Subframe Selector - What am I looking at?

[UlteriorModem]

When using the subframe selector script and looking at the plots, I am often confused as to what am I looking at exactly?

It seems that in some plots the higher numbers are worse (FHWM) that's fairly obvious. But when looking at other aspects lower numbers are worse?

Is there a definitive guide anywhere that explains all of the aspects and how to best choose which to keep and which to toss?

Thanks.

[John_Gill]

Hi,

Basically you want the highest SNR and the lowest Eccentricity and or FWHM. With Ecc and FWHM, scores lower than 0.4 is not detectable by eye. I use a formula to weight each frame, calculating the result based on 50% SNR and 25. % Ecc and 25% FWHM.

space is not not black
John

[UlteriorModem]

Thankyou John,

I will have to admit that pixel math is not my strong suit. What would that formula look like?

[John_Gill]

Hi,

Here is the formula I use:
(15*(1-(FWHM-FWHMMin)/(FWHMMax-FWHMMin)) + 15*(1-(Eccentricity-EccentricityMin)/(EccentricityMax-EccentricityMin)) + 20*(SNRWeight-SNRWeightMin)/(SNRWeightMax-SNRWeightMin))

So I use this formula to "weight" each frame and make a note of the best image name.  In SFS you can then sort on "weight".....Output the frames to an "Approved" folder.  This will write the weighting to the "FITS header" with a name SSWEIGHT.  When doing StarAlignment, use the best frame from SFS.  Then in ImageIntegration under "weights" select "FITS Keyword" and type in SSWEIGHT.
This will create you new image using the highest weighted image contributing the most going down to the least weighted image contributing the least.

space is not black
John
 

[UlteriorModem]

Thank you very much John for taking the time to type all that out

I will give it a try!

[John_Gill]

No problem.  Copy and paste works great 

[dave_galera]

Thanks for the formula John, I will also give it a try.

[UlteriorModem]

I copy pasted the formula into my version of PI and it was 'invalid'. I checked the syntax twice and it seems like it would be okay but PI did not think so.

Something about SNRWeightmin not being valid.

[John_Gill]

Hi,

Here is the formula again, please double check that there are two ) at the end of the formula.

(15*(1-(FWHM-FWHMMin)/(FWHMMax-FWHMMin)) + 15*(1-(Eccentricity-EccentricityMin)/(EccentricityMax-EccentricityMin)) + 20*(SNRWeight-SNRWeightMin)/(SNRWeightMax-SNRWeightMin))

John

[UlteriorModem]

Thanks but that still did not work. I got it to work though.

It seems that FHWMMin and such have to be fully spelled out as FHWMMinimum. After I corrected all the abbreviated versions it started working.

Thanks!

[pfile]

i think the keywords for the subframe selector script are different from the subframe selector process. could that be the problem?

rob

[UlteriorModem]

i think the keywords for the subframe selector script are different from the subframe selector process. could that be the problem?

rob

I did not even know there was a subframe selector process. So I went and looked at it and did not see where a formula could be plugged in to it?

So to answer your question, I don't know.

[pfile]

well the SFS process has multiple windows. one of them has a weighting expression and the other a acceptance/rejection expression if i remember correctly.

rob

[John_Gill]

Hi,

Remember this is for the SubFrameSelector Process and not the Script.

When you load the SFS, it should open three windows, first - SubFrameSelector window, second - Measurements window and thirdly the Expressions window.  If the second and third window do not open, then in the SubFrameSelector window, click the two buttons in the top right corner (Fx & Graphs) and that should open the "missing" windows.

In the "Expressions" window under Weighting, is where you input the formula:   (15*(1-(FWHM-FWHMMin)/(FWHMMax-FWHMMin)) + 15*(1-(Eccentricity-EccentricityMin)/(EccentricityMax-EccentricityMin)) + 20*(SNRWeight-SNRWeightMin)/(SNRWeightMax-SNRWeightMin))


The "graphs and results" window will allow you to view the results.  When you are happy with your file selection, go back to the main window under "Routine" select "Output Subframes" and in the "Output Files" put in the folder location (I call my folder, "approved") and in the "Keyword" type in SSWEIGHT.

The SSWEIGHT keyword will be embedded into the image and will be used when doing an ImageIntegration and using the keyword SSWEIGHT.

space is not black
John

[UlteriorModem]

This will work in the script...

(15*(1-(FWHM-FWHMMinimum)/(FWHMMaximum-FWHMMinimum)) + 15*(1-(Eccentricity-EccentricityMinimum)/(EccentricityMaximum-EccentricityMinimum)) + 20*(SNRWeight-SNRWeightMinimum)/(SNRWeightMaximum-SNRWeightMinimum))

All I did was spell out the imum's.