izadanicpc2009

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November 2009

Novel Applications of Colour Science

University of Leeds, UK

Department of Textile Engineering

Isfahan University of Technology

Hossein Izadan



Overview

- Conventional colour measurement instruments

- Digital systems, Medical applications

- Digital systems, Conservation applications

- Digital systems, Food applications

- Digital imaging devices, digital camera and scanner

- Digital colour reproduction, colour management

- Digital systems, Dentistry applications

- Digital systems, Textile applications

- Digital systems, Cosmetic applications



Conventional colour measurement

instruments

- Colorimeters

- Spectroradiometers

- Spectrophotometers



Measurement of Radiance

Spectroradiometers measure the spectral radiance for an

illuminated object ± note that this is a non-contact instrument

and that the spectral radiance confounds reflectance and

illumination



Measurement of Reflectance

Reflectance spectrophotometers measure the spectral

reflectance factors of objects ± note that this is a contact

instrument and that the reflectance factors are independent of the light source

Colorimeters measure CIE XYZ and L*a*b* values directly



Limitations of Measurement

- Non-contact instruments (spectroradiometers) readings depend upon thedistance from the sample and the ambient lighting

- Many non-specialist contact reflectance spectrophotometers or

colorimeters are too bulky for use in many applications

- Some specially designed instruments ± such as the X-Rite ShadeVision

system ± can be used but practical use is difficult and often leads to

inconsistent results. They also usually only measure part of the samples.

- Conventional instruments measure colour by analysing the total light

reflected from the area of the object placed against the measurement port

- The object¶s surface presume to be uniform in colour and flat

- The flash of spectrophotometers lamp may contribute to the destruction

of some samples, such as fine art paintings



Dental Instruments

X-Rite ShadeVision



Digital Imaging Devices

Digital Camera Scanner

- Non-contact

- Non-colorimetric

- Need a lighting cabinet

- Sample in contact

- No need to a lighting cabinet

- Non- colorimetric



Accuracies of Digital imaging devices for Colour

Measurement

NPL Report: Digital Cameras for Colour Measurement, 1999

R

ef. Device Mean DE Max DE Attridge&Pointer Camera 3.70 15.47

Finlayson&Drew Camera 2.00 10.87

Hong Camera 0.97 3.7

Burns&Berns Camera

(7 channels)

2.2 5.1

Hung Scanner 1.8 5.8

Kang Scanner 3.32 -----

Wandell&Farrell Scanner 3.33 10.82

Chart1 Chart2 Chrart3

Average DE 0.579 0.673 0.511

Median DE 0.528 0.695 0.533

Max DE 1.887 1.275 1.304

Results of characterisation using a skin colour chart



Examples of Digital Camera Systems

DigiEye

SmartScan



Colour fastness assessmentcolour fastness assessment: a daily experiment in

most of textile factories

Colour fastness ³is the resistance of the colour of

textiles to the different agents to which these

materials may be exposed during manufacturing

and their subsequent use´ (ISO 105-A01:1995)

The magnitude of the visual contrast between

treated and untreated samples compared to a

series of standard pair of greys



Digital Systems, Textile Applications

Colour fastness assessmentColour fastness ³is the resistance of the colour of textiles to the different

agents to which these materials may be exposed during manufacturing and

their subsequent use´ (ISO 105-A01:1995)

The magnitude of the visual contrast between treated and untreated samplescompared to a series of standard pair of greys



Quality and Standards

Authority of Ethiopia

BeijingInstitute of

Fashion

Technology

Saudi Military

Uniforms

Who Uses Digital Systems - Textiles



Whiteness

~20% of UK adults are dissatisfied with their tooth colour (Alkhatib et al. 2005, Gerodontology)

~34% of USA adults are dissatisfied with their tooth colour

(Odioso et al. 2000, Comp. on Con. Ed. in Dentistry)

~53%% an urban Chinese population are dissatisfied with

their tooth colour (Xiao et al. 2007, Journal of Oral

Rehabilitation)

Some evidence that tooth appearance is more important to

younger patients and to females (Vallittu et al. 1996, Journal

of Dentistry)



Whiteness

Consumer tooth-whitening market > $500M per year inUSA alone



Interaction of Light and Tooth

Transmitted light

Reflected light ±

combination of surface

and body reflectance

Colour is determinedmainly by the thickness

and translucency of the

dentine



Intrinsic StainIntrinsic stains divided into pre- and post eruptive

Pre-eruptive

diseases such as haematological, liver

developmental diseases of enamel and dentine

medication (tetracycline and fluoride)

Post eruptiveamalgam, smoking, minocycline

Incorporation of extrinsic stains into the enamel,

Ageing, trauma



Extrinsic Stain

Chromogenic bacteria

Chlorhexidine

Tea

Coffee

Wine Antibiotics and iron supplements



Whitening ProductsToothpastes (abrasives and/or blue dyes)

Over-the-counter consumer products

Clinical chair-based treatments

Treatments with blue lights

25% Hydrogen Peroxide

19% Sodium Percarbonate



Clinical Assessment

Advantages: Quick, Easy, Inexpensive

Disadvantages: Subjective, Unreliable



Shade Guide Order

Vita standard B1, A1, B2, D2, A2, C1, C2, D4, A3, D3, B3, A3.5, B4, C3, A4, C4

Buisson B1, A1, C1, B2, D2, A2, A3, D3, C2, D4, B3, A3.5, B4, C3, A4, C4

Colgate B1, A1, C1, D2, B2, A2, D4, C2, A3, B3, D3, A3.5, B4, C3, A4, C4



Shade Guide Order

1 16

B1, A1, C1, D2, B2, A2, D4, C2, A3, B3, D3, A3.5, B4, C3, A4, C4



Effect of Surround



Effect of Surround

Generally, colours take on the opposite colour attribute of their

surround



Take Home MessageColour is subjective and the use of shade guides is often

inaccurate.



Cameras record RGB

R = 190

G = 175B = 160

Different cameras record different RGB values; even the

same camera will record different RGB values depending

upon the settings



RGB is not standard

CRTLED

plasma

Mobile displays

The same RGB values displayed on these deviceswould most likely result in different colours

CRT LED

plasmaMobile displays

The same RGB values displayed on these deviceswould most likely result in different colours



Device-dependent colour

Uncalibrated screens on the airplane trip home.



RGB is not a complete colour specification

Effect of brightness setting




Effect of contrast setting




Effect of colour temperature

warmercooler




Effect of gamma

gamma > 2gamma < 1




inaccurate.

Taking a digital image and displaying it on an uncalibrated

display device is likely even less accurate than using the

shade guides.



Measurement




inaccurate.



shade guides.

An international standard for colour specification exists ±

however, most instruments are not designed for dental use

and even those that are may be difficult to use.



Development of System at Leeds University / Colgate

The use of digital imaging is growing. Is it possible tocombine the benefits of digital imaging with those of the

CIE system of colour measurement?

This is possible if the camera and capture conditions are

very carefully controlled and if the camera RGB valuescan be converted into CIE values. This work was carried

out by Wen Luo and supported by Colgate.




3 CCD Camera

Annular LED

array

Lip retractor and chin

rest

The imaging system was designed and constructed at theColgate Dental Health Unit (Manchester)

The intensity of the light source is calibrated before each patient¶s

measurements by adjusting the intensity to yield standard RGB values

for a standard (tooth-coloured) card.



Leeds Tooth Measurement System



Tooth Imaging System

before after

control

test

Test shows effect of a tray-based whitening system for 14 days



Yellowness

Increasing yellowness

Yellowing is usually associated with a discoloration process such as ageing

or burning; in the paper and textile industries, yellowing is normally

accompanied with a decrease in Lightness (since the impurities produced by

the discoloration process induce yellowness by absorbing the shorter

wavelengths of light).

Yellowness



bluer yellower

darker

Whiteness



Whiteness

Experiments were carried out at Leeds University torank tabs from the Shade Guide and to measure their

colour values ± an optimal whiteness index was then

developed for tooth whiteness

WIO = Y + 1075.012 ( x n- x ) +145.516 (yn-y).




WIO = Y + 1075.012 ( x n- x ) +145.516 (yn-y)

Changes in WIO in the whitening trials

-4-2

0

2

4

6

810

12

14

16

18

Baseline vs 4th

day

Baseline vs 7th

day

Baseline vs

11th day

Baseline vs

14th day

W I O D

i f f e r e n c e s

Control

Test

r 2 L* a* b* WIC W WIO

Visual 0.865 0.941 0.933 0.949 0.957 0.968




inaccurate.



shade guides.

An international standard for colour specification exists ±

however, most instruments are not designed for dental use

and even those that are may be difficult to use.

A calibrated and characterised imaging system ± inconjunction with a specially designed whiteness equation ±

can quantitatively assess the efficacy of whitening

systems.

izadanicpc2009

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