Deer Lick group and Stephan's Quintet

[alan4908]

Well, my last image of 2016 - the Deer Lick group and Stephan's quintet. I've also included an annotated version for the galaxy hunters. Constructive comments and criticism is welcome.

The image is an LRGB and represents about 7 hours integration time, it was going to be a bit longer but I decided to discard quite a few subs due to poor seeing conditions.  

I also had a bit of a struggle trying to get (what I hope) is the correct colour for the main galaxy (NGC7331). My conclusion is that when processing RGB data, I should first use Pixinsight's Linear Fit route to achieve colour balance before attempting DBE or Colour Calibration - any thoughts on the optimum order for application of these functions would be appreciated. 

Alan

 

 

LIGHTS: L:14, R:9, G:10; B:8 x 600s. DARKS: 30; BIAS 100; FLATS:40 all at -20C.

[faulksy]

awesome pic mate

[StuartJPP]

Very nice...love to see the wide FOV with these objects.

[alan4908]

22 hours ago, faulksy said:

awesome pic mate

Thanks Mike !

20 hours ago, StuartJPP said:

Very nice...love to see the wide FOV with these objects.

Thanks Stuart

Alan

[PatrickGilliland]

Thats a nice and tidy version of the area, like that, well done. Paddy

[alan4908]

16 hours ago, PatrickGilliland said:

Thats a nice and tidy version of the area, like that, well done. Paddy

Thanks for the complement Paddy.

Alan

[Barry-Wilson]

Hi Alan

Linear Fit is really designed to match the relative brightness of integrated stacks rather than set a colour balance AFAIK.  Colour balance is a separate process and number of steps as I'm sure you know.  I have read about balancing colour with Linear Fit on the PI forum however I wonder if the balance arises becuase brightness/luminosity within the colour channels is better matched.  If you think Linear Fit is needed - should be obvious from the STF of the individual colour channel stacks - I would apply it after a crop experilment with the effect before DBE and after DBE.  Personally I have very rarely used it and if I have I've felt it has been detrimental to the image.

I aim to apply the minimum processing steps and tools for my images.  I study the image and data and use my judgement about which process/script to use and to what degree.  There clearly are defined steps with LRGB/NBRGB especially with the linear RGB process, but I have not found Linear Fit to be a benefit with my data so I do not use it simply because it is in the PI arsenal and forum posts suggest it is advantageous.

Therefore I would first assess whether you actually need Linear Fit - try LRGB without it and gauge the results.

HTH.

[alan4908]

12 hours ago, Barry-Wilson said:

Hi Alan

Linear Fit is really designed to match the relative brightness of integrated stacks rather than set a colour balance AFAIK.  Colour balance is a separate process and number of steps as I'm sure you know.  I have read about balancing colour with Linear Fit on the PI forum however I wonder if the balance arises becuase brightness/luminosity within the colour channels is better matched.  If you think Linear Fit is needed - should be obvious from the STF of the individual colour channel stacks - I would apply it after a crop experilment with the effect before DBE and after DBE.  Personally I have very rarely used it and if I have I've felt it has been detrimental to the image.

I aim to apply the minimum processing steps and tools for my images.  I study the image and data and use my judgement about which process/script to use and to what degree.  There clearly are defined steps with LRGB/NBRGB especially with the linear RGB process, but I have not found Linear Fit to be a benefit with my data so I do not use it simply because it is in the PI arsenal and forum posts suggest it is advantageous.

Therefore I would first assess whether you actually need Linear Fit - try LRGB without it and gauge the results.

HTH.

Barry 

Thanks for the suggestions regarding Linear Fit.

Further to my post, I did of bit of searching around and found one explanation of Linear Fit in the book "The Astrophotography Manual" by Chris Woodhouse:  "it effectively removes the extreme (often red) colour cast in the background of an RGB image and achieves an approximate colour balance between the channels".  So, if this is correct, it would appear to be connected to the colour balance but only at small (eg background) pixel levels. 

As you suggest, I think I need to experiment a little more with this function. 

Alan