image segmentation - mahidol universityimage segmentation is a task to distinguish the features...
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Chaiwoot BoonyasiriwatNovember 9, 2020
Image Segmentation
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▪ Image segmentation is a task to distinguish the features
(objects or structures) or the foreground from the
background in an image.
▪ Here we concentrate on two approaches: thresholding
and boundary-based segmentation.
Image Segmentation
Russ and Neal (2016, p. 381)
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▪ Selecting features in a scene can be accomplished by
thresholding brightness values. The resulting image is a
binary or two-level image.
▪ Threshold values may be set based on the histogram.
Brightness Thresholding
Russ and Neal (2016, p. 381-382)
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Histogram can be interpreted as a sum of 3 Gaussian
peaks representing R, G, and B to colorize an image.
Colorizing an Image
Russ and Neal (2016, p. 384)
MRI image
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Thresholding of Multiband Images
Russ and Neal (2016, p. 394)
Original image Pixel color values plotted
in biconic HSI space
Resulting binary
image
Selection of HS values
for green candy
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Image Histogram in Various Spaces
Russ and Neal (2016, p. 395)
RGB Cylindrical HSI Spherical L*a*b*
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▪ Texture can be used for image segmentation.
▪ Below is an image containing 5 regions with different
texture. The brightness of pixels in each region has a
different probability distribution.
Thresholding from Texture
Russ and Neal (2016, p. 400)
Probability distribution of pixel
brightness in each region
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(a) Result of applying a variance operator with 4-pixel radius.
(b) Histogram showing that each region has a distinct
brightness.
(c) Each region can be selected by thresholding the histogram
Thresholding from Texture
Russ and Neal (2016, p. 401)
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Multiple Thresholding Criteria
Russ and Neal (2016, p. 402)
Original image Texture image using variance Intensity image
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K-Mean Clustering
Russ and Neal (2016, p. 424)
Original 3 arbitrary center
locations assigned
Resulting labels
for the current
centers
The centroids of
the regions are
assigned as the
new centers.
Regions are
redefined and
labeled.
Repeat the
process
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Region-Growing Methods
https://en.wikipedia.org/wiki/Image_segmentation#Clustering_methods
▪ Assign a set of seeds that marks the objects to be selected.
▪ The pixel with the smallest difference between its intensity
value and a region’s mean is assigned to the region.
▪ The process continues until all pixels are assigned.
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▪ J. C. Russ and F. B. Neal, 2016, The Image Processing
Handbook, 7th edition, CRC Press.
References