New Narrowband Image Blending Method in Pixinsight:

There are a number of ways of blending Narrowband channels in astrophotography. The three channels are Ha (Hydrogen Alpha); OIII (Oxygen) and SII (Sulpher)

These are classically combined in the Hubble Palette with SII mapped to RED; Ha mapped to GREEN and OIII mapped to BLUE. This can be seen in the Rosette Nebula photo below. This palette allows for the three separate channels to contribute to the structure of the image instead of OIII and SII being overwhelmed by the much stronger Ha signal.  

Click on an image to get a closer view

Hubble Palette

There are a couple of new Scripts in Pixinsight that allow the colouring, balancing and blending of each of the channels to any colour combination. This can be achieved in Photoshop quite easily but required complex formula’s in Pixinsight. 

The balancing of two or three channels is carried out in Narrowband Normalisation. Colouring is carried out in Narrowband Colour Mapper and blending in Image Blend. These three processes/scripts allow for more creativity and experimentation 

when combining the separate monochrome channels to a colour image. One recent use of these scripts was described by Adam Block a renowned astro photographer.

In simple terms two images are created from the three mono NB channels and then blended together. 

An HOO image is created and calibrated in Narrowband Normalisation.

Then the SII channel is coloured to yellow/orange in Narrowband Colour Mapper script.

These two images are then blended together in Image Blend to produce the image above. 

This image is more dramatic than the Hubble Palette. Neither are a true representation of the actual nebula colour that we see as this is completely red. However they both represent the structure of the nebula and the contribution of each of the

gasses that comprise the majority of the nebula. This is just one of the ways to use these scripts.

Paul Howat