How to use the reduce noise tab
Info Reduce noise is an approach to remove noise by means of 2D Fourier analysis. The idea is to find the noise spectrum in constant areas and subtract it the "Wiener optimal" way.
A simplified approach (called "non-automatic" by me) is to subtract an amplitude-limited random noise spectrum.
While perhaps some limited cleaning of larger speckles is possible, the method is most effective with point-like noise and small, simple wave-patterns.
In case you wonder why this method is better than JPEG compression at high quality, the answer is that our analysis is much finer, cleaning 2x2 pixel blocks at a time. This also explains why 2D cleaning is so slow.Settings It is best to take the automatically found noise level with a grain of salt. You may want to change it, effectively scaling the found noise spectrum up or down.
1D cleaning is faster and may be good enough in some cases.
The idea behind vertical cleaning is that perhaps some sorts of noise may be horizontally but not vertically correlated.
BTW, in order to do 2D cleaning be sure to check both "horizontal" and "vertical".Selection rectangle for noise definition See "remove logo" for manipulation of the selection rectangle in the preview. "Automatic" and "Selection rectangle" must be checked and the noise reduction pane must be selected in the main window.
Noise spectrum Equally sized dots correspond to random noise.