Noise reduction when linear then restretch = horrible

[stevek]

Struggling with this one a bit.

On my master luminance (20 x 15 minutes is often my default luminance integration).  Crop>DBE>Deconvolution.  Cool.

Then to remove fine grain noise I can use maybe MLT with a mask or TGV (whilst linear).  Both work great. I apply these to the main image (not previews).  it looks nice and much of the noise gone. I then might even do some MMT too.  But when/if I then do a restretch with STF it looks horrible and seems to show a ton of noise again, worse than if I never even bothered reducing the noise in the first place.  Why?  Why can't it keep the settings of the stretch after application of the noise reduction tool?  This is even with long intergration times I have this problem.

You could say then don't restretch it then.  But you have to don't you?  You have to show it without the stretch in order to apply the HT nudges to the histogram?

Appreciate your thoughts please!  This is driving me mad!

Best, Steve

[pfile]

just save the STF settings from before the NR and reapply the original STF after the NR. or forget about STF and just manipulate HT to your liking. there is nothing that says you have to accept STFs auto-computed stretch...

this is a common issue because STF looks at the noise properties of the image to compute the stretch. after NR the image seems worthy of a harder stretch as far as STF is concerned, but in reality it is not.

rob

[stevek]

Thanks Rob. 

So I get my picture all nice on the original STF (the one applied to the image before noise reduction) with noise reduction tools.  Cool.  Time to stretch permanaently.  How would I now do that?  I'm thinking to drag the instance of the original stretch (and *don't* restretch) to the HT tool?  That may work for HT but what about other stretching tools? Surely I have to reset the stretch if I want to use another stretching tool such as masked stretch?  There is no way to drag the STF instance to Masked Stretch tool?

And this could apply to RGB too....  If after noise reduction a potential restretch is too harsh, how to pull the STF from the first (pre noise rediction) stretch into, say, arcsin stretch?

[pfile]

yes if you save a process icon from STF before the stretch, you should be able to drag that onto HT. if for some reason that doesn't work, you can always double-click the saved STF icon which will re-load the STF process with the old parameters, drag STF's triangle to the HT control bar at the bottom, and then apply HT to the NRed image.

another way to do it would be to copy the STF settings to HT before doing the NR, and then after the NR apply the HT process.

there is no way to copy STF's settings to masked stretch (or other stretching processes) because they work very differently. STF just sets the midtone transfer point and the black clipping and those are concepts that the HT tool understands. while the other stretching tools do similar stuff i guess the "how" is different enough that a fixed midtone and black point don't mean that much to them.

rob

[stevek]

Thanks for your help with this Rob.  This has helped me very much.