http://imagej.273.s1.nabble.com/reverse-unsharp-mask-tp3696607p3696609.html
students develop. Always nice to have a quantitative gauge of effectiveness,
> On Apr 9, 2008, at 9:33 AM, Michael Doube wrote:
>
> > Hi all
> >
> > I'm the disappointed recipient of a bunch of CT scans of bones in air,
> > to which overzealous unsharp masking was applied (at least, that's how they
> > look) - dark black borders of air surrounding over-bright bone edges.
> >
> > Is there any way to reverse this effect to get at least partially back
> > to the original contrast?
> >
> >
> Well, let's see. Unsharp masking works by subtracting a blurred image
> from the original, to get the USM image:
>
>
> Iusm = I - Ib
>
> If you can approximage Ib, then you can add it back:
>
> I' = Iusm + Ib'
>
> I imagine that blurring Iusm might give an acceptable Ib'.
>
> Of course, there are numerous parameters to this process that you'll also
> have to estimate.
>
> [note: instead of subtracting and adding, I generally prefer blending.
> e.g.,
>
> Iusm = a*I + (1-a)*Ib
>
> where (in the case of unsharp masking) a > 1.0.
>
> the reverse process would use 0.0 < a < 1.0, and, of course, the imperfect
> approximation of Ib by Ib']
>
> Interesting question - I'll toss it out to my class on Thursday and see if
> anyone has a spare hour to try it out.
> If one of them picks up the ball and runs with it, can I get a sample
> image to test on?
>
> --
> Kenneth Sloan
>
[hidden email]
> Computer and Information Sciences +1-205-934-2213
> University of Alabama at Birmingham FAX +1-205-934-5473
> Birmingham, AL 35294-1170
http://KennethRSloan.com/>