Read this power point presentation Enrich your knowledge about color physics in textiles.

1. Bangladesh university of textiles
Subject : color physics and color measurement
presented to
ummul Khair fatema
Associate Professor
Dept. of wet process Engineering, BUTEX
presented by
Nusrat Jahan
ID :2017-2-3-003
MSc in textiles engineering (6th batch )
Dept. of wet process engineering , BUTEX

3. • science of color is sometimes called chromatics, colorimetry, or simply
color science. It includes the perception of color by the human eye and
brain, the origin of color in materials
• Color is the visual property that human eye perceives when detecting the
visible spectrum of light.
Color
Colors are the native language of the subconscious.
–Carl Jung, Psychiatrist
• Humans see color as our eyes process the interaction of light hitting an object
• if we replace eyes with an instrument it can see and record color

4.  Numerical comparison of a sample's color to the standard.
 Indicates the differences in absolute color coordinates
 The difference or distance between two colors is a metric of interest
in color science.
 It allows quantified examination of a notion that formerly could only
be described with adjectives. Quantification of these properties is of
great importance to those whose work is color critical.
 Color measuring instruments and industry accepted color difference
systems are widely utilized in industrial color acceptability
applications.
color difference

5.  A limit to how big the difference in color between a sample and the
standard is allowed for the sample to be considered acceptable.
 The end goal of implementing a color process is to get the color you want,
or your customer wants, for the finished product through an efficient and
streamlined process.
 If the color of a product doesn't match the standard, customer satisfaction
is compromised and the amount of rework, waste, and costs increase.
 Establishing color tolerances objectively within the color process is an
effective way to maintain color consistency and accuracy, as well as to
meet standards more efficiently.
color Tolerance

6. Color difference and its tolerance systems
Color difference and its Tolerance Systems are used in the management of
production and customer acceptability activities.
They are :
 CIE L*a*b* Color Difference and toerance – 1976
 CIE L*C*h* Color difference and Tolerances – 1994
 CMC (l :c ) Color Difference and Tolerances
 CIE94 Color Difference and Tolerances
 CIE lab 2000
 ANLAB
 FMC
 JPC 79
 BFB
 Hunter lab

8. Hue: Any single color in the spectrum
(red, yellow, blue, etc).
Colors can be of the same hue and
still have varying degrees of saturation
Color attribute

9. Tint : A color with white added
Tone : A color with grey added
Shade: A color with black added.
Tint and shade
Color attribute cont.

10. Color attribute cont.

12. CIE L*a*b* Color space
Designed for the human eye
Describes and orders colors based
on the opponent theory of color
vision.
Colors cannot be perceived as both
red and green at the same time, Or
yellow and blue at the same time
However, a color can be perceived
as a combination of red and yellow,
red and blue, green and yellow, or
green and blue.
Rectangular color coordinate
system

13. CIE L*a*b* Color Difference
Difference between any two colors in CIE
1976 color space, is the distance between
the color locations.
This distance is typically expressed as
delta E or D E
Here ,
Δ L* being the lightness difference.
Δ a* being the red/green difference.
Δ b* being the yellow/blue difference
Two points in LAB color space
These two color patches are
made up with the indicated
CIE L*a*b* values:
Redder
+a
Greener
- a
Yellower
+b
Bluer
-b
L = 100
L = 0

14. CIE L*C*h* Color space
CIELAB uses Rectangular coordinates to calculate a
color in a color space, CIELCH uses polar
coordinates.
color expression can be derived from CIELAB.
Here ,
L* = lightness
C* = chroma
h° =hue angle, an angular measurement
L* coordinates are the same as in L*a*b*, while the
C* and h* coordinates are computed from the a*
and b* coordinates.
The same color is still in the same location in the
color space, but CIE L*a*b* and CIE L*C*b* are two
different ways to describe its position.

15. CIE L*C*h* Color Difference
Differences are the same for any pair of colors like
using CIE L*a*b*
L*C*h color difference is preferred by some industry
professionals because its system correlates well with
how the human eye perceives color.
Difference is typically expressed as delta E or D E
ΔC* =chroma difference.
Δh* =hue angle difference.
ΔH* = being the metric hue difference.
The metric hue difference (ΔH*) is the color difference that remains when the
lightness and chroma differences are zero.
ΔH* is used in the total color difference computation, where all terms are
distances (not angles)

17. Compare two colored flower one is standard and other is batch
Separately they are yellow rose.
But what is their relationship when set side by side? How do the colors
differ?
Using CIE LAB color Difference equation :
∆E*ab = [(+ 11.1)2 + (–6.1)2 + (–5.25)2]1/2 ∆E*ab
= 13.71
Here
∆L* = +11.10,
∆a* = –6.10,
∆b* = –5.25
Summary :
On the a* axis, reading of –6.10 indicates greener or less red.
On the b* axis, reading of –5.25 indicates bluer or less yellow.
On the L* plane, the measurement difference of +11.10 shows that
Flower (b) is lighter than Flower (s)
Expressing Colors Numerically
standard
Batch

18. same two flowers are now compared using
CIELCH
color differences would be expressed as:
∆L* = +11.10
∆C* = –5.88
∆H* = 5.49
Summary
∆C* value of –5.88 indicates that Flower (B)
is less chromatic, or less saturated.
The ∆H* value of 5.49 indicates that Flower (B)
is greener in hue than Flower (s).
The L* and ∆L* values are identical for CIELCH
and CIELAB.
Expressing Colors Numerically
standard
Batch

20. Poor color memory, eye
fatigue, color blindness and
viewing conditions can all
affect the human eye’s
ability to distinguish color
differences.
Limitations
Eye does not detect
differences in hue, chroma
or lightness equally.
In fact, the average observer
will see hue differences first,
chroma differences second
and lightness differences
last.
So,
Visual acceptability is best
represented by an ellipsoid
Visual Color Tolerance
An ellipsoid usually described as Visual acceptability
Tolerance ellipsoid

21. When tolerancing with CIELAB, you must choose a difference limit for ∆L*
(lightness),
∆a* (red/green), and ∆b* (yellow/blue).
These limits create a rectangular tolerance box around the standard
CIELAB Tolerance
A rectangular must acceptable

22. When comparing this tolerance box with the visually accepted ellipsoid, some
problems emerge.
A box-shaped or rectangular tolerance around the ellipsoid can give good numbers
for unacceptable color.
If the tolerance box is made small enough to fit within the ellipsoid, it is possible to
get bad numbers for visually acceptable color
CIELAB Tolerance cont.
Numerically correct Versus visual acceptable

23. CIELCH Tolerance
CIELCH users must choose a difference limit for ∆L* (lightness), ∆C* (chroma)
and ∆H* (hue). This creates a wedge-shaped box or conic shaped around the
standard.
Since CIELCH is a polar-coordinate system, the tolerance box can be rotated
in orientation to the hue angle
CIELCH Tolerance wedge or conic shaped

24. When this tolerance is compared with the ellipsoid, we can see that it more
closely matches human perception.
This reduces the amount of disagreement between the observer and the
instrumental values
CIELCH Tolerance cont.
CIELCH Tolerance ellipsoid

25. Is not a color space but rather a tolerance system based on CIELCH, provides better
agreement between visual assessment and measured color difference.
The CMC calculation mathematically defines an ellipsoid around the standard color
with semi-axis corresponding to hue, Chroma and lightness.
The ellipsoid represents the volume of acceptable color and automatically varies in
size and shape depending on the position of the color in color space. .
The quasimetric has two parameters: lightness (l) and chroma (c), allowing the users
to weight the difference based on the ratio of l:c that is deemed appropriate for the
application.
Commonly used values are 2:1 for acceptability and 1:1 for the threshold of
imperceptibility
Equation of color difference :
CMC Tolerance

26. The variation of the ellipsoids throughout color space:
In figure
The ellipsoids in the orange area of color space are longer and narrower than the
broader and rounder ones in the green area. The size and shape of the ellipsoids
also change as the color varies in Chroma and/or lightness
CMC Tolerance cont.

27. The CMC equation allows to vary the overall size of the ellipsoid to better match
what is visually acceptable.
By varying the commercial factor (cf), the ellipsoid can be made as large or small as
necessary to match visual assessment.
The cf value is the tolerance, which means that if cf=1.0, then ∆E CMC less than 1.0
would pass, but more than 1.0 would fail
Since the eye will generally accept larger differences in lightness (l) than in chroma
(c), a default ratio for (l:c) is 2:1. A 2:1 ratio will allow twice as much difference in
lightness as in chroma. The CMC equation allows this ratio to be adjusted to achieve
better agreement with visual assessment
CMC Tolerance cont.

28. In 1994, the CIE released a new tolerance method called CIE94.
Like CMC, the CIE94 tolerancing method also produces an ellipsoid. The user has
control of the lightness (kL) to chroma (Kc) ratio, as well as the commercial factor (cf).
Equation of color difference :
SL, SC, SH are weighting functions that adjust the CIE differences (ΔL*, ΔC*, ΔH*)
depending upon the location of the standard in CIE 1976 color space. SL = 1; SC = 1 +
0.045 C* ; SH = 1 + 0.015 C* . kL, kC, kH are numeric parametric factors that permit
the independent weighting of lightness (ΔL*), chroma (ΔC*), and hue (ΔH*) differences
These settings affect the size and shape of the ellipsoid in a manner similar to how the
l:c and cf settings affect CMC.
However, while CMC is targeted for use in the textile industry, CIE94 is targeted for use
in the paint and coatings industry.
If the surface is textured or irregular, CMC may be the best fit.
If the surface is smooth and regular, CIE94 may be the best choice.
CIE94 Tolerance

29. First major revision of the delta E 2000 equation since CIE94 (or dE94).
Unlike dE94, which assumes that L* correctly reflects the perceived differences
in lightness, dE2000 varies the weighting of L* depending on where in the
lightness range the color falls.
Equation of color difference :
dE2000 is becoming increasingly popular in graphic arts applications
CIE Lab 2000/Delta E 2000

30. Five rules :
1. Select a single method of calculation and use it consistently.
2. Always specify exactly how the calculations are made.
3. Never attempt to convert between color differences calculated by different
equations through the use of average factors.
4. Use calculated color differences only as a first approximation in setting
tolerances, until they can be confirmed by visual judgments.
5. Always remember that nobody accepts or rejects color because of numbers
— it is the way it looks that counts, especially when consumers are making
buying decisions at the shelf or in the showroom.
Choosing the Right Tolerance