TerryMcK Posted July 23, 2021 Share Posted July 23, 2021 This is not a reference to the users of PixInsight, although some may say I'm eccentric, but rather the output of star eccentricity measurements in the SubframeSelector process (not the script as that seems to have disappeared). I have just run a bunch of Ha images through the tool and Eccentricity goes from 0.377 up to 0.791. I thought most of the frames showed quite tight stars when I Blinked them. From what I have been reading an Eccentricity value of 0.42 cannot be perceived by the eye of most people so the closer to that value you get the better. My subframe scale on the ZS103 with x0.8 reducer and ASI183MM is 0.87 arcseconds/pixel In the subframeSelector Expressions table I entered FWHM < 6 && Eccentricity <= 0.6 (as Amy Astro suggests) with a weighting of SNRWeight The results for 93 subframes is 51 ok for approval. It was a lot less for OIII and SII making me wonder if doing image analysis is actually detrimental. Approved frames start like this: Unapproved frames end like this: Raising eccentricity in the approval formula to 0.7 results in far more usable subs but of course more eccentric stars. I then compared the stacked images in SHO after doing some very basic processing first with all subs stacked and then with only subs that SFS approved. Zoomed in images showing all subs on the left and SFS approved subs on the right integrated as SHO - not a pretty picture but was not meant to be The only difference I could see in the Hubble pallet was less red ringing around stars with the frames output by the SFS process. This is after magenta halo removal. Although the SNR of the all subs stacked integration was far better than the one which only had 50% of frames integrated. I then changed the approval to the generally accepted formula through SFS which is 20*(1-(FWHM-FWHMMinimum)/(FWHMMaximum-FWHMMinimum))+20*(1-(Eccentricity-EccentricityMinimum)/(EccentricityMaximum-EccentricityMinimum))+10*(SNRWeight-SNRWeightMinimum)/(SNRWeightMaximum-SNRWeightMinimum)+50 and guess what? Every frame passed muster. Surely that cannot be right as the FWHM and Eccentricity values were still the same as before. There might be issues with that formula. I wonder if the residual red rings remaining after magenta deringing are caused by the Sulphur filter bloating the stars so might invest in 3nm filters soon. Mine are all 6nm currently. I may be being a little picky on this but SHO red ringing around stars irritates me. What Eccentricity values are you seeing? 1 Quote Link to comment Share on other sites More sharing options...
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