This tool performs a median filter on a raster image. Median filters, a type of low-pass filter, can be used to emphasize the longer-range variability in an image, effectively acting to smooth the image. This can be useful for reducing the noise in an image. The algorithm operates by calculating the median value (middle value in a sorted list) in a moving window centred on each grid cell. Specifically, this tool uses the efficient running-median filtering algorithm of Huang et al. (1979). The median value is not influenced by anomolously high or low values in the distribution to the extent that the average is. As such, the median filter is far less sensitive to shot noise in an image than the mean filter.

Neighbourhood size, or filter size, is specified in the x and y dimensions using the `filterx` and `filtery`flags. These dimensions should be odd, positive integer values (e.g. 3, 5, 7, 9, etc.).

## Reference

Huang, T., Yang, G.J.T.G.Y. and Tang, G., 1979. A fast two-dimensional median filtering algorithm. IEEE Transactions on Acoustics, Speech, and Signal Processing, 27(1), pp.13-18.

## See Also

bilateral_filter, edge_preserving_mean_filter, gaussian_filter, mean_filter

## Function Signature

`def median_filter(self, raster: Raster, filter_size_x: int = 11, filter_size_y: int = 11, sig_digits: int = 2) -> Raster: ...`

## Project Links

WbW Homepage User Manual Support WbW