ppmdescreen

Descreen filter for PPM images.

Compile

Depends

Edit FFTW and possibly FFTWINC and FFTWLIB in Makefile to refect where you installed fftw (www.fftw.org).

Build

Type make

You're done

Usage

The power spectrum.

ppmdescreen -i sample.ppm -p ps.ppm

Now you can either paint over the spots in the power spectrum yourself, or ask undither to do it for you.

ppmdescreen -i sample.ppm -a 0.01 -p akill.ppm
ppmdescreen -i sample.ppm -k akill.ppm -o automatic.ppm

or better still do it all in one step

ppmdescreen -i sample.ppm -a 0.01 -o automatic.ppm

This does a pretty good job, but it can't get the monochrome spots.

With a little help from the gimp I've drawn over the four white spots in akill.ppm and called it mkill.ppm.

ppmdescreen -i sample.ppm -k mkill.ppm -o manual.ppm

Links

Homepage: http://www.madingley.org/james/resources/undither/ GIT: https://github.com/ImageProcessing-ElectronicPublications/ppmdescreen