how to set x-axes in a histogram of gray scale image and how to see if the image is saturated (12 bit)

Hi, I am trying to plot a histogram of a unit16 picture (actually its a 12 bit image) and plot the gray scale. I am interested to see if the image gets saturated or not (again 12 bit image). Which btw i find weird its only the first 12 that is populated with a very huge number. Why is that? i only have a image of an laser lobe in the picture.

So my question is, because the histgram looks weird in the appdesigner plot, i think it doesn't seem to adjust to the pixel count in the picture in the x-scale. Y-scale has a huge number. What does this represent? How can i see if the picture is staurated? 2^12 = 4096 should be the max intensity of the image. but I get maxcount = 2123959

Any ideas how set the x-axes as well?

Bits of the code (from the appdesigner)

            % Create histograms based on number of color channels
            switch size(im,3)
                case 1
                    % Display the grayscale image
                    imagesc(app.Image,im);
                    
                    % Plot all histograms with the same data for grayscale
                    hist = histogram(app.HistAxes,im, 'FaceColor',[1 0 0],'EdgeColor', 'none');
                    %[counts,binLocations] = imhist(im);
                    
                otherwise
                    % Error when image is not grayscale or truecolor
                    uialert(app.UIFigure, 'Image must be grayscale.', 'Image Error');
                    return;
            end
                % Get largest bin count
                maxim = max(hist.BinCounts);
                maxcount = max([maxim])
                
                % Set y axes limits based on largest bin count
                app.HistAxes.YLim = [0 maxcount];
                app.HistAxes.YTick = round([0 maxcount/2 maxcount], 2, 'significant');  

Answer 1

[Image Analyst]

If the maxcount is 2123959, then that just means that the highest bin has a y value of 2123959. That bin could be anywhere along the x (gray scale) axis. If you look at the bin for 4095, and there are some values in there, and you have 4096 bins, then yes, some pixels are saturated. It is also possible to saturate at a gray level value that is not the maximum for the number of bits you're using for a variety of reasons. So you should look to see if the last bin or two is much higher than the bins just a little darker than those.

[Happy PhD]

@Image Analyst There seem to be 770 binCounts, each with its own value. The image is about the size of 1200 x 900 pixels, What does the number 770 represent and what is 2123959? If I plot the intensity profile the maximum pixel value is below the intensity value 2^12 (see image below),.. that is what i don't get what the histrogram shows.

K>> maxcount

maxcount =

     2123959
     
K>> hist.BinCounts(1:20)

ans =

  Columns 1 through 6

        9199     2123959      124940       29258       10904        5065

  Columns 7 through 12

        2933        1943        1385        1049         778         730

  Columns 13 through 18

         513         454         505         377         328         264

  Columns 19 through 20

         300         280  //
 
  Columns 745 through 750

           0           1           0           0           1           1

  Columns 751 through 756

           1           0           0           0           0           0

  Columns 757 through 762

           0           0           0           0           0           0

  Columns 763 through 768

           0           0           0           0           0           0

  Columns 769 through 770

           0           1

Around 679 it becomes just zero and ones.

The image is 12 bit due to the camera only gives 12 bit snapshots via gigecam and snapshot function but MATLAB converts the image matrix to 16 bit.

Answer 2

[Cris LaPierre]

Have you tried imhist?

[Happy PhD]

It doesn't seem to be working plotting it in appdesigner and it doesn't show much. I can barely see any lines.

Answer 3

[Steven Lord]

You haven't specified the bin edges, the bin method, or the bin width in your histogram call. Because of this I'd be concerned that your bins may be wide enough that they count multiple values in your data.

x = randi(1e4, 1, 1e6);
subplot(2, 1, 1)
h1 = histogram(x);
subplot(2, 1, 2)
h2 = histogram(x, 'BinMethod', 'integers'); % Each integer gets its own bin

fprintf("The bins in histogram h1 are %d units wide, " + ...
        "while the bins in histogram h2 are %d unit wide.\n", h1.BinWidth, h2.BinWidth)

The bins in histogram h1 are 100 units wide, while the bins in histogram h2 are 1 unit wide.

fprintf("The first bin in h1 is the range [%d, %d) " + ...
        "while the first bin in h2 is the range [%g, %g).\n", ...
        h1.BinEdges(1:2), h2.BinEdges(1:2))

The first bin in h1 is the range [0, 100) while the first bin in h2 is the range [0.5, 1.5).