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ArcsinhStretch...

Khushrow Machhi
in PixInsight
Hi Adam,

After following your tutorials I have been getting excellent results on processing several galaxies I have imaged this season, M51, M81&M82, M101.  I am now processing the galaxy trio in Draco (NGC5985, NGC5982).  This galaxy is in a richer star field with many bright stars and while the ArcsinhStretch worked well with the previous galaxies with a sparse star field (star colors came out nice), the stars in the Draco trio field are getting blown out, that is I have color in the outer part of the stars but the centers are white, and when I do the LRGB blending they do not look "natural".  I have used multiple incremental stretches with ArcsinhStretch but it has not helped.  Should I use a different process to do the RGB stretching in this case or is there a better technique while using ArcsinhStretch?

Thanks,
Khushrow

Comments

  • BlockHeadBlockHead
    Yes, definitely. ArcSinhStretch is really only one of many ways to stretch the color data.
    I get this question  a lot... which means I think I came across as saying this is a primary method. It is a good one... but certainly not the only one. Multiple non-linear stretches to RGB data (midtones of HT or Curves) plus iterative raises of saturation can also do an excellent job. I haven't done this.. but masked stretch on the color data might also be a neat thing to go for!

    -the Blockhead
  • Khushrow Machhi
    I believe what is happening is that with a rich star field with brighter stars, the core of the the brighter stars is saturated and so does not "respond" to Arcsinhstretch, while the outer region of the star gets the color, the core remains white and so there is a colored halo effect after the stretch.  You do go over multiple use of non-linear stretches, but that is painful compared to using ArcsinhStretch (which is almost magical).  
    Thanks, Khushrow
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