Star Shrinking Under Tracking

Guides, tutorials, tips & tricks.

Star Shrinking Under Tracking

Postby Rkonrad » Tue Oct 24, 2017 5:28 pm

Though this procedure may not be new to some, I discovered it by accident working more extensively under the "life" module. Michele generously offered her data of a wide view of the Veil Nebula - an area with a particularly dense field of stars. Shrinking the stars early in the process helps with revealing the faintest parts of the nebula, particularly in the centre. Here is my process:

1. Autodev
2. Crop as usual then wipe with a dark anomaly setting of about 3 px.
3. Autodev with an emphasis on either the eastern or western nebula. I adjusted the ROI influence until I could see as much of the central nebula region as possible without enlarging the stars too much.
4. No deconvelution at this point as the image is too noisy (done after tracking and near the very end)
5. I did a linear mask of the stars (fat stars) with default setting then hit "grow" one or two times - "keep"
6. I masked the stars a second time under (stars) with default settings. Make sure you select "add new to old". At this point you will notice that the stars and noise are selected. Click "shrink" (maybe twice) to remove the selected noise. Invert mask so stars are *not* selected
7. Under "life" select "isolate" and "do". This will emphasize all but the stars. The following screen shots show the result just after "3. autodev", then after "7. life-isolate"

autodev.jpg (274.34 KiB) Viewed 2359 times

isolate.jpg (185.89 KiB) Viewed 2359 times

8. To further separate the nebula from stars, you will do a second iteration of isolate. First highlight all visible parts of the nebula using the default "flood fill lighter pixels". This is the fiddly part where it may take time to find faint central parts - be generous looking for all the "red". Click grow once.
9. So as not to emphasise the stars within the nebula, mask the stars with default settings but "subtract new from old". Once done, invert the mask to view the masked stars. If noise is also masked, click shrink then grow.
10. Invert then apply "isolate". Following is the result after 2nd isolate.

isolate_result.jpg (190.09 KiB) Viewed 2359 times

11.To sharpen details in the nebula, keep the same mask.
12. At this point, or even earlier, I prefer to desaturate the image so I can clearly see how dark the background is. In this case I might apply a small amount of equalization under the HDR module.
13. Following, go to the colour module and then disengage tracking for noise reduction.
14. In my case, I found further emphasising the faint parts of the nebula were achieved by applying the default setting of "life" over the whole image but changing the glow threshold to 0 and bumping up the "airy disk radius" 2/3 towards the end. This gave a nice glow but kept more detail.

The end result looked like this (private view - thanks Michele)

Cheers Richard
Posts: 202
Joined: Sun Feb 07, 2016 2:55 am

Re: Star Shrinking Under Tracking

Postby admin » Sat Oct 28, 2017 5:14 am

The Isolate preset in the Life module is great for isolating larger scale nebulosity from a busy star field (or noise!). It really is extremely useful if you want to "re-focus" the viewer's attention on latent nebulosity, as it imparts coherence to the scene.

If you use it with a mask to selectively apply it (rather than globally), just be aware that you're getting into a "grey area" with regards to documentary value, as you are now making guesses (though very educated!) at where nebulosity exists and where it doesn't exist - all without having recorded it through an instrument in order to substantiate your decisions. It's not exactly "photoshopping" or "painting on" nebulosity, but it may be frowned upon by some if presented as a scientific rendition of a dataset.

Of course, for a lot of us, astrophotography is more about making amazing pictures, rather than hard-core science. And where you stand on this is totally up to you!
Ivo Jager
StarTools creator and astronomy enthusiast
User avatar
Site Admin
Posts: 2203
Joined: Thu Dec 02, 2010 10:51 pm
Location: Melbourne

Return to Tutorials & Guides

Who is online

Users browsing this forum: No registered users and 1 guest