Linear (convolution) filters consist of a matrix with values and a gain factor. When considering a linear filter of size 3x3, the 9 matrix values are multiplied with 9 pixel values in the input raster map, this is summed and then multiplied with the gain factor. The result is assigned to the center pixel in the output map.

Standard linear filters:

The following standard filters are linear filters: AVG3x3, EDGESENH, LAPLACE, SHADOW. Also the standard gradient filters are linear filters: DFDX, DFDY, DFDDN, DFDUP, D2FDX2, D2FDY2, D2FDXDY.

User-defined linear filters:

You can create, edit and store your own linear filters, for instance from the Filter : dialog box, through the File menu in the Main window or by clicking the NewFilter item in the Operation-list or the Operation-tree. For more information, refer to the Create Filter dialog box and the (Linear) Filter editor. You need to specify the size of your filter, fill out the values in the matrix and specify a gain factor. Experienced users may wish to experiment with the definition of a linear filter by an expression on the command line. For more information on using standard and user-defined linear filters, refer to User-defined linear filters.

Furthermore, you can interactively define an Average filter in the Filter dialog box or by an expression on the command line. For more information, refer to User-defined average filters.

See also:

Filters : standard filters

Filters : user-defined linear filters

Filters : user-defined average filters

Filter (operation)