Median filter: IBA::median_filter and oiiotool --median.

Median filters can be good for removing high-frequency outlier value
noise, but without also blurring edges like a blurring filter would do.

Also, IBA::unsharp_mask and oiiotool --unsharp, if you say "median" for
the kernel, will use a median filter rather than the gaussian blur for
the smoothing step of the unsharp mask. This tends to have the effect of
sharpening small details, while not over-sharpening long edges as the
traditional unsharp mask sometimes does.