Trouble with star alignment in livestacking

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zerolatitude
Posts: 63
Joined: Mon Mar 01, 2021 5:24 am

Trouble with star alignment in livestacking

Post by zerolatitude »

Failure due to lack of stars to align has been discussed several times in this forum - it continues to be the one area where I find it difficult to get SC to work reliably.

I have so far tried all the suggested methods - reset, reduce black threshold, histogram adjustments, digital gain, etc etc. I got it working for one set of data by setting the dark and flats. Adding background subtraction caused it to fail again.

The settings that worked for one dataset did not for another.

When the stack is run through a stacking program, it finds several stars to align on.

For one image that showed 0 stars, the log is reproduced below. the image, saved as Exactly as seen, is also enclosed. ASTAP solves it in 0.3 sec, so the stars are there. It had darks and flats, no background subtraction.

I am enclosing the screenshot version as the file size is more than the limit allowed. But even in this, the number of stars visible is much more than 3.

Any suggestions?

21:54:06 INFO Detected 0 in the stacked image, mean FWHM is NaN
21:54:06 INFO Detected 0 stars in the frame image, mean FWHM is NaN
21:54:06 ERROR Less than 3 stars found in the frame image
21:54:06 ERROR Alignment failed
21:54:06 ERROR System.InvalidOperationException: Less than 3 stars found in the frame image - cannot align.
at SharpCap.ImageProcessing.Aligner.CheckFrameStars() in C:\Documents\Source Code\SharpCap\src\SharpCap.ImageProcessing\Aligner.cs:line 251
at SharpCap.ImageProcessing.Aligner.GetFrameTriangles() in C:\Documents\Source Code\SharpCap\src\SharpCap.ImageProcessing\Aligner.cs:line 240
at SharpCap.ImageProcessing.Aligner.GetAlignmentMatrix(Boolean lockToScaleOne, Int32 width, Int32 height) in C:\Documents\Source Code\SharpCap\src\SharpCap.ImageProcessing\Aligner.cs:line 129
at SharpCap.ImageProcessing.Aligner.GetAlignmentMatrix(ICapturedFrame frame, Boolean lockToScaleOne) in C:\Documents\Source Code\SharpCap\src\SharpCap.ImageProcessing\Aligner.cs:line 114
at SharpCap.FrameTransforms.LiveStacking.LiveStackProcessor.CalculateAlignment(ICapturedFrame frame) in C:\Documents\Source Code\SharpCap\src\SharpCap\FrameTransforms\LiveStacking\LiveStackProcessor.cs:line 493
21:54:06 ERROR Failed to calculate alignment.
21:54:06 WARN Frame not stacked because : Could not align
Screenshot as original is too large
Screenshot as original is too large
Screenshot 2021-04-29 221105.png (320.24 KiB) Viewed 241 times
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admin
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Re: Trouble with star alignment in livestacking

Post by admin »

Hi,

one of the challenges in the current (3.2, recent 4.0) versions of SharpCap is that the star detection settings are hard to use. What do I mean by that?

Want to detect more stars? Consider some of the following:
* Reduce minimum star width
* Increase maximum star width
* Increase digital gain
* reduce Black threshold level
* reduce noise reduction

That's 5 things you could try that might or might not work - what's more, if you take the digital gain route you probably are going to need to make corresponding adjustments to the black threshold or you will just make things worse.

Similarly, if you want to get rid of stars being wrongly picked up from hot pixels, you might

* Increase minimum star width
* Increase noise reduction

Again, 2 possible ways to try to achieve this goal, no real guidance on which is best or what combination to use.

Over the past few weeks I have been working through SharpCap 4.0 replacing the star detection code with a new version that is (a) better and (b) easier to configure. This is available now in the latest SharpCap 4.0 beta for multi-star FWHM measurement and polar alignment, but not yet for live stacking.

Next week's update will have this in live stacking - I have this working in tests here, you can see the new star detection area from live stacking below
Capture.JPG
Capture.JPG (20.71 KiB) Viewed 233 times
In general, all you might need to do here is turn up or down the sensitivity setting - higher sensitivity will detect more/fainter stars. In some cases with very noisy cameras you might want to increase the noise reduction. If you have very faint stars then you can check the 'optimize for faint stars' box which boosts detection of stars just above the background level.

Hopefully this will help make the whole thing more reliable - I'd certainly be interested to hear if it helps you.

cheers,

Robin
zerolatitude
Posts: 63
Joined: Mon Mar 01, 2021 5:24 am

Re: Trouble with star alignment in livestacking

Post by zerolatitude »

Hi,

I tried all those options and various combinations.

I'll wait for the next version and give it a shot.

Thanks
zerolatitude
Posts: 63
Joined: Mon Mar 01, 2021 5:24 am

Re: Trouble with star alignment in livestacking

Post by zerolatitude »

Hi,

Finally got to try it out. Cloudy so tried on folder monitor camera.

Much better - thanks. getting hardly any dropped frames. In some cases, had them and the Faint Star option worked well.

So far so good.

Thanks
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admin
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Re: Trouble with star alignment in livestacking

Post by admin »

Excellent - glad to hear that the changes have improved things!

cheers,

Robin
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