Bio-medical Ontologies Maintenance and Change Management

96 L. Stanescu, D. Dan Burdescu, and M. Brezovan
2
( R − G)
l1(
R,
G,
B)
=
2
2
2
( R − G)
+ ( R − B)
+ ( G − B)
2
( G − B)
l3(
R,
G,
B)
=
2
2
2
( R −G)
+ ( R − B)
+ ( G − B)
2
( G − B)
l3(
R,
G,
B)
=
2
2
2
( R − G)
+ ( R − B)
+ ( G − B)
(3.12)
Its characteristics are [28, 80]: nonlinear transformation, H is independent on
viewing direction, object geometry, direction and intensity of the illumination and
highlights.
3.5 The Representation of the Color Features
3.5.1 Color Histograms
Indexing images by global color distribution has been achieved by using color histograms.
For example, an image that contains different levels of grey can be transformed
in a histogram that defines the number of pixels of each color (level of
grey). For the color images, the color histograms can have a dimension higher than
2, because the colors are represented as arrays with three components [18, 86].
For a specific image there is only one histogram, but different images might
have identical histograms. Swain and Ballard confirmed that histograms are
invariant to translations, rotations and they are slightly variant when the viewing
angle or the scale is changed, but when the image is transformed in the histogram,
spatial information is lost. Color histograms can be considered a good solution for
comparing images in content-based visual query.
The next definition can be given [86]:
The distribution of colors in an image, region or object is represented by a
histogram.
Having an image I[x,y] with three color channels I = (I R ,I G ,I B ), the histogram is
given by:
∑∑
− X 1 Y −1
1,
if : Qc
( Tc
I[
x,
y])
= m
h c [ m]
= ⎨⎧ (3.13)
0,
otherwise
x = 0 y = 0 ⎩
Where X, Y represent the width and the height of the image.
In the content-based retrieval process, the histograms are normalized. This
process is necessary to make the histograms and image matching invariant to
image size.
3.5.2 Binary Color Sets
The images or regions color content can be represented more compact with the
binary color sets. J.R. Smith and Shih-Fu Chang introduced this solution at the