M81, M82 and the Intergrated Flux Nebula processed by Scott Rosen
|Bringing Out the Faint Stuff
As an astrophotographer, I spend a great many hours gathering data before I begin processing my images.
The purpose of investing so much time and energy in data collection is because the more time the camera shutter
is open, the more photons are captured by the sensor. Ultimately, this means a better signal to noise ratio, and
that means that I can more aggressively stretch my images to bring out those very faint, subtle, and often
beautiful portions of my field of view.
However, when its time to process this data, what techniques can be used to bring out these very faint parts
without having an overly noisy or unnatural looking image? After all, it does me no good to have great data
that results in a crummy looking image.
Along with fellow astrophotographers Neil Heacock,
and Chuck Kimball,
I am one of the moderators of the
DSLR Astro Image Processing Yahoo Group.
Roughly once a month, one of the group members provides their calibrated, stacked, and unprocessed 16 bit .tif
file for members of the group to process (we call these "challenges"). The goal of the group is to share knowledge
and techniques to help all the members improve their processing skills. By having a
non-competitive and supportive environment, we've seen many budding astrophotographers
enjoy great improvement in their image processing capabilities. I know this, because I'm one of those budding
astrophotographers who has benefitted immensely from this group.
For our May 2014 challenge (C025), I have provided my data showing a roughly
6 degree by 4 degree region of the sky containing galaxies M81, M82, and the
Integrated Flux Nebula (IFN).
The IFN is very faint nebulosity composed of dust and gas that surrounds our galaxy.
It shines by reflecting the light from our entire galaxy, thereby coining the term
"Integrated Flux Nebula". The IFN is an excellent example of a VERY faint target
and is quite tricky to capture and process. It requires dark skies and usually a
great deal of integration time. For this image, I used a Canon EF 200mm f/2.8L II USM lens at f/3.5,
a Gary Honis modified Canon 450D, and a total of 17 1/2 hours of imaging time.
To help group members process the C025 challenge, I prepared the video below
to demonstrate some of the techniques I use in processing images with very faint
nebulosity. In this video, I use my
DSLR-LLRGB Style Processing Workflow
wherein I create a luminance layer from the RGB image, process the luminance data, and then
recombine it with the RGB. Although I use this workflow, the general techniques
I demonstrate in this video do not require LLRGB style processing - they can be done
with straight RGB processing as well. In the video, I make little effort to try to
explain the nuances of using LLRGB Style Processing. My assumption is that the viewer
is watching this video with the intent of seeing aggressive stretching techniques more so
than DSLR-LLRGB style processing. If you're interested in a detailed explanation
of the how and why behind DSLR-LLRGB style processing, I would encourage you to sample
my DSLR-LLRGB Walkthrough Video.
As with my DSLR-LLRGB Walkthrough Video,
I apologize for the video being so long (I managed to keep it just under 2 hours this time!).
Unfortunately, I simply don't know how to process an image without taking a long time to do
so (and, frankly, I still feel like I rushed this video as well as the processing). Nonetheless, you may be interested to know that all of the stretching techniques I demonstrate
are contained in the first hour and 10 minutes of the video. The balance of the video
is geared towards combining the RGB and Luminosity layers and mostly focuses on color
saturation, color correcting, etc.
In order to make it easier for you to view the video, I have also broken it down into smaller, bite size chunks. I intended
each of these clips to be a lesson on its own. So, if you're not particularly interested in how I stretch my data, but you're
curious about my technique for doing a Screen Mask Invert, you can simply go to the Screen Mask Invert link and watch that clip
Thank you for stopping by my website,and I hope that you'll find some of this information helpful to you.
Bringing Out the Faint Stuff Walkthrough Video