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Comparison normal vs. pre-stacking

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#1 TorstenEdelmann

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Posted 22 May 2018 - 12:46 AM

During my recent sessions using a QHY290M once more the outcome wasn't what I was hoping for. Despite low elevation and mostly poor seeing conditions this camera seems to be very noisy even at mid-range gain settings. But at least during the most recent session the live-view offered some details so I stopped banging my head on the scope and started some recordings with the good feeling that stacking had to deliver at least a reasonable output this time. That wasn't the case. Fighting the noisy frames I tried different noise robust settings in AS3 (v3.0.14) but wasn't happy with the result. Then I had the idea to feed the original recording (drag&drop) into FC (dummy cam mode) and using the stacking pre-processing tool to create a recording with a number of frames pre-stacked to lower the noise levels. The original recording had 27000 frames so I selected 10 frames to pre-stack in FC and a limit of 2700 frames resulting into the same amount of data. Then I stacked both recordings in AS3 using exactly the same settings. Here the comparison after identical processing:

 

Jup_18052018.gif

 

and another one from the next night...

Jup_18052018_2.gif

 

 

I tried other recordings from the same night as well and at least for these high-noise levels the pre-stack recordings always delivered a better stacking result.

 

 

Next I played with some older not-so-noisy recordings:

 

Jup_20150703.gif

 

Some little improvement is visible but not as obvious as in the noisy recordings...

 

Sat_18072016.gif

 

For low-noise and high-contrast recordings like Mars normal stacking seems to deliver better results than pre-stacking:

 

Mars_04232014.gif

 

Remember this was just a qick test but I thought the outcome might be interesting although it might reflect only my specific setup. Need to do more tests especially playing with different noise robust settings in AS3.

 

Torsten


Edited by TorstenEdelmann, 22 May 2018 - 01:36 AM.

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#2 troyt

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Posted 22 May 2018 - 02:58 AM

Interesting observation. I tried to recreate your experiment using my data, but I just got a bright planet! using both monochrome and raw colour files. 

I was just trying to see if the improvements was related to your data/circumstances or not. 

 

Anyhow if you would like to experiment with some of mine data just let me know? to see if it's related to your data. 

 

Cheers

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#3 TorstenEdelmann

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Posted 22 May 2018 - 04:02 AM

A short instruction how to do this (see screenshot):

- start FC in dummy cam mode and drag&drop your AVI or SER file (might not work in all cases)

- enable AutoAlign (#1) and make sure to uncheck the debayer option (#1)
- click on pre-processing (#2) and select/check 'Average' from the list (#3)

- set the number of frames to pre-stack (#4) and the matching limit (5)

- start recording

Torsten

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