The consequences of letting Hydrogen alpha dominate the image construction
I like to think that these are two of my best narrow band images yet. The raw data were recorded using a Televue NP127is scope @ f/4.2, Astronomik 12 nm filters, and a QSI683wsg camera.
I used the following color palette when building the two images:
Luminance = H alpha, Red=H alpha, Green= H alpha, Blue=OIII
For most nebulas, far more information content is recorded using an H alpha filter than an OIII filter. Hence I chose to let the H alpha channel dominate the image construction.
I also posted these images to the QSI group. There is no need to look if you have already seen them.
Excellent!. Very sharp and detailed to be sure.
This is entirely personal taste of course, but lots of Ha doesnt need to mean lots of green. I would prefer the attatched pallete myself, just sayin .
Whoa there, Murray. Before you diss that image, from an astrophysics point of view it's a very informative one. Minimizing the OIII has made for better contrast in the HII, and hence more previously unseen detail. I see much finer nuances in the Southern Wall and the two shock fronts where the bulk outflow out of the centre hits slower-moving previous ejecta; a modest star cluster of low- mass stars will one day emerge from those two fronts, and will look like a wobbly star line until Galactic torque shepherds them into the disc. The bar magnet structure that presently dominates gas flow in the Lagoon and Herschel 36 region are more clearly deleted and fine-grain than most images I see. In the lower left centre there is a structure of inky shreds whose hemispherical shape gives me to think this might be a former dense core that never reached supercritical levels and hence never collapsed. There doesn't seem to be a stellar overdensity in its middle zone which would indicate core cluster stars. I never saw this before and it bears a closer look.
OK, so maybe you rushed in where angels feared to tread, but find me an angel who knows HII data when he sees it. Could you send me a full-sized uncompressed copy and your credit info wording. I've got an M8 article on the back burner waiting for Sagg to show up again and yours would be a good image to feature. Address is <danadezoysa@gmail.com>.
If you ever get around to the Liberty and Carina nebs with this level of HII detail, post 'em! I'll be all eyes.
=Dana in S Africa
Last edited by Weltevreden SA; 13-12-2015 at 11:45 PM.
Reason: typo correx
Dear Marcus, the raw data were recorded from the southern suburbs of Sydney. Sydney is a great place to visit for a week of general sight seeing. But to visit for viewing the stars? Nay.
Some people don’t like the colour palette [Luminance = H alpha, Red=H alpha, Green= H alpha, Blue=OIII] and some people do. One can’t please everyone, but I will try. Here is the same data except using the colour palette [Luminance = H alpha, Red=H alpha, Green= (H alpha + OIII)/2, Blue=OIII]. Hopefully this is more pleasing to the “red is better” camp. I am agnostic.
I would still argue there is a strong case for allowing the H alpha data to dominate the luminance and colour channels to maximize the information content for many, but not all, nebula images. We need a mathematician with expertise in image processing to develop an algorithm estimating some measure of “information content” in an astronomical image. Perhaps this could be done using wavelets? Then we can prove or disprove my point.
Sydney is a great place to visit for a week of general sight seeing. But to visit for viewing the stars? Nay.
Well that clearly wrong, I cant see any deficiency in your image that would make make me think its no good because it was taken in Sydney.
I agree that there is a strong case for allowing the H alpha data to dominate the luminance channel, thats what I do too for artistic/asthetic reasons (well, I use only Ha for Lum), but that has nothing to do with "information content". Ha as Lum will bury OIII/SII content where Ha is lacking, certainly meaning less "content" generally. Ha dominating in colour channels is another thing entirely to Ha as Lum.
Dear Marcus, the raw data were recorded from the southern suburbs of Sydney. Sydney is a great place to visit for a week of general sight seeing. But to visit for viewing the stars? Nay.
Thanks for that, and I agree with Fred, can't see anything wrong with that sort of data to work with
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Don't mind green either.
