Hi All,
This image represents the pinnacle in one of my imaging chapters – image scale amalgamation i.e. successfully combining data acquired at different focal lengths. Most importantly, this project prompted the redevelopment of some processing techniques that I had thought about, but never acted on until now to deliver a pleasing end result. I have explained parts of the process below. So, without further ado, I’m pleased to present
M83 – Southern Pinwheel Galaxy.
The Southern Pinwheel Galaxy (M83) is located in the constellation Hydra and is a member of the Centaurus group of galaxies which includes peculiar radio galaxy Centaurus A (NGC5128). M83 is classified as a between a normal and barred spiral galaxy based on its characteristics. The immense spiral structure of the arms contain various blue and red knots of star clusters and diffused gaseous (HII) regions respectively. M83 is the southernmost galaxy in Messier’s catalogue and resides approximately 15,000 light years distant.
About the image (for those interested);
This image is an LLRGB composite totalling 6.1 hours (Luminance:100min;RGB:90min each). The luminance data was acquired from GRAS008 – 12.5” F/9 RC operating at ~2800mm. The Chrominance (RGB) data was acquired using the FSQ-106ED 4” F/5 Petzval APO operating at 530mm. As one could image, we are dealing with vastly different image scales. The chrominance data was solely to be used for colour information on the high resolution luminance data. Calibrated all frames – usual process. Firstly, I worked on the luminance. Excellent data was obtained from the RC (10x10min subs) shooting the target while it was +80 degrees (no AOL used here!). Very slight gradient present which was removed using GradientXTerminator, then continue with a multi strength deconvolution blend to bring out the details. Minor background noise removal in NeatImage. On to the chrominance - from past experience, upscaling of any data requires good quality data to ensure noise isn’t introduced into the image. I dedicated an imaging run solely for RGB, collecting 90min in each channel (6x15min subs). In the past, I’ve found that simply upscaling the chrominance to match the luminance gave strange results, in particular with the stars (due to the considerably large difference in image scales). So to counter act this, I first downsized the hi-res luminance to match the low-res RGB chrominance. The two were blended using lighten mode, blurred, boosted in colour saturation and flattened. This new image had become the superRGB chrominance frame which I then upscaled to match the luminance frame for final composition. The end result provided a greater improvement on star matching and colour correction. The luminance was layered twice so I could bring back the colour hues while keep detail. Minor noise reduction performed on the chrominance layer. Star halos subtly accentuated using colour masking. Image flattened, before final selective noise reduction. Seasoned to taste. The shear number of faint fuzzy galaxies that dot the background is impressive in the full res version.
I’ve also imaged its northern counterpart M101, which can be
viewed here. Though I think this version needs some colour balance work considering it was processed on a old laptop, not a calibrated monitor (which I now have access to).
The full size image presented (2400x1800) is a 75% image size reduction of the total image. The 100% is remarkable – will use this for prints. The crop shows M83 slightly offset to show the brilliant blue star (HIP 66549 – spectral class F2III/IV). I’ve attached TheSky imaging plan to provide an insight into the composition planning along with some background PGC galaxies. I composition is actually incorrect as the instrument rotator should have been at 168’, instead of 186’ shown. However, I still found a guide star that allowed for 7sec exposures!
I hope you enjoy it as much as I did processing it!
As always, all comments welcome.