Strange patern when isolating large scales

[gvanhau]

Hello
I was "playing" with PI,
What I was willing to do is isolate part of a nebula.

I selected with ATWT layers 10-11-12 and disabled small scales and residual layer.
The result was quite good, but with a strange pattern.

On the image you can see a preview of the image, and the result of applying the furier transform to it.

Can someone tell me why this occurs, and better, can someone tell me how to do remove the fundamental frequency and then apply the inverse fft?

Regards
Geert

[Philip de Louraille]

Did you use several images and were they stacked correctly?

[gvanhau]

Yes, it is a LRGB composition.
Calibrated, aligned and stacked with PI. I can not say if they were stacked correctly, but image looks ok.

regards
Geert

[Philip de Louraille]

Try opening the calibrated-aligned-stacked file and just use the ScreenTransferFunction and see if the underlying image has a repeating pattern. STF ought to bring this up if it is misaligned.

[Carlos Milovic]

It also may be an artefact from the ATWT process. Try another scaling function. Perhaps a 5x5 gaussian or bspline.

[gvanhau]

Hello
Using gausian 5x5 I still got a pattern, using gausian 7x7 was ok.
Using bspline worked ok, but I had to go to scale levels downwards in order to achieve more or less  the same result.

Thanks Carlos and Philip.

Regards
Geert