M101 Pinwheel Galaxy – Pixinsight

After quite a long while of cloudy skies, I finally had a few hours where the clouds cleared from the sky. The conditions were not ideal, as there was more skyglow than usual. But as this was a very rare opportunity to image with my Orion VX12, I decided to grab at the opportunity, albeit without collimating my telescope.

Having spent over 3 hours setting up and imaging a few targets in the sky, I was hoping to be have some usable subs for stacking. Imagine my disappointment when Deep Sky Stacker failed to stack the images. I had to find another way to stack the images. Now I have heard of users being able to stack with Pixinsight where Deep Sky Stacker failed. Hence I thought there is no harm in trying.

I have to say that the whole process is time-consuming, requiring the mastering of many of the processes in Pixinsight. But the results are very impressive. I have put the steps I used into this thread in case I need to refer to in in future.

Processes:

1) ImageIntegration – to create master bias, dark and flat files prior to image calibration (these files can be reused for future).

2) ImageCalibration – to calibrate sub files

3) StarAlignment – register sub files with star alignment, prior to image integration of sub files.

4) ImageIntegration – registered files stacked to create integrated image.

M101 - high rejection pixels following integration
M101 – high rejection pixels following integration which are removed from the stacked image
M101 linear image prior to stretching
M101 linear image prior to stretching (only bright stars are visible)
M101 - initial stretched image following integration
M101 – initial stretched image following integration

5) Do Automatic background extraction – very mild extraction done.

Automatic background extraction - background removed from image
Automatic background extraction – background removed from image

6) Do Dynamic background extraction to further improve the image – requires multiple steps.

Dynamic background extraction - background removed from image
Dynamic background extraction – background removed from image
M101 - following automatic and dynamic background extraction
M101 – following automatic and dynamic background extraction

7) BackgroundNeutralization and ColorCalibration done to remove the color cast.

8) MaskedStretch done to stretch the curve for subject (M101) without stretching the stars.

9) Mask applied prior to increasing saturation in CurvesTransformation.

10) Final adjustment with HistogramStretch to produce the final image.

M101 final image
M101 final image

I am pretty pleased with the final image, particularly as it could not be stacked in Deep Sky Stacker. I know the stars are not all round (due to not collimating the scope prior to imaging, but I did not have much time having only set up the scope at midnight), and the sky had significant skyglow affecting the final captured subs. But considering all that, I managed to get a pretty decent image of M101. And it is all part of the learning process – to get the best out of my imaging setup and the postprocessing. With practice, I can only get better at this. And I have found a way to stack images which Deep Sky Stacker cannot process. Looks like I will be buying Pixinsight after all.

Boon