deconvolution and masking

[ChoJin]

quick/stupid question to know whether I'm doing it wrong...

Do you remove/protect the big stars (the one with refraction spikes on newtonian scopes) from the general mask when applying a deconvolution or not?

If I don't, the dark rings are harder to prevent from on those stars because they are emphasized by the spikes surrounding them. And if I do prevent from them, the deconvolution is far less effective (on what I really care about), because I had to reduce the effect too much while adjusting the global dark parameter.

So, should I remove the few big stars from my general mask to just ignore them during deconvolution? or should I try to include the spikes as well in that mask? Or am I doing something wrong when fine tuning the deringing parameters and maybe I shouldn't have this issue if I were doing it somehow better/differently?

(it seems to me that reducing deringing also reduces the deconvolution effectiveness)

[Alejandro Tombolini]

Hi ChoJin,

I use the star mask to protect the cores of the big stars. See this processing example or other in this section with similar procedure.

Saludos, Alejandro. 

[MikeOates]

Alejandro,

Looking at your processing examples you produce a star mask to protect the larger to medium stars, but I don't see how you use that mask in the deconvolution process. I thought it was used in the local deringing section, but your screenshots do not show it used there. So I am a little confused.

Mike

[ChoJin]

Alejandro, just to make sure we're on the same page.

On most tutorials, they use a L mask to protect the background and only apply the deconvolution where there's data (the bright part usually).

If I understand correctly, what you're saying is that I should generate a starmask for the big stars (especially the ones with spikes) and subtract those from the L mask before applying it (hence excluding the big stars from the deconvolution as well)?

Intuitively that's what I would do, but I want to make sure you're saying the same thing.

[Alejandro Tombolini]

Looking at your processing examples you produce a star mask to protect the larger to medium stars, but I don't see how you use that mask in the deconvolution process. I thought it was used in the local deringing section, but your screenshots do not show it used there. So I am a little confused.

Hi Mike, In general I have managed to solve the deringing problems with "Global dark" and "Global bright" settings, but Local support may help if necessary.

On most tutorials, they use a L mask to protect the background and only apply the deconvolution where there's data (the bright part usually).

ChoJin, if you use a Regularizated Algorithm like Richardson-Lucy which is the default it enables "Wavelet Regularization" at the bottom of  Deconvolution tool. Adjusting those setting allows you to control the effect of deconvolution on the background of your images. In most of the cases this is enough in medium and high SNR image.

If I understand correctly, what you're saying is that I should generate a starmask for the big stars (especially the ones with spikes) and subtract those from the L mask before applying it (hence excluding the big stars from the deconvolution as well)?

No, I suggest only to mask the big stars. Check this mask article in the "StarMask with StarMask tool" section where I have created an star mask to protect only big stars before applying deconvolution.

Saludos, Alejandro.   

[ChoJin]

Thank you very much, that's very helpful as usual 

Unfortunately my data has quite a low SNR (only 12min exposure due to guiding nightmares, but I'm still trying to get what I can out of my data). I'll try anyway to use the wavelet parameters to prevent from having to use a mask for the background.

I have a question about your starmask tutorial:
why are you setting a small scale factor to 1 and compensation to 2 instead of 0? You don't want to apply the deconvolution to the small stars either (and reduce them slightly)?

[Alejandro Tombolini]

why are you setting a small scale factor to 1 and compensation to 2 instead of 0? You don't want to apply the deconvolution to the small stars either (and reduce them slightly)?

Hi ChoJin,

Which part are you referring to? If it is at the beginning of "StarMask with StarMask tool" I started with default values and was changing them to show how the mask was varying.
See the part that says: The Structure Growth section on the StarMask tool allow to control the protection of large and small structures in the mask. In this example, if we need to extend the area of protection only on the largest stars it has to be increased the "Large-scale" parameter which apply mask protection to larger regions in the image, and at the same time we can control the growth of protection of small stars by decreasing "Compensation" value, or even setting it to zero.
Any way, always depend on the image, you may have a galaxy and want to protect all the stars and perform deconvolution only on the galaxy.

Saludos, Alejandro.

[MikeOates]

Alejandro,

Thank you, I did not know it could be used that way, I will have to try it.

Regards,

Mike