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How to add a boundary into a image for saving

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R G on 27 Jun 2017
Commented: Image Analyst on 19 Jul 2019
As the title, I have an image A and boundary B = bwboundaries(C) if I wanna show it, I can use imshow (A); hold on; visboundaries(B,'Color',''); if I use save button. the image I save don't have the same resolution as my source image so what should I do now?


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Accepted Answer

Gopichandh Danala
Gopichandh Danala on 28 Jun 2017
The problem may just be with either the way you save or with way you used bwboundaries. I wrote some sample code using bwperim to get boundary image of a region then save it in png format to save lossless
img = imread('peppers.png');
figure, imshow(img);
% getting a segment
position = wait(h);
figure,imshow(region); title('Segmented Region');
% use bwperim rather than bwboundaries to get an Image of boundary.
boundImg = uint8(bwperim(rgb2gray(region),4));
boundImg(boundImg ~=0) = max(img(:));
figure, imshow(img + boundImg)
% save image without loosing information..
imwrite(img + boundImg, 'writeImg.png');
% check
read = imread('writeImg.png');
figure, imshow(read)
isequal(read, img + boundImg)


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Warid Islam
Warid Islam on 19 Jul 2019
Hi Gopichandh,
Is it possible to crop the image specified by the boundary above?
Image Analyst
Image Analyst on 19 Jul 2019
Of course. Use find() on region or position, then use max() and min() to find the max and min rows and columns, then use indexing to extract the cropped region.
[rows, columns] = find(region);
row1 = min(rows);
row2 = max(rows);
col1 = min(columns);
col2 = max(columns);
croppedImage = img(row1:row2, col1:col2, :);

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