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DeBayerization: VNG or AHD?

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#1 MCovington

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Posted 13 February 2018 - 11:57 PM

Particularly in PixInsight, which do people prefer?



#2 Jim Waters

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Posted 14 February 2018 - 12:25 AM

I have the same question.  Is there a good review of each and the pro's / con's?

 

You may want to post this in the PixInsight Forum.


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#3 whwang

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Posted 14 February 2018 - 12:46 AM

It will be the best if someone can stack a bunch of raw images of reasonable quality with VNG and AHD, and compare them.

 

I had compared DSS Bayer drizzle, DSS AHD, Nebulosity VNG, PI VNG, and PI Bayer drizzle.  For image sharpness and noise correlation between pixels, for a scale from 0 to 10, 0 being bilinear, and 10 being the best I have seen, I would rate as following:

 

DSS Bayer drizzle: 10

PI Bayer drizzle: 9.5

PI VNG: 9.0

Nebulosity VNG: 8.0

DSS AHD: 6.5

bilinear: 0

 

All of them are substantially better than bilinear.  PI's VNG does remarkably well and can give results almost as good as Bayer drizzle, at least in my cases.  

 

However, I have a feeling that PI's VNG is somewhat better than Nebulosity's VNG.  So probably even with the same algorithm (VNG), different implementations can give you different results.  Because of this, there is a possibility that PI's AHD is better than DSS's AHD.  I can't tell since I have never tried AHD in PI.

 

Personally I use PI's VNG as default, and only switch to PI's Bayer drizzle when the images are taken under exceptionally good conditions and when I absolutely want the highest resolution.  PI's VNG is much faster than its Bayer drizzle, and can give very good results.

 

Cheers,

Wei-Hao


Edited by whwang, 14 February 2018 - 12:46 AM.

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#4 MCovington

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Posted 14 February 2018 - 05:39 PM

The background is that I have my own version of the PixInsight BatchPreprocessing script with a few functions added.  I am wondering if I should put AHD on the menu (for some reason it is not there; VNG is the default).



#5 whwang

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Posted 14 February 2018 - 09:07 PM

Interesting.  I had the impression that AHD is there, but when I open my PixInsight BPP, I do not see it either.


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#6 sharkmelley

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Posted 15 February 2018 - 01:55 AM

It's definitely worth making AHD available.

 

However, I use bayer drizzle - it avoids artifacts in regions of high contrast - especially around stars.

 

Also, take a look at Juan's recent comments on the demosaicing in the libraw replacement for dcraw:

https://pixinsight.c...g74359#msg74359

 

By the way, demosaicing is the word that PixInsight will using in future instead of debayer (which now has connotations of physically stripping the CFA layer off a sensor to make it monochrome).

 

Mark


Edited by sharkmelley, 15 February 2018 - 01:56 AM.

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#7 xiga

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Posted 15 February 2018 - 03:48 AM

You should download the trial version of Astro Pixel Processor. It has a special demosaicing algorithm called Adaptive Airy Disc (AAD). The author swears that it gives superior results to any other algorithm out there.

https://www.astropix...nique-features/

#8 17.5Dob

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Posted 15 February 2018 - 08:22 PM

Another vote for Bayer Drizzle in PI




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