M81 – Bode’s Galaxy

This is the newest edition to my portfolio, and it is, I think, my best image yet. This image was taken across three nights and consists of 10 hours of luminance and eight hours of RGB data. I’ve recently been on a bit of a roll with the new setup consisting of a Celestron C8, CGEM DX hypertuned mount and a ZWO ASI1600MM-Cool. The biggest addition that I also got to use for the Whirlpool image was the motorized filter wheel, which has been an unbelievable addition to my workflow. Being able to get data on every filter I need in one night completely automated has sped up my capture times significantly.

This image took about two weeks to go from raw data to finished image and it took a lot of processing and reprocessing to get to this point. I had some sensor tilt which you can just barely see off to the left side of the image which is now fixed for the next image, but that was really the only “flaw”. I used a couple new strategies for processing I’d like to go over here because they were pretty game changing for detail.

The first is HDR Multiscale Transformation. In the past, when I attempted to use this tool, I never got anything good looking out of it, but after doing some deep research on the tool I now know how to get some pretty amazing results out of it and it isn’t that hard. What you need to do is mask out everything except the core of the galaxy, being sure to stop at the edge of where M81 goes from orange to blue. Once you’ve done that, change the number of layers to eight in the tool and check off “to lightness” and “lightness mask”. These can vary from image to image to play around with it and see what kinds of results you get, but these values worked for me. After that, just run it and you should see a huge amount of detail return to the core. Remember, you’re not creating detail that isn’t there, you’re simply manipulating the data to bring out detail that’s trapped behind the glow of the core and sharpen things up.

Once that’s done, you’ll also want to use the local histogram equalization tool to rebalance the new core to match the rest of the galaxy, otherwise you’ll have a very unnatural brightness and color difference between the two areas.

Other than that, I went through my fairly standard processing workflow, except one extra thing. One issue with M81 is that it’s a pretty low saturation galaxy out of camera and if you try to just pump up the saturation, you’re going to be left with a lot of color noise and unnatural color. To counter this, run a photometric color calibration on the RGB data and make sure you get things pretty neutral. Then, mask off the background so it doesn’t get oversaturated and open LRGB combine. Extract the Cie-L from the RGB data and move the saturation slider in LRGB combine to around 0.3. Now take that luminance layer you just extracted and reapply it using LRGB combine back to the RGB image. After three or four applications you should have a near oversaturated image. That’s okay, because you’re going to be applying a monochrome luminance layer you’ve had laying around later which will desaturate things a bit. Once you have both the luminance and RGB layers processed to where you want them, apply the final luminance layer and you should see huge amounts of detail pop into your image.

Now all you have to do is some rebalancing of colors, background work and final cropping and you should be good to go. This worked out great for me, but I would caution restraint. If you overdo any of these steps, you’ll be left with a very unnatural looking final image which you should try to stay away from. The first round of processing I did left me with an M81 that had a near purple core that looked very fake, and I redid the entire process to fix it.

The hardest part of all of this is just learning where to start. Pixinsight is a very daunting program, but just going through the steps once carefully and slowly will teach you a lot and for the next image you should have a much better time working through everything. Just from my M51 image to this one, I have completely changed my process and now I’m thinking of going back and redoing the M51 image simply because I think I can get a lot more out of it. I’m definitely excited to see how far I can take this new setup this summer as I’ll be starting narrowband imaging soon, which in light polluted areas should be a lot easier to do than galaxies.


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