PROPERTIES OF LIGHT

1. RGB-COLOR MODEL
Submitted By
Mrs.R.CHINTHAMANI,
Assistant Professor,
Department of Computer Science
E.M.G.Yadava Women’s College,
Madurai-14.

2. LIGHT
 A Light is a narrow frequency band within the
electromagnetic spectrum
Spectrum of light:
 A few of the other frequency bands within this
spectrum are called radio waves, microwaves, infrared
waves, and X-rays.
 Each frequency value within the visible corresponds to
a distinct color.
The Electoromagnetic Spectrum
Red : 4.3×1014
hertz , violet: 7.5×1014
hertz

3.  Light is an electromagnetic wave. The various
colors in terms of either the frequency f or the
wavelength λ of the wave.

4.  The wavelength and frequency of the
monochromatic wave are inversely proportional to
each other with the proportionality constant as the
speed of light c:
c = λ𝑓

5.  Frequency is constanty for all materials, but the
speed of light and the wavelength are material
dependent .
 In vaccum, c=3×1010 cm/sec.
 Light wavelengths are very small, so length units
for designating spectral colors are usually either
angstroms(1Å= 10−8 cm)or nanometers (1 nm=
10−7cm).
 An equivalent term for nanometer is millimicron.
 since, wavelength units are more convenient to
deal with than frequency units, spectrual colors
are typically specified in terms of wavelength

6.  A light source such as the sun or a light bulb
emits all frequencies within the visible range to
produce white light.

7.  The combination of frequencies present in the
reflected light determines what we perceive as the color
of the object.
 If low frequencies are predominant in the reflected
light, the object is described as red. In this case, the
perceived light has a dominant frequency at the red end
of the spectrum.
 The dominant frequency is also called the hue or
simply the color of light.
 The characteristics of the dominant frequency are
brightness and purity are commonly used to describe
the different properties we perceive in a source of light ,

8.  Each frequency component within the range from
red to violet contributes more or less equality to
the total energy ,and the color of the source is
described as white.
 Energy distribution of a light source with a
dominant frequency near the red end of the
frequency range

9.  The two or three colors used to produce other colors
in such a color model are referred to as Primary colors.
 No finite set of real primary colors can be combined
to produce all possible visible colors.
 The amount of red, green, blue needed to produce an
spectral color. The curve plotted is called color-
matching functions, were obtained by averaging the
judgements of a large number of observes.

11.  Based on the tristimulus theory of vision, our eyes
perceive color through the stimulation of three
visual pigments in the cones of the retina.

12.  The visual pigments have a peak sensitivity
at wavelength of about 630nm(red),
530nm(green) and 450nm(blue) .
 By comparing intensities in a light
source,we perceive the color of the light.
 This theory of vision is the basis for
displaying color output on a video monitor
using the three color primaries, red, green,
blue referred to as the RGB model.

13. The RGB color models, defining colors with an additive process within the
unit cube.

14.  Vertices of the cube on the axes represent the
primary colors, and the remaining vertices
represent the complementary color for each of the
primary colors.
 The XYZ color system, the RGB color scheme is
an additive model.
 Intensities of the primary colors are added to
produce other colors.
 Each color point within the bounds of the cube
can be represented the triple(R,G,B), where values
for R,G,B are assigned in the range from 0 to

15.  A color Cλ expressed in RGB component as,
Cλ = RR+GG+BB
 The magenta vertex is obtained by adding red
and blue to produce the triple (1,0,1) and white at
(1,1,1)
is sum of the red, green, and blue vertices.
 Shades of gray are represented along the main
diagonal of the cube from the origin to the white
vertex .
 Each point along this diagonal has an equal
cotribution fro each primary color, so that a gray
shade halfway between black and white is
represented as (0.5,0.5,0.5).

16. The color gradutions along the front an top planes of the RGB cube

17.  Chromaticity coordinates for an NTSC standard
RGB chromaticity coordinates for the CIE RGB color
model and the approximate values used for
phosphors in color monitors.
NTSC Standard CIE model Approx. color
monitor values
R (0.670,0.330) (0.735,0.265) (0.628,0.346)
G (0.210,0.710) (0.274,0717) (0.268,0.588)
B (0.140,0.080) (0.167,0.009) (0.150,0.070)

18.  Also listed are the RGB chromaticity coordinates
for the CIE RGB color model and the approximate
values used for phosphors in color monitors.
Color Gamut:
 color gamut is defined as the range of colors
which a particular device can produce or record.
 Various standards govern color gamuts. The
three standards frequently cited in relation to
personal computers are sRGB, Adobe RGB and
NTSC.

19.  The color gamut defined by each standard
is depicted
 As a triangle on the xy chromaticity
diagram

20. END