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Re: Finding local maxima (repost?)

  • Subject: Re: Finding local maxima (repost?)
  • From: "Tilman JOCHEMS" <mfjnet@tele2.fr>
  • Date: 14 Jan 2005 07:55:02 -0800
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Hi Jon,

> I have to find the local maxima in an image surface. Is there a more
> elegant/efficient method than simply comparing each pixel to its
> neighbours?

Comparing each pixel to his 8 neighbors is not sufficient, because
local maxima can have a size of several pixels that form a plateau.

Here is the morphological way for computing maxima on gray-level

Let "rec" be a reconstruction function (geodesic dilations until
stability, often realized in a queue-based manner in order to be fast),
G0 the original image and B0 the result.

B0=threshold(G0-rec(G0-1,G0), 1, 1)

- "G0-1" is an image, which you obtain by decrementing all the pixels
of G0 by 1
- "rec(G0-1,G0)" will give an image that has the same values as G0 for
all pixels excepting the local maxima
- the following subtraction and thresholding will give the final result
as a binary image.

Calculation time depends mostly on the reconstruction algorithm, and
queue-based reconstruction depends on the image information. To give
you an idea: it is about 200ms for a 640x480 gray (8 bits) level image
on a 500MHz computer with our image analysis system Qlisp.

Best regards,

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