matlab percentage always showing zero

I want to calculate how much image has higher 'red channel entropy' than 'blue channel entropy'. i wanted the result in percentage. But it is always showing zero. But i have checked random single image, and some of them satisfy the conditon. how can i solve this error?

folder = 'F:\raw-890\';
filePattern = fullfile(folder, '*.png');
myFiles = dir(filePattern); % the folder inwhich ur images exists

for k = 1 : length(myFiles)
  fullFileName = fullfile(folder, myFiles(k).name);
   I= imread(fullFileName);
Red = I(:,:,1);
Green = I(:,:,2);
Blue = I(:,:,3);

%I = I(:); % Vectorization of RGB values
p = imhist(Red); % Histogram
p(p == 0) = [ ];% remove zero entries in p
p = p ./ numel(I); % normalize p so that sum(p) is one.
Er = round(-sum(p.*log2(p)),3);

p = imhist(Blue); % Histogram
p(p == 0) = [ ];% remove zero entries in p
p = p ./ numel(I); % normalize p so that sum(p) is one.
Eb = round(-sum(p.*log2(p)),3);

end
percentage = sum(Er > Eb) / numel(Er) * 100; % Percentage of images with red entropy higher than blue entropy
disp(['Percentage of images with red entropy higher than blue entropy: ' num2str(percentage)])

Answer 1

[Jan]

After: p = p ./ numel(I), sum(p) is not 1.0, but 0.333. You do not want to divide by numel(I), but by numel(Red), or equivalently: size(I,1)*size(I,2).

I = rand(640, 480, 3);

Red   = I(:,:,1);
Green = I(:,:,2);
Blue  = I(:,:,3);

p = imhist(Red);      % Histogram
p(p == 0) = [];       % remove zero entries in p
p = p ./ numel(Red);  % normalize p so that sum(p) is 1,0
Er = round(-sum(p .* log2(p)), 3)

Er = 7.9990

p = imhist(Blue);      % Histogram
p(p == 0) = [];        % remove zero entries in p
p = p ./ numel(Blue);  % normalize p so that sum(p) is one.
Eb = round(-sum(p .* log2(p)), 3)

Eb = 7.9990

You see, that the results are not 0 for random inputs.

If you want to collect the data, follow Scott's advice:

nFile = numel(myFiles);
Er = zeros(1, nFile);
Eb = zeros(1, nFile);
for k = 1 : nFile
   ...
   Er(k) = round(-sum(p .* log2(p)), 3);
   ...
   Eb(k) = round(-sum(p .* log2(p)), 3);       
end

percentage = sum(Er > Eb) / nFile * 100;
fprintf('Percentage of images with red entropy > blue entropy: %f\n', percentage);