Horizontal banding in image

Discussion of using SharpCap for Deep Sky Imaging
Moonstruck
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Horizontal banding in image

#1

Post by Moonstruck »

I was imaging M51 the other night, and the final image (after processing in DSS and GIMP) had a series of horizontal bands going through it. Any idea what caused this?

I used Sharpcap Pro for capture, and have a ZWO asi 294 MC pro color camera, set to -10C during capture. When I processed the image in DSS, I incorporated darks, flats, and bias frames. I suspected this horizontal banding may have been caused by one or more of these calibration frames, so I processed just one light frame in GIMP to see if that was banded, and it was, leading me to believe whatever caused the banding was caused during capture (not during DSS or GIMP processing).

During capture, I had the gain set to 120, if that helps, or makes any difference. Any idea what is going on here? Note- in addition to the banding, my image background was a greenish color.

Thanks for any input you can provide. For a picture showing the horizontal banding and green colored screen, see my other recent Sharpcap forum post titled "Images appear black and white instead of color."
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turfpit
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Re: Horizontal banding in image

#2

Post by turfpit »

John

To help with this, zip up the following into a single file and post to googledrive or equivalent:
  • camera settings files for light, dark, flat and bias captures
  • one each unprocessed FITS file for light, dark, flat and bias frames
Dave
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Re: Horizontal banding in image

#3

Post by admin »

Hi,

if the dark bands all seem to have a bright star in them then the problem is most likely using the 'Banding Suppression' feature in SharpCap without properly calibrating the settings (see this section of the documentation for info on how to calibrate : https://docs.sharpcap.co.uk/4.0/#!2!Pre-processing).

Note that very recent versions of SharpCap (last 4 weeks or so) have changes that make it less likely for the banding suppression feature to cause this sort of problem (although not impossible).

cheers,

Robin
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turfpit
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Re: Horizontal banding in image

#4

Post by turfpit »

John

From the capture settings file in this post viewtopic.php?t=5289 your Banding Suppression = 25 (the default= 0). Capture more data but when you connect to the camera in SharpCap, hold down the Control key. This will reset all camera control values to defaults.

It might be worth having a read of viewtopic.php?t=2552

Dave
Moonstruck
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Re: Horizontal banding in image

#5

Post by Moonstruck »

Dave,
Here is the info for lights, flats, darks and bias frames. I put these files on google drive, and the links are in the attached document. Camera settings are also in the attached doc. Thanks for taking a look at this.

Note- this was my first time taking darks, flats, and bias frames so I am sure they are not what they should be! The flats are WAY overexposed- I used a white T-shirt stretched around the end of the OTA and I had a very bright light shining above it... I didn't know at the time I needed a much lower brightness.

Hopefully you can use this info to diagnose what is going on with the horizontal banding, and give me any advice you think is appropriate with regard to the calibration frames. Note that the single light frame has this banding, which makes me think the calibration frames didn't cause it.

John
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Sharpcap info to diagnose banding.docx
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Re: Horizontal banding in image

#6

Post by admin »

Hi,

yes, it's the incorrect use of the 'banding suppression'/'banding threshold' options that are causing your problem. Best thing to do is to turn 'banding suppression' down to zero until you have time to go through the proper calibration of the banding threshold parameter.

cheers,

Robin
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turfpit
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Re: Horizontal banding in image

#7

Post by turfpit »

John

Conformation of the banding in a single light frame.

banding-demo.JPG
banding-demo.JPG (37.32 KiB) Viewed 5275 times


Time to recapture M51 with some changed settings. It looks like you will have a decent M51 with a set of 60s expsoures.

I will post some info about the flats issue in your other post.

Dave
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Re: Horizontal banding in image

#8

Post by admin »

Hi,

actually, those frames can be rescued (at least to a degree).

Run them through the folder monitor camera and this time set the banding suppression to 35 and the threshold to about 10 - view the image with auto stretch in the mini histogram to confirm that the reprocess with banding suppression is removing the bands that were incorrectly inserted previously.

cheers,

Robin
Moonstruck
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Re: Horizontal banding in image

#9

Post by Moonstruck »

Robin, how do I run the existing frames through the folder monitor camera with the new banding suppression and threshold settings, and save the resulting (corrected) files? I have never used the folder monitor function before. Perhaps there is a tutorial on this?
Last edited by Moonstruck on Sun Apr 24, 2022 8:44 pm, edited 1 time in total.
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turfpit
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Re: Horizontal banding in image

#10

Post by turfpit »

Use the slider, you will find it in the Camera Control Panel at the right of the screen - might have to scroll down to see it.

Also see the manual link in post #3 above.

Dave
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