Pixel value difference histogram of two images

Suppose I have two matrices for cover and stego images. I want to draw the pixel value difference histogram as shown in the above figure. I am facing problem in setting edges. I need the x-label as [-20 -15 -10 -5 0 5 10 15 20] as shown in the above figure. I could not able to show the Legents as the above figure. Please help me.....

edges = [-20 -5:0:5 20];

histogram(cover,edges,'DisplayStyle','stairs');

hold on;

histogram(stego,edges,'DisplayStyle','stairs');

legend('Cover Image');

legend('Stego Image');

Answer 1

[Darshak]

Hi @PRATAP MANDAL,

From the image you have provided, the plot you are looking for is for the centre of histogram bins not the histogram itself, due to which you are not getting the expected plot and the legend. You can use the code given below to do calculate the bin centers and plot them to generate the plot shown as in the given image:

edges = [-20, -15, -10, -5, 0, 5, 10, 15, 20];
  
 
  
% Calculate histogram data manually
  
[coverCounts, ~] = histcounts(cover, edges);
  
[stegoCounts, ~] = histcounts(stego, edges);
  
 
  
% Calculate bin centers
  
binCenters = (edges(1:end-1) + edges(2:end)) / 2;
  
 
  
plot(binCenters, coverCounts, 'ro-', 'MarkerFaceColor', 'r');
  
hold on;
  
plot(binCenters, stegoCounts, 'bs-', 'MarkerFaceColor', 'b');
  
legend('Cover Image', 'Stego Image');
  
xticks(edges);
  
xlabel('Prediction Error');
  
ylabel('Frequency');
  
hold off;

You can explore the “plot” function in the given documentation page – https://www.mathworks.com/help/releases/R2021a/matlab/ref/plot.html