Gauss filter is a smoothing filter. The simplest of rectangular smoothing filters is averaging filter.

The smoothing filters are used mostly for noise reduction. Since the noise changes independently from pixel to pixel noises from neighboring pixels compensate each other when summed. The bigger filtration window, the less average intensity of the noise. The side effect of these filters is blurring of image details. The significant flaw of the averaging filter is that all pixels in filter’s mask at any distance from a point being processed have the same effect on the result. More efficient noise reduction can be carried out if the effect of each pixel decreases with the distance. This is the principle of Gauss filter. It uses the following matrix:

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The Gauss filter can be called up from menu Mathematics → Linear filters.