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 Image Processing using
 NEBULOSITY

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I've been using Nebulosity 2 for primary image processing for a few years now and found it to  be a powerful and inexpensive tool to  capture and process astro-images. (To  see some of my images click on the Gallery link on the left)

Nebulosity is the brain child of Craig Stark and can be purchased on his web site http://www.stark-labs.com/purchasing.html. Craig has versions for Windows and MAC computers.

I have found that  collecting the images is the easy part. However, processing the images to bring out the details and color of the object and reduce the noise is quite a bit more challenging.

To  help others that  might be interested and to park the info where I can find it easily, I thought that  I would put some  processing notes on my site. Some are excerpts from the Nebulosity user guide.

The basic steps in order are as follows:

  •  Decide on how you’ll deal with hot pixels (Bad Pixel Map vs. Dark subtraction)
     
  •  Prepare sets of darks, flats or bias frames to remove hot pixels, vignetting, etc.
     
  •  Batch Preprocess B&W/RAW images using the darks & flats from above. I have been using the simple dark subtraction method and select auto scale the darks. Now you'll have a set of images named "pproc_OriginalImage.fit"
     
  •  Convert RAW images into color via Demosaic (if one-shot CCD used and captured in RAW, which you really should do) and square-up your pixels (if needed)
  1.  Pull down Batch, Batch Demosaic + Square (if images are from a one-shot color camera) or Batch Square (if images are from a monochrome camera or you just feel like squaring up a color cam's but keeping the image as monochrome for some reason).
  2.  Select your frames
  3.  Ideally, Nebulosity will start loading and reconstructing the frames. If it pops up a dialog asking for things like offsets, it means it did not recognize what camera captured the image (or you have “manually override color reconstruction” checked in the Preferences). If this happens, consult the Reconstruction: Demosaic’ing and Pixel Squaring section in the manual.
  4.  In the end, you'll have a set of images named "recon_pproc_OriginalImage.fit"
     
  •   Grading and Removing Frames. I use the Grade image Quality  option in the batch mode. Then I look at the lower quality  images and see if they should be removed from the stack using the Preview image option.  At this point you'll have a set of images named "Qnnn_recon_pproc_OriginalImage.fit
     
  •  Match Histogram using Highest Quality frame ( the one with the lowest Q number) as master.
  1. Pull down Batch, Match Histograms
  2. Select a reference frame and press OK. This will serve as the template image   that others will be matched to.
  3. Select the set of frames you wish to normalize
  4. In the end, you'll have a set of images named "histm_Qnnn_recon_pproc_OriginalName.fit"
  •  Stack the images (Align and Combine) Don't use Auto Align if you have stars for alignment points. I use Drizzle 2X and Atomizer set to 3. This is slower but more accurate.
     
  •  Crop the image to clean it up - Make sure that you crop off the edge of your image,
    removing any shaded area due to image shift prior to using the AUTO COLOR BALANCE
     
  •  (color only) Remove skyglow hue - Auto Color balance
     
  •  Stretch the image (Levels, DDP, etc)
    I've been experimenting with  the Digital Data Processing (DDP) option and found it works well on some images. However for most of the images I use Levels and Curves. I also increase the color by upping the Saturation some. Usually I start with  50%  and see how it looks. One of the final things I do is reduce the noise using the GREYCstoration Noise Reduction function followed by the Tighten Star Edges tool. I usually use the default value of 1.0
     
  • Once the Image is to  my liking I save it as a FIT as well as a JPEG.
     Since Nebulosity lacks the filter and layer functions that  are found in Photoshop, I typically  import the JPEG into PS and do some final tweaking there.
    At the present I only  have PS6 which processes image in 8 bit color depth only so I keep the processing to  a minimum. 

 

The complete Nebulosity 2.3 user manual (PDF) can be found HERE  

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