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11.2.2 Texture Feature Descriptors
Many natural and artificial pictures contain strong visual patterns, called
texture, as a result of multiple colors or intensities in the image. Several fea-
ture descriptors based on texture are specified in MPEG-7.
11.2.2.1 Homogeneous Texture Descriptor (HTD)
This descriptor specifies the region texture using the energy and energy
deviation in a set of frequency channels. It is extracted from the parti-
tioned frequency space in the polar frequency domain with equal angles
of 30° in the angular direction and with an octave division in the radial
direction. The frequency layout of 30 feature channels is shown in
Figure 11.1. The 2-D Gabor function is applied in each feature channel.
The energy e i of a feature channel is defined as the log-scaled sum of the
square of the Gabor-filtered Fourier transform coefficients of an image.
The energy deviation d i of a feature channel is defined as the log-scaled
standard deviation of the square of the Gabor-filtered Fourier transform
coefficients of an image.
The homogeneous texture descriptor captures the texture of homogeneous
properties.
The similarity matching for homogeneous texture descriptor can be mea-
sured by the following function
TD
()
k
Dk
()
1
D
=
2
,
(11.10)
α
()
k
k
where TD 's are descriptors of two images and the normalization value α( k )
is recommended as the standard deviation of the descriptors of all candidate
images.
The homogeneous texture descriptor is sensitive to intensity, rotation,
and scaling of images. The following matching methods provide invariant
matching.
Intensity-Invariant Matching
The average intensity of the image in the feature descriptor is elimi-
nated for similarity matching.
Rotation-Invariant Matching
The query Image feature vector is shifted in angular directions,
TD query | m φ , and the similarity is computed as the minimum among
all shifted versions as
DTD
(
,
D
)min{(
=
D TD
,
TD
,
m φ 05
)|,
,},
(11.11)
query
database
query
datab
ase
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