When I first opened PixInsight I found it utterly bewildering, so over time I've settled on a quick and easy nebula workflow that gets me from a freshly stacked image to a finished picture without getting lost in the weeds. In this post I'll walk through it using the Eastern Veil Nebula as the example. Whether you're a beginner or a seasoned astrophotographer, hopefully there's something here for you, and if you'd rather watch it all happen on screen, the video at the top of this post covers every step.
I use a few additional plugins along the way:
- BlurXTerminator and NoiseXTerminator (paid): www.rc-astro.com/
- StarNet2 (free): www.starnetastro.com/download/
- EZ Processing Suite (free): discontinued, but likely still downloadable
Remove gradients with DynamicBackgroundExtraction
My starting image has a really strong green hue, so the first job is DynamicBackgroundExtraction. I click on the image and generate samples with a tolerance of 1, leaving the rest at defaults, which scatters boxes across the frame. The trick is to nudge the boxes so none of them sit on stars, nebulosity or any other bright elements, adding extras into any gaps. I run it first in subtraction mode, replacing the target image directly, but I keep a copy of the process so I can run it again in division mode afterwards. The subtraction pass kills the green hue, and the division pass then removes the remaining background gradient.
Colour calibration with SCNR and PhotometricColorCalibration
Next comes colour calibration. I run SCNR with the defaults to strip out the last of the green cast, then PhotometricColorCalibration, which I think is a really useful and powerful tool. It corrects the colours further based on existing recorded data. It takes a little while to run and produces some graphs you can just close, but the result is a subtly improved image: the background looks more properly black and the nebula colours come into line.
Stretch with EZ Soft Stretch
Rather than fiddling with the screen transfer function every time, I run EZ Soft Stretch from the EZ Processing Suite. There's not much to it, it's quick and easy, and it leaves the image looking pretty decent, although there's still detail to pull out and a fair amount of noise to deal with.
Sharpen with BlurXTerminator
For deconvolution I use BlurXTerminator from RC-Astro. It's a paid tool, but worth every penny in my opinion; the level of clarity it can bring out is pretty spectacular. It takes a little while to run, but the before and after speaks for itself: the stars are shrunk down a touch and the detail in the nebula is dramatically cleaner.
Clean up with NoiseXTerminator
RC-Astro's NoiseXTerminator (also paid, also worth it in my view) handles the noise reduction. The values I use seem to work well and it runs a bit faster than BlurXTerminator. The grainy image comes out the other side much smoother.
Separate the stars with StarNet2
Now I can process the nebula independently of the stars. I run StarNet2 (the successor to StarNet++) with the generate star mask option, which splits the picture into two images: the nebula in isolation and the stars on their own. It takes a little while, and once it's done I set the star image aside (don't close it, you'll need it later) and get to work on the nebula.
Boost the nebula with CurvesTransformation
On the nebula image I open CurvesTransformation with the live preview and aim for a subtle S-shaped curve: drop the black point a little and maintain the highlights without blowing them out. Little and often is better here, so I apply multiple small transformations and check the result each time. I keep an eye on the black level too, aiming for roughly 0.06 or 0.07 rather than a harsh zero. Then I bump the saturation, again subtly. You could go crazy and make it ridiculously rich, but it doesn't look great; the goal is a sweet spot where the blues pop and the deep orangey reds come through while still looking somewhat natural.
I then run a second CurvesTransformation on the stars image, mainly to lift the saturation slightly and bring out the colour variation in the bigger stars, the blues, oranges and reds. It's subtle, but worth doing. Finally I extract the luminance layer from this image, which I'll need for star reduction in a moment.
Recombine with PixelMath
To put the stars back into the nebula image I use PixelMath. I can't remember where I originally found the formula I use, but it gives a better result than a simple stars plus nebula addition. Run it, and the recombined image replaces the original in line.
Finish with EZ Star Reduction
The stars are still fairly prominent at this point, so the last step is EZ Star Reduction, again from the EZ Processing Suite, using the extracted luminance layer. I run it on 10 cycles and it does a decent job of taking the stars down so they're less in your face and the nebula can really pop. A subtle transformation, but worthwhile.
And that's as far as I take the simple workflow. You could obviously do a lot more, and my image processing still leaves much to be desired, but this gets you a result you can be really happy with. Here's where the Eastern Veil ended up:
Eastern Veil Nebula4h 12m · William Optics Zenithstar 81 APO · ZWO ASI 294MC ProView in gallery →
Clear skies!