Hi All,
Many may recall by previous
IC1848 [LHa][RHa]GB post…
Well, I’m pleased to present
IC1848 in narrowband (mapped colour).
The faint emission nebulae and overlapping open cluster of IC1848 resides in the constellation Cassiopeia. It is commonly known as the Soul or Baby nebulae, due to the nebulosity displaying the contours of what appears to be a foetus.
When imaged through narrowband filters, it is evident that the nebulosity characteristics contains more than energised hydrogen. The subtle blue hues indicate oxygen (OIII), while the red and green hues show sulfur (SII) and hydrogen (Ha) respectively. Present near the top of the foetus head is the bright nebulae IC1871, while the open cluster dots the foetus stomach. The nebulae is estimated as being 6,500 light years distant.
About the image;
Total exposure time of 6 hours (SII:120min;Ha:120min;OIII:120min) using 15min subs for all exposures. I found the SHO “Hubble palette” displayed the object better than HOS and other permutations, so SHO was mapped to RGB respectively. For those who aren’t familiar with narrowband imaging, the individual filters (SII, Ha and OIII) display specific emission lines providing an insight into the gaseous characteristics of the nebula. SII (672nm) is Singly ionised Sulfur, Ha (656.3nm) is Hydrogen alpha and OIII (500nm) Doubly ionised Oxygen. The joys of a monochrome chip. This is my first “serious” attempt at narrowband imaging. I don’t believe it will be my last, but I underestimated the quantity of work compared to RGB imaging (and it’s variations such as HaRGB etc). In some ways it’s easier as there are no correct methods for balancing the colours, but to deliver the desired result takes time. Overall, I’m pleased with the final output.
Image processing;
Well, what I know about RGB image processing goes out the window. All subs calibrated/reduced in MaximDL (dark/flat/bias/hot and dead pixel removal). Subs registered in Registar and Sigma Rejected back in MaximDL before saving as tiffs. Loaded on channels (SII,Ha and OIII) in PS, the applied levels and curves. Created clipping masks per channel for greater colour mapping control (see below attachment). Clipping masks are nothing new and are extremely flexible. This is defined in section B.3.1 of the “Image-Processing Techniques for the Creation of Presentation-Quality Astronomical Images” by Travis Rector. Each mask contains a colour mapping (hue/saturation) and levels for fine adjustments. After reaching the optimal mapping distribution, I added a new deconvoluted Ha channel as the luminance at 100% opacity. Typical of narrowband images, the stars appear to go a purple tone. Many just leave this, but I find it detracts from the image depending how deep they go. To counteract this, I used a separate luminance channel as a new layer which was blended using the lighten mode and stretched using curves. This brought the stars back to a whiter tone. I thought about using the original balanced RGB palette for the stars, but this didn’t appeal pleasing to me. SII, Ha and OIII layers flattened, then Gaussian blur of 3 pixels applied – this smoothed the hue transitions between the specific wavelengths. A minor adjustment to boost the red balance (up mid-tone +2). All layers flattened. Minor adjustments to levels and saturation before finalising.
I thoroughly enjoyed working on this image. Watching it progressively development through the processing workflow. I hope you enjoy it too. Thanks for looking.
Cheers