Fourier transform descreen (anti-Moiré) filter
An implementation of GIMP descreen plugin in python with OpenCV. It utilizes a custom normalization of magnitude spectrum, found in fft plugin, which assigns more energy to pixels further away from the center, thus allowing to use regular binary threshold to localize high frequency areas and create a mask automatically. It turned out to be very helpful in case of periodic pattern removal, therefor I adapted it for python.
Usage
./descreen.py
usage: descreen.py [-h] [--thresh THRESH] [--radius RADIUS] [--middle MIDDLE] input output
Example
python descreen.py images/example.png images/result.png
Optional arguments include
--thresh INT, -t INT- Threshold level for normalized magnitude spectrum--radius INT, -r INT- Radius to expand the area of mask pixels--middle INT, -m INT- Ratio for middle preservation
The normalized spectrum and its multi-channel mask of the above example respectively
Motivation
Originally intended to clean up deconvolution checkerboard artifacts, found in style transferred images, I thought it may have its uses in other areas, like cleaning low-dpi scans and therefor would be better off as a separate script. I excluded the optional despeckle step, found in original plugin for being too destructive. Instead, I find waifu2x to give a superior result in case of artistically styled images, thus tend to use it with maximum noise reduction as a second step.
Attribution
The script was taken from / originally written by https://github.com/6o6o/fft-descreen .