Interference stripes

[ggreybeard]

Hi Robin,

I have been successfully using SharpCap Pro for five years but I am now getting a dark striping effect in my images. These narrow horizontal interference stripes have occurred right across my last three sessions. They become visible in the live stack frame on the monitor, along with the saved PNG file.

Every stripe has a bright star associated with it. The brighter the star, the more noticeable is the dark stripe. If I bump up the exposure setting in my image processing software, even more stripes become visible, associated with the dimmer stars.

At first I thought it might be the PHD setting for the mount, as the stripes were first noted when processing the images taken during a session where I accidentally reset the mount method in the camera connection dialogue box for PHD guiding. I experimented with different settings until I found that “On Camera” was the only available option which worked in my current setup (I’m not using ASCOM for guiding). So that’s how I must have set it previously and it seems unlikely to be the cause. (Despite this, it seems quite a coincidence that the stripes began with this muck up).

My procedure in SharpCap is to select FITS files for the camera image downloads. I then live stack and save the final stack as a PNG file.

During live stacking, when I flipped from viewing the stack to viewing the latest frame (which is presumably a FITS file), the interference did not immediately appear - but as soon as the next FITS frame arrived, the stripes were there.

I do not normally save the FITS files any more but I did resort to saving some of them in my latest session. Later, these raw images were viewed in Deep Sky Stacker – and they showed no sign of the stripes, which surely rules out the camera.

So it seems the incoming FITS files are stripe free but at some early stage during the SharpCap live stacking process the images become corrupted.

I hope you can help me identify the cause of these stripes.

You should be able to view a processed 4-stack image here, complete with stripes:



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SharpCap Pro v 4.0.8667.0
Windows 11 HP laptop
PHD 2.6.11
Cartes du Ciel
ZWO ASI071
Skywatcher EQ6-R Pro
Meade LX-90
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Regards

Roger

[admin]

Hi Roger,

the issue you are seeing is related to turning on the 'Horizontal banding suppression' feature in SharpCap without performing the (necessary) tuning steps to ensure that you get the best results.

Your options are to turn the banding suppression off completely, or to adjust the 'banding threshold' setting downward until the effect goes away (that's what the threshold setting is for - see https://docs.sharpcap.co.uk/4.0/#!2!Pre-processing for more details on how to adjust).

You should also upgrade to the very latest SharpCap 4.0 from the downloads page, since I have made changes to the banding suppression code in the last few weeks to make this problem much less likely, even with incorrect settings for the threshold.

Finally, if you want, you can probably rescue your existing light frames by processing them through the SharpCap Folder Monitor camera in the latest version of SharpCap - have banding suppression turned on, but with a reduced threshold as per the calibration guide - it should almost completely remove the dark lines. Once adjusted you can then 'Capture' from the folder monitor camera to re-save the frames with the bands removed.

cheers,

Robin

[ggreybeard]

Robin,

Thanks very much for providing the above detailed solution and suggestions. I was able to successfully process some previously saved light frames. No bands!

Don’t ask me how Horizontal Banding Suppression was activated, it was set to 10/35. I don’t normally play with controls I have not yet read up on - but I'm sure you hear that all the time . . . .

Regards,



Roger

[admin]

Hi Roger,

glad to hear that fixed things for you

cheers,

Robin