63053RE: [ccd-newastro] Re: Processing Dilemma
- Aug 1, 2008It took forever to download, but I think the answer is pretty simple: you
have an image with some issues (vignetting; gradients; severe color bias;
light pollution). It's not reasonable to expect automatic tools to handle
that kind of stuff gracefully. You can also do some damage on your own by
not being very careful with what you do. This is the kind of image I would
easily spend an hour on cleaning up, and I have a fair amount of experience.
So that translates into "pretty challenging to process."
I would back off of the automatic stuff, and focus on carefully learning to
manipulate the image. First thing is to clean up the color bias - gradient
removal tools can be badly fooled. And in this case, with so much background
nebulosity, it's probably not going to work to use automated gradient
removal because the tool requires a background to analyze to figure out what
the gradients are.
Flats would be a huge help in this case. You'll still be left to deal with
the bright background, but you won't have to fight so hard with the
vignetting gradients; the flats will take that out.
I could teach a 2- or 3-day course with all the lessons there are to be
learned from processing this image. <G>
From: email@example.com [mailto:firstname.lastname@example.org] On
Behalf Of mandellgl
Sent: Thursday, July 31, 2008 11:36 PM
Subject: [ccd-newastro] Re: Processing Dilemma
I have place 3 TIF files on my FTP site to demonstrate the problem.
"M17...Processed" is an image of M17 that I processed using PS CS3
including histogram stretching and black point adjustment,
GradientXTerminator and noise reduction with Noise Ninja. I did not
use any sharpening techniques.
"M17...OverStretched" is the same image with an extreme histogram
stretch demonstrating the problem.
"M17...Unprocessed" is the image before any processing.
Please note that each TIF file is very large, 32MB.
Thank you for your help.
--- In email@example.com, Yahoo Wodaski <yahoo@...> wrote:
> You should post an image in the Files section so we can get a look
> problem. The most common cause, if I understand your description, is
> Ron Wodaski
> On 7/31/08 12:07 AM, "mandellgl" <gmandell@...> wrote:
> > Hi Friends.
> > I have a processing dilemma.
> > After processing an image, particularly an emission nebula, I
> > end up with areas adjacent to bright stars or a bright area of the
> > nebula that are too dark. The dark areas prevents me from
> > the histogram further because it becomes even more evident.
> > I use a Starlight Xpress SXVF-M25C color camera. I calibrate the
> > light frames with a master bias and master flat frames but no dark
> > frames. The frames are captured with MaxIm DL, calibrated and
> > combined using ImagesPlus and aligned with RegiStar. I process
> > median-combined image with Photoshop CS3. I also use
> > GradientXterminator and Noise Ninja in PS.
> > I try to follow "The Zone" method. I'm not sure if I am
> > setting the black point.
> > Any help would be appreciated.
> > Gordon
> > ------------------------------------
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