Median Filter

The median represents the middle data point that half of data is smaller and half of data larger than this point. This is a robust estimator to remove outliers from a data set. Consequently, this tool can be useful as a naive denoiser, effective against impulse noise.


Median dialog window.

The layout of the window dialog is quite simple and few settings are available.

  • Kernel size: From \(3\times 3\) to \(15\times 15\), this defines the size of a squared kernel that is used to apply the filter. The larger the kernel, the more blurred the result will be.

  • Iterations: This defines the number of passes of the kernel.

  • Modulation: In Siril, modulation is a parameter between 0 and 1 mixing the original and processed images. A value of 1 keeps only the processed image, a value of 0 does not apply any median filter at all.

Siril command line

fmedian ksize modulation
Performs a median filter of size ksize x ksize (ksize MUST be odd) to the loaded image with a modulation parameter modulation.

The output pixel is computed as : out=mod x m + (1 − mod) x in, where m is the median-filtered pixel value. A modulation's value of 1 will apply no modulation