Sunday, August 15, 2010

M31 ... now in Color!

I spent a couple, a few  5 hours today trying to get a handle on the color image of M31.  First I had to figure out the best settings in Nebulosity for the debayer step.  There are no default settings for the T2i - the camera is still rather new.  While I could have chosen just about any setting and done the color correcting later (in Nebulosity or PS) my previous attempts were rather garish.

To get a handle on this I took a RAW picture outside in sunlight that included a gray card.  Verified in PS that the RGB values were the same (check).  Then I opened the file in Nebulosity and debayered with every setting possible (hair shirt?  check).  Then I wrote down the RGB values reported by Nebulosity for the same spot on the nominally gray card and selected the conversion profile that gave the "most gray" (equal RGB) values (double hair shirt, check).

Next I proceeded to reprocess all the images with the new setting.  Which, by the way if you are reading this and happen to be in same situation and don't want to spend 2 hours going through the exercise the answer is ... ta-da ... straight color scaling (not a specific camera like stock 40D or unmodded 300D or whatever).

After all that I cropped and did a Auto Color Balance.  Saved every file en route.  Then I post processed the image in Nebulosity.  The spirit was willing but the body was too weak to start postproc in Photoshop.

The image is still too pale, greenish bluish or something.  And I have orange star halos, some noise to bang down and so on.  After some well deserved rest I'll tackle the image again in Photoshop to see what I can do about color issues.  In some sense I like the more muted colors.  Going forward I'll have to think about how I will use colors in these images.  But, for now, here is M31 in all it's Ghost Ranch glory.

As for all images ... click to see a larger version.
M31 processed entirely in Nebulosity

Taken at Ghost Ranch near Abiquiu,  New Mexico August 4th and 5th, 2010
Canon T2i (stock), 200mm EF-L @ f2.8
Astrotrac Travel System mount
Imaging temperature range:  52-58F
87 60sec exposures @ ISO3200  (taken over two evenings)
64 darks,  21 flats (1/5" ISO 100) 21 flatdarks (still not sure about needing these)
pre and post-processed in Nebulosity

1 comment:

  1. I can't respond on the yahoo group page for some reason, so responding here instead...
    That is brilliant. You've got so much more detail than I would have imagined possible for 60 seconds and at 200mm. You've inspired me a little there!