Posted by
Kenneth Sloan-2 on
Apr 09, 2008; 7:48pm
URL: http://imagej.273.s1.nabble.com/reverse-unsharp-mask-tp3696607p3696608.html
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/