I created a script for Siril that takes as its input, calibrated L, R, G, and B images and produces a final image that’s ready for finishing touches, or saving to a preferred format for sharing.

Introduction to LRGB Image Processing with Siril

Astrophotography is a fascinating hobby that allows us to capture the beauty of the cosmos. One technique used by astrophotographers is LRGB image processing, which combines separate luminance (L) and color (R, G, B) channels to create stunning images with enhanced detail and vibrant colors. Siril, a powerful open-source software for astronomical image processing, offers an efficient way to process these LRGB images.

In this guide, we will walk you through using a custom script designed for Siril 1.2.0 that automates the LRGB image processing workflow. This script streamlines the entire process from stacking calibrated images to applying various enhancements like noise reduction and saturation boosting. By following the steps outlined in this guide, you’ll be able to produce high-quality astrophotographs ready for final touches or sharing with others.

Script Requirements

The script requires that you have Siril 1.2.0 installed and that you have at least two L, R, G, and B images (if you have only one image, just make a copy of the image).

Acquiring and Installing the Processing Script

Click the following link to download three scripts, which includes the complete processing script:

Download Siril processing scripts

Open the ReadMe.txt file and review the installation instructions there – it is very straightforward.

Sample Observation Download

If you don’t have any LRGB files handy, download my sample observation of Messier 20 which contains FITS files that are similar to what Canary Two produces:

Download sample observation of Messier 20 (116Mb)

Using the Processing Script

1. Create an empty folder someplace convenient on your system

2. Create an L, R, G, and B folder

3. Ensure there aren’t any subfolders named stacks or process

4. Copy your L, R, G and B files to their respective folders (ensure that you have at least two files – make a copy if you have just one of the files)

5. Start Siril and set the home folder to the folder from step one (click the icon that looks like a house)

6. From the Scripts menu, select ErikWestermann_FullProcLRGB

7. The script will run for some time – here are the processes it executes:

a. Stack all of the L, R, G, and B files and run background extraction on each channel.

b. Combine the RGB files to create an RGB image.

c. Deconvolve the luminance image.

d. Combine the L with the RGB image.

e. Denoise the image.

f. Reduce green noise.

g. AutoStretch the image.

h. Adjust the stretch and boost the saturation.

8. Review the script’s outputs:

  • unstretched_lrgb.fit – this is the LRGB image in its linear state with deconvolution applied to the L image
  • unstretched_denoised_lrgb.fit – the linear LRGB image that has had noise reduction applied to it
  • stretched_lrgb.fit – the final image that is stretched and has boosted saturation applied to it

9. Note that you may have to set the display mode to Linear to see the image properly (at the bottom, center of Siril is a menu – if it says Linear, you have the correct setting, if it says anything else, you need to switch it to Linear)

Conclusion

Congratulations! You’ve successfully processed your LRGB images using the ErikWestermann_FullProcLRGB script in Siril. This powerful script has streamlined the process and produced a high-quality result that’s ready for final touches or sharing. Keep experimenting and refining your technique to achieve even more stunning astrophotography results.