Selection of roi for multiple images

I have 50 images in one folder. For one image I can select roi by clicking the mouse but now i need automatic selection of roi for multiple images.How to do this ?

Answer 1

[Rik]

If you want to apply the same ROI to all images: export the ROI as a logical array.

If you want to select a different ROI for each image, generate the list of file names with dir() and loop through the elements.

[swati mane]

Thank you for your reply. I want same roi for all images ..how to do it? Please explain.

[Rik]

What code are you using to create a single ROI? And what release of Matlab are you using? Do you have access to the Image Processing Toolbox as well?

[swati mane]

To select roi , I have to click by mouse .I want the parallelogram shaped roi for my project.

Thanks in advance.

This code I am using for the selection of ROI.(numFiles=50)

%Selection of ROI
 for m=1:1:numFiles;
             
a=imread(imgFiles(m).name);% read RGB image (frame no. 1)
imshow(a);
%Selection of ROI
[r c]=ginput(4);
 
BW=roipoly(a,r,c);
figure;imshow(BW);
ROIArea = bwarea(BW);
[R C]=size(BW);
 
for i=1:R
    for j=1:C
        if BW(i,j)==1
            Out(i,j)=a(i,j);
        else
            Out(i,j)=0;
        
        end
        
    end
end
 
      
figure;imshow(Out,[]);title('Output Image');

[Rik]

The point is to create the ROI only once. Something like the code below should be easy to adapt to your needs.

numFiles=numel(imgFiles);
for m=1:numFiles
    a=imread(imgFiles(m).name);% read RGB image (frame no. 1)
    if m==1
        %generate ROI for first image
        figure(1),clf(1)
        imshow(a);
        %Selection of ROI
        [r,c]=ginput(4);
        ROI=roipoly(a,r,c);
        %ROI is a 2D binary mask
        ROI_RGB=repmat(ROI,1,1,3);
    end
    Out=a;
    Out(~ROI_RGB)=0;%set all pixels outside the mask to 0
    
    figure(m),clf(m)
    imshow(Out,[])
    title(sprintf('Output Image (%d)',m))
end

[swati mane]

Thank you very much !!!

[HARISH KUMAR]

@Rik Dear Sir/madam,

I am also facing problem,I have 12 images in one folder. For one image I can select roi by clicking the mouse but now i need automatic selection of roi for remaing 12 images.

I want rectangle ROI, i have image proceesing toolbox, R2022b version i am using.

Below is code i am using to creat ROI

Sample=3; % which sample to analyse
FileNames=ImageNamesLoad(Sample); % load appropriate images for chosen sample
A = imread(FileNames{1});
figure, imshow(A);
h = imrect;
position = wait(h); %Pause until user double clicks on rectangle
%position contains [x y width height]
startx = position(1);
endx = position(1)+position(3);
starty = position(2);
endy = position(2)+position(4);
%Use the coordinates to grab a submatrix of A
B = A(starty:endy, startx:endx); % no. of rows,no of columns
imwrite(B, 'C:\Users\Admin\Documents\MATLAB\DIC Challenge 1.0\Sample3\my_image123.jpg');

Please guide me asap.

Thanks in advance

[Rik]

You mean you want to apply this same ROI to the other images? Did you follow the advice in my answer?

Have a read here and here. It will greatly improve your chances of getting an answer.

Feel free to @-mention me in a comment to your own question. Make sure you read and understood both pages I linked to.

[HARISH KUMAR]

@Rik Thank you your response. Yes, you are right. I want to apply same ROI to the other images.

[HARISH KUMAR]

@Rik Thanks for guidance on posting questions.

I have followed the advice in your answer. I ran it and i am getting error.

I need to get rectangular ROI for all images Please guide me.

I am attaching error screenshot and code below please look into it.

Sample=3; % which sample to analyse
%FileNames=ImageNamesLoad(Sample); % load appropriate images for chosen sample
numFiles = numel(FileNames);
for m = 1:numFiles
    a = imread(FileNames{m});
    if m==1
        figure(1), clf(1)
        imshow(a)
        [r,c] = ginput(4);
        
        ROI=roipoly(a,r,c);
        %ROI = imrect;
        %ROI is a 2D binary mask
        ROI_RGB=repmat(ROI,1,1,3);
    end
    Out=a;
    Out(~ROI_RGB)=0;%set all pixels outside the mask to 0
    
    figure(m),clf(m)
    imshow(Out,[])
    title(sprintf('Output Image (%d)',m))

end

Thanks in advance

[Rik]

Based on this error message I expect the image sizes are not the same. I cannot give you a solution, since that depends on what you intend to do.

[HARISH KUMAR]

okay, Thank you.

I will into it once.

[Image Analyst]

Perhaps the poorly-named a is a gray scale image, not a color image.