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5847Re: gradients & normalization

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  • jfeldhou
    Feb 1, 2002
      this is good to know.
      more questions...

      do I need to switch to 8 bit to do the combine in photoshop?
      I was unable to get layers, nor "Apply image" to work in
      15/16 bit mode? is switching to 8 bits before doing advanced
      processing (ddp,unsharp,L-R) a bad idea?
      is switching to 8 bits a bad idea in general?

      thanks, jim

      --- In ccd-newastro@y..., "Ron Wodaski" <ronw@n...> wrote:
      > You are dealing with two very different reference systems here. I've
      > had success this way, at least not without considerable mental
      gymnastics to
      > try to get the two files to have similar levels.
      > The simplest solution is to apply the gradient removal to the image
      > Photoshop. Photoshop just doesn't seem to understand the 16-bit
      format when
      > it comes to saving. I've heard that it actually only saves 15 bits,
      not 16,
      > and if this is true it would be just about impossible to use
      Photoshop to
      > create a gradient removal image in the way you describe.
      > Since I had so much trouble with the approach, I only documented the
      > all-Photoshop methods in the book. I just can't recommend this
      > because Photoshop seems intent on making it not work.
      > Ron Wodaski
      > The New CCD Astronomy
      > http://www.newastro.com
      > -----Original Message-----
      > From: jfeldhou [mailto:jfeldhou@y...]
      > Sent: Thursday, January 31, 2002 5:05 PM
      > To: ccd-newastro@y...
      > Subject: [ccd-newastro] gradients & normalization
      > is it a bad idea to attempt to produce a gradient
      > from an image that has been normalized during stacking?
      > I attempted to do the following procedure, with very
      > poor results. I had 11x600s luminence images,
      > preprocessed, stacked(sigmamean). M51 occupied most
      > of the corner quadrant, the rest stars of varying bloat.
      > I saved the stacked fits image as 16 bit tiff, then
      > opened it in photoshop. I used the dust&scratches
      > tool at (12,16) cause some stars were big. Then I clone
      > tooled out any remaining stars, and the M51 portion.
      > after a gausian blur 19, I copied the 16 bit tif back
      > to my PC, changed it back to fits, and attempt to
      > subtract the blur from my original M51 stack.
      > I attempted to subtract the blur, after multiplying
      > the blurred pixels by .8 then .7 then .5 .4
      > no matter my choice, the target image was erradicated.
      > my blur wasn't so good in the area of m51, but I had
      > hoped I'd see some worthwhile results on the rest of
      > the target frame, and then I could make a better blur.
      > is there an obvious place where I went wrong?
      > thanks, jim
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