Possible Duplicate:
Raster generalization - buffers in rasters, expand pixels?
I have a 1m LIDAR DEM which I'm manipulating in QGIS.
I'd like to smooth the DEM, such as by having each pixel become the average of its 3x3 neighbourhood (a low-pass filter?).
Is there a way to do this in QGIS?
r.mfilter
andr.neighbors
directly solve your question as asked. I found this answer (among many others) through the search linked in my comment and offered it as one of many possible duplicates because it provides a broad range of solutions to your question.