Adding Dark Frame to Eliminate Hot Pixels

Using SharpCap for other Astro Imaging such as all sky cameras and meteor detection
Post Reply
Zi Hao
Posts: 1
Joined: Sun Aug 19, 2018 11:53 am

Adding Dark Frame to Eliminate Hot Pixels

Post by Zi Hao » Sun Aug 19, 2018 1:16 pm

Hi Everyone,
I was using ASI120MC in conjunction with the All Sky Camera provided to capture the Perseid Meteor Shower event last week. I managed to get about 3000 frames during the show and I am intending to make a timelapse using Lightroom. But there are a lot of hot pixels in the frames, I can't even identify the real stars in my images, then I search up on the internet, found out a method called dark frame subtraction, can eliminate hot pixels or noise efficiently by shooting frames with the lens cap on and with the same settings you use to shoot your images previously. So, my question is, is there a tool in Sharpcap that can remove all hot pixels in the 3000 frames using only one dark frame? Or I can do it in Photoshop? But how? Thanks. Any help or advice will be appreciated.
39575574_1928874317155840_6788299710881857536_n.png
39575574_1928874317155840_6788299710881857536_n.png (802.46 KiB) Viewed 903 times
Debayer Preview=On
Pan=0
Tilt=0
Output Format=PNG files (*.png)
Binning=1
Capture Area=1280x960
Colour Space=RAW8
Temperature=29
Discard Split Frames=Off
High Speed Mode=On
Turbo USB=56(Auto)
Flip=Vert
Frame Rate Limit=Maximum
Gain=52
Exposure=3.957988
Timestamp Frames=Off
White Bal (B)=100(Auto)
White Bal (R)=50(Auto)
Brightness=0
Auto Exp Max Gain=50
Auto Exp Max Exp M S=30000
Auto Exp Target Brightness=100
Mono Bin=Off

User avatar
admin
Site Admin
Posts: 3090
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Adding Dark Frame to Eliminate Hot Pixels

Post by admin » Sun Aug 19, 2018 1:24 pm

Hi,

SharpCap can create dark frames and automatically subtract them for you. Make sure that your dark frame has exactly the same settings (gain, exposure, etc) as your normal frames.

see

https://docs.sharpcap.co.uk/2.9/#!2!Pre-processing

and

https://docs.sharpcap.co.uk/2.9/#Capture

Robin

GaryS
Posts: 1
Joined: Sun Mar 31, 2019 5:18 pm

Re: Adding Dark Frame to Eliminate Hot Pixels

Post by GaryS » Thu Aug 01, 2019 9:05 pm

Hi
Can someone list specifically which settings must be maintained in order to utilize captured Dark frames?
I get that exposure and gain are critical but I can"t find anywhere a complete list and I have been unable to apply any dark frames due to some setting change problem that is not identified.
thank you for your help!
Gary

User avatar
admin
Site Admin
Posts: 3090
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Adding Dark Frame to Eliminate Hot Pixels

Post by admin » Fri Aug 02, 2019 8:22 pm

Hi,

The easy answer is don't change anything! In practice anything that changes the output image could mess up dark frame subtraction – that includes

Gain
exposure
offset/brightness/black level
colour balance controls
gamma/contrast

Ideally you want the temperature of the sensor to be the same when taking the dark frames as when taking the images that you are going to use the dark frames against (or as close as possible).

Cheers, Robin

roelb
Posts: 93
Joined: Wed Mar 08, 2017 11:36 pm

Re: Adding Dark Frame to Eliminate Hot Pixels

Post by roelb » Fri Aug 02, 2019 11:43 pm

What about the BIN setting?
Roel
Celestron Nexstar Evolution 8 - Celestron Nexstar 6 SE - OTA 5 SE - StarSense
Starlight Xpress Lodestar X2 Mono -- ATIK Infinity Colour -- ZWO ASI290MM -- ZWO ASI224MC

User avatar
admin
Site Admin
Posts: 3090
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: Adding Dark Frame to Eliminate Hot Pixels

Post by admin » Sun Aug 04, 2019 12:57 pm

Sorry, yes. I should have also included anything that affects the size of the image such as binning or ROI selection. Additionally anything that affects the bit depth of the image or the format of the image (for instance the choice of RGB24, RAW8 or RAW16) must be identical between the dark frames and the like frames.

Cheers, Robin

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest