HUNTER COLOR LAB
COLOR
▪ Color is the one of the most important image features because it
contains the basic human vision.
▪ Color significantly affects the consumer perception of quality.
▪ If the color is unacceptable, the other two major quality factors,
flavor and texture, are not
likely to be judged at all.
COLOR
▪ Color may be defined as the impact of the wavelengths of light in
the visual spectrum from 390-760 nm on the human retina.
▪ The retinal cells may be sensitive to black and white only or to red,
green and blue (RGB) wavelengths of light.
▪ The correct interpretation by the brain in terms of color depends
on the adequacy of signals.
COLOR
• Light is the basic stimulus of colors, it is important to consider the
electromagnetic spectrum.
• Visible light forms only a small part of the electromagnetic spectrum, with a
spectral range from approximately 390 nm (violet) to 750 nm (red).
• The sensitivity of the eye varies even within this narrow visible range. Under
conditions of moderate-to-strong illumination, the eye is most sensitive to
yellow-green light of about 550 nm.
Color scales
• There are three characteristics of light by which a color may be
specified: hue, saturation, and brightness.
• Hue is an attribute associated with the dominant wavelength in a
mixture of light waves, i.e., it represents the dominant color as
perceived by an observer.
• Saturation refers to relative purity or the amount of white light mixed
with a hue.
• Brightness is a subjective term, which embodies the chromatic notion of
intensity.
• Hue and saturation taken together are called chromaticity.
• Therefore, a color may be characterized by brightness and chromaticity.
Color scales-CIE System
• Sometimes, tristimulus systems of representation of colors are not easily
understood by the users in terms of object color. Other color scales
therefore were developed to relate better to how we perceive color,
simplify understanding.
• A 3-dimensional rectangular L, a, b, color space was evolved, in which at L
(lightness) axis – 0 is black and 100 is white, a (red-green) axis – positive
values are red; negative values are green and zero is neutral, and b
(blue-yellow) – positive values are yellow; negative values are blue and
zero is neutral.
Color scales-CIE System
• There are two popular L, a, b color scales in use today – Hunter L, a,
b, and CIE L∗, a∗, b∗.
• They are similar in organization, but will have different numerical
values.
• Hunter L, a, b and CIE L∗, a∗, b∗ scales are both mathematically
derived from X, Y, Z values.
• Hunter scale is over expanded in blue region of color space, while CIE
scale is over expanded in yellow region. The current recommendation
of CIE is to use L∗, a∗, b∗.
Color scales-CIE System
• The basic colors however are only three: red, green and blue, and other colors
are derived by mixing these three.
• The Commission Internationale de l’Eclairage (CIE) defined a system of
describing the color of an object based on three primary stimuli: red (700 nm),
green (546.1 nm), and blue (435.8 nm).
• The amounts of red, green, and blue needed to form any given color are
called the’ ‘tristimulus” values, X, Y, and Z, respectively.
• A plot that represents all colours in x (red)-y (green) coordinates is known as a
chromaticity diagram
Color scales-CIE System
Color scales-CIE System
