A weighted average algorithm for edge-preserving smoothing on MRI images

Medical images such as MRI images normally have smooth edges and round corners, but the existing general edge-preserving smoothing algorithms often result in coarse edges and sharp corners. A new image smoothing algorithm, based on a filter utilizing the weighted average of 21 average pixel values in 21 neighborhood subregions in a 3x3 square around the center pixel, is proposed to deal with the problem. Subregions with the center point being smoothed on its sharp corner are avoided from selection to make the edges being preserved smooth and round. During the smoothing process, each subregion is assigned a weight according to its homogeneousness which is evaluated by the variance of its pixel values. The weighted average of averages for all subregions is assigned to the center pixel being smoothed. The more homogeneous neighborhood has more influence on the center pixel, so that the edges can be well preserved. But contributions from all neighborhoods are also taken into consideration especially when their homogeneousness is largely equal so that the resultant areas are smoother. An evaluation of the algorithm on the simulated MRI images is carried out. Experimental results showed that the new algorithm can smooth the MRI images better while keeping the edges better compared with the existing smoothing algorithms.