README.Moire

This plug-in to Gimp does a FFT of an image.

I've used this with success to remove moiré patterns from
images scanned from books:

The image should be in RGB. Remove the alpha layer,
this makes it easier (Layers|Flatten image).

Select Filters|Render|FFT directe

In the Layers window, select the layer, and "Duplicate Layer".

Select Image|Colors|Brightness-Contrast. Increase Contrast so
you can see the patterns.

The area in the upper left and upper right is the FFT of the
real image; don't modify this. The FFT of the moiré pattern
is outside these regions. Use the Rectangular Selection or
Elliptical Selection tools to select these regions.

Remove the copy layer: This will leave the original FFT
image with the selections.

Choose (128,128,128) as the background color.

Select Edit|Fill with BG color.

Remove the selections from the image.

Select Filters|Render|FFT inverse

Voilà, now you have an image without the moiré pattern!

It was originally written by Rémi Peyronnet <remi.peyronnet@via.ecp.fr>,
I have corrected a few bugs in it.

Files:

gpplugin.tar.gz:	Contains these files:
gpplugin.c:		The source code
Makefile:		The Makefile
README:			This file

Mogens Kjaer
mk@crc.dk
May 5, 2002