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Unformatted text preview: inal image. Many image processing systems provide this
operation as part of their image output procedures. Usually, the original image is a gray-tone
image and t he overlay color is something that stands out well on the gray tones, such as red or
white. To show a region segmentation, one could convert the pixels of the region borders to
white and display the transformed gray tone image.
2.2 Labeled images
Labeled images are good intermediate representations for regions that can also be used in further
processing. The idea is to assign each detected region a unique identifier (usually an integer)
and create an image where all the pixels of a region will have its unique identifier as their pixel
value. A labeled image can be used as a kind of mask to identify pixels of a region in some
operation that computes region properties, such as area or length of major axis of best fitting
ellipse. It can also be displayed in gray-tone or pseudo-color.
2.3 Boundary coding
Chain codes are used to represent a boundary by connected sequence of straight line segments of
specified length and direction. Typically this representation is based on the 4 or 8- connectivity
of the segments.
Digital images are usually acquired and processed in a grid format with equal spacing in the x
and y directions , so a chain code could be generated by following a boundary in, say, a
clockwise direction, and assigning a direction to the segments connecting every pair of pixels.
Regions can be represented by their boundaries in a data structure instead on an image. The
simplest form is just a linear list of the border pixels of each region. A variation of the list of
points is the Freeman chain code, which encodes the information from the list of points at any
desired quantization and uses less space than the original point list. Conceptually, a boundary to
be encoded is overlaid on as square grid whose side length determines the resolution of the
encoding. Starting at the beginning of the curve, the grid intersection points that come closest to
it are used to define small line segments that join each grid point to one of its...
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- Spring '14