Bio-medical Ontologies Maintenance and Change Management

Multimedia Medical Databases 95
The Saturation describes the intensity of the color. If the saturation is 0 (center
of the cylinder), the color has no intensity (there is a grey color). The maximum
value of the saturation (to the border of the cylinder) gives a maximum intensity of
the color.
The long axis represents the Value, the brightness of the color. The 0 value for
this component means the lack of light, resulting black and the maximum value
gives the maximum brightness of the color.
The transformation from RGB to HSV is non-linear but it is easy reversible.
The HSV color space is natural and approximately uniform from the perceptual
point of view. That is why it can be defined a quantization Q c of the HSV color
space that produce a compact and complete collection of colors.
The transformation from RGB to HSV is done using the following equations
[84, 85, 87, 86]:
v c = (r, g, b) represents a color point in the RGB color space;
w c = (h, s, v) represents the color point transformed to HSV, with w c =T c (v c ).
For r, g, b ∈ [0…1], then the transformation gives h, s, v ∈ [0…1] that:
Let:
v = max( r,
g,
b)
v − min( r,
b,
g)
s =
v
v − r
r'=
v − min( r,
b,
g)
v − g
g'=
v − min( r,
b,
g)
v − b
b'=
v − min( r,
b,
g)
ßh=5 + b' if r = max(r,g,b) and g = min(r,b,g)
ßh=1 – g' if r = max(r,g,b) and g ≠ min(r,b,g)
ßh=1 + r' if g = max(r,g,b) and b = min(r,b,g)
ßh=3 – b' if g = max(r,g,b) and b ≠ min(r,b,g)
ßh=3 + g' if b = max(r,g,b) and r = min(r,b,g)
ßh=5 – r' otherwise
(3.10)
(3.11)
The characteristics of this color space are [29]: device dependent, not perceptual
uniform, intuitive, nonlinear transformation.
H is dependent on the color of the illumination, S is dependent on highlights
and changes in the color of the illumination and V is dependent on viewing direction,
object geometry, direction, intensity and color of the illumination.
3.4.7 l1l2l3 Color System
Gevers and Smeulders proposed a new color system l1l2l3 uniquely determining
the direction of the triangular color plane in RGB-space. The transformation is
[28, 80]: