#1  
Old 08-09-2013, 08:09 PM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
Removing a bright centre without a flat?

Hey guys, is there any way I can remove this bright centre while preserving the details of the star field? Screen shot below.

I have Photoshop elements 6 so please keep it simple.

Cheers!

Baz.
Attached Thumbnails
Click for full-size image (BasStarDSSSCrnsht.jpg)
134.3 KB38 views
Reply With Quote
  #2  
Old 08-09-2013, 08:24 PM
h0ughy's Avatar
h0ughy (David)
DOGHOUSE REBORN

h0ughy is offline
 
Join Date: Apr 2005
Location: NEWCASTLE NSW Australia
Posts: 30,559
simple DBE in pixinsight
Reply With Quote
  #3  
Old 08-09-2013, 08:25 PM
naskies's Avatar
naskies (Dave)
Registered User

naskies is offline
 
Join Date: Jul 2011
Location: Brisbane
Posts: 1,865
It depends upon whether this is a light pollution gradient (you have extra light that needs to be subtracted) or vignetting (you're missing light in areas that need to be multiplied to compensate). I'm going to assume that it's the latter - vignetting.

Since there isn't any nebulosity in the image, you can just remove the stars from the image and use it as a flat. Here are instructions for PS (I assume they'll work in Elements - but I've never used it before):

1. Open the image in PS.
2. Convert to 16-bit mode
3. Duplicate layer.
3. Gaussian blur the new layer 100 px (depends upon image size - you want to remove all stars and other interesting features, and keep the image gradients smooth).
4. Open Levels and stretch the white point left until it reaches right-most edge of the histogram (53 with your web sized image).
5. Change the blend mode of the layer to Divide.
6. Flatten the two layers.

Your vignetting is extremely severe - there was no detail around the edges in your image, so this won't help with that. You can see that the central region becomes more evenly illuminated (this will work much better with full sized images - convert from RAW directly to a 16-bit image for editing if you can).

Hope this helps.
Attached Thumbnails
Click for full-size image (BasStarDSSSCrnsht copy.jpg)
191.0 KB23 views
Reply With Quote
  #4  
Old 08-09-2013, 08:36 PM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
Quote:
Originally Posted by naskies View Post
It depends upon whether this is a light pollution gradient (you have extra light that needs to be subtracted) or vignetting (you're missing light in areas that need to be multiplied to compensate). I'm going to assume that it's the latter - vignetting.

Since there isn't any nebulosity in the image, you can just remove the stars from the image and use it as a flat. Here are instructions for PS (I assume they'll work in Elements - but I've never used it before):

1. Open the image in PS.
2. Convert to 16-bit mode
3. Duplicate layer.
3. Gaussian blur the new layer 100 px (depends upon image size - you want to remove all stars and other interesting features, and keep the image gradients smooth).
4. Open Levels and stretch the white point left until it reaches right-most edge of the histogram (53 with your web sized image).
5. Change the blend mode of the layer to Divide.
6. Flatten the two layers.

Your vignetting is extremely severe - there was no detail around the edges in your image, so this won't help with that. You can see that the central region becomes more evenly illuminated (this will work much better with full sized images - convert from RAW directly to a 16-bit image for editing if you can).

Hope this helps.
Awesome and working well until I got to the blend mode bit....

where is that?
Reply With Quote
  #5  
Old 08-09-2013, 09:00 PM
naskies's Avatar
naskies (Dave)
Registered User

naskies is offline
 
Join Date: Jul 2011
Location: Brisbane
Posts: 1,865
Doh... looks like PSE doesn't have the "Divide" blending mode - only PS does.

Okay, an alternative way is to do the Gaussian blur step, but then save that blurred (but don't apply Levels) image out as a separate file. You can then use that image as a flat frame in DeepSpaceStacker or whatever stacking program you use.
Reply With Quote
  #6  
Old 08-09-2013, 09:01 PM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
Quote:
Originally Posted by naskies View Post
Doh... looks like PSE doesn't have the "Divide" blending mode - only PS does.
Story of my life man.... every time.
Reply With Quote
  #7  
Old 08-09-2013, 09:02 PM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
Quote:
Originally Posted by naskies View Post
Okay, an alternative way is to do the Gaussian blur step, but then save that blurred (but don't apply Levels) image out as a separate file. You can then use that image as a flat frame in DeepSpaceStacker or whatever stacking program you use.
Nope, can't do that either. DSS won't stack RAW files with JPEG or TIFF files.
Reply With Quote
  #8  
Old 08-09-2013, 09:14 PM
naskies's Avatar
naskies (Dave)
Registered User

naskies is offline
 
Join Date: Jul 2011
Location: Brisbane
Posts: 1,865
Quote:
Originally Posted by bloodhound31 View Post
Nope, can't do that either. DSS won't stack RAW files with JPEG or TIFF files.
Maybe not JPEG (avoid using JPEGs for any kind of stacking - it ruins the fine detail that stacking relies on), but it definitely will with TIFF - master calibration frames in DSS are written out as TIFF by default.

Just load in the RAW as a light frame, and your artificial flat frame as a 16-bit TIFF.
Reply With Quote
  #9  
Old 08-09-2013, 09:45 PM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
OK I'll try that. Thanks Dave.
Reply With Quote
  #10  
Old 09-09-2013, 08:52 AM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Hinchinbrook
Posts: 18,138
Quote:
Originally Posted by naskies View Post
It depends upon whether this is a light pollution gradient (you have extra light that needs to be subtracted) or vignetting (you're missing light in areas that need to be multiplied to compensate). I'm going to assume that it's the latter - vignetting.

Since there isn't any nebulosity in the image, you can just remove the stars from the image and use it as a flat. Here are instructions for PS (I assume they'll work in Elements - but I've never used it before):

1. Open the image in PS.
2. Convert to 16-bit mode
3. Duplicate layer.
3. Gaussian blur the new layer 100 px (depends upon image size - you want to remove all stars and other interesting features, and keep the image gradients smooth).
4. Open Levels and stretch the white point left until it reaches right-most edge of the histogram (53 with your web sized image).
5. Change the blend mode of the layer to Divide.
6. Flatten the two layers.

Your vignetting is extremely severe - there was no detail around the edges in your image, so this won't help with that. You can see that the central region becomes more evenly illuminated (this will work much better with full sized images - convert from RAW directly to a 16-bit image for editing if you can).

Hope this helps.
Very cool tip. Gotta try it on my color shots from last session.
Reply With Quote
  #11  
Old 09-09-2013, 11:25 AM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
It's a lost cause. I'm going to throw the data away and shoot it again with flats.
Reply With Quote
  #12  
Old 09-09-2013, 12:31 PM
Octane's Avatar
Octane (Humayun)
IIS Member #671

Octane is offline
 
Join Date: Dec 2005
Location: Canberra
Posts: 11,158
DPP, Peripheral Illumination Correction.

H
Reply With Quote
  #13  
Old 09-09-2013, 12:32 PM
Octane's Avatar
Octane (Humayun)
IIS Member #671

Octane is offline
 
Join Date: Dec 2005
Location: Canberra
Posts: 11,158
http://www.iceinspace.com.au/forum/s...4&postcount=14
http://www.iceinspace.com.au/forum/s...5&postcount=15
http://www.iceinspace.com.au/forum/s...6&postcount=16

H
Reply With Quote
  #14  
Old 09-09-2013, 12:47 PM
Octane's Avatar
Octane (Humayun)
IIS Member #671

Octane is offline
 
Join Date: Dec 2005
Location: Canberra
Posts: 11,158
If your images weren't taken with a Canon lens, ignore my posts above.

H
Reply With Quote
  #15  
Old 09-09-2013, 04:29 PM
bloodhound31
Registered User

bloodhound31 is offline
 
Join Date: Aug 2006
Posts: 4,628
Quote:
Originally Posted by Octane View Post
DPP, Peripheral Illumination Correction.

H
Thanks H. You da man. Fixed.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 10:49 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
Lunatico Astronomical
Advertisement
Bintel
Advertisement
Celestron Australia
Advertisement
OzScopes Authorised Dealer
Advertisement
Meade Australia
Advertisement
SkyWatcher Australia
Advertisement
NexDome Observatories
Advertisement
Astronomy and Electronics Centre
Advertisement