MATLAB: ‘Image’ or ‘ConvexImage’ of regionprops into a grayscale instead of a binary one

MATLABregionprops

How can i create the image that makes the propertie 'Image' or 'ConvexImage' of regionprops into a grayscale instead of a binary one? I have tryed with PixelValues but it doesn't give me the same number of pixels…

Best Answer

You cannot. regionprops defines both of those properties as returning a binary mask.

One way to proceed is to ask for BoundingBox as well as Image, and imcrop() your original image according to the bounding box, and then .* the result with the binary mask from the Image property. The result would be 0 for locations that were 0 originally or were outside the boundary, and the grayscale value otherwise.

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Use regionprops with 'PixelList' property:

Locations of pixels in the region, returned as a p-by-Q matrix. Each row of the matrix has the form [x y z ...] and specifies the coordinates of one pixel in the region.

If you need those relative to their bounding box for some reason, then you can subtract the bounding box and add 1:

relative_indices = arrayfun(@IDX) bsxfun(@minus, Properties(IDX).PixelList, Properties(IDX).BoundingBox(1:2))+1, 1:length(Properties), 'Uniform', 0);

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Make a mask from the circle, then

hasBlackInside = min(grayImage(mask)) == 0;

hasBlackInside will be true if there is at least one black pixel inside the mask.

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