fundamentals of color

1. FUNDAMENTALS OF COLOR
CHAPTER-2
By Granch BerheBy Granch Berhe

2. 2.1 Introduction Color is a visual sensation
arising from simulation of
retina of the eye.
Thus color is define as
psychophysical i.e. a
psychological response to a
physical stimulus.
Color is perceived when the wavelengths constituting white light are absorbed
reflected, refracted, scattered, or diffracted by matter on their way to our eyes

3. Color may be different meanings to different people.
To chemist: it is a chemical compound (dye
or pigment)
To physicist: it is a scattering and absorption
of light or reflectance spectra of an object
To artists and others it is the means to
create sensation to the mind, for example red
and yellow treats the sustentation of
warmness and green and blue associated with
feeelingness of coolness.

4. ?......?.....?....... Dye
Is a benzenoid aromatic compound which
makes materials coloured.
Possess unsaturated groups called chromophores
and substituent groups called auxochromes
Chromophores:- Provide coulor
Auxochromes:- Intensify and deepen colour
-Impart colour to the substrate

5. Examples of Chromophores or its combination
chromogen
N=N Azo Chr.
C=O Antraquinone Chr.
NO Nitrso Chr,
NO2 Nitro Group Chr.
C= Triarylmethane Chr.
Examples of Auxochromes
NH2
NHMe
NMe2 as Cations E.g +NMeCl2
SO3H, OH, COOH as anions E.g O-, SO3-

6. Molecule is coloured but Useless as a dye
Coloured Molecule and used as a dye

7. ?......?......?....Light
An energy producing a sensation of brightness
that makes seeing possible propagating in the
form of electromagnetic waves from 1nm to
kilometers of wavelength .
The different wavelength are identified by
different names as γ-ray X-ray, Ultra-violet,
Visible light, Infra-red…..
Visible Light is distinguished from the other by
its ability to be detected in the retina of human
eye.

8. Violet
400-435
nm
Blue
435-480
nm
Indigo
480-500
nm
Green
500-560
nm
Yellow
560-595
nm
Orange
595-605
nm
Red
605-750
nm
y-rays X-rays Ultra-violet Visible
Light
Infra-red

9. When white light falls on a substance
If the light totally reflected – The
substance appears White
 If the light totally Absorbed- The
substance appears black
If certain Portion of the light is absorbed
and the rest are reflected-The substance
has colour of reflected light
If only single band is absorbed-The
substance has the complementary colour of
the absorbed band

10. Coloured absorbed Visible (Complementary)
Violet Yellow-Green
Blue Yellow
Green-Blue Orange
Blue-Green Red
Green Purple
Yellow-green Violet
Yellow Blue
Orange Green-Blue
Red Blue=Green

11. The relationship b/n absorption and wavelengthThe relationship b/n absorption and wavelength
is given by a combination of Lambert’s andis given by a combination of Lambert’s and
Beer’s Law(Beer-Lambert LawBeer’s Law(Beer-Lambert Law))
Lambert's Law states that equal amount of absorption occurLambert's Law states that equal amount of absorption occur
when light passes in equal thickness of materialwhen light passes in equal thickness of material
Beer’s Law states that equal amount of absorption occursBeer’s Law states that equal amount of absorption occurs
when light passes through equal amount of material (i.e.when light passes through equal amount of material (i.e.
Concentration)Concentration)
II00= Intensity of incident light= Intensity of incident light
IItt = Intensity of transmitted light= Intensity of transmitted light
ε = moral absorbanceε = moral absorbance
c = Proportionality constant (absorption coefficient)c = Proportionality constant (absorption coefficient)
d = the path length through which the light passesd = the path length through which the light passes
Beer-Lambert Law is written asBeer-Lambert Law is written as IItt = I= I00*10*10εcdεcd

12. The colour of dye is mainly determined by the
wavelength of maximum absorption and
intensity of the colour depends mainly on the
value of maximum absorption.
The phenomenon that wavelength of maximum
absorption (λmax) is shifted to longer wave
length(red shift) is called Bathochromic effect
and shift to shorter wavelength(blue shift) is
called hypsochromic effect.
An increase in the value of maximum moral
absorbance (εmax) is termed as hyperchromic
effect and its reverse is hypochromic effect.

13. SIGNIFICANCE OF COLORS
EVERY COLOR
HAS A MEANING!
Hot, Dangerous!
Environmental, Productive
Cool,
Supernatural
Pure

14. Perception of color involves a series
of events which are interdisplinary in
nature. To perception colour these
things should be fulfilled.
How is color perceived?
2.2 Perception of Colour

16. The Human Eye

22. How Materials Modify By Light?
Apple illuminated under white
light appears normal (red).
Apple illuminated under green
light appears dark or black.
This kind of effect is called Rendition

27. The illuminating radiations are
modified by physical process of
object such as
Scattering
Absorption
reflection
Transmission
Object
The relative proportions of these
processes depend on the
characteristics of the material

28. Scattering of light is travelling of light in many
directions other than incident directions.
The colour presented by a group of colorants
depends on their scattering and absorption
efficiencies.
Molar absorbance coefficient (i.e. ) depends onε
the property of dye and incident light
wavelength.
The colour of the dye depends mainly by λmax and
intensity (deepness) on the value of (εmax)

29. Reflectance of light is divided into two types:
Defuse reflection:-scattered or reflection in multi
direction
Specular reflection:-reflection in one direction.

30. Transmitted

31. The common detector of light and color is eye, nerve system and
brain.
The eye focuses the image of object on retina.
The photosensitive detector on retina is called as rods and cons
from their shape.
Rods are used to detect the light and
cons detect the color.
To humans, color sensation is a matter of subjective perception
resulting from the effect of light on the cones of the eyes. There
are three types of cone receptors in the retina, each one with a
particular sensitivity to different wavelengths.
Red sensitive cones
Green sensitive cones
Blue sensitive cones
Observer

32. This decomposition of light into three color
components is called the tristimulus theory of
color and is the basis for the RGB color model.
The light reflected from pigmented object
stimulates the three types of colors sensitive
cones in the eye and brain interprets the color
as cumulative effect of the signals received from
cones.
The mechanism of the perception of colour is
based on additive color mixing.
Equal simulation of the tree cones gives the
sensation of gray to white.
If blue and red cone receptors are
simultaneously existed, the sensation of purple
is created.
How yellow impression created? R+G

34. Additive Color Mixing
Additive color mixing occurs when two or more
lights are added by focusing them on white
screen.
Applied to light
Primaries are red, green, and blue (RGB)
Colors are produced by adding various
amounts of each primary
Mixing additive primaries produces white
2.3 Color Mixing Laws premier color scan.EXE

36. Subtractive Color Mixing
Applied to pigments and dyes
Primaries are cyan, magenta, and
yellow (CMY)
Light is subtracted through the process
of selective absorption
Mixing additive primaries produces
black

37. Subtractive Color Mixing
Applied to pigments and dyes
Primaries are cyan, magenta, and yellow (CMY)
Light is subtracted through the process of selective
absorption
Mixing additive primaries produces black

38. Subtractive color mixing occurs also when one or
more spectral components are removed from
incident light, by absorption and scattering.
Subtraction made by absorption only, it is said to be
simple subtractive mixing.
On the other hand when the light is removed by
scattering and absorption, it is said to be complex
subtractive mixing.
The most commonly used primaries in subtractive
color mixing are; yellow, magenta and cyan.
The subtractive primaries are obtained by
removing blue, green and red light from white light.
 White-blue=yellow
 White-green=magenta
 White-red=cyan

39. This is achieved by using broadband filters known as
subtractive filters, which absorb a particular
wavelength of color.
Magenta filter Absorb green
Cyan filter absorb red and
yellow filters absorb blue radiations.
Simple filters
M C Y
R RRG G GB B B
Combined filters
M C Y
MYC
G G GR RB B R B

40. For technological application the most widely
approximate equation for complex subtractive
color mixing is given by, Kubellka Munk
equation.
F(R) =k/s= (1-R)2
/2R
Where,
k=absorption coefficient,
s=scattering coefficient,
R=reflectance and
F(R)=Function of reflectance factor.
This equation is basic for color matching for
industrial products (e.g. paint, plastics, textiles/
leathers, papers, etc.).