# How to recostruct ROI on an image and diaplay it?

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Pramod Bhat on 20 Oct 2011
dear friends, I hav got a set of co ordinates of an ROI. Now i want to reconstruct the ROI on an image and display it. How can i do this? plz help....
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Jonas Reber on 20 Oct 2011
of what kind are these coordinates? is it a list of all pixels in the ROI or is it the marker/vertices of a boundary polygon (e.g., 4 points for a rectangle) or else?

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### Answers (3)

Jonas Reber on 20 Oct 2011
after having read your first question ( http://www.mathworks.com/matlabcentral/answers/18789-how-to-save-an-image-displayed) I think I understand what you try to accomplish. Since you are using imfreehand, I assume you have Image Processing Toolbox.
I have written an example code that opens an image, lets you select a ROI and saves it to a new file with transparent background. have a look at it - you should now be able to do what you are looking for:
%%example code for Pramod Bhat from Jonas:
% get file to be displayed
[FileName,PathName] = uigetfile('*.*','Select the Image');
[img, map] = imread(fullfile(PathName,FileName));
% display image and select region
f = figure;
imshow(img, map);
roi = imfreehand(gca);
wait(roi);
% get the mask
mask = roi.createMask;
% extract the boundarybox of the ROI
S = regionprops(mask,'Boundingbox');
b = floor(S(1).BoundingBox);
% crop the interesting part of the image (bounding box)
imgcut = img(b(2):b(2)+b(4), b(1):b(1)+b(3));
maskcut = double(mask(b(2):b(2)+b(4), b(1):b(1)+b(3)));
% finally, save the image
[FileName,PathName] = uiputfile('*.png','Save the Image As');
imgcutrgb = ind2rgb(imgcut,map);
% note: only what is inside of your ROI will be displayed,
% the rest is set to be transparent:
imwrite(imgcutrgb,fullfile(PathName,FileName),'Alpha', maskcut);
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Mohammad on 24 Dec 2012
Edited: Mohammad on 24 Dec 2012
hello there how can i exclude ROI and save only RONI which is whole image except selected ROI. plz help
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Walter Roberson on 24 Dec 2012
extract ~ROI
Image Analyst on 24 Dec 2012
I don't see any such function as "extract". Where do you get it?

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Image Analyst on 24 Dec 2012
Edited: Image Analyst on 24 Dec 2012
See my BlobsDemo http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862. It finds coins in an image, finds the bounding box of each coin, and then extracts (crops) each bounding box to its own image.
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