Author Topic: NB star halos?  (Read 417 times)

Offline Ron Kramer

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NB star halos?
« on: 2018 September 01 18:46:57 »
I sold my ZWO NB filters because of these halos.  I'm using astrodons now and I have the same thing!?
What would cause this?  All I can think of is my SII and OIII were not as tight as my HA. The SII mapped to RED and OIII mapped to B  (makes red - and blue and purplish rings?)
Is this because the SII and OIII are bloated and not as tight as the Ha?



Offline RickS

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Re: NB star halos?
« Reply #1 on: 2018 September 01 22:18:30 »
It is because the Oiii and Sii is usually a lot weaker than the Ha.  That means they need to be stretched more and the stars bloat in the channels you're using as Red and Blue.

My preferred solution to this is to remove the stars from a copy of each of the NB masters.  I use the starless versions to make the colour component of the image and the originals (still including stars) to build the luminance.  This idea is shamelessly stolen from JP Metsavainio's tone mapping process and works brilliantly.

Cheers,
Rick.

Offline Ryderscope

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Re: NB star halos?
« Reply #2 on: 2018 September 02 21:11:11 »
It is because the Oiii and Sii is usually a lot weaker than the Ha.  That means they need to be stretched more and the stars bloat in the channels you're using as Red and Blue.

My preferred solution to this is to remove the stars from a copy of each of the NB masters.  I use the starless versions to make the colour component of the image and the originals (still including stars) to build the luminance.  This idea is shamelessly stolen from JP Metsavainio's tone mapping process and works brilliantly.

Cheers,
Rick.

A quick question on this one Rick. When your are building your luminance, are you doing this at the linear or non linear stage?

Offline RickS

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Re: NB star halos?
« Reply #3 on: 2018 September 02 22:46:38 »
A quick question on this one Rick. When your are building your luminance, are you doing this at the linear or non linear stage?

Hi Rodney,

I build the lum and colour from the linear masters and then stretch and mostly process them separately.

Cheers,
Rick.

Offline troypiggo

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Re: NB star halos?
« Reply #4 on: 2018 September 04 03:48:36 »
You could use Rick's excellent scalpel - his colormask script - to mask out the magenta.

Alternatively, you could use a pixelmath sledgehammer - https://pixinsight.com/forum/index.php?topic=7377.0
:)