Sunday, March 2, 2014

NGC 1491

NGC 1491 is an emission nebula in Perseus. It's 10,700 light years away in the Perseus arm of the Milky Way. Stars are created in this nebula - and the ultraviolet light from those newborn stars excite the atoms of the nebula - which makes it glow.
Click on the image for more details on capturing this image.

I did not have enough time to capture more SII (red) data. But with a lot of processing (see below), I could bring out quite some detail. Here is the core part of the nebula:

Some nice detail, but it shows that this image could use more data to increase the SNR.

Because this object turned out to be rather faint, I really had to stretch my post processing skills on this one:
  1. I calibrated, stacked and aligned the images in CCDStack and cropped them.
  2. Then I neutralized the background of all 3 images
  3. I combined them by summing them up for a synthetic luminance image
  4. Deconvolved this image
  5. Stored all of them (scaled) as TIFF's
  6. Then, I used Straton to create a star-only image of the synthetic luminance image.
  7. Loaded the SII, Ha and OIII images in Photoshop and used a tutorial by Paul Kanevsky for DDP (Digital Development Processing) in Photoshop (unfortunately, the action that Paul made out of his tutorial does not work in Photoshop CS6)
  8. In Photoshop, I combined the SII, Ha, OIII images as described by Ken Crawford.
  9. Of each individual image, I "brought out the faint stuff" using a great recipe by Scott Rosen.
  10. Then I adjusted the levels of each individual image to darken the background
  11. Adjusted opacity of each layer to get a good mix of all colors (as always the green from Ha was dominant)
  12. Added a CAB layer and applied GradientXTerminator
  13. Used a "Selective Color" layer to reduce the amount of magenta (mostly in the stars) and to bring out the orange parts more
  14. Loaded the synthetic luminance image
  15. Used an adjustment layer with a mask to reduce the brightness of the core and increased its contrast (see e.g. http://helpx.adobe.com/photoshop/using/masking-layers.html for an explanation)
  16. Layered the luminance image over the combined image using "Soft Light" mode and adjusted Opacity to find a balance between bringing out details and still showing the fainter parts of the nebula
  17. Loaded the star-only image and used a simple levels adjustment to remove all nebula remnants (but being careful not as to remove any faint stars)
  18. Layered this star-only image on top (using Screen mode)
  19. Finally, I created a CAB layer on top and applied the "Star Diffraction Spikes Fat Stars" from Carboni's Astronomy Tools.
There are so many steps here that I tried for real for the first time. Considering that, I'm pretty happy with the result.