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

### Pramod Bhat (view profile)

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....

Jonas Reber

### Jonas Reber (view profile)

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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### Jonas Reber (view profile)

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');
``` % display image and select region
f = figure;
imshow(img, map);
roi = imfreehand(gca);
wait(roi); ```
``` % get the mask
``` % extract the boundarybox of the ROI
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));
``` % 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:

on 24 Dec 2012

on 24 Dec 2012

hello there how can i exclude ROI and save only RONI which is whole image except selected ROI. plz help

Walter Roberson

on 24 Dec 2012

extract ~ROI

Image Analyst

### Image Analyst (view profile)

on 24 Dec 2012

I don't see any such function as "extract". Where do you get it?

### Image Analyst (view profile)

on 24 Dec 2012
Edited by Image Analyst

### Image Analyst (view profile)

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.