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A question of sampling

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#1 pyrasanth

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Posted 12 August 2020 - 04:35 AM

The ASI6200 has a pixel size of 3.76 um- over sampled for long focal length instruments. However in the case of the Celestron RASA 11 which I'm using the smaller pixel size might be advantageous.

 

If I image at 1x1 bin which will be 1.25 arc secs per pixel that would be nice but the files would be pretty big at 32 mb each or 64 mb at 32 bit. I could image at 2x2 bin but I feel I would be possibly, depending on conditions, lose precious detail as the exposures I intend to use are 10 seconds each so effectively lucky imaging.

 

So if I took the images at 1x1 bin then rescaled these in PI to say 3x3 bin would I be losing or gaining anything?- I'm not sure how rescaling works with CMOS cameras. If there is a better way then let me know but I'm anxious to get maximum resolution with good signal under my very poor skies.

 

Please let me know your thoughts.

 

Clear skies to you all & stay safe.

 

Best wishes

Mark

 

 

 



#2 AtmosFearIC

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Posted 12 August 2020 - 04:46 AM

My understand is that the binning function on this camera is just a software bin anyway so as long as you use a good rescaling algorithm then you won't see any difference capturing at 1x1 and downscaling as opposed to 2x2 binning.


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#3 pyrasanth

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Posted 12 August 2020 - 05:01 AM

My understand is that the binning function on this camera is just a software bin anyway so as long as you use a good rescaling algorithm then you won't see any difference capturing at 1x1 and downscaling as opposed to 2x2 binning.

Thanks for this.

 

Am I right in assuming from your post that if I capture at 1x1 bin then rescale this to 4x4 bin it would look the same after the rescale as if I had originally captured at 4x4 bin?



#4 AtmosFearIC

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Posted 12 August 2020 - 07:11 AM

From what I've heard it is as long as you do IntergerResample and not just the ordinary Resample as they use a different algorithm.



#5 Midnight Dan

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Posted 12 August 2020 - 08:29 AM

So if I took the images at 1x1 bin then rescaled these in PI to say 3x3 bin would I be losing or gaining anything?- I'm not sure how rescaling works with CMOS cameras. If there is a better way then let me know but I'm anxious to get maximum resolution with good signal under my very poor skies.

Hi Mark:

 

Binning will, of course, lose resolution.  But as you've pointed out, if you're already oversampled, that's not an issue.

 

Binning also gains SNR.  According to theory and calculations, a 2x2 bin will get you double the SNR compared to no binning.  I've been doing some testing on this and my results show a little less than double, but still a substantial increase.

 

I've been testing this on my ASI071 camera.  I'm cinsuderung buying an ASI6200 and binning, and I wanted to be sure I would get the gains I expect.  The ASI071 supports in-camera binning as does the ASI6200.  However, when I tried that, I got a significant blurring effect on the image, which I did not see if did software binning.  I'm not sure if the ASI6200 will experience the same thing, but just wanted to mention it.  Bottom line - you can count on software binning to do the right thing.

 

-Dan


Edited by Midnight Dan, 12 August 2020 - 08:33 AM.



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