Image rotation is performed by computing the inverse transformation for every destination pixel. Output pixels are computed using bilinear interpolation. RGB images are computed by evaluating one color plane at a time. There are no gamma corrections so purists might want to correct for image gamma before and after rotation.
An original image that you might want to rotate.
A five degree counter-clockwise rotation with bilinear interpolation produces an image that is slightly larger than the original surrounded by black regions that do not map to any pixels in the original image.
Igor Pro 8
Igor XOP Toolkit
Igor NIDAQ Tools MX