Fig. 6
From: Two dimensional smoothing via an optimised Whittaker smoother
Smoothing a two dimensional histogram: Mammography completely distorted by noise. [Upper left graph:] A breast mammography. An area that seems like a tumour has been marked with a cross. [Upper right graph:] obscured by Gaussian noise, [Lower left graph:] smoothed by Whittaker smoother with optimised penalties and [Lower right graph:] smoothed by Whittaker smoother without optimisation