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LRGB Processing Workflow for stars

David Stearn
in PixInsight
Adam,

In your LRGB course processing M83 I you did not remove the stars and process them separately. Is there a reason why you did not stretch and saturate them separately?

Comments

  • BlockHeadBlockHead
    Can you suggest some reasons why I might not remove the stars and process them separately based on the this video and others on my site? It might be instructive to format this exchange in this way based on my videos and overall philosophy I take about in my lessons.

    -the Blockhead
  • David Stearn
    If you want to use it for SPCC but after SPCC and BlurXT using PSF.
  • BlockHeadBlockHead
    That is not the direction I am thinking about. I think this is more about what is important in the image. 
    Keep in mind the LRGB lesson, as many lessons do, do not have every consideration taken into account. The lessons become too long and viewers lose the important points being actually highlighted. 

    So let us put aside your criticism. 
    Given I am not going to show every step in every lesson in order to make the main points stand out more- 
    why might you guess I did not remove the stars? What is it about this picture that is different than say LDN 183 or NGC 1491 in which I do exactly what you expect? 

    Again consider the final result: https://www.astrobin.com/lgv7y8/

    -the Blockhead
  • David Stearn
    It does not have the nebulosity like the other two.
  • BlockHeadBlockHead
    And anything else?
  • David Stearn
    M83 has stars in the galaxy
  • BlockHeadBlockHead
    Would you agree that this field has less stars than the other fields? 

    So now I will reiterate what I teach in various lessons. 
    What is the subject here - the stars or the galaxy. I would argue the galaxy is the primary subject.
    Next, do the stars interfere with the primary subject in the field?
    I would say no. They do not distract from the galaxy. I can clearly see the galaxy's features with or without the stars. Unlike a nebula- galaxies have symmetry. The outer halo (and arms) are circular- if you tried to make the argument that the stars are a distraction- it is compensated by the symmetry of the object.

    So, now what? Is the next step to blindly apply some step like removing the stars. What is the purpose of doing so? Is it to minimize the distraction? I say no.

    But maybe you think minimized stars look better. I would argue that isn't always the case and fewer stars show the downsides more. The adjustment of the MTF to a stars-only image does change the relative visible PSFs depending on to what degree the adjustment is made. With fewer stars, this is more easily noticed. To me, if I can see what was done- it loses a bit of the wow factor. This doesn't mean I wouldn't do it... it depends on how proportionally important/significant the effect is. The natural PSFs given a typical stretch of the stars looks better to me and better matches the stretch of the galaxy (which is actually good because it communicates how faint the galaxy is) and slightly "larger" stars are easier to show their colors. When the stars are not too numerous, this can also be a nice benefit.

    So... you asked me why didn't I blindly do some particular step. At every step I think along the lines of what I have described above. This is what an artist does.

    Should I explain all of this stuff when I skip a step and give reason for every exception. No, but I do clearly state these ideas as a theme through my demonstrations. 

    -the Blockhead
  • David Stearn
    I was not suggesting that the stars be permanently removed.
  • BlockHeadBlockHead
    Nor am I.
  • David Stearn
    My final result https://app.astrobin.com/i/qs07wi
  • BlockHeadBlockHead
    Nice result!
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