Indeed the Image-Filter operator is not well documented and it does not have the same functionality as the GUI “Create Filtered Band”.
We have it on our agenda to harmonise all these inconsistencies, but this will take a while.
The non-linear and morphological filters can’t be used from the command line. That’s not implemented.
Regarding the file format:
It must be like the attached file:filter.txt (31 Bytes)
On the first line the number of rows and columns. Following lines the values. All tab separated, or on separate lines.
The number of iterations is fixed to one. Probably you can overcome this limitation by using multiple Image-Filter operators in a chain.
I once wrote an example script which shows how filtered bands can be generated with Python. Maybe it is useful.
create_filtered_band.py (2.0 KB)