Tuesday, April 1, 2014

Giving Pixinsight another try

My current workflow for (narrowband) images gets more and more convoluted. First CCDStack, then Photoshop - and then sometimes back to CCDStack. And in Photoshop I am using various plugins. Pixinsight on the other side (apparently) has everything that is needed to process images.

found this tutorial how to process narrowband images with Pixinsight - it gives step-by-step instructions. I wanted to try it out on my recent images of the Parrot Nebula. I did the calibration, alignment, stacking in CCDStack.

First, here is what I get with Photoshop:

And here is my first try with Pixinsight (using the color combination from the tutorial):
There isn't a lot of color here (the Ha is so dominating) and I was clearly too ambitious and made the image WAY too bright and saturated.

So, I tried again using the standard Hubble Palette resulted in this image:

I like the colors of the Photoshop version better. But with Pixinsight, I could get WAY more detail and the sky looks much better too.

I asked on both the narrowbandimaging mailing list as well as the Pixinsight forum how to better color combine narrowband images. The two ideas that I received were to use CurvesTransform or HistogramTransformation.

I played with the CurvesTransform but found it very hard to manage. I could not find a way to boost the signal in one channel (red) and reduce another channel (green). But every change that I tried to make had broad heavy impact on the entire image and color scheme.

I had more luck with the HistrogramTransformation process. I could boost the red a little and reduce the green a little. Unfortunately, it had the side-effect that the background became too noisy. I tried to mitigate that by creating a mask by extracting the L component of this image and clipping the black point. With this mask, I could protect the background and apply the changes mostly to the nebula. This was the result:

Overall, I like the detail and the color in this image the most.