NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/comp/graphics/8203

Text File | 1992-07-27 | 1.6 KB | 39 lines

Newsgroups: comp.graphics
Path: sparky!uunet!wupost!usc!venice!gumby.dsd.trw.com!deneva!news
From: [e-mail] (Mark Thomsen)
Subject: Re: Noise Reducing w/ Edge Enhancement
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Organization: TRW Inc., Redondo Beach, CA
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Date: Mon, 27 Jul 92 18:50:33 GMT
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Jon Elion writes
> Would be interested in from anyone who has experience with image
> filtering techniques for noise reduction that simultaneously ENHANCE
> edges.  Normally, these two operations are mutually exclusive (as
> noise reduction can tend to BLUR edges, not sharpen them).  There
> exist non-linear approaches that achieve this goal (although
> tending to be computationally very intensive).

For SAR speckle reduction the goal (in general) is to remove the
"noise" that results from coherent illumination of surfaces "rough"
at the illumination wavelength. Most techniques are either based on
multiple looks (different angles or different frequencies), where
the signal reinforces and the "noise" averages out, or on filters
that effectively smooth the image (causing edges and point features
to smooth/blur as well). The speckle tends to be complex Gaussian.

An approach we found to work well is the Crimmins filter. It is
morphological (and non-linear) and seems to be good for reducing the
graininess while preserving high frequency features. The reference
I know of is

  T.R. Crimmins, "Geometric Filter for Speckle Reduction", Applied
  Optics, Vol. 24, pp. 1438-1443, 1985.

Best of luck,

Mark R. Thomsen