Use the 'crop' option of imrotate() if it is acceptable to throw away the part of the image that does not fit within a horizontal / vertically aligned rectangle.
If you need the entire image to be preserved but without the border, then one way of doing it is to pad the image with NaN before rotating, and then for each rotation, locate the NaN and set those locations to be transparent in the Alpha parameter of image() or imshow()
Another approach is to create a hgtransform and parent the image to it, and then use makehgtransform to create the appropriate rotation matrix. This method does not use imrotate() at all, and does not require dealing with Alpha. This technique is best if you only need to display the rotated image, rather than needing to process the rotated image.
