segmentation and representation - image processing...
TRANSCRIPT
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Segmentation and Representation
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Topics Segmentation
Texture Based Segmentation
Level Set Segmentation
Watershed Segmentation
Representation Introduction
Chain Codes
Polygonal Approximations
Signatures
Boundary Segments
Skeletons
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Introduction• Image segmentation is the process of partitioning the
digital image into multiple regions that can be
associated with the properties of one or more objects
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Topics Segmentation
Texture Based Segmentation
Level Set Segmentation
Watershed Segmentation
Representation Introduction
Chain Codes
Polygonal Approximations
Signatures
Boundary Segments
Skeletons
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Texture Texture provides measures of properties such as
smoothness, coarseness, and regularity.
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Texture Based Segmentation
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Co-Occurance Matrix Let P be a position operator, and A a k x k matrix.
aij shows the number of times that pixels with gray level zi occur at position given by P relative to points with gray level zj.
Matrix A is called co-occurance matrix and can provide statistical properties of the texture.
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Example Assume P is one pixel to the right and one pixel below
Gray level values are : 0, 1, and 2
Image data:
Co-occurance matrix is:
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Statistical Moments of Texture Let Matrix C be formed by dividing every element of A by the number
of point pairs that satisfy P.
The following moments are defined to compare textures:
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Topics Segmentation
Texture Based Segmentation
Level Set Segmentation
Watershed Segmentation
Representation Introduction
Chain Codes
Polygonal Approximations
Signatures
Boundary Segments
Skeletons
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Level Set Segmentation Instead of manipulating the contour directly, the
contour is embedded as the zero level set of a higher dimensional function called the level-set function y(X, t).
The level-set function is evolved under the control of a differential equation.
At any time, the evolving contour can be obtained by extracting the zero level-set G((X), t) = {y(X, t) = 0} from the output
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Zero Set in a Level Set
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Example
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Topics Segmentation
Texture Based Segmentation
Level Set Segmentation
Watershed Segmentation
Representation Introduction
Chain Codes
Polygonal Approximations
Signatures
Boundary Segments
Skeletons
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Watershed Segmentation Algorithm:
Convert the gray level image into a topographic image where the height of each point is proportional to its gray level intensity.
Punch a hole at each region minimum at let the whole topography be flooded from below.
The points where the water from different regions join are boundaries of the regions
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Watershed Segmentation
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Example
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Example
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Topics Segmentation
Texture Based Segmentation
Level Set Segmentation
Watershed Segmentation
Representation Introduction
Chain Codes
Polygonal Approximations
Signatures
Boundary Segments
Skeletons
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Representation The result of segmentation should be represented and
described in a form suitable for further computer processing.
A region can be represented in terms of its external characteristics (boundary).
A region can be represented in terms of its internal characteristics.
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Topics Segmentation
Texture Based Segmentation
Level Set Segmentation
Watershed Segmentation
Representation Introduction
Chain Codes
Polygonal Approximations
Signatures
Boundary Segments
Skeletons
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Chain Codes Chain codes are generated by following a boundary in a
clockwise or counter-clockwise direction and assigning a direction to the segments connecting every pair of pixels.
Disadvantage: Can be unacceptably long.
Solution: Re-sampling (down sample) the boundary
Disadvantage: Is starting point dependent
Solution: Normalize the representation string to the smallest integer.
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Chain Code Directions
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Sample Chain Code
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Down Sampling
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Topics Segmentation
Texture Based Segmentation
Level Set Segmentation
Watershed Segmentation
Representation Introduction
Chain Codes
Polygonal Approximations
Signatures
Boundary Segments
Skeletons
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Polygonal Approximation A boundary can be represented with arbitrary accuracy
by a polygon.
The approximation is exact when the number of sides is equal to the number of points in the boundary.
Finding a polygonal representation can be very time-consuming.
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Minimum Perimeter Polygons
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Splitting Techniques
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Topics Segmentation
Texture Based Segmentation
Level Set Segmentation
Watershed Segmentation
Representation Introduction
Chain Codes
Polygonal Approximations
Signatures
Boundary Segments
Skeletons
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Signature A signature is a 1D representation of a boundary.
e.g. Plotting distance to centroid as a function of angle
Invariant to translation
Disadvantages:
Rotation and scaling dependant
Defined only for convex regions
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Signature Example
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Topics Segmentation
Texture Based Segmentation
Level Set Segmentation
Watershed Segmentation
Representation Introduction
Chain Codes
Polygonal Approximations
Signatures
Boundary Segments
Skeletons
![Page 34: Segmentation and Representation - Image Processing Courseceng503.cankaya.edu.tr/uploads/files/file/Digital... · Chain Codes Polygonal Approximations Signatures Boundary Segments](https://reader036.vdocuments.us/reader036/viewer/2022062402/5f5979a0afa4520ae1630d5a/html5/thumbnails/34.jpg)
Boundary Segments Decomposing a boundary into segments simplifies
representation.
Convex Hull can be used for decomposition.
A new segment can be started whenever a Convex Hull deficiency is entered or exited.
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Boundary Segments Example
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Topics Segmentation
Texture Based Segmentation
Level Set Segmentation
Watershed Segmentation
Representation Introduction
Chain Codes
Polygonal Approximations
Signatures
Boundary Segments
Skeletons
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Skeleton The structural shape of a region can be represented by
a graph.
The structural graph is obtained by thinning the region and finding the skeleton.
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Questions?