[SOLVED] Live Stack and problems applying dark frames

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BlackWikkett
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[SOLVED] Live Stack and problems applying dark frames

Post by BlackWikkett » Mon Oct 15, 2018 4:18 pm

Equipment:
ZWO ASI183MC Pro (latest native driver 3.0.0.5)
SharpCap 3.2.5781.0 (has also occurred in ver. 3.1x)

I'm getting some weird artifacts and color cast when applying dark frame to live stack in SharpCap. Using the drop down dark frame creation tool in SharpCap to create the dark that is then applied to the live stack. I've also captured some individual dark frames and created a master dark via Astrotoaster. This master dark was applied to raw frames captured in ShapCap and stacked in Astrotoaster. The resulting images are below. I'm not sure if this is something I"m doing wrong or and issue in how the dark frame is applied to live stack. Any help is much appreciated.

Thanks!

Image
Live stack with stretch no dark frames added

Image
Live stack with stretch dark frames added

Image
Live stack in Astrotoaster with individual dark frames captured and master dark applied to live stack, over stretched to show no amp glow

Image
Master dark created in Astrotoaster and stretched. Used as master dark in previous image (3 frames)

Image
Master dark created in SharpCap and used in previous SharpCap live stack images (5 frames)
Last edited by BlackWikkett on Thu Oct 18, 2018 6:57 am, edited 1 time in total.

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Re: Live Stack and problems applying dark frames

Post by admin » Mon Oct 15, 2018 6:55 pm

Hi,

I'm not familiar with AstroToaster, but the symptoms sound like a scaling issue between the lights and the darks.

If they are in FITS format then have a look at the headers and range of each of the following in FitsLiberator

* An unsubtracted light frame
* A single dark frame captured in SharpCap
* The SharpCap saved master dark

particularly see if there is anything significantly different between the last two. Feel free to share the above files on Google Drive/Dropbox etc and someone on here will take a look at the header info.

cheers,

Robin

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Re: Live Stack and problems applying dark frames

Post by BlackWikkett » Tue Oct 16, 2018 12:07 am

Astrotoaster is a live stack application that uses Deep Sky Stacker. It can be found here http://www.astrotoaster.com/
I used Astrotoaster as an example that I'm able to create dark frames and apply to light frames with the final images not containing amp glow or artifacts / color gradients. I'm using SharpCap to capture the raw data and processing via Astrotoaster. My hunch is the problem lies in how SharpCap applies the dark to the live stack. The master dark that Astrotoaster creates is in .tif format. No fits file header available but Astrotoaster generates a .txt file with fits information. This is included below.

I have been unable to see any differences between the files. Hope someone may find something I overlooked. Please let me know if you need further information or testing.

Thanks for your assistance!

Here is google drive for raw fits files https://drive.google.com/drive/folders/ ... sp=sharing

Image
This image has had Photoshop Equalize applied to show the amp glow captured in the dark frame.

Bitmap.BitPerChannels=16
Bitmap.FileName=C:\Users\Chris\Desktop\SharpCap Captures\2018-10-15\Dark_120s_250g_bin2\00_50_48\MasterDark_ISO0_120s.tif[10/15/2018 12:57:07 AM]
Bitmap.Height=1836
Bitmap.NrChannels=1
Bitmap.Width=2744
Dark_Iteration=5
Dark_Kappa=2.0000
Dark_Method=1
Fits.BayerPattern=1
Fits.BlueScale=1.0000
Fits.Brighness=1.0000
Fits.DSLR=Generic RGGB
Fits.FITSisRAW=1
Fits.ForceUnsigned=0
Fits.RedScale=1.0000
----FileList----
C:\Users\Chris\Desktop\SharpCap Captures\2018-10-15\Dark_120s_250g_bin2\00_50_48\Dark_120s_250g_bin2_00001.fits[10/15/2018 4:50:59 AM]
C:\Users\Chris\Desktop\SharpCap Captures\2018-10-15\Dark_120s_250g_bin2\00_50_48\Dark_120s_250g_bin2_00002.fits[10/15/2018 4:53:00 AM]
C:\Users\Chris\Desktop\SharpCap Captures\2018-10-15\Dark_120s_250g_bin2\00_50_48\Dark_120s_250g_bin2_00003.fits[10/15/2018 4:55:00 AM]

Image
This image stretched in FITS Liberator to show amp glow captured in the dark frame

Header Information for SharpCap created dark frame 5x120s 250gain bin2
Image #1
SIMPLE = T / C# FITS: 10/14/2018 21:32:15
BITPIX = 16
NAXIS = 2 / Dimensionality
NAXIS1 = 2744
NAXIS2 = 1836
EXTEND = T / Extensions are permitted
BZERO = 32768 /
BSCALE = 1 /
COLORTYP= 'GBRG ' / NOTE: Use RGGB on some software (eg PixInsight)
BAYERPAT= 'GBRG ' / NOTE: Use RGGB on some software (eg PixInsight)
BAYOFFX = 0 /
BAYOFFY = 1 /
SWCREATE= 'SharpCap' / 3.2.5781.0
DATE-OBS= '2018-10-15T01:32:15.4052656' / System Clock:Frame Received

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Re: Live Stack and problems applying dark frames

Post by admin » Tue Oct 16, 2018 8:20 pm

Ok, now I start to see what is going on - your dark frame is brighter in the amp glow region than the light frames - that means that SharpCap's hot pixel removal algorithm kicks in with a vengeance. It's normally not noticeable for single hot pixels as it steals a pixel value from the pixel to the left, but with a whole area of hot pixels you get the lines effect.

Probably the best next step is to check that the settings for taking the darks are identical to those used for the light frames - something like the black level control being changed could easily have this effect. It may be worth re-taking darks to be sure of this. If this still happens with new darks known to be taken at exactly the same settings as the lights then shout and I will dig further.

cheers,

Robin

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Re: Live Stack and problems applying dark frames

Post by BlackWikkett » Tue Oct 16, 2018 8:44 pm

Thanks for taking the time to look into this!

All dark frames and light frames posted were taken with the same settings. Currently my next forecast clear night is Sunday 10/21. I'll repeat all steps from scratch.

For the time being here's the camera settings text file generated when I created individual dark frames. Settings were the same when using SharpCap's "Capture Dark" tool.

[ZWO ASI183MC Pro]
Debayer Preview=On
Pan=2
Tilt=0
Output Format=FITS files (*.fits)
Binning=2
Capture Area=5496x3672
Colour Space=RAW16
Hardware Binning=Off
High Speed Mode=On
Turbo USB=70
Flip=None
Frame Rate Limit=Maximum
Gain=250
Exposure=120
Timestamp Frames=Off
White Bal (B)=70
White Bal (R)=99
Brightness=0
Temperature=-15
Cooler Power=56
Target Temperature=-15
Cooler=On
Auto Exp Max Gain=225
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off
Banding Threshold=20
Banding Suppression=0
Apply Flat=None
Subtract Dark=None
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.321583455021738
#White Point
Display White Point=0.998046875
TimeStamp=2018-10-15T04:50:48.9130991Z
SharpCapVersion=3.2.5781.0

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Re: Live Stack and problems applying dark frames

Post by admin » Wed Oct 17, 2018 7:03 am

Hmm, another possibility is if the 'brightness' level you have set is too low - check the histogram when taking darks - if the peak is touching the left hand side then you need to turn up that control to separate it.

cheers,

Robin

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Re: Live Stack and problems applying dark frames

Post by turfpit » Wed Oct 17, 2018 8:06 am

Robin
Brightness=0
Is Brightness = Offset for a ZWO?

Chris - if Robin's answer is yes then have a good read at all of this viewtopic.php?f=9&t=1209

Dave

BlackWikkett
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Re: Live Stack and problems applying dark frames

Post by BlackWikkett » Wed Oct 17, 2018 2:50 pm

I'll check the links you provided. It'll be several days before I have another clear night. I'll try to capture some new dark frames with a higher brightness level tonight. As a test I'll apply these new darks with previously capture raw frames in SharpCap via Folder Monitor Camera. This potential solution seems very promising. I'll post results soon as they're available.

Thanks all for your help!

saguaro
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Re: Live Stack and problems applying dark frames

Post by saguaro » Wed Oct 17, 2018 3:13 pm

For ZWO cameras, Brightness does indeed equal "Offset".

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Re: Live Stack and problems applying dark frames

Post by turfpit » Wed Oct 17, 2018 3:23 pm

Thank you Saguaro. Not the Robin I expected!

Dave

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