change the .png for whatever file extension you are using. Are your image greyscale? If not, it might not make sense to background mean subtract different color channels of data.
myDir = '';
fileList = dir(fullfile(myDir,'*.png'));
nfiles = length(fileList);
totalValuePerImage = zeros(nfiles,1);
nPixelsPerImage = zeros(nfiles,1);
for ifile = 1:length(fileList)
I = imread(fullfile(myDir,fileList(ifile).name));
totalValuePerImage(ifile) = sum(I(:));
nPixelsPerImage = double(numel(I));
end
globalMean = sum(totalValuePerImage)/sum(nPixelsPerImage);
for ifile = 1:length(fileList)
I = imread(fullfile(myDir,fileList(ifile).name));
[~,fileLeaf,~] = fileparts(fileList(ifile).name);
I = double(I) - globalMean;
save([fileLeaf '.mat'],'I');
end
