I really like [1] 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.

[2]

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.