Reprocessing the Helix


During the dark sky imaging window in October, 2017 I made it out to capture some data on the Helix. Like most of my images it needs more exposure but I played around with processing it anyway. With the Helix having a low surface brightness at my latitude and because of the shorter than optimal exposure, it was very tricky to bring out the nebula.

My processing started out with my normal masked arcsinh stretch, but somehow I goofed and ended up with an image that had far too much contrast for the data and the colour was off quite a bit.

Now that my schedule allowed a few hours to work on the image again I did some experimenting with the settings I used in the arcsinh stretch. Getting a much better result from the masked stretch I moved on the noise reduction. This got tricky as there was quite a bit of photon noise in the image. The bright sky near the horizon has some light pollution even at our club’s dark sky observatory and the nebula was smack dab in the middle of it.

Using the frequency filter in Images Plus and a suitable mask I managed to get most of the noise under control. Having the ability to control the slope of the filter makes all the difference when tackling this type of noise. After multi-scale sharpening I ended up with an image that after binning by two wasn’t too bad. A final levels tweak and I finally got a Helix Nebula shot that is worth posting.

The image was processed entirely in Images Plus using arcsinh stretches, masked noise reduction using a frequency filter, multiscale sharpening and star reduction. For more information visit my webpage detailing the exposure and camera settings as well as a higher resolution version of the final image.


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