Wipe settings for light pollution

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soulearth
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Joined: Mon Jan 04, 2021 10:36 am

Wipe settings for light pollution

Post by soulearth »

Hello,
I have fits files take with a dark and a flat. The image is well calibrated ( not too badly). However, I have a lot of light pollution around me (image taken in town). What parameter or preset should I use in this case ?

thanks for your help.
Best regards,
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admin
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Re: Wipe settings for light pollution

Post by admin »

Hi,

The default settings should do a good job in most scenarios, however in extreme widefield cases with very fast light pollution gradient undulation, things may be a lot trickier.

If you'd like to post an image (or even better - the stack), we can probably be of more help.
Ivo Jager
StarTools creator and astronomy enthusiast
soulearth
Posts: 4
Joined: Mon Jan 04, 2021 10:36 am

Re: Wipe settings for light pollution

Post by soulearth »

Hi,
Thank you for this response.
Lately with the covid, I observe from my home, the conditions are very bad regarding light pollution.
There is no miracle solution, but I am interested in solution to mitigate the impact.

Here are two images made this week with a screenshot and the file fits. ( I have no tracking,it needs big crop )


This is the link for two example fits ( M65 & 65 and NGC 2903 ) :
https://www99.zippyshare.com/v/VTe1fJOL/file.html
https://www99.zippyshare.com/v/vbspKVEk/file.html

Best regards,
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admin
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Re: Wipe settings for light pollution

Post by admin »

Thank you for sharing.

It is important to distinguish light pollution and gradients from stacking artefacts.
Right now, your dataset contains many stacking artifacts that, which can be hard to distinguish from light pollution gradients (please also note that "a" flat and "a" dark frame is not enough!)

To help avoid such artifacts, look for an "interesection" stacking mode in your stacker (some popular stackers here) where the final stack will only conists of a square image that guarantees that every pixel was represented in all frames and not just some.

For now, you can visualise them using AutoDev;
StarTools_470.jpg
StarTools_470.jpg (148.85 KiB) Viewed 1148 times
...and then crop the dataset to just the part that has proper signal for all pixels;
StarTools_471.jpg
StarTools_471.jpg (137.1 KiB) Viewed 1148 times
For more information on how to prepare your dataset for use in the Wipe module (with walkthroughs + screenshot), see here.

Once you have aequately prepared your dataset to only contain celestial signal (object + light pollution) and not some other artifacts, you can use the Wipe module.

The default settings tend to do a good job for most situations, however if your datasets are exceedingly noisy as is the case here, dark anomalies (such as dark noise clumps/grain) will cause Wipe to back off. In this case, bump up the Dark Anomaly Filter until no material change (in both Color and Luminance) can be spotted any further. E.g. something like this would be reasonable;
StarTools_472.jpg
StarTools_472.jpg (288.3 KiB) Viewed 1148 times
From there You can use AutoDev once more for the final stretch - again in cases of very noisy data as is the case here, compensating for this using the Ignore Fine Detail < parameter will be necessary;
StarTools_473.jpg
StarTools_473.jpg (161.28 KiB) Viewed 1148 times
From there, process as you see fit.

Hope this helps!
Ivo Jager
StarTools creator and astronomy enthusiast
soulearth
Posts: 4
Joined: Mon Jan 04, 2021 10:36 am

Re: Wipe settings for light pollution

Post by soulearth »

Hi Ivo,
My English is very poor. Sorry.
My practice of astronomy is a bit special. I don't do astrophoto, but I begin in electronically assisted astronomy (EAA).
I am using a dobsonian without tracking which is not ideal. Stacking artifacts are unfortunately a mandatory constraint.
My images are therefore very bad and noisy. :cry: I'm just looking to improve them a bit.

Thank you very much for your help. You answered my question perfectly. :thumbsup:

Regards,
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admin
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Re: Wipe settings for light pollution

Post by admin »

My English is very poor. Sorry.
Not at all! Actually, re-reading what I wrote yesterday, it appears that my English is very poor. :D
That's what writing messages after a 14h coding marathon does to your brain... I hope you got the gist of it though.

Indeed, if you do EAA, then considerations change. If practical though, please see if you can find an 'intersect' stacking mode, as it will remove the stacking artefacts.

I am working hard on creating more tools that will benefit EAA greatly. Because dithering is not practical with your setup, you will benefit from the walking noise reduction (short video demo here) that was introduced in StarTools 1.7.

Clear skies!
Ivo Jager
StarTools creator and astronomy enthusiast
soulearth
Posts: 4
Joined: Mon Jan 04, 2021 10:36 am

Re: Wipe settings for light pollution

Post by soulearth »

Hi,
14H !!! Indeed it is huge, but often good things emerge from these marathons.
Thank you very much for your work on startools. That's great.

Thank you very much for your answer. It helps me a lot and it answers all of my questions.

Regards,
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