Narrowband Imaging V: Image Processing

There's not much I can write here that hasn't been written better by others with vastly more experience than I have. Here are a few observations:

• Calibration, aligning and stacking of the collected light frames is important, but the processing that follows is where the art enters in. Most software packages dedicated to astrophotography will do the calibrations, alignment and stacking in an automated fashion. All you need to do is set a few preferences and wait.
• Whatever software you use for postprocessing, try to become familiar with its many features.
• Experimentation is good. Try to jot down the steps you take when in the final stages of postprocessing. This will help you replicate your methodology.
• Don't delete your original images.  As you learn more you may wish to reprocess them.
• These are your images.  You're the ultimate audience, and the only person you're trying to please.

When posting images for others to view:

• Don't post large full-scale images to forums. Reduce your images to a maximum dimension of about 800 pixels. Provide a link to a full-scale image housed on a web-based photo service if you want to people to see it. 
• When posting .jpg images, don't overdo the compression.  Overcompressing produces distracting artifacts, particularly around stars.
• Placing copyright text on an image is basically a waste of time. The only way to prevent people from using your images without your permission is to not post them. (This is a personal thing with me; I think copyright notices look pretentious.)

Speaking of matters of personal taste; here are some of mine:

• I don't like backgrounds that are absolutely black; a dark neutral gray is perfectly fine and more realistic.
• Stretching an image is easy to overdo and can cause hard edges on nebulae. I usually prefer a softer-looking image that is a bit understretched.
• If you want diffraction spikes on your stars, don't use software to create them. Get a telescope with a spider-supported secondary, or create a mask that holds fine threads across the optical path.  Better yet, learn to like images without spikes. 
• Don't overdo filtering. Unsharp masks and other sharpening algorithms can introduce artifacts that detract from image quality. Toggle between before and after to watch what an enhancement does to nebular texture. If it introduces features that are barely there in the "before" image weaken the enhancement.