Hello,

I decided to make a test and see If I can make a HARGB version of the Andromeda Galaxy with a color camera from the city. Here is the data that I started with:
1/ My RGB data taken with the Celestron Light Pollution filter for the RASA8:
- 300 x 60 seconds;
- 292 x 120 seconds;
- 225 x 300 seconds;
Or a total of 33 hours - taken on 30.08, 31.08, 01.09, 03.09 and 06.09.2021

2/ My Narrowband data taken with the IDAS NBZ filter:
- 59 x 120 seconds;
- 84 x 300 seconds;
Or a total of 9 hours taken on 04.10.2021

So my processing steps were as follows:
- integrated all of the RGB data;
- integrated all of the narrowband data separately;
- used one and the same frame for star alignment in order for the two images to be aligned;
- processed both versions separately - used one and the same dynamic crop followed by DBE, Deconvolution, Background Neutralization and Color Calibration and stopped after I applied noise reduction through MLT;
- then I extracted the red channel from the RGB data and the red channel from the narrowband data. Used the following to combine both frames in Pixelmath:
// RGB/K: ((HA * RGB_R_bandwidth) - (RGB_R * HA_bandwidth)) / (RGB_R_bandwidth - HA_bandwidth) // Symbols:RGB_R_bandwidth=200, HA_bandwidth=10
In theory this formula should have reduced the HA only to what was not already included in the RBG_R frame. This wasn't the case with me. It had combined both reds in a nice way. I used ChannelCombination and added the new "red" to the original RGB image. Then used BackgroundNeutralization to clear the red background and the colors looked balanced but with a lot of red in the HA regions of the galaxy.

Despite this version I tried to achieve the same result through several other approaches (including formulas from the Internet and NBRGBCombination script) but the above processing steps gave me the best result.

As a next step I decided to try something more. I integrated all of the frames of Andromeda in one - RGB and Narrowband. Then extracted the Luminance from this frame, processed it and added it to the HARGB from the previous step.

The steps that followed were standard:
- EZ soft stretch;
- TGV Denoise;
- HDRMultiscaleTransform;
- LocalHistogramEqualization with 25 and 100;
- MLT for sharpening;
- Curves Transformation for boost of colors;
- Dark Structure Enhance script.

This time I managed to keep the blue and purple from the RGB data and add a lot of Red to the HA regions. Adding this HA made the red regions really stand out and glow.

I hope you like my version of the Andromeda Galaxy in HALRGB with a color camera and under the city lights.

Clear skies,
Ivan