M31 Astrophotography: A Processing Deep Dive and Feedback

Hello fellow stargazers! I've just completed a significant project capturing and processing the magnificent Andromeda Galaxy, M31, and I'm eager to share my workflow and get some valuable feedback from more experienced astrophotographers.

My M31 Processing Workflow:

This endeavor involved a meticulous processing pipeline designed to bring out the best details in the galaxy.

Data Acquisition:

• Exposure Breakdown: 3 master stacks comprising 60, 180, and 300-second exposures.
• Calibration Frames: Flats and Bias frames were used for calibration.
• Shooting Conditions: Bortle 3.5 sky.
• Equipment: 80/480 Photoline Apo triplet telescope with a 0.79x reducer/flattener and an ASI533MCPro camera.
• Total Integration Time: 18.5 hours.

Processing Steps (PixInsight):

1. Initial Calibration & Stack: Standard calibration and stacking procedures were followed.
2. Preprocessing: SPCC (Super Pixel Combination) was applied, followed by Graxpert, BlurX, StarAlignment, and StarEx on each master light frame. These steps are crucial for noise reduction, sharpening, and aligning star data.
3. HDR Composition: The three master light stacks were combined using HDRComposition to capture a wider dynamic range.
4. Stretching & Enhancement:
   • StatisticalStretch from SetiAstro was used for initial signal stretching.
   • Generalized Hyperbolic Stretch (GHS) was applied for further stretching and contrast enhancement.
   • Curves adjustments were made for luminosity and saturation.
   • HDRMultiscaleTransform was employed to manage high dynamic range details.
   • Additional curves adjustments refined the tonal range.
5. Star Handling:
   • Stars were stretched using GHS and a touch of saturation.
   • These processed stars were then merged back with the starless image using PixelMath.
6. Final Touches: NoiseEx was applied to the final image to minimize any remaining noise.

Seeking Your Expertise:

I'm particularly interested in feedback regarding the processing side. While I'm happy with the result, I know there's always room for improvement. For instance, I used GHS without a mask, targeting specific regions with the symmetry point. I also used a range mask for some curves adjustments. I'm curious if using a mask with GHS could yield better results, especially in avoiding potential overstretching or flatness in certain areas. I also understand that adding Ha data can significantly enhance galaxy images, which is something I plan to explore in the future as I don't currently have a narrowband filter.

I look forward to hearing your thoughts and suggestions!