create mask from expansion from xy position in image according to pixel values of threshold t in matlab

To create a binary mask from an image based on a threshold value, you can follow the steps below in Matlab:

1. Load the image in Matlab using the imread() function.

main.m
img = imread('image.png');
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2. Convert the image to grayscale if it is in RGB format using the rgb2gray() function.

main.m
if size(img, 3) == 3
    img = rgb2gray(img);
end
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3. Apply thresholding to convert the grayscale image to a binary image using the im2bw() function.

main.m
t = 0.5;    % threshold value
binaryImg = im2bw(img, t);
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4. Create a binary mask of the same size as the binary image using the false() function and set the pixels above the threshold value to true.

main.m
mask = false(size(binaryImg));
mask(binaryImg > 0) = true;
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5. Expand the mask using the bwmorph() function with the 'dilate' operation to include adjacent pixels as well.

main.m
se = strel('disk', 1);   % structuring element
mask = bwmorph(mask, 'dilate', se);
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The resulting mask will be a binary image containing pixels that are true wherever the pixel value in the original image was above the given threshold value t. The mask can then be used for further image segmentation and processing operations.