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square halo in Synth tool on OSX

Posted: Mon Dec 23, 2019 2:42 am
by GLM
A square halo is present around synthesized stars on OSX (iMac running High Sierra or Mojave) ST 1.5.369MR3 (see attachment as an example). No issue with previous release (1.4.340)

Thanks, Gianlorenzo

Re: square halo in Synth tool on OSX

Posted: Tue Dec 24, 2019 1:34 am
by admin

Would you be able to tell me what settings you used? These artifacts may happen if you specify a very small (incorrect?) image diameter for the image you acquired and the scope you acquired it with. It is all based on real physical parameters and scope modelling of the diffraction of point lights (it doesn't just paint spikes on like other programs :) ) , so incorrect input may result in incorrect output. What you are seeing is caused by the modelled point spread function not tapering off quickly enough, before it runs out of sample space.

To fix and/or ameliorate the issue, you can specify a larger image diameter, use the Gamma Adjust parameter, and specify an increase Sample Size (first screen) when computing the stellar profile.

To give you an idea of what image diameter to aim for;


(from M33 - Triangulum Galaxy)

Does that help?

Re: square halo in Synth tool on OSX

Posted: Tue Dec 24, 2019 6:22 am
by GLM

many thanks for the quick reply!
I tried to play with the image diameter, and indeed the halo tends to became more "transparent" at larger diameter (I have attached a composite picture with 4 settings: 70, 100 top row, 120, 140 bottom row).
Still the "70" settings does not produce any halo with the previous version (1.4.340) of the software, so I am a little confused, still. Also, the image is probably just ~50arc-min across, so 70 should work?
A couple of details on the image. Maybe might help the troubleshooting:
- ~600 1' shots with the Panasonic Lumix FZ200 @ 2.8 aperture, 600mm (35mm eqv.), 1600+400+800 ISOs, raw
- DSS stacked using Entropy, drizzle 3X, on a cropped rectangle, exported as FITS
- Star tools to Wipe/develop/color/denoise, then add star spikes.
- for the spikes all settings are default

Thanks! Gianlorenzo

Re: square halo in Synth tool on OSX

Posted: Thu Dec 26, 2019 12:56 pm
by admin
Thank you, I will investigate and try to replicate any differences between 1.5 and 1.4 on macOS.