'cameraman.tif' and 'coins.png' are both grayscale, meaning your im is a NxM array and your code works.
For any image with color, such as 'pears.png', im is a NxMx3 array. Per the documentation for size():
"When dim is not specified and fewer than ndims(A) output arguments are listed, then all remaining dimension lengths are collapsed into the last argument in the list. For example, if A is a 3-D array with size [3 4 5], then [sz1,sz2] = size(A) returns sz1 = 3 and sz2 = 20."
Therefore, columns equals M*3, not M, and you get the error.
If you are open to the possibility of im being a 3D array, i.e.
[rows, columns, ~] = size(Y);
instead of
[rows, columns] = size(Y);
then you won't get an error for images with color. However, to be honest, I've got no idea if this one change alone would give you the correct results. I believe making this change alone would pass each channel of your image (red, green, and blue) through each of your filters separately. Maybe that is correct?
