Radius: this control selects the gliding window size used for the filter. Larger values do not increase the amount of time needed to filter each pixel in the image but can cause blurring. This window moves across the image, and the color in it is smoothed to remove imperfections. In any case it must be about the same size as the noise granularity or somewhat more. If it is set higher than necessary, then it can cause unwanted blur.
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