https://heasarc.gsfc.nasa.gov/docs/software/lheasoft/help/imfilter.html
imfilter HEADAS help file
helpfile
https://se.mathworks.com/help/images/filter-images-using-imfilter.html
Filter Grayscale and Truecolor (RGB) Images Using imfilter Function - MATLAB & Simulink
Filter an image with a 5-by-5 averaging filter containing equal weights.
filtergrayscaletruecolorrgb