There's a number of ways to process an image taken by a telescope.. and this can be a huge challenge for beginners. Processing was actually the bane of my existence when I first started this hobby, even though I'm quite adept with software like Photoshop which I've been using since 1998. Working on processing an astro image takes care and special techniques, because it's nothing like anything else you've worked on.
Here's a brief overview of the tools I use:
DeepSkyStacker: This free program stacks all the frames you've captured. Many purists will use more complicated programs to stack, but after my own comparisons I found that DSS will stack just as well as any other program. What I love about it: It's completely free and ridiculously easy to use.
PixInsight: Priced at 230EUR, this is a pricey piece of software. However, many experienced astrophotographers will tell you it's an essential program for processing. This is where most of the hard work is done, where the initial image is stretched, aligned with the other images, combined into RGB channels, color calibrated and more. I'm not going to lie, this software takes some learning to get used to. It's very intimidating to use at first, but once you get a hang of it, it becomes an essential part of your workflow.
Adobe Photoshop: While many purists will finish the entire workflow in Pixinsight, after the image becomes color and color calibrated, I bring it into photoshop because I feel extremely comfortable with processing it further here, using layers and other advanced tools. This is where I create star masks, do selective sharpening using masks, non-linear curve adjustments, noise-reduction, and other touch ups. Essentially, this is where the image goes to put on some make-up before the big show, where as Pixinsight is the "dressing room".
Why touch up astro images?
Many folks who are not in this hobby may wonder why astro images don't look amazing right out the box. Several reasons:
- The images are taken in sequence, with various filters in monochrome. Each image capture is a black and white image. For example, for an RGB (color image), you need to capture frames using the Red, Green and Blue filter. Then, in post-processing, you combine those images for each RGB channel and you have a color image.
- A typical astro shot is extremely dark, and needs to be brightened significantly. Here's a typical astrophotograph and what it looks like after being captured:
Here's the exact same image, given a linear stretch in Pixinsight:
Hope this was informative. If tutorials are of any interest, just let me know!