A new family of non--linear filters for background subtraction of   wide--field surveys
  In this paper the definitions and the properties of a newle dedicated set of high-frequency filters based on smoothing-and-clipping are briefly described. New applications for reduction of wide--field 2048x2048 CCD spectral and direct images of a new deep survey KISS (KPNO International Spectral Survey) are also presented. The developed software is available both as a C subroutine and as an installed MIDAS environment command. 
V.S.Shergin, A.Yu.Kniazev, V.A.Lipovetsky (Special Astrophysical   Observatory, Russia)