SPCC and adding RGB stars to narrow band images

Mark Mayer

Recently I was processing the TelescopeLive HSORGB data for the 'Squid Nebula' loosely following Adams guide in Horizons for this data set. 

I noticed that after adding my nicely color corrected stars to the close to final narrow band image, the stars took on an ugly red hue. I want back and checked the images in Adams tutorial and ... the same thing happened in his data!

On the one hand this makes sense because there is a huge amount of Ha and Sii Nebulosity over most of the field, that's boosted in the narrow band image compared to the SPCC corrected image assembled from the R G and B data sets which has weak nebulosity compared to the stars, so when these images are blended the narrow band nebula dominates. Any ideas how to get a better image with more accurate star colors?

BlockHead

This is just due to the screening method. There are other more nuanced ways of blending the stars to avoid this. You could, for example, subtract the stars from the NB image before you blend with screen. This is a pretty cool technique...I should do a video on it.

-the Blockhead

Mark Mayer

Yes - a video on star blending techniques would be great. 

In the case I mention I used SXT on the SHO data prior to blending with the RGB stars. If there's a better way to do this I'm keen to learn.