5847Re: gradients & normalization
- Feb 1, 2002this is good to know.
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?
--- 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
> 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
> it comes to saving. I've heard that it actually only saves 15 bits,
> and if this is true it would be just about impossible to use
> 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
> -----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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