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Old 15-08-2020, 11:55 AM
vesko
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ZWO ASI533MC Pro debayering issue

M16 from Bortle Class 5
TeleVue85 + TeleVue 0.8 reducer/flattener + ZWO ASI533MC Pro
Guiding: PHD2 + ZWO ASI120MC-S
Software: AstroImager on MacBook Pro (Gain 100, Offset 70)
Images acquired as fits.
Debayering in PixInsight using RGGB pattern and VNG method
Autostretched with the STF function in PixInsight
All the images appear very different. After star aligning them and image integrating them in PixInsight the resulting image is unusable.
I tried to debayer them with the demo version of Nebulosity4 and the results are very similar.
As I've been imaging with DSLR up until now, debayering is new to me.
If clear skies tonight, I'll try to acquire them as XISFs and experiment with the Gain and Offset settings in AstroImager but I have the feeling I'm missing something fundamental somewhere along the way.
Please refer to the attached images.
Attached Thumbnails
Click for full-size image (1.jpg)
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Click for full-size image (Raw Fits Simple Stretch.jpg)
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Click for full-size image (3.jpg)
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Click for full-size image (2.jpg)
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Click for full-size image (Integrated imge.jpg)
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Click for full-size image (Integrated image close up.jpg)
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  #2  
Old 15-08-2020, 01:19 PM
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Atmos (Colin)
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If debayering is new to you, are you doing it before or after star registration?

Debayering is after calibration but before registration.
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Old 15-08-2020, 01:23 PM
vesko
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I didn't use any calibration frames only lights. The images from the ZWO ASI533 come very clean, so I was hoping not to muck around with calibration frames. My workflow is: 1. Debayer in PixInsight; 2. Star Align; 3. Image integrate; 4. DBE and Colour Calibration ...
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Old 15-08-2020, 01:24 PM
vesko
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https://www.dropbox.com/s/pgk5rrmh2m..._001.fits?dl=0

Here's a link to a light frame
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  #5  
Old 15-08-2020, 01:25 PM
vesko
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https://www.dropbox.com/s/220m9yzd8t..._005.fits?dl=0

and another one to compare
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Old 15-08-2020, 01:26 PM
vesko
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I'm puzzled by the fact that light subframes taken within close succession under virtually identical circumstances get debayered looking completely different. From decent looking to magenta oversaturated ones.
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Old 15-08-2020, 02:01 PM
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Atmos (Colin)
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I thought I recognised the look of the images. I was also surprised by the size of the files (quite small) and even looked at the FITS Header; all of which are pointing to it only being an 8-bit image.

For some reason, AstroImager is only saving them as 8-bit and not 16-bit files. Think of it as being the difference between a JPEG and RAW camera file. Are all of the FITS files the same size?
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Old 15-08-2020, 02:21 PM
vesko
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You might be onto something. Yes, they're exactly the same 9.1mb. Weather permitting, I'll try to save them as XISFs tonight and see whether, it'll make any difference. AstroImager doesn't allow changing the bit-size in preferences. The only options are FITS, XISF, TIFF, SER, AVI, MOV. Is there a way to verify the bit-size of the image apart from guessing from the file size?
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Old 15-08-2020, 02:42 PM
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The sensor of the ZWO ASI533 has 3008x3008 = 9.048mp. If each pixel is expressed as 3 8-bit values for the R, G and B, a 9mp image would occupy 27mb uncompressed. I'm getting a bit confused.
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Old 15-08-2020, 02:45 PM
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You'll only need to have them saved as FITS, XISF is only really used by PixInsight.
It'll be around 9mb when it's in 8-bit but it'll double when at 16-bit so around 18mb. If in 32-bit it'll be 36mb so when you run the debayering process in PI it'll be 36x3 = 108mb as it saves them as 32-bit.

You're best playing around during the day and seeing if you can get FITS files at 18mb, that means they'll be being saved as 16-bit.
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  #11  
Old 15-08-2020, 03:28 PM
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Another look of desperation in the AstroImager for Mac. I've been saving them by default as 8-bit files. Hopefully, this explains all my troubles. Weather permitting, I'll take some 16-bit Raw images tonight and see what happens. Thank you Colin for your help!
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Old 15-08-2020, 03:46 PM
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No worries Get the 16-bit files going and you'll be delivering the goods!
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Old 15-08-2020, 09:29 PM
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Given the file size they are certainly 8-bit as has been suggested. I use this camera and every file is 17,677kb (from APT.)

That said, I was able it integrate a usable result from the two light frames you provided here in APP. The limitations of the 8-bit files are evident, but it's a much better result than PixInsight gave you. Attached is a quick screencap at 100% from integrating the two files you provided. When you look at the debayered files seperately in APP, they look essentially the same.
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Old 15-08-2020, 09:46 PM
vesko
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Thanks Craig! Yes, I hear only good things about the APP. I might have a good look at it. The integrated image from APP looks significantly better than the one I managed to pull out in PixInsight from 27 light frames.
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Old 17-08-2020, 05:36 PM
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I managed to debayer it in PI.


As is, using Auto CFA in PI Debayer process, the result is incorrect, UNTIL you make it a SuperPixel interpolation (VNG won't work on this image properly). So, I ran it as a SuperPixel, did an STF stretch and a Histogram using the STF output triangle. I then did slight colour saturation boost. The signal is weak from that single sub on Dropbox, so if you uploaded the lot, it may work better.


This is a noisy lossy-JPEG scaled WAY down in quality etc, but I can out the rather smooth original processed on Astrobin if you wish to see it.
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Old 17-08-2020, 07:05 PM
vesko
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The subs were exported in 8-bit format. Hence, the problem. I took some in 16-bit and the debayering was straight forward. Thanks!
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  #17  
Old 18-08-2020, 10:02 AM
vesko
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Decided to check the ASI533 on a more forgiving target this time around.

The16-bit images debayered without issues and were pleasure to work with.

Bortle Scale 5
40 x 180” lights
No calibration frames
ZWO ASI533MC Pro
Tele Vue-85 + Tele Vue 0.8x Reducer/Flattener
Orion Mini 50mm Guide Scope + ZWO ASI 120MC-S + PHD2
Sky-Watcher AZ-EQ5
PixInsight and PS

https://www.dropbox.com/s/6yxk33bmyf...la_M8.jpg?dl=0
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