pnmnlfilt

Apply a non-linear filter onto a PNM image. More information: https://netpbm.sourceforge.net/doc/pnmnlfilt.html.

• Apply the “alpha trimmed mean” filter with the specified alpha and radius values onto the PNM image:

pnmnlfilt 0.0..0.5 radius path/to/image.pnm > path/to/output.pnm

• Apply the “optimal estimation smoothing” filter with the specified noise threshold and radius onto the PNM image:

pnmnlfilt 1.0..2.0 radius path/to/image.pnm > path/to/output.pnm

• Apply the “edge enhancement” filter with the specified alpha and radius onto the PNM image:

pnmnlfilt -0.9..(-0.1) radius path/to/image.pnm > path/to/output.pnm