Anyone care to comment on processing of this image

[rcheshire]

Anyone care to comment on this one? In particular, the background? Different method of calibration... I didn't work hard on aesthetics, colour, contrast.

[irwjager]

Hi Rowland,

I'm seeing a bit of (bayer?) pattern. What does your new method of calibration entail? I'd be interested to know!

Cheers,

[multiweb]

That's great data. You just need to curve the histogram a little to raise the black point. As Ivo pointed out there is a faint moire reminiscent of a bayer pattern. May be a mis-registration of the RGB channels. Other than that it's a corker, well worth the time spending on reprocessing it. :thumbsup: What did you use for capture. Any info on exposure times?

[rcheshire]

Ivo and Marc. Thanks for taking the time to comment. The method is called superbias. I confess, it's a Pixinsight module that takes a master bias and emulates a bias of hundreds perhaps thousands of frames.

I notice that the same data calibrated with a conventional bias doesn't show the same detail. Perhaps the pedestal needs increasing.

The Bayer appearance is a consequence of the superbias subtraction - it's very flat, except for the chequered appearance. Not sure what you think Ivo but areas of high saturation seem less affected.

Imaging details - Canon 1000D, sensor cooled to 7C, Astrodon spectrum enhanced. 46 x 2.5 minutes, 200mm, f4, ISO800. Bias and flats - no darks.

If the weather holds I hope to add a couple of hours to it. Although I'm not happy with tracking and focus. Looking at making a Carey Mask.

[irwjager]

Hmmm... Though interesting, I'd be a bit skeptical about the universal applicability of the superbias algorithm.
They make a lot of assumptions about your CCD circuitry, which don't necessarily make sense for a good number of models out there.
The only way to find out if their assumptions are correct for your particular CCD/model, is to actually integrate a huge number of frames yourself and see if you see the same sort of vertical (or horizontal) banding (and nothing else!), for which they use their 'shortcut'. This would kind of defeat the purpose of using that shortcut, as you would have a very good master bias that way.
I'm not sure I would trust this method without being absolutely sure it is applicable to my particular CCD circuitry. Maybe they can start a database containing the CCDs/models for which this is an appropriate solution?

[irwjager]

Actually, now knowing you're using the super bias method, the pattern we're seeing is probably caused by either applying the super bias the wrong way (ex. after debayering instead of before), or by generating it the wrong way for your particular CCD. My money is on the latter.

[rcheshire]

Thanks Ivo, That's good feedback. I suspect that the latter is correct. It's that kind of detail that's hard to come by.

[DavidU]

Black point adj.

[kinetic]

:shrug:...damn fine data...as per Marc, Dave etc...black point, levels, and
an auto background in Nebulosity. Be great to know how to smooth the
bayer artifact. M4 looks awesome.

Steve

[rcheshire]

Thanks Dave and Steve. Both those look good. I will investigate the superbias thing a little more. In future I will aim to take a stack of bias frames at different temperatures and form a library.