I have found why ! but I am not sure we can solve
One parameter to take into account is “denoise”
Denoise limits the number of levels for luminance to 6 and for chrominance to 7 (denoise consumes a big lot of memory…)
So if denoise is “enable” all levels greater than 6 are inactive. However if you want to see the 7th level with “denoise enabled”, one of the two “fine chroma or coarse chroma” sliders must be greater than zero.
Perhaps there is a way to solve ??
jacques
@jdc Jacques, I more thought of this stuff, though not sure about
// adap maximum level wavelet to size of crop
if (minwin * skip < 1024) {
maxlevelcrop = 9; //sampling wavelet 512
}
if (minwin * skip < 512) {
maxlevelcrop = 8; //sampling wavelet 256
}
if (minwin * skip < 256) {
maxlevelcrop = 7; //sampling 128
}
if (minwin * skip < 128) {
maxlevelcrop = 6;
}
There is the 2, but (at least for my case , where my preview is large enough) I have tested with denoise : try enable / disable denoise, and try for level 7 with slider chroma 
But, should we look for a solution? or just put it in the documentation
I tend rather to documentation
jacques
I suggest adding an unobtrusive notice to indicate this in-app to avoid confusion, pointing to the docs.
I think it needs to be fixed. If denoise is active then levels 7 and above simply do not work at all. I am not sure a simple not in the on-line documentation will suffice. Is it possible to put something in the wavelet levels selector or else somehow to toggle the sliders for levels 7 and above if denoise is selected?
I would be disappointed to lose the frequency based denoise if I want to keep the shape enhancing abilities of the higher levels.
Should I file a bug report to formalize this discussion?
Yes, please!
There is a further problem. If I have selected 9 levels and denoise then the residual image adjustments work only on the residual after the 10th level even though contrast adjustments work only on levels 1-6. If I have selected 6 levels then the residual image adjustments work on the residual after the 6th level.
I change the GUI (see issue above), to disable Denoise in some cases
jacques
Hi @jdc,
with developement version 5.8-2530-g5fd640f97 Commit: 5fd640f97 if I open a detail window at last an more 800% and move the detail on the image with Wavelets and Denoise and refine enabled I have strange colored halos in te datail windows and 98% of the times after RT crashes into Segmentation fault.
When you have time…could you investigate , thanks 
I tried with various files…nothings happens…
Can you provided a raw and pp3
Thank you
Jacques
I think I have found the bug…In some cases, when windows is too small, with denoise enable I think wavelet works bad
I try another time, and I will push a commit
I tried with dev into the git and it behaves the same…
OK… what I do:
I,
No Desmis,
now RT crashes when detail window goes beyond 500% and wavelet and refine is enabled and I move the refine slider
Ciao @dafrasaga, Salut @jdc ,
Manjaro/KDE RT Version: 5.8-2535-g051145850
still crashes when one follows Gabriele’s steps.
Have fun!
Claes in Lund, Sweden
I will look tomorrow
jacques
Hello
Excuse my bad english.
I push a change 8e9e397 in branch “waveletcrash”
I think (I hope) the crash is solved…
But an explanation.
To work wavelet needs a minimum space to realize the decomposition, for each channel L*, a*, b*
The minimum size (in the preview window in pixels) for each level
But beware, if you have settings wavelet to level 7 or above, now the system will not crash (I hope), but process for this level will be ignored.
As a result, either your setup (like mine with a separate screen, and no left panel and you can examine up to level 10) allows it, or you have to limit the zoom. Usually up to 300% or 400% you shouldn’t have any problems viewing level 7
jacques