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DSLR PixInsight Processing - What Are These Dark Spots?

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#1 Jim Waters

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Posted 21 February 2019 - 08:00 PM

See the picture below.  What's causing these dark pixels?  Are my Sigma High / Low values set wrong?  These dark pixels are all over the place.

 

Ha Modified Canon 6D

Canon 200mm f/2.8L II lens

 

52 Lights (80 Sec), 60 Darks (80 Sec), 60 BIAS and 40 Flats

 

Steps so far:

  • BatchPreprocessing
  • ImageIntegration
  • DynamicCrop
  • DynamicBackgroundExtraction
  • MultiscaleMedianTransform

 

 

Attached Thumbnails

  • What Are These.jpg

Edited by Jim Waters, 21 February 2019 - 08:01 PM.


#2 bnickeson

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Posted 21 February 2019 - 08:22 PM

What integration pixel rejection method are you using (Windorized sigma, linear fit, etc.) and what are your high/low values?



#3 zxx

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Posted 21 February 2019 - 08:30 PM

I got the same spots when I used the wrong temp dark's 



#4 Jim Waters

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Posted 21 February 2019 - 08:48 PM

What integration pixel rejection method are you using (Windorized sigma, linear fit, etc.) and what are your high/low values?

Windorized Sigma with default Sigma High and Low for BPP and ImageIntegration.



#5 Jim Waters

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Posted 21 February 2019 - 08:50 PM

I got the same spots when I used the wrong temp dark's 

That may be it.  I take my Darks after my Lights.  The temperature usually drops 2 to 5 degrees give or take.



#6 bnickeson

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Posted 21 February 2019 - 09:03 PM

Could be the darks though I've never seen that many pixels go wrong just from a few degrees of difference.  I always take mine afterwards and haven't had any issues yet.

 

Have you checked your images to see when these start to appear?  RAW?  Calibrated?  Integrated?  That will give you your answer.  Also, Cosmetic Correction would likely clean some of those up as well if you don't use it already.



#7 Ron359

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Posted 21 February 2019 - 09:16 PM

Are they in the raw lights or darks before processing or stacking. Do they have any brightness or color value relative to nearby not totally 'black' pixels?    Looks like something in processing is setting some pixels to zero unless they appear in raw files too.  



#8 Jim Waters

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Posted 21 February 2019 - 09:22 PM

Could be the darks though I've never seen that many pixels go wrong just from a few degrees of difference.  I always take mine afterwards and haven't had any issues yet.

 

Have you checked your images to see when these start to appear?  RAW?  Calibrated?  Integrated?  That will give you your answer.  Also, Cosmetic Correction would likely clean some of those up as well if you don't use it already.

I will walk through my subs tonight and try to find where they start.



#9 Jim Waters

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Posted 21 February 2019 - 09:23 PM

Are they in the raw lights or darks before processing or stacking. Do they have any brightness or color value relative to nearby not totally 'black' pixels?    Looks like something in processing is setting some pixels to zero unless they appear in raw files too.  

Need to check this out.



#10 whwang

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Posted 21 February 2019 - 09:29 PM

Those are highly likely imperfectly subtracted hot pixels.  This can happen even if your darks and lights were taken at similar temperatures and even if you turn on the dark optimization option in BPP, for reasons I do not yet fully understand.  However, if your images are well dithered and if you turn on the rejection function during stacking, they should go away.

 

Cheers,

Wei-Hao


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#11 Jim Waters

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Posted 21 February 2019 - 09:58 PM

However, if your images are well dithered and if you turn on the rejection function during stacking, they should go away.

 

Cheers,

Wei-Hao

Turn on Rejection Function?  During ImageIntegration after BPP?



#12 Jim Waters

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Posted 21 February 2019 - 11:44 PM

I wasn't entirely honest about my Darks.  I took 20 Darks after I took my Lights.  The air temperature that night was between 42 and 38F degrees .  I decided to take 40 more Darks by putting my 6D in our refrigerator today.  The internal temperature was 37F degrees.  

 

I just walked through the Camera recorded EXIF temperature and the run I did in the refrigerator today is 8 to 10 degrees colder.  Could this be causing my problems?



#13 fmeschia

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Posted 22 February 2019 - 12:20 AM

Can you post the same area before MMT had a chance to mess it up? Are the dark dots present even before MMT?



#14 Jim Waters

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Posted 22 February 2019 - 12:29 AM

Too late.  I am redoing everything with Clip High Range selected.  I plan to use MMT on this run too.  It would be hard to tell because of the background noise before MMT.



#15 fmeschia

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Posted 22 February 2019 - 12:30 AM

I remember reading somewhere that MMT is known to introduce this type of artifact.



#16 fmeschia

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Posted 22 February 2019 - 12:32 AM

I wasn't entirely honest about my Darks.  I took 20 Darks after I took my Lights.  The air temperature that night was between 42 and 38F degrees .  I decided to take 40 more Darks by putting my 6D in our refrigerator today.  The internal temperature was 37F degrees.  

 

I just walked through the Camera recorded EXIF temperature and the run I did in the refrigerator today is 8 to 10 degrees colder.  Could this be causing my problems?

Do you use Dark Optimization when calibrating your light frames in PixInsight?

Francesco



#17 Jim Waters

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Posted 22 February 2019 - 12:36 AM

Where's this option located in BPP?

 

BTW - I just got done with this new run and the dark pixels are back.  Lots of them.  You can only see them at high magnification.



#18 fmeschia

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Posted 22 February 2019 - 12:42 AM

Here:

Screen Shot 2019-02-21 at 9.41.25 PM.png



#19 Jim Waters

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Posted 22 February 2019 - 12:43 AM

It 'looks like' the dark pixels are gone if I use MLT.



#20 Jim Waters

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Posted 22 February 2019 - 12:44 AM

Thanks - let me try this tomorrow.



#21 Jim Waters

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Posted 22 February 2019 - 12:50 AM

Yes - Optimize Darks Frames is checked on all my runs.



#22 fmeschia

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Posted 22 February 2019 - 12:51 AM

Yes - Optimize Darks Frames is checked on all my runs.

Then MMT is, for some reason, not playing nice with your data.



#23 Jim Waters

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Posted 22 February 2019 - 12:55 AM

It looks that way.  I will do more testing tomorrow.

 

BTW - I was Dithering my Lights.



#24 Jim Waters

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Posted 22 February 2019 - 01:54 PM

Yep - MMT will eat holes in your data if you aren't careful...

 

https://pixinsight.c...hp?topic=4650.0




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