PixInsight Processing Question – Adding Ha to a RGB Image

I use a script called HaRGB Combo written by Jürgen Terpe - it works really well. I’ve attached a couple of images that describe it in more detail.

Screenshot 2026-02-11 at 8.30.34 PM.pngScreenshot 2026-02-11 at 8.33.58 PM.png

Continuum subtraction is required for any type of target, not just galaxies. It’s required because the broadband red channel includes H-a so it’s designed to avoid ‘double-counting’ the Ha. As mentioned above, the ContinuumSubtraction script is one way to achieve this.

For adding H-a to RGB I find the ImageBlend script by Mike Cranfield works very well (it also works well for adding Lum to RGB).

Jim Waters · Feb 12, 2026, 04:21 AM

I have been looking through YT off and on for 2 days and haven’t come across a good video on how to add Ha to a RGB image. Many of the processes available within PixInsight use a Blend or Add function. IMO this has a tendency to destroy fine details or produce odd Ha colors. Many of the video’s use Continuum Subtraction which is focused at galaxies based on my understanding. How can I add Ha to an existing RGB target like the California Nebula or other targets that include large Ha regions? Right now I am trying to process an image of the M38 area that has a lot of background Ha. Any help would be appreciated.

Jim

Phoenix, AZ

This is similar to what I wanted to do on Ngc2264. I imaged about 8 hours of IR/UV, but it didn’t have the Ha of the nebula that I wanted. So I imaged about 8 more hours with a L-Extreme. I processed each seperately to get the best “I” could out of each, and removed the stars in both. Then used the imageblend script to combine and add back in the ir/uv stars.

📷 Ngc2264_The Christmas Tree Cluster & The Fox Fur Nebula

https://app.astrobin.com/i/vrzzwp/

Doug