Read here: http://lightvortexastronomy.blogspot.com/2013/02/tutorial-nebulae-pixinsight-workflow.html
This is my latest tutorial for PixInsight, producing my entire workflow for narrowband post-processing (S-II, H-a and O-III) to make an LRGB image. As usual, this tutorial workflow goes from the raw calibrated monochrome images to the final result with everything in-between. S-II and H-a are blended for Red, H-a and O-III are blended for Green and O-III is used purely for Blue. For Luminance, H-a data is used. Post-processing is very similar to my other HaRGB tutorial workflow but with distinct differences in colour-combining and noise reduction. This tutorial workflow is also applicable to anyone interested in pure LRGB (non-narrowband) image post-processing as besides colour-combining, the techniques very much apply. It is particularly useful for post-processing images of nebulae.
Please feel free to browse my other tutorials as well. I enjoy writing extensive ones!

By Gib007
Link to discussion: viewtopic.php?f=42&t=15508