When I was in high school band, I had to master the rudiments — the basic elements of playing the drum. Well, now I am working my way through the rudiments of post-processing my images. This time, I wanted to experiment with combining narrowband data into RGB.

M27, the Dumbell in Vulpecula, has lots of signal in OIII and H-Alpha, and so I was able to combine some narrowband images from 2021 along with RGBL images taken in the Summer of 2022.

I love some of the false color work being done with narrowband — I’m especially keen on the work of @Alex Ranous . He is making some fine images from the heart of Silicon Valley, where sodium and mercury emissions are especially strong! But I also am trying to stay as true to the science as I can and trying to fairly and subtlety represent color is important to me.

Where possible, I want OIII to be a vivid blue-green and H-Alpha brilliant red with just a smidge of blue. Recently, I managed to uncover some analysis and a companion program to transform CIE chromaticity values for key narrowband wavelengths into their RGB equivalents. I was then able to use a Pixelmath script to render the narrowband data into the appropriate RGB values and then blend those into a RGB image of M27. 

The first image shows the RGBL image – all taken this last summer. I kept the busy star background, cause that’s the way it is –  Vulpecula being located just south of Cygnus in a rich portion of the Milky Way!

The second image is a blend of the H-Alpha data taken from 2021 using a different camera, an ATIK Horizon. (This is where I get to use the line “Whose really the dumbbell here?”) My 2022 narrowband images with the QHY camera used too low of a gain setting and there just isn’t enough signal in them but the Horizon images were much better. The H-alpha just adds signal in the right place to pump up the vivid photoionization fronts in the “cusps” of the nebula.

Finally, image three brings in the halo of the forbidden lines of OIII that surrounds M27 and using that nice, characteristic green.

I have SII data on the nebula, but it’s a much weaker signal, and being near H-Alpha, will be hard to represent without resorting to false color.

Perhaps I need to prepare a fully false color image with just NB data.Some additional data would expose the shells of material getting pushed off the white dwarf progenitor at the center of the nebula. Perhaps next season I’ll add those in!