Asymmetric Recursive Gaussian Filtering for Space-Variant Artificial Bokeh

This paper describes a recursive filter that handles discontinuous space-variant blur. The two-dimensional space-variant blur is approximated by separable Gaussian filtering along the x- and y-dimensions. Within each dimension, the one-dimensional Gaussian filter is further approximated by a pair of forward and backward Infinite Impulse Response (IIR) filters applied in parallel. By modifying the blur sigma's of the IIR filters as they approach a blur discontinuity, smearing artefacts are eliminated. Different modifications of the forward and backward filter sigma's results in an asymmetric space-variant IIR Gaussian filter. Our asymmetric IIR filters produce visually pleasing background blur for a complicated scene whose contents are at different depths to the camera.