How to split a binary mask in square 1000x1000 and keep only ROI?

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France
France on 22 Oct 2019
Commented: Image Analyst on 23 Oct 2019
Hello! I have got a binary mask (0 background and 1 inside the ROI) and I need to split it in square 1000x1000 and keep only square where there is ROI, e.g. where sum of pixel is more than 80% Many thanks in advance

Answers (1)

Image Analyst
Image Analyst on 22 Oct 2019
Use indexing. For example
croppedImage = originalImage(row1:row2, column1:column2, :);
You need to figure out what row1, row2, column1, and column2 are. Should be easy.
Not sure of what your definition of ROI is. There are lots and lots of squares in the image that contain 80% of the number of pixels in the image.
  2 Comments
Image Analyst
Image Analyst on 23 Oct 2019
Fill, take largest blob, find centroid, crop.
mask = imfill(mask, 'holes');
mask = bwareafilt(mask, 1);
props = regionprops(mask, 'Centroid');
col1 = round(props.Centroid(1) - 500);
col2 = col1 + 499;
row1 = round(props.Centroid(2) - 500);
row2 = row1 + 499;
croppedImage = originalImage(row1 : row2, col1 : col2, :);
Or, if you want the blob to be 80%, do this
mask = imfill(mask, 'holes');
mask = bwareafilt(mask, 1);
props = regionprops(mask, 'Centroid');
width = sqrt(props.Area / 0.8);
halfWidth = width / 2;
col1 = round(props.Centroid(1) - halfWidth);
col2 = col1 + width - 1;
row1 = round(props.Centroid(2) - halfWidth);
row2 = row1 + width - 1;
croppedImage = originalImage(row1 : row2, col1 : col2, :);
It will probably not be 1000x1000 though.

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