A step-by-step guide on creating true color images with DS9
Installing the necessary software: DS9
DS9 is an astronomical imaging and data visualisation software that almost all astronomers use (the name is a Star Trek reference, from a story called Deep Space Nine). Most images that we take using research grade telescopes are in fits/fts image format, which not many image software support. DS9 has a huge array of functions that are helpful for amateur and professional astronomers alike. One of the most popular functions on DS9 is to create basic RGB images.
DS9’s UI is quite intuitive, and it only takes a few moments to familiarise yourself with the functions available in this powerful application. You can configure the GUI of DS9 if you like too. The default displays are the coordinate display, panner, magnifier, horizontal and vertical graphs, button bar, and colour bar. You don’t need any additional installation for DS9 to work.
Example with M22
In this example, I’m going to tricolor M22 with the images taken by the Nieves Observatory. You can download the images here and follow along this tutorial.
Step 1: Select new RGB Frame
Frame > New Frame RGB
Step 2: Open your i’ image for red
What it does is to paint all of the source of your image to red (as they are).
There are also various scaling options you can use. For our purpose, to highlight the source, I’ll be using zscale.
Step 3: Do the same for r’ image for green, and g’ for blue.
This stacks all of the colors together, and you now have a full RGB image.
The final result:
To save the file, go to File > Export > PNG or JPEG.
Python solution for creating tricolor image
For those who are familiar with Python, there is a Python solution to this that is much faster (though it might not be as customisable as creating an RGB image on DS9). You can find the code below.