Bio-medical Ontologies Maintenance and Change Management

88 L. Stanescu, D. Dan Burdescu, and M. Brezovan
There is no color system that it is universal used, because the notion of color
can be modeled and interpreted in different ways. Each system has its own color
models that represent the system parameters [30].
There were created several color systems, for different purposes: RGB (for
displaying process), XYZ (for color standardization), rgb, xyz (for color normalization
and representation), CieL*u*v*, CieL*a*b* (for perceptual uniformity), HSV
(intuitive description) [29, 30].
There have been proposed systems for content-based retrieval that uses
different technologies for color characteristics representation: color histograms,
color moments, color edge orientation, color texture, color correlograms. These
uses color systems like: RGB, HIS, L*a*b* or L*u*v* [29].
The color systems were studied taking into consideration different criteria
imposed by content-based visual query [28, 30]:
• The independence of the imaging device
• Perceptual uniformity
• Linear transformation
• Intuitive for user
• Robust for imaging conditions.
– Invariant to a change in viewing direction
– Invariant to a change in object geometry
– Invariant to a change in direction and intensity of the illumination
– Invariant to a change in the spectral power distribution of the illumination
3.2 Color Fundamentals
Color is the visual perceptual property corresponding in humans to the categories
called red, yellow, white, etc [15, 29]. Color derives from the spectrum of light
(distribution of light energy versus wavelength) and interacts in the eye with the
spectral sensitivities of the light receptors. Color categories and physical
specifications of color are also associated with objects, materials, light sources,
etc., based on their physical properties such as light absorption, reflection, or
emission spectrum.
The visible spectrum is the portion of the electromagnetic spectrum that is
visible to the human eye [29, 102]. The human eye is able to respond to
wavelengths in air from 380 to 780 nm [29, 102].
Newton first used the word spectrum (Latin for “appearance” or “apparition”)
in print in 1671 in describing his experiments in optics [29, 102]. Newton
observed that, when a narrow beam of sunlight strikes the face of a glass prism at
an angle, some is reflected and some of the beam passes into and through the
glass, emerging as different colored bands. Newton hypothesized that light was
made up of particles of different colors, and that the different colors of light
moved at different speeds in transparent matter, with red light moving more
quickly in glass than violet light. The result is that red light was refracted less