Nebulosity 3 in a nutshell

Posted by XTSee on 15th October , 2012

I really like Nebulosity 3 for processing my astrophotography images. The Help manual provided with the software is excellent, and the website provides very good tutorials which explain how to operate the software, and provides excellent detail to help understand all about Darks, Lights, Flats, Dark-Flats, Bias/Offset and BPM (Bad Pixel Mapping), not only what these things are, but when and how they should be used in the pre-processing stages. The manual then goes on to explain about the various tools available for post-processing the images.

NGC869 part of Double Cluster

NGC869 part of Double Cluster

However, while it is quite necessary to take the time to read the manual to know what to do, and I have learned a tremendous amount by doing so, the manual is fairly long (it’s a good thing), I felt that it lacked a simple crib-sheet to remind you of the basic steps without having to paw through the manual over again….

So I wrote the following basic notes for what to do:-

(This process is for one-shot colour camera in RAW mode, such as my Canon EOS600D, but can be different for other cameras, e.g. mono, unsquare/square pixels, etc.)

  • Create Master Darks or Bad Pixel Map (BPM), Biases, Flats: Menu>Batch>Align and Combine. Use Average/Default or Std Deviation, alignment=None(fixed). Select all dark frames. Save/name as Master_Dark_<exposure-time>_stack.fit.
  • Filter out obviously bad Light frames: File>Preview Files. This is a manual review process, (different to Grading which can be done later) and will save processing time if dud lights are removed now (rename as bad_*).
  • Apply Darks/BPM/Biases/Flats to Lights: Menu>Batch>Pre-Process Image Sets. (Dark subtraction works better before converting to colour). Gives pproc_*. (If using traditional Dark subtraction, no need to subtract Bias, but if using Bad Pixel Map need to subtract Bias too).
  • Normalizing (optional): Standard deviation-based stacking is better when Lights have equal brightness. Menu>Batch>Normalize Intensities. Select pproc_*, gives norm_*.
  • Colour reconstruction (Debayer / Demosaic): Menu>Batch>Batch Demosaic+Square RAW colour. Select norm_*, gives recon_*.
  • Grading images (optional, helps decide to use only the sharpest images): Grading images works better after debayer/demosaic. Gives Qnnn_*
  • Stacking: Menu>Batch>Align and Combine. Alignment=Translation. Stacking=Average/Default. Select recon_* (or Qnnn_* if you Graded). Pick best bright but not huge star (not saturated/faint/noisy). Click it. Next image, click + (Shift=skip, Ctrl=keep guess, Alt=auto all). Repeat til done. Save as avgstack_v0. (If hot pixel streaks appear in final stack, try Standard Deviation method instead).
  • Post-processing:-
  • Crop.
  • Adjust Background Colour Offset (optional, removes skyglow).
  • Save!
  • Stretch (Levels, DDP, Curves,etc).
  • Save!
  • Adjust Colour, Hue Saturation, Noise reduction, Blur, Sharpen, etc.
  • Post-processing in Photoshop.
The importance of saving to newly named files during the post-processing stages helps save time if you mess things up, or want to experiment with a different type of procedure to get the best results. Things like Normalisation, DDP and especially GREYCStoration noise reduction can take quite a long time to process.
Also if you use a laptop for image capture at the telescope (mine is an old Dell with Win XP), but have a faster desktop machine (blinged up, quad or eight core, super charged gaming machine with tons of RAM!?) it is a good idea to transfer the RAW captures across and do the processing there, as it can make a considerable difference to the speed of the processing.
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2 Responses to “Nebulosity 3 in a nutshell”

  1. Bob Riggs (1 comments)

    Hello Jim,

    I am a new owner of an XT8i. I have really enjoyed all of your comments on the Intelliscopes and used your suggestions during assembly. I recall you made mention of taping the azimuth encoder to the base. I can’t find it anywhere now. Would you please point me in the right direction?

    Thanks and clear skies!

    Bob

  2. XTSee (24 comments)

    Hi Bob,

    I’m not sure exactly what you mean about the tape. The only page I can think of is at:-
    http://orion-xt10.com/lazy-susan-azimuth-bearing.html
    but this relates to taping some strips of carpet to act as a kind of brake to slow down the azimuth bearing after it has been converted to use a lazy susan bearing.
    I wonder if this was what you remembered?
    The other page where I discuss various improvements relating to the azimuth bearing is this one:-
    http://orion-xt10.com/orion-skyquest-azimuth-bearing.html

    Best wishes
    Jim


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