After some googling about moiré patterns and fast fourier transforms (FFT, it is also used in MRI) I found this very helpful discussion:
- especially the point about FFT.
Here is the technique with FFT:
- Download the ImageJ software
- Select the part of the image with pattern (e.g. somewhere in the corner). The idea is to see just the pattern.
- Apply FFT on the selected image pattern and notice how does it look like in the frequency space.
- Apply FFT on the whole image and find the pattern that was present on the selected image after FFT.
- Using paintbrush paint the pattern with black color. Do not paint the center.
- Apply inverse FFT.
Here is my example:
There is another interesting technique where you scan the image twice with rotation of the second scan about 180°. Then align the images. I didn't use this because the FFT method was much more interesting for me. I would use it probably if I couldn't find the clearly defined pattern in the image (e.g. no clear background).