31     61      42     127     -43      41           0   
    62    100      42     127     -43      41           0   
     0     30    -128     -44      42     127           0   
    31     61    -128     -44      42     127           0   
    62    100    -128     -44      42     127           0   
     0     30     -43      41      42     127           0   
    31     61     -43      41      42     127         314   
    62    100     -43      41      42     127        1293   
     0     30      42     127      42     127           0   
    31     61      42     127      42     127           0   
    62    100      42     127      42     127           0
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