Author Topic: Can't tell if this image has a gradient  (Read 132 times)

Offline tomb18

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Can't tell if this image has a gradient
« on: 2019 December 05 10:04:18 »
Hi,
I have an image of the California nebula (Ha) which was done with 5, 30 minute exposures from Bortle 8 skies.  You can take a look at the xisf file here: icom.va2fsq.com/temporary-page.  This is a calibrated and integrated image.
Now, I can't tell if there is a gradient or not.  If I try to remove a perceived gradient from the upper left corner I end up with a mess. Can anyone tell me if there is and if so a good way to try and remove it? 
Thanks

Offline tdgm

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Re: Can't tell if this image has a gradient
« Reply #1 on: 2019 December 05 12:42:52 »
Hello Thomb18


Yes I can see a gradient from top left towards the bottom right . I used DBE with sample generation Tolerance of 3 smoothing .6 sample size 24 and samples per row 7. I then just removed the samples over the nebula and any large stars in the samples. It came up with a really nice image. Congrats


TDGM

Offline tomb18

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Re: Can't tell if this image has a gradient
« Reply #2 on: 2019 December 05 18:27:00 »
Hi,
I thought the gradient is what you said.  Turns out I think the DBE processes are the ones that need the most experience in PixInsight.  I've had luck with ABE but not DBE.  I will try what you suggested.
This will be my first narrowband Hubble pallet image. On to the S2 and O3 (no nebulosity there !).
 Thanks very much for the hints.
Regards, Tom

Offline pfile

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Re: Can't tell if this image has a gradient
« Reply #3 on: 2019 December 05 22:04:50 »
here is a process icon you can try... it loads on Workspace01 on the bottom right. i don't think you need as many samples as TDGM has described. the gradient is not super complex.

rob

Offline pfile

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Re: Can't tell if this image has a gradient
« Reply #4 on: 2019 December 05 22:05:46 »
by the way is that an FSQ or something? it is razor-sharp.

rob

Offline tomb18

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Re: Can't tell if this image has a gradient
« Reply #5 on: 2019 December 06 10:52:52 »
Hi,
Yes, it is an FSQ106ED.  I would never buy another though.  It has always had a tilt in it.  I have thrown 2K$ on trying to fix it, new starlight instruments focuser, Pyxis rotator... The tilt is in the upper right corner. It doesn't show up much at a print size of 16x24 and a little crop will get rid of it. I have now learned to live with it.
I will try the DBE tonight.
Thanks for all the tips.
Tom

Offline pfile

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Re: Can't tell if this image has a gradient
« Reply #6 on: 2019 December 06 11:50:37 »
yes i have heard that some FSQs have problems and getting them sorted out is a huge hassle given the level of support over here. regardless when they work they really make some beautiful images.

rob