Astrophotography Workflow
This is an image of a huge cloud of gas and dust in the constellation Sagittarius. It is estimated to be 4,000 – 6,000 light-years from us and the size is estimated to be approximately 110 light years across. It reportedly is visible to the naked eye under good sky conditions. It has been named the “Lagoon Nebula”. The nebula is an area of active star formation. For more information, check out the Wikipedia entry.
This image was captured remotely from a telescope in the Canary Islands via the web site slooh.com. Like telescope.live, it is possible to set up “observing” sessions to capture images of objects in space. As mentioned in my previous post, the image files they provide are files that are not readable by Photoshop or any other standard image editor. So my first challenge was to figure out how to process these images.
After some experimentation and research, I have settled on PixInsight. This is a massive (and not inexpensive) software package that has been built to serve the scientific community with an emphasis on astronomy and astrophotography. I am still trying to wade through the many aspects of using the program, hoping I can achieve some competence before the trial period runs out and I have to make the decision to pay for it.
In the previous post I wrote that I would provide more information on how the process works. So …
The basic procedure to capture a color image generates four files taken through red, green, blue, and luminance filters. (Luminance is essentially clear.) They are all grayscale images but since they are captured through different color filters, when the files are combined with the the images assigned to the appropriate RGB and luminance channels the color image is created. That’s where PixInsight comes in.
When first downloaded, the images look like this:
Red, green, blue, and luminance, in order. The first time I saw this, I was worried I had not captured anything! What I eventually realized was, that these cameras provide 16-bit files with a massive dynamic range. In order to bring out the image, it must be “stretched”. The result of initial stretching on the luminance file looks like this:
Each of the four files are stretched and then combined in to one LRGB (Luminance, Red, Green, Blue) file. It is now a color image.
Granted, there is not a lot of color here. So the next step is to save it as a standard .tif file so it can be opened in Photoshop. Once in Photoshop, I adjust the levels (light and dark), boost the color saturation, do some sharpening and noise reduction, which gets to this:
For the final touches, I opened it in Luminar 4, and applied some contrast enhancements and other tweaks. As they say, “season to taste”. The end result is the image at the top of the post.
Telescope: Plane Wave Insruments 17-inch modified Dall-Kirkham design
Focal Length: 2938mm f/6.8
Location: Spain
Camera: Finger Lakes Insruments 4096×4096 pixels
Exposures:
Luminence, Red, Green, Blue; time unknown.
Light, Shadow, Form, and Texture 