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Do blown out regions in an image make FWHM and eccentricity measurements in PI unreliable?

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#1 SimonIRE

SimonIRE

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Posted 23 February 2021 - 04:40 AM

Hi All, 

 

Quick question regarding image analysis in PI - specifically FWHM and eccentricity maps. 

 

If you have an image that is blown out by stars such as this single sub of M42, does this make it difficult/impossible to analyse star eccentricity in this region.

 

Screenshot 2021 02 19 At 18.00.16
 
Screenshot 2021 02 19 At 09.03.43
 

 

Intuitively I assume so but I am keen on some expert opinions. I am trying to understand the limitations of these analysis techniques and when not to read too much into them. 

 

Thanks, 

 

Simon


Edited by SimonIRE, 23 February 2021 - 04:40 AM.


#2 sharkmelley

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Posted 23 February 2021 - 05:25 AM

You need to set the parameter "Upper Limit" in the FWHMEccentricity script.  This specifies the saturation level and any stars with peak values hitting that saturation level will be ignored and will not affect the results.

 

In your example of the Orion Nebula it could definitely mean that a whole area of the image will then be ignored. 

 

If the purpose of running the FWHMEccentricity script is to analyse your optics then you obviously wouldn't want to use the image of a bright nebula!

 

Mark


Edited by sharkmelley, 23 February 2021 - 06:25 AM.



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