Auto Stretch Issues

[OtherWebbTelescope]

Greetings, licensed user for a few years now. Just moved from 8SE + ZWO 1294 + all the usual furniture to the Ashkar 71F with ZWO 1294. Something is way off in viewing and stacking compared to working with my old 8SE. Sharpcap V 4.1.12925.0.
I am posting one as viewed from Sharpcap processing and one as viewed from ZWO's processing. Also looked that way uring the Live Stack. Same FITS from SharpCap capture used. Everything "Auto" -- no human intervention.
Looking on what may need to do to get better views in Sharpcap.
SharpCap FITS stacked in SharpCap

SharpCapStackNSave.png (326 KiB) Viewed 2420 times

SharpCap FITS stacked in ZWO

ZWOStackNSave.png (510.75 KiB) Viewed 2420 times

Thanks, Michael

[admin]

Hi Michael,

I think the best place to start would be to work with the colour balance adjustments in the SharpCap live stacking area - the most obvious thing about the top image is that there is excessive red, both in the background and the nebulosity - taming that red down to a more reasonable level will probably lead to a big improvement.

The colour adjustments are found to the right hand side of the live stack histogram - see the documentation here : https://docs.sharpcap.co.uk/4.1/#Histogram%20Tab . What I would start out by doing is trying each of the two colour 'auto adjust' buttons below the colour sliders - the lightning bolt and the star. These try to auto-adjust the image colours using different approaches, and usually one or the other will give decent results which can then be fine-tuned using the colour level sliders.

The next step beyond that is to see how much more stretching the image will take to reveal fainter nebulosity without looking too noisy or un-natural. The default 'auto' stretch is quite conservative in the amount of stretch it applies, but you can easily boost this by moving the middle of the three vertical dashed yellow lines left. The exact amount depends on the image and your taste in how you want the image to look.

cheers,

Robin

[OtherWebbTelescope]

Thank you, I am generally familiar with (crude) stretching the histogram and I was losing too much data to get a black background during that session. I have clear skies this coming Sunday and after going through the documentation I see I have options that I can try.

Regards, Michael

[OtherWebbTelescope]

Nope. I have been a user of licensed Sharpcap for over three years. Something is not right.
Screencap - that black streak shows up on every image regardless of where I'm pointed to, stretching, whatever
No amount of automatic or manual stretching fixes it without losing everything
Note my histogram at this point is pretty good to start and there shouldn't a false artifact on the image.

Screenshot 2025-01-07 120040.png (684.35 KiB) Viewed 2399 times

Here's the saved as view. Just wonderful. It's on a 4TB NAS with over 2TB of space left, not a disk space issue.

Screenshot 2025-01-07 120547.png (584.96 KiB) Viewed 2399 times

Here's ZWOs stack of the Sharpcap FITS. Only 7 because Sharcap started crashing.

Screenshot 2025-01-07 120910.gif (335.25 KiB) Viewed 2399 times

My rig is capturing good data. Sharpcap is having problems displaying the data even with all the tips and tricks.
Thank you.

[admin]

Hi,

my first suggestion for this would be to go to the 'Preprocessing' section of the camera controls on the right and turn everything to 'off' - Dark subtraction, flat correction, background subtraction, etc. I think it's most likely one of those controls at an inappropriate setting for your current configuration that is introducing the problems in the image rather than doing its proper job of correcting the problems. That would tie in with the images processing correctly in the ZWO software.

The only other thing that comes straight to mind is that the ZWO image looks to be less strongly stretched than the SharpCap one - it's just possible I suppose that some of the strange image pattern is present in the raw images but not showing in the ZWO image due to the smaller stretch - I think that's unlikely though. If the problem does show up on a stronger stretch of the ZWO image then maybe check for dew or frost on the sensor or sensor window.

cheers,

Robin