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63053RE: [ccd-newastro] Re: Processing Dilemma

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  • Wodaski - Yahoo
    Aug 1, 2008
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      It 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>

      Ron Wodaski

      -----Original Message-----
      From: ccd-newastro@yahoogroups.com [mailto:ccd-newastro@yahoogroups.com] On
      Behalf Of mandellgl
      Sent: Thursday, July 31, 2008 11:36 PM
      To: ccd-newastro@yahoogroups.com
      Subject: [ccd-newastro] Re: Processing Dilemma

      Thanks Ron.

      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 ccd-newastro@yahoogroups.com, Yahoo Wodaski <yahoo@...> wrote:
      > You should post an image in the Files section so we can get a look
      at this
      > problem. The most common cause, if I understand your description, is
      > over-sharpening.
      > 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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