Segmentation01

7/30/2019 Segmentation01

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Image Segmentation

Content

Definition and methods classification

Detection of discontinuities

Point detection

Line detection

Edge detection

Edge linking and boundary detection

Thresholding

Region-based segmentation


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Definition: Segmentation subdivides an image into its constituent

regions or objects.

Basic formulation: LetR represent the entire spatial region occupied

by an image. Image segmentation is a process that partitionsR into

n sub-regions,R1,R2,,Rn, such that

a)

b) Ri is a connected set. i = 1, 2,, n

c) RiRj= for all i andj, i j

d) Q (Ri) = TRUE for i = 1, 2,, n

e) Q = FALSE for any adjacent regionsRi andRj

where Q(Rk) is a logical predicate defined over the points in set Rk

Fundamentals


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Classification: based on one of two basic categories dealing withproperties of intensity values

discontinuity and similarity

discontinuity-based: the partition of an image is based on abrupt

changes in intensity, such as point, line and edge.

similarity-based: partitions an image into regions that are similaraccording to a set of predefined criteria. Thresholding, regiongrowing, and region splitting and merging are examples.

Methods Classification


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Edge pixels: pixels at which the intensity of an image functionchanges abruptly

Edges/Edge segments: sets of connected edge pixels

Edge detectors: local image processing methods designed to detectedge pixels

Line: an edge segment in which the intensity of the background on

either side of the line is either much higher or much lower than the

intensity of the line pixels

Isolated point: a line whose length and width are equal to one pixel

Detection of discontinuities: background


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Conclusions

First-order derivatives generally produce thicker edges in an image

Second-order derivatives have a stronger response to fine detail,

such as thin lines, isolated points, and noise

Second-order derivatives produce a double-edge response at ramp

and step transitions in intensity

The sign of the second derivative can be used to determine

whether a transition into an edge is from light to dark or dark tolight

Detection of discontinuities: background (contd)

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Segmentation01