Diagonal banding on image - Forums

Topic starter

Mar 28, 2023

Last night was my first night with my new Vixen SD81S II and I was very excited that it was meant to be clear all night. Of course, it wasn't clear all night and actually started raining at 4am (thanks rain alarm app!). As a result, I only managed to get 22 x 180" subs, which I've stacked in DSS using x20 flats and a master dark and master bias from earlier this year.

After processing in Pixinsight; DBE, ABE and a photometric colour calibration (I'm still downloading the catalogues for SPCC), I got this (tiff file here)

There's diagonal banding across the image; what have I done wrong?!

Engaging

andrea tasselli

Frequent contributor

Mar 28, 2023

Short answer: don't use DSS, at all. Do it again, all in PI.

Piers Palmer

Topic starter

Mar 28, 2023

But I'm 52…I might only have 30 years left to live. Is there time?

Actually, I did try that first but it was giving me an error message about compatibility…or something. I shall try again this evening.

Jonny Bravo

Mar 28, 2023

That's an artifact from running DBE with low sample rate data. Try this:

Hopefully it'll get rid of the issue for you

andrea tasselli

Frequent contributor

Mar 28, 2023 · Edited: Mar 28, 2023

Piers Palmer:
But I'm 52...I might only have 30 years left to live. Is there time?

Actually, I did try that first but it was giving me an error message about compatibility...or something. I shall try again this evening.

Take heart. I'm 61-ish and still learning...

If PI complains of something is best to take heed and figure out what is wrong. If you still have the flats and dark as well as the raw lights you can do it all over again. I mean, it is just 22 of them and clouds are forecast for weeks ahead of us.

By the way, I don't think it is the sampling, it is the flat fielding and using DSS. Don't use tiff either. Use 32 bit .fits or .xisf (better). Good news is that the banding won't be of much relevance once you get additional exposures.

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Piers Palmer

Topic starter

Mar 28, 2023

Jonny Bravo:
That's an artifact from running DBE with low sample rate data. Try this:

Hopefully it'll get rid of the issue for you

That could come in useful considering my weather!

Piers Palmer

Topic starter

Mar 28, 2023

andrea tasselli:
Piers Palmer:
But I'm 52...I might only have 30 years left to live. Is there time?

Actually, I did try that first but it was giving me an error message about compatibility...or something. I shall try again this evening.

Take heart. I'm 61-ish and still learning...

If PI complains of something is best to take heed and figure out what is wrong. If you still have the flats and dark as well as the raw lights you can do it all over again. I mean, it is just 22 of them and clouds are forecast for weeks ahead of us.

By the way, I don't think it is the sampling, it is the flat fielding and using DSS. Don't use tiff either. Use 32 bit .fits or .xisf (better). Good news is that the banding won't be of much relevance once you get additional exposures.

Quite right! I’m currently shooting new flats and darks just to have a clean starting point.

Strangely, the flats shot with my Lacerta flat panel show horizontal banding except at the lowest brightness. I’ve never had a problem with it before and there's no strobing of the light when viewed through my phone’s camera (which has show strobing with other set ups). I’ll see how I get on!

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andrea tasselli

Frequent contributor

Mar 28, 2023 · Edited: Mar 28, 2023

Piers Palmer:
Strangely, the flats shot with my Lacerta flat panel show horizontal banding except at the lowest brightness. I’ve never had a problem with it before and there's no strobing of the light when viewed through my phone’s camera (which has show strobing with other set ups). I’ll see how I get on!

If it shows banding at higher brightness then the issue isn't the brightness per se is the flickering (or strobing). Increase the exposure lengths to 2-3 seconds and add diffuser screens in between to dim the panel brightness, if needed. Personally I use sky flats whenever I can.

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Piers Palmer

Topic starter

Mar 28, 2023

I thought the whole point of a led flat panel was to give a uniform non-strobing light. I’ll try the sky method next time it’s not raining. I might be some time.

Piers Palmer

Topic starter

Mar 28, 2023

Actually, the banding happened when the light panel was powered from the asiair. I then tried powering it directly from my portable battery and no banding at all.

Odd, but workaroundable.

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Piers Palmer

Topic starter

Mar 28, 2023

I think I did everything right.

It's certainly a lot better, and it'll do for around one hour of integration.

Djennings

Apr 11, 2023

Yup, that last photo looks a lot better. I see no banding as I did in the first shot.

BTW, I'm 62 and still learning as well. With the will of God, hope to live a little longer to enjoy all his handy work in the skies.

Clear skies,

DJ

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