How to stock a previously calculated variables so I can reuse them to draw a curve?

Here is my code :

        clc;
        close all;

        %Read color image and convert it to gray level image
        %Display the original image
        imagefiles = dir('*.jpg');      
        nfiles = length(imagefiles);    % Number of image files found
        for ii=1:nfiles
            currentfilename = imagefiles(ii).name;
            I = imread(currentfilename);
            myimage = rgb2gray(I);
            subplot(2,2,1);
            imshow(myimage);title('Original Image');
            treshold = [0.08] ;
            sigma = 1;
            %Apply Sobel Operator
            %Display both Edges
            sobel = edge(myimage,'sobel',treshold,'both');
            subplot(2,2,2);
            imshow(sobel,[]);title('Sobel');
            %Apply Canny Operator
            cannyedge = edge(myimage,'Canny',treshold,sigma);
            subplot(2,2,3);
            imshow(cannyedge,[]);title('Canny edge');
            %Calcul du PSNR
            A = im2double(myimage);
            B = im2double(sobel);
            C = im2double(cannyedge);
            error_diff = A - B;
            PSNRsobel = 20*log10(1/(sqrt(mean(mean(error_diff.^2)))));
            fprintf('PSNRsobel = +%5.2f dB\n',PSNRsobel);
            error_diff = A - C;
            PSNRcanny = 20*log10(1/(sqrt(mean(mean(error_diff.^2)))));
            fprintf('PSNRcanny = +%5.2f dB\n',PSNRcanny);
            figure;
            x = [];
            y = [];

            for i = 1:nfiles
                x = [x,PSNRsobel];
                y = [y,PSNRcanny];
                y1 = linspace(0,1,nfiles);
                plot(y1(i),x(i),y1(i),y(i));
            end
            %Calcul du SSIM
            [ssimsobel] = ssim(A,B); 
            fprintf('The SSIM sobel value is %0.4f.\n',ssimsobel);
            [ssimcanny] = ssim(A,C); 
            fprintf('The SSIM Canny value is %0.4f.\n',ssimcanny);
            figure;
            Y1 = [];
            Y2 = [];
            for i = 1 : nfiles
                X = linspace(0,1,nfiles);
                Y1 = [Y1,ssimsobel;
                Y2 = [Y2,ssimcanny];
                plot(X(i),Y1(i),X(i),Y2(i));
            end
        end

I want to get the values of PSNRsobel and PSNRcanny of all images in one array and then plot them and the same thing with the values of ssimsobel and ssimcanny. Please can someone help me out?

Answer 1

[Stephan]

Hi,

this should do the job:

%Read color image and convert it to gray level image
%Display the original image
imagefiles = dir('*.jpg');
nfiles = length(imagefiles);    % Number of image files found
stored_values = zeros(nfiles,4); % Preallocate the array for saving the values
for ii=1:nfiles
    currentfilename = imagefiles(ii).name;
    I = imread(currentfilename);
    myimage = rgb2gray(I);
    subplot(2,2,1);
    imshow(myimage);title('Original Image');
    treshold = 0.08;
    sigma = 1;
    %Apply Sobel Operator
    %Display both Edges
    sobel = edge(myimage,'sobel',treshold,'both');
    subplot(2,2,2);
    imshow(sobel,[]);title('Sobel');
    %Apply Canny Operator
    cannyedge = edge(myimage,'Canny',treshold,sigma);
    subplot(2,2,3);
    imshow(cannyedge,[]);title('Canny edge');
    %Calcul du PSNR
    A = im2double(myimage);
    B = im2double(sobel);
    C = im2double(cannyedge);
    error_diff = A - B;
    PSNRsobel = 20*log10(1/(sqrt(mean(mean(error_diff.^2)))));
    fprintf('PSNRsobel = +%5.2f dB\n',PSNRsobel);
    error_diff = A - C;
    PSNRcanny = 20*log10(1/(sqrt(mean(mean(error_diff.^2)))));
    fprintf('PSNRcanny = +%5.2f dB\n',PSNRcanny);
    stored_values(ii,1) = PSNRsobel;  % All PSNRsobel values in 1. column
    stored_values(ii,2) = PSNRcanny;  % All PSNRcanny values in 2. column
    %Calcul du SSIM
    ssimsobel = ssim(A,B);
    fprintf('The SSIM sobel value is %0.4f.\n',ssimsobel);
    ssimcanny = ssim(A,C);
    fprintf('The SSIM Canny value is %0.4f.\n',ssimcanny);
    stored_values(ii,3) = ssimsobel;  % All ssimsobel values in 3. column
    stored_values(ii,4) = ssimcanny;  % All ssimcanny values in 4. column
end

stored_values is an array of size [number files x 4]. For every Picture there is a new row, corresponding to the filenumber in imagefiles. The 4 columns in each row save the values for every file. Then you can plot the values with:

% Plot PSNRsobel and PSNRcanny
figure(1)
plot(1:nfiles, stored_values(:,1),1:nfiles,stored_values(:,2))
% Plot ssimsobel and ssimcanny
figure(2)
plot(1:nfiles, stored_values(:,3),1:nfiles,stored_values(:,4))

Best regards

Stephan

[Nour Sd]

Thank you a lot for your prompt response, as I can understand that (stored_values) save values in 4 different rows so my question now how can I reuse the first and second row to draw a plot? I've added plot as showed below in the code but I've got 10 empty figures with just 2 axis as showed in the attached image and I want to get just 2 figures one that shows PSNRsobel and PSNRcanny in the same plot according to the number of imagefiles and another one that shows the ssimsobel and ssimcanny according to the number of imagefiles. Thank you.

stored_values(ii,1) = PSNRsobel;  % All PSNRsobel values in 1. column
      stored_values(ii,2) = PSNRcanny;  % All PSNRcanny values in 2. column
      figure;
      plot(stored_values(ii,1),stored_values(ii,2));
      x = [];
      y = [];

[Stephan]

i would recommend to do this not inside the loop. for the values of PNSRsobel and PSNRcanny from the first two pictures use:

plot(1:2,stored_values(1:2,1),1:2,stored_values(1:2,2))

or - maybe better:

scatter(1:2,stored_values(1:2,1),1:2,stored_values(1:2,2),'or')

at the end of your code

[Nour Sd]

Thank you very much! Plot has given a result with this code after the end of the loop

% Plot PSNRsobel and PSNRcanny
figure()
plot(1:nfiles, stored_values(:,1),1:nfiles,stored_values(:,2))
% Plot ssimsobel and ssimcanny
figure()
plot(1:nfiles, stored_values(:,3),1:nfiles,stored_values(:,4))

Excuse me for being slow but that's because I'm still not used to matlab. Now the problem is solved but still just one more thing and it's that only the processing of the last image is shown (the original, the filtred with sobel and the filtred with canny in one figure) and I want the processing of all the image files to be shown each one in a figure. (PS: It was working before I add the plot). Thank you.

[Stephan]

I will be back - give me some hours. Please accept helpful answers.

So i understood that if you have for example 5 pictures you want 1 figure with 5x3 pictures in it. In every row the same picture with column 1 the original, column 2 the sobel and column 3 the canny - correct?

[Nour Sd]

Yes I accepted your answer and it solved my problem. For example, now in my file I have 9 images so after running the code you wrote above I get the figure shown in the attached image with the two other figures of the plot. I want to get the 8 other figures that show the processing of the rest of the images of the file. Thank you a lot for you precious help.

[Stephan]

Check this one - it gives you the expected result in 3 different figures:

%Read color image and convert it to gray level image
%Display the original image
imagefiles = dir('*.jpg');
nfiles = length(imagefiles);    % Number of image files found
stored_values = zeros(nfiles,4); % Preallocate the array for saving the values
for ii=1:nfiles
    currentfilename = imagefiles(ii).name;
    I = imread(currentfilename);
    myimage = rgb2gray(I);
    figure(1)
    subplot(nfiles,3,3*ii-2);
    imshow(myimage);title('Original Image');
    treshold = 0.08;
    sigma = 1;
    %Apply Sobel Operator
    %Display both Edges
    sobel = edge(myimage,'sobel',treshold,'both');
    subplot(nfiles,3,3*ii-1);
    imshow(sobel,[]);title('Sobel');
    %Apply Canny Operator
    cannyedge = edge(myimage,'Canny',treshold,sigma);
    subplot(nfiles,3,3*ii);
    imshow(cannyedge,[]);title('Canny edge');
    %Calcul du PSNR
    A = im2double(myimage);
    B = im2double(sobel);
    C = im2double(cannyedge);
    error_diff = A - B;
    PSNRsobel = 20*log10(1/(sqrt(mean(mean(error_diff.^2)))));
    fprintf('PSNRsobel = +%5.2f dB\n',PSNRsobel);
    error_diff = A - C;
    PSNRcanny = 20*log10(1/(sqrt(mean(mean(error_diff.^2)))));
    fprintf('PSNRcanny = +%5.2f dB\n',PSNRcanny);
    stored_values(ii,1) = PSNRsobel;  % All PSNRsobel values in 1. column
    stored_values(ii,2) = PSNRcanny;  % All PSNRcanny values in 2. column
    %Calcul du SSIM
    ssimsobel = ssim(A,B);
    fprintf('The SSIM sobel value is %0.4f.\n',ssimsobel);
    ssimcanny = ssim(A,C);
    fprintf('The SSIM Canny value is %0.4f.\n',ssimcanny);
    stored_values(ii,3) = ssimsobel;  % All ssimsobel values in 3. column
    stored_values(ii,4) = ssimcanny;  % All ssimcanny values in 4. column
end

% Plot PSNRsobel and PSNRcanny
figure(2)
plot(1:nfiles, stored_values(:,1) ,1:nfiles,stored_values(:,2))
% Plot ssimsobel and ssimcanny
figure(3)
plot(1:nfiles, stored_values(:,3), 1:nfiles,stored_values(:,4))

[Nour Sd]

it's almost good but it's not clear, look how is it shown.

it should be each 3 in a figure apart so they will be clear. like this example: here one picture.

and here another one

Thank you for your time and understanding.

[Stephan]

I see, 5 figures for 5 pictures is what you want

[Nour Sd]

I want the number of imagefiles of figures. If for example I have 5 pictures like you said I will get 5 figures in each one there's the original image, sobel, and canny edge like it's shown in the previous picture. Thank you.

[Stephan]

Try:

%Read color image and convert it to gray level image
%Display the original image
imagefiles = dir('*.jpg');
nfiles = length(imagefiles);    % Number of image files found
stored_values = zeros(nfiles,4); % Preallocate the array for saving the values
for ii=1:nfiles
    currentfilename = imagefiles(ii).name;
    I = imread(currentfilename);
    myimage = rgb2gray(I);
    figure(ii)
    subplot(2,2,1);
    imshow(myimage);title('Original Image');
    treshold = 0.08;
    sigma = 1;
    %Apply Sobel Operator
    %Display both Edges
    sobel = edge(myimage,'sobel',treshold,'both');
    subplot(2,2,2);
    imshow(sobel,[]);title('Sobel');
    %Apply Canny Operator
    cannyedge = edge(myimage,'Canny',treshold,sigma);
    subplot(2,2,3);
    imshow(cannyedge,[]);title('Canny edge');
    %Calcul du PSNR
    A = im2double(myimage);
    B = im2double(sobel);
    C = im2double(cannyedge);
    error_diff = A - B;
    PSNRsobel = 20*log10(1/(sqrt(mean(mean(error_diff.^2)))));
    fprintf('PSNRsobel = +%5.2f dB\n',PSNRsobel);
    error_diff = A - C;
    PSNRcanny = 20*log10(1/(sqrt(mean(mean(error_diff.^2)))));
    fprintf('PSNRcanny = +%5.2f dB\n',PSNRcanny);
    stored_values(ii,1) = PSNRsobel;  % All PSNRsobel values in 1. column
    stored_values(ii,2) = PSNRcanny;  % All PSNRcanny values in 2. column
    %Calcul du SSIM
    ssimsobel = ssim(A,B);
    fprintf('The SSIM sobel value is %0.4f.\n',ssimsobel);
    ssimcanny = ssim(A,C);
    fprintf('The SSIM Canny value is %0.4f.\n',ssimcanny);
    stored_values(ii,3) = ssimsobel;  % All ssimsobel values in 3. column
    stored_values(ii,4) = ssimcanny;  % All ssimcanny values in 4. column
end

% Plot PSNRsobel and PSNRcanny
figure(nfiles+1)
plot(1:nfiles, stored_values(:,1) ,1:nfiles,stored_values(:,2))
% Plot ssimsobel and ssimcanny
figure(nfiles+2)
plot(1:nfiles, stored_values(:,3), 1:nfiles,stored_values(:,4))

I think we got it now.

[Nour Sd]

I really don't know how to thank you enough! It finally works! Thank you a lot! The best version is here now:

clc;
close all;

%Read color image and convert it to gray level image
%Display the original image
imagefiles = dir('*.jpg');
nfiles = length(imagefiles);    % Number of image files found
stored_values = zeros(nfiles,4); % Preallocate the array for saving the values
for ii=1:nfiles
    currentfilename = imagefiles(ii).name;
    I = imread(currentfilename);
    myimage = rgb2gray(I);
    figure(ii)
    subplot(2,2,1);
    imshow(myimage);title('Original Image');
    treshold = 0.08;
    sigma = 1;
    %Apply Sobel Operator
    %Display both Edges
    sobel = edge(myimage,'sobel',treshold,'both');
    subplot(2,2,2);
    imshow(sobel,[]);title('Sobel edge');
    %Apply Canny Operator
    cannyedge = edge(myimage,'Canny',treshold,sigma);
    subplot(2,2,3);
    imshow(cannyedge,[]);title('Canny edge');
    %Calcul du PSNR
    A = im2double(myimage);
    B = im2double(sobel);
    C = im2double(cannyedge);
    error_diff = A - B;
    PSNRsobel = 20*log10(1/(sqrt(mean(mean(error_diff.^2)))));
    fprintf('PSNRsobel = +%5.2f dB\n',PSNRsobel);
    error_diff = A - C;
    PSNRcanny = 20*log10(1/(sqrt(mean(mean(error_diff.^2)))));
    fprintf('PSNRcanny = +%5.2f dB\n',PSNRcanny);
    stored_values(ii,1) = PSNRsobel;  % All PSNRsobel values in 1. column
    stored_values(ii,2) = PSNRcanny;  % All PSNRcanny values in 2. column
    %Calcul du SSIM
    ssimsobel = ssim(A,B);
    fprintf('The SSIM sobel value is %0.4f.\n',ssimsobel);
    ssimcanny = ssim(A,C);
    fprintf('The SSIM Canny value is %0.4f.\n',ssimcanny);
    stored_values(ii,3) = ssimsobel;  % All ssimsobel values in 3. column
    stored_values(ii,4) = ssimcanny;  % All ssimcanny values in 4. column
end
% Plot PSNRsobel and PSNRcanny
figure(nfiles+1)
plot(1:nfiles, stored_values(:,1) ,1:nfiles,stored_values(:,2))
% Add a legend and axis labels
title('PSNR of images')
legend('PSNRSobel', 'PSNRCanny')
xlabel('Number of images')
ylabel('PSNR')
% Plot ssimsobel and ssimcanny
figure(nfiles+2)
plot(1:nfiles, stored_values(:,3), 1:nfiles,stored_values(:,4))
% Add a legend and axis labels
title('SSIM of images')
legend('SSIMSobel', 'SSIMCanny')
xlabel('Number of images')
ylabel('SSIM')

Thank you again Stephan Jung!