Friday, February 3, 2012

The Orion nebula: Reworking some year-old data

If you've not yet had the opportunity to look at M42, the great Orion nebula, through a telescope, you owe it to yourself to try and find an opportunity to do so. Even though today's entry is part of an `imaging blog', M42 is the kind of object that's beautiful any way you look at it. As long as you've got a clear sky, and are (hopefully) away from city lights, you can see this nearby star-forming complex in some way, regardless of the gear you've got.

I just now spent a moony evening reworking some unbinned R, G, and B data that I shot about a year ago. Every winter, it's the same old routine: Try to get some decent data on M42. Something always gets in the way, though. In early 2011, it was bad weather and camera issues... a story for another time. I managed to shoot some unbinned L, R, G, and B data, but not a heck of a lot. To the best of my memory, the data for this image don't amount to much more than several hours total. Since it's now February, and I'm not 100% sure if I'll get in a decent M42 dataset in 2012, I thought I'd fool around with this old stuff from last year. See if I could make something semi-presentable.

After an evening spent in front of the computer, I happened to go outside, and as I was walking back in, I looked up, and there he was: Orion, the hunter. The constellation was just passing across the meridian, with the bright gibbous moon due north of it. Even with lights in my eyes, and under a city sky, I could make out the bright stars that delineate the pattern: Betelgeuse, Rigel, Bellatrix, Saiph, Alnitak, Alnilam, Mintaka. And there was the sword of Orion, with the middle `star' being M42. This object is so bright that it (or at least the stars in and around it) can be seen under almost any sky, it seems.

Unlike most deep-sky objects, M42 is worth looking at with virtually any optical instrument. The belt and sword of Orion are great in binoculars. Small telescopes show the nebulosity. Large telescopes under dark skies provide one of the few `imaging-like' experiences in visual observing. A greenish color can even be seen in the brightest part of the nebula, in a big scope. The details just go on for days and days.

As an imaging project, M42 presents an almost limitless field of challenges and rewards. With modest equipment and short exposures, one can still get something. Advanced imagers have gotten some incredible results.

Processing in Pixinsight:

This image certainly isn't incredible, but I'm glad that I was able to squeeze a bit of detail out of such data as I had. I spent a fair amount of time on this in Pixinsight, and eventually I gave up on trying to combine the luminance data with the color data. Both my RGB image and my Luminance image were the result of high-dynamic range combinations, for which I'd shot long- and short-exposure frames. Matching the histogram from the L image to the histogram from the RGB image seemed to be taking forever, with little end in sight. I bailed and just went for the RGB.

Getting a good color balance was really tricky, and I just couldn't get it quite right. The stars in the linear image had all sorts of blue and cyan issues, and by the time I got them to look semi-normal, the blue color in the nebula was pretty well gone. I could have (and should have) worked that problem harder, but since this was a `let's see what we can get out of this stuff without too much struggle' project, I didn't sweat it that hard.

I did a bit of Richardson-Lucy deconvolution while the image was still linear, but nothing drastic. I would have liked to have gotten a better sharpening result, but I found that I kept getting bright `wormy' artifacts if I wasn't careful. I think that a really good deconvolution would be pretty substantial project, even with the help of Dynamic PSF.

After histogram stretching, I had to spend a fair amount of time finding the right parameters for an application of HDR Multiscale Transform, to knock down the over-brightness of the area around the Trapezium. Once I got that area tamed, it was rather washed out, as usual. Some additional luminance masking and an extra saturation boost in that area helped a bit, although it left some purple haze around the Trapezium stars.

There's plenty of room for improvement in this image, but I'm glad that I can at least post some sort of M42 image. I hardly feel like `an imager' without one. With a little luck, maybe I can finally get a decent set of data later this month and in March. It would be nice to really go deep on this thing, and under good seeing. We'll see how it goes!

As per usual, there's an amazing image of the object from the Hubble Space Telescope.

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