December 31, 2009

Horsehead and Flame, HaRGB combined (“MartinB method”)

After reading about MartinB’s method for combining Ha into/onto RGB data for his Cone nebula image a while back, I was itching to have a play with some of my own data.

Erik Larsen has very nicely allowed me to use his RGB data in this combined image, and to post the results. His data was 11x300s, taken with a modded Canon 500D through an Orion ED80. Many thanks for allowing me to show this.

So, I took Erik’s RGB Horsehead and Flame RGB data

and the Ha data that I took on Christmas Day

Threw them both into Registar, aligned the Ha data to the RGB data, saved them out.

Now using MartinB’s method, I load the RGB data into a layer, then duplicated that RGB layer on top with “soft light” mode. This increases the contrast, but also drops the black point, so I used some levels/curves to bring that back up a little.

I then pasted the greyscale Ha data into a layer on top, set the green and blue channels to black (only the red was left), then set that layer method to “lighten” to it only affected the reds.

After some careful levels and curves on the duplicate RGB and the Ha layers, it got somewhere close to what I wanted. The stars have a slight red halo from the larger Ha stars, which should be easy to fix later, and maybe I over did it with the Ha lightening 🙂

This is the result. Lots of lovely reds, but no loss of contrast like previous attempts of using just an additiona Ha layer, plus the other colours are not washed out. I am currently digging out all my previos Ha RGB images to see if I can improve on them with the same method.

(Click on image for larger version)

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