A spatial philtre for which the grey shade assignment at coordinates (x, y) in the transformed image is made by some weighted average (linear combination) of grey shades located to a particular spatial pattern around coordinates (x, y) of the domain image. The linear spatial philtre is often used to change the spatial frequency characteristics of the image. For example, a linear spatial filter, which emphasises high spatial frequencies (high-pass), will tend to sharpen, the edges in an image. A linear spatial filter, which emphasises the low spatial frequencies (low-pass), will tend to blur the image and reduce noise.