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How do you fix Chromatic Aberration in PixInsight?

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#1 Phillip Creed

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Posted 18 September 2019 - 03:10 PM

My personal imaging setup is an SV70T + 0.8X FF/FR on a Sirius EQ-G mount.
 

But I occasionally use our club's old 6" f/8 AP triplet for imaging.  It is one of Astrophysics' pre-Starfire triplets, and has color correction roughly comparable to a 6" f/20 FH doublet.

 

So when I image with the 6" f/8 AP, I get some noticeable blue/purple haloes around the brightest stars in my subs, even though it's color-corrected enough that I can't see them on any stars dimmer than 1st magnitude.
 

Question--what's the best way to minimize/eliminate the blue haloes in PixInsight?

Clear Skies,

Phil



#2 View2

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Posted 18 September 2019 - 03:13 PM

There is a script in pixinsight to reduce halos might try that?

Edited by View2, 18 September 2019 - 03:14 PM.


#3 Phillip Creed

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Posted 19 September 2019 - 11:26 AM

There is a script in pixinsight to reduce halos might try that?

I tried that, but it seems like it's geared towards off-center haloes.  Any pointers on how to center the corrective action on the stars themselves?

I've tried a quick-and-dirty method of inverting a range mask on the object and then lowering the blue saturation for everything else, followed by background extraction in subtraction mode.  But something a bit more specific to the "purple aura" would be better.

Clear Skies,

Phil



#4 jdupton

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Posted 19 September 2019 - 11:31 AM

Phil,

 

   I have seen a few tutorials that indicate that LocalNormalization can help with some halos. I have never tried it myself. Do a couple of Google searches to  see if you can find any tutorials which apply the LocalNormalization process to halo reduction.

 

 

John



#5 Alen K

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Posted 19 September 2019 - 11:56 AM

Maybe this? (I haven't tried it - yet.)

 

https://pixinsight.c...hp?topic=9685.0


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#6 Stelios

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Posted 19 September 2019 - 12:09 PM

Are you imaging with a mono camera? In any case, you could separate the channels and perhaps reduce stars in the Blue channel before recombining? 


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#7 the Elf

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Posted 19 September 2019 - 12:11 PM

You are a OSC imager, right? If so, use the split channels command to create three individual mono frames. The professional way is to get the point spread function from each one using dynamic psf and perform an individual deconvolution on each layer. Find details about deconvolution here: https://www.youtube....h?v=9N6I2JmEKkg at 1:42:35 or use the hop in table in the comments

As an alternative or additionally you can shrink the stars using morphology, minimum (erosion) on the layer with the largest halos, blue in your case. Do channel combination with the modified image and check the result, do more corrections if necessary and combine again. I was able to remove red halos in my super takumar using erosion. You might want to use a star mask to save red nebulosity if there is some in the image. If you upload an example file I can try and send you a short processing log with actual figures.


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#8 Phillip Creed

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Posted 20 September 2019 - 06:25 AM

You are a OSC imager, right? If so, use the split channels command to create three individual mono frames. The professional way is to get the point spread function from each one using dynamic psf and perform an individual deconvolution on each layer. Find details about deconvolution here: https://www.youtube....h?v=9N6I2JmEKkg at 1:42:35 or use the hop in table in the comments

As an alternative or additionally you can shrink the stars using morphology, minimum (erosion) on the layer with the largest halos, blue in your case. Do channel combination with the modified image and check the result, do more corrections if necessary and combine again. I was able to remove red halos in my super takumar using erosion. You might want to use a star mask to save red nebulosity if there is some in the image. If you upload an example file I can try and send you a short processing log with actual figures.

Elf,

Here's an example of what I'm up against.  Again, the chromatic aberration isn't too extreme, but it's there.

Clear Skies,

Phil

Attached Thumbnails

  • Swan Nebula-J2-CN.JPG


#9 Bretw01

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Posted 20 September 2019 - 09:26 AM

Invert the image, run SCNR to remove green, then invert again. You will need to play with saturation afterwards to boost the red back to where it was in the nebula.

 

I don't think this is chromatic aberration.



#10 ChrisWhite

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Posted 20 September 2019 - 11:35 AM

Try this pixelmath formula:

R: $T[0]
G: iif(min($T[0],$T[2])>$T[1],min($T[0],$T[2]),$T[1])
B: $T[2]

#11 bmhjr

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Posted 20 September 2019 - 11:38 AM

Here is what I have done.

 

- Make a star mask to include the stars with the Halos.  Be sure to include all the Halo you are trying to remove.

- Use MultiscaleMedianTransfrorm or ATrousWaveletTransform to nuke the halos at the proper scale while keeping everything else.

 

Here is a detailed tutorial. It is for a different type of halo but should work all the same

 

http://nunopinacphot...g-wavelets.html



#12 Jcwillis4

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Posted 20 September 2019 - 10:49 PM

I know you’re asking about PI specifically, but I wanted to recommend an alternate tool if you don’t like the suggestions above.  I use PI for just about everything, but none of the methods I’ve seen for halo reduction are easy and 95% reliable for all my images.  So I started playing around with Adobe Lightroom Classic just for my halo reduction and subtle tweaks.  It has a chromatic aberration tool that’s as simple as pointing an eye dropper at a single star halo to remove them instantly.  It runs about $10 a month with creative cloud.  For me, it’s worth it just for the one click halo removal.

 

https://youtu.be/meZ5ozVmVTo



#13 ChrisWhite

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Posted 21 September 2019 - 11:26 AM

Did you try the PM formula I gave you.  It perfectly removes your purple halos.



#14 Phillip Creed

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Posted 23 September 2019 - 06:04 AM

Chris,

I found that Pixel Math formula removed the purple, but not the haloes.  I'm trying to remove both.

Clear Skies,

Phil




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