Rather than trying to dim the bakground I have tried to process this one by emphasizing it. Thus showing backgound is rich and not just a dark noisy area.

Processing this one has been a pain, I believe over 200 hours, back and forward until I was satisfied. I have perfected my skills since last post. In particular thanks to Jon Ristas tutorials, again, I have greatly improved my deconvolution. Also thanks to Nico Carvers M42 processing walkthrought some really good information for Local Histogram Equalization (I diverted slightly by using a mask poduced with a 8 layer MMT showing only residual layer rather than a range slection mask).

I shot it with 1x1 narrowband binning so I could use a synthetic luminance. But despite light pollution real luminance subs showed much deeper results. For RGB processing I resampled narrowband integrations very early in the process to simulate 2x2 binning.

I am now now 99% satisfied. My camera lens is a big limitation and I think I achieved best possible result with such gear. Also shooting M42 in the middle of a city, moreover low in the sky (20-30°), is far more difficult than I expected.

Artefacts are kept to a minimum, core stars are nice, noise levels are acceptable... I am finally happy :-)

Please give me your thoughts and advices in comments, I'm still a noob, I need and look forward to that!

My detailled workflow is:

* 1 - Pre-process

- Calibration with no bias (ZWO)

- Cosmetic Correction

- Subframe Selector

- Star Alignment

- Local Normalization

- Integration

- Drizzle Integration

* 2 - Process

** 2.a - L

- DBE

- Deconvolution (Jon Ristas technic)

- TGV Denoise (Jon Ristas technic)

- MMT denoise (Jon Ristas technic)

- Stretch (Combination of light HT followed by Masked Strech to avoid/reduce big stars and center bloating)

- Morphological Transformation to reduce bloated stars

- Local Histogram Equalization (Nico Carvers technic)

- 2 layers MMT to increase sharpness

** 2.b - Ha/S2/O3

- DBE

- Linear Fit

** 2.c - RGB

- HOS pixel math to produce RGB image (0.76*ha+0.24*s2; o3; 0.85*o3+0.15*ha)

- Background Neutralization

- Photometric Color Calibration

- SCNR

- Resample 50% to simulate 2x2 binning

- TGV Denoise (Jon Ristas technic)

- MMT denoise (Jon Ristas technic)

- Stretch (Combination of light HT followed by Masked Strech to avoid/reduce big stars and center bloating)

** 2.d - LRGB

- LRGB Combination

- TGV Denoise (Jon Ristas technic)

- MMT denoise (Jon Ristas technic)

- Curves Transformation