Updated: Oct 20, 2019

Trying to make an HaRGB image for the first time can be frustrating. We had a little bit of trouble combining our Ha frames with our RGB master in Pixinsight, we had no idea how to do it and the tutorials we found online were pieces by pieces. Here is our own little tutorial of how to combine your Ha data to your RGB from A to Z... in 8 short steps!

Pre-requisites: You must have a Master Light ready for RGB, which will be combined later with the Master Light Ha we are about to make.

  • Go to Script - Batch Processing - Batch Preprocessing.

  • Add your Lights, Darks, Bias, and Flats

  • Uncheck "CFA Images"

  • Check "Calibrate Only"

  • Pick a Reference Image from one of your RGB shots, make sure you remember which one it is as you will re-use it later.


This will separate the channels of your images in subfolders. (CFA0, CFA1, CFA2, CFA3). CFA0 is the red channel.

  • Go to Process - All Processes - SplitCFA

  • Add your Calibrated Files (should end in "_c")

  • Launch the Instance

  • Go to Process - All Processes - StarAlignment

  • Add the files that are in the CFA0 subfolder (should end in "_c_CFA0")

  • In "Reference Image', make sure to use the same image you used in the Reference Image in Step 1

  • Check "Create Drizzle Files"

  • Launch the Instance

  • Go to Process - All Processes - ImageIntegration

  • Add your Registered files (should end in "c_CFA0_r"

  • Add your Drizzle files

  • Launch the Instance


  • Go to Process - All Processes - DrizzleIntegration

  • Add your Drizzle files

  • Launch the Instance

You should now have your Master Ha Drizzle file, which is the one we will be combining to the RGB file! So open up your RGB file as well and put them side by side on your workspace.


Since our Ha image isn't exactly framed the same as our RGB image (unless you took both on the same night and did no move your camera at all when you installed your filter), we need to make sure both are cropped the same so that they can stack correctly.

  • Go to Process - All Processes - DynamicCrop

  • Get the perfect crop on your Ha file, make sure to not get any of the black bands. Rotate if needed. DO NOT press the green checkmark, instead, drop the instance on your RGB file first, then select your Ha file again and you can then click on the green checkmark.

  • Close the Instance


It is a good idea to apply a background extraction before actually combining the two masters.

  • Go to Process - All Processes - DynamicBackgroundExtraction (or AutomaticBackgroundExtraction, up to you)

  • Apply the same Background Extraction to both images

  • Close the Instance


Last step! We will now use this script to combine our RGB master and our Ha master.

  • Go to Script - Utilities - NBRGBCombination

  • For "RGB", identify your RGB Master and put your bandwidth at 200mm

  • For "R Channel", identify your Ha Master and insert the bandwidth of your filter (in our case, we use the Astronomik 12mm Ha clip-on filter so it is 12mm). For the scale, you can play around with it but we found that 4.0 to 5.0 worked great for Barnard's Loop.

  • Click on "NBRGB" near the preview spot to get a preview of the combined image

  • Click "OK"

And... That's it! You now have successfully combined your RGB and your Ha images into one! See below for an example of our combined image of Barnard's Loop (only 15 Ha frames for this example).

The color may make you think that something went wrong, but don't worry, that is normal and can be fixed during your regular processing steps.

Your next steps should be to do another Background Extraction if needed, followed by a Background Neutralization, Color Calibration and so on.

Let us know in the comments if you have any question or tips for others :)

You can also watch our video below if you are still having trouble with these steps.

Q1: "My combined image is not aligned at all!"

Answer: You did not select the same RGB Reference Image in Steps 1 and 3

Q2: "NBRGB Combination gives me an Error message saying that the two files aren't the same size!"

Answer: You did not properly take care of the Drizzle files. Either re-do a Drizzle Integration or double check that you have correctly created the Drizzle files in the previous steps.

Clear Skies,

Antoine & Dalia Grelin

Galactic Hunter


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