MATLAB image processing technique

I have this 3D array in MATLAB (V: vertical, H: horizontal, t: time frame)

Figures below represent images obtained using imagesc function after slicing the array in terms of t axis

area in black represents damage area and other area is intact

each frame looks similar but has different amplitude

I am trying to visualize only defect area and get rid of intact area

I tried to use 'threshold' method to get rid of intact area as below

NewSet = zeros(450,450,200);

for kk = 1:200
    frame = uwpi(:,:,kk);
    STD = std(frame(:));
    Mean = mean(frame(:));
    for ii = 1:450
        for jj =1:450
            if frame(ii, jj) > 2*STD+Mean 
                % I also tried abs(frame(ii,jj)) but doesn't seem to work
                NewSet(ii, jj, kk) = frame(ii, jj);
            else 
                NewSet(ii, jj, kk) = NaN;            
            end           
        end
    end
end

however, since each frame has different amplitude, result becomes

Is there any image processing method to get rid of intact area in this case?

Thanks in advance

Answer 1

[Image Analyst]

You have to come up with some kind of thresholding algorithm that can get you the corect threshold despite the overall brightness varying. Try imbinarize() or else plot the histogram and look for something that makes sense. Perhaps triangle thresholding will work well if you have a skewed hump in your histogram.