The discrete Fourier transform (DFT), used by the deblurring functions, assumes that the frequency pattern of an image is periodic. This assumption creates a high-frequency drop-off at the edges of images. In the figure, the shaded area represents the actual extent of the image; the unshaded area represents the assumed periodicity.
This high-frequency drop-off can create an effect called boundary related ringing in deblurred images. In this figure, note the horizontal and vertical patterns in the image.
To avoid ringing, use the edgetaper function to preprocess your images before passing them to the deblurring functions. The edgetaper function removes the high-frequency drop-off at the edge of an image by blurring the entire image and then replacing the center pixels of the blurred image with the original image. In this way, the edges of the image taper off to a lower frequency.