Author Topic: Purple green splotches  (Read 472 times)

Offline diggymacd

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Purple green splotches
« on: 2018 November 04 15:32:52 »
I'm guessing it's insufficient signal, but I sometimes struggle with purple and green blotches in the background of images.  This noise isn't removed with repeated applications of DBE, and are very difficult in noise reduction processes due to their large size.  I've attached an example: a crop of NGC 681, 50x60sec subs , with an ES127ED apo refractor, ZWO ASI183MC Pro, from an urban environment on the edge of red zone.  Integrated with dark library and master flat, no bias with this camera. Several iterations of DBE but no other processing.

Can anyone help me with suggestions on how to tackle this noise?  Thanks in advance,

Doug

Offline pfile

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Re: Purple green splotches
« Reply #1 on: 2018 November 04 18:01:26 »
i can never find it on his website - but i remember long ago that Alejandro Tombolini gave a technique where you make a mask to protect the foreground (a very strong one, such as with RangeSelection) and then remove a bunch of large-scale layers with AtrousWavelets set to chrominance mode.

it's not really a solution to the underlying problem, and needs to be used with care (as you risk desaturating the galaxy) but it does work.

rob

Offline diggymacd

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Re: Purple green splotches
« Reply #2 on: 2018 November 04 23:37:52 »
Thanks, Rob, I'll give it a try.

Doug

Offline speach

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Re: Purple green splotches
« Reply #3 on: 2018 November 05 15:07:01 »
when you debayer, if it's set on auto this will happen some times, use the pattern that is correct for your camera that should solve it