1. Colour and Colour Measurement (TX-2046)
Dr Huw Owens
© Huw Owens - University of Manchester : 10/11/2018

2. Colour in an industrial context Reading List and Resources
Introduction
Aims and Objectives
Syllabus
Course structure
Colour in an industrial context
Reading List and Resources
I’ll tell you what you should get out of this module.
So we’ll briefly look at what we’re covering up until Christmas.
That’s what you will be taught and now I’ll tell you what I expect from you.
© Huw Owens - University of Manchester : 10/11/2018

3. To give an appreciation of the electromagnetic basis of colour
Aims
To give an appreciation of the electromagnetic basis of colour
To provide an understanding of additive and subtractive colour mixing and the related applications
A basic introduction to the Human Visual System (HVS)
An understanding of the different methods of colour specification and colour difference.
A basic knowledge of a range of colour issues faced in industry
An ability to problem solve with respect to specific colour issues
An ability to measure colour using the correct technique
© Huw Owens - University of Manchester : 10/11/2018

4. Syllabus Light and colour Colour mixing Colour vision The CIE system
Colour atlases
Colour difference
Psychology of colour
Reflectance
Absorption
Reflection
© Huw Owens - University of Manchester : 10/11/2018

5. 24 hours of laboratory work Assessment method and relative weightings
Course Structure
12 hours of lectures
24 hours of laboratory work
Assessment method and relative weightings
Unseen examination questions - 50%
Assessed Laboratory reports – 50%
Module worth 10 credits
© Huw Owens - University of Manchester : 10/11/2018

6. Reading List and Resources (1)
WYSZECKI, Günter, and W. S. STILES Color science: concepts and methods, quantitative data and formulas (New York: John Wiley & Sons). 2nd ed
HUNT, R. W. G Measuring colour (Chichester, England: Ellis Horwood). 2nd ed
HUNT, R. W. G The reproduction of colour in photography, printing and television (Tolworth, England: Fountain Press).
WRIGHT, William David The measurement of color (London: Adam Hilger). 2nd ed. (New York: Macmillan, 1958). 3rd ed. (Princeton, New Jersey: Van Nostrand, 1964). 4th ed
© Huw Owens - University of Manchester : 10/11/2018

7. Reading List and Resources (2)
WANDELL B, 1995, Foundations of Vision, Sinauer Associates.
BOYNTON and McLeod, Colour Vision, Optical Society of America.
Berns RS, 2000, Billmeyer and Saltzman’s Principles of Color Technology, 3rd Edition, John Wiley & Sons, New York.
MACDONALD R(editor), 1997, Colour Physics for Industry, Society of Dyers and Colorists, Staples printers Rochester Ltd,
NASSAU K, 2001, The physics and chemistry of colour, The fifteen causes of colour 2nd Edition, Wiley Series in Pure and Applied optics, John Wiley & Sons, ISBN
© Huw Owens - University of Manchester : 10/11/2018

8. Reading List and Resources (3)
Internet :
© Huw Owens - University of Manchester : 10/11/2018

9. Light and Colour - Summary
The Electromagnetic Spectrum
Visible spectrum/monochromators
Light Sources
Absorption and Reflection
Metamerism and colour constancy
Fluorescence
© Huw Owens - University of Manchester : 10/11/2018

10. Light and Colour - Definitions
Light – That aspect of radiant energy of which the human observer is aware, through visual sensations arising from stimulation of the retina by the radiant energy.
Colour – That aspect of visual perception dependent on the spectral composition of observed radiant energy.
Colour – “Color is the aspect of appearance of objects and lights which depends upon the spectral composition of the radiant energy reaching the retina of the eye and upon its temporal and spatial distribution thereon.” (Judd, DB)
© Huw Owens - University of Manchester : 10/11/2018

11. Aristotle concluded that light travels something like waves
What is Light?
Greeks
Pythogorean school assumed every visible object emits a steady stream of particles
Aristotle concluded that light travels something like waves
Ancient Greeks knew that light travels in straight lines
Hero – discovered the angle of incidence and the angle of reflection are always equal
1621 Snell tried to explain why a straight pole stuck in the water at an angle no longer appears straight to the observer. He named the bending of the light through a medium refraction.
© Huw Owens - University of Manchester : 10/11/2018

12. Snell failed to discover why the light bends.
What is light?
Snell failed to discover why the light bends.
1678 Huygens suggested the answer – he suggested that the refractive index of any material is determined by the speed with which light travels through it. The greater the refractive index the slower light would travel through the medium. (Light as a wave.)
Newton (1666) (Light as a particle)
Young (Light as a wave)
Maxwell (mid 19th century) – identified light as part of a vast continuous spectrum of electromagnetic radiation. (Light as a wave)
Einstein (1905) applies Planck’s quantum theory and postulates light may have wave and particle properties.
© Huw Owens - University of Manchester : 10/11/2018

13. Light and Colour – The Electromagnetic Spectrum
The spectrum and coloured light – Newton (1666)
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14. Light and Colour – Prism Monochromator
Blue light refracted more, Red light refracted less
Newton’s experiments
© Huw Owens - University of Manchester : 10/11/2018

15. Light and Colour – Diffraction Grating
Where θ is the angle of diffraction, λ is the wavelength of the incident light, d is the groove spacing (eg 300 lines per mm gives spectrum 10mm in length) and n is the integer defining the spectral order.
© Huw Owens - University of Manchester : 10/11/2018

16. Light and Colour – The Rainbow
Descartes (1637)
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17. Light and Colour – The Rainbow (An explanation)
Sunlight
Secondary Rainbow
Sunlight
Primary Rainbow
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18. Light and Colour- Spectral Power Distributions
Light sources are specified by their spectral power curves. This is a graph that plots power (or energy) against wavelength.
© Huw Owens - University of Manchester : 10/11/2018

19. Light and Colour – Light Sources
White light sources can be divided into two categories:
1. Continuous
These are usually incandescent light emitted by hot bodies such as the sun, flames or heated metallic filaments such as tungsten. The most important light source is the sun.
2. Line
© Huw Owens - University of Manchester : 10/11/2018

20. Two of these lines (D1 and D2)correspond to the yellow sodium lines.
Fraunhofer Lines
The spectrum of light was carefully examined by Joseph von Fraunhofer in Using a similar setup to Newton (except he used a narrow slit to define a ray of sunlight).
He found the solar spectrum contained a number of sharp dark lines where certain colours of the spectrum were missing.
Two of these lines (D1 and D2)correspond to the yellow sodium lines.
© Huw Owens - University of Manchester : 10/11/2018

21. Colour Temperature – Blackbody Radiators
Max Planck (1900) – If a body is heated, like a black iron poker placed in a fire, it will become a barely perceptible dull red when it reaches about 700° C.
More visible light is produced as the temperature rises (shifts from red to orange and then to yellow). This gave rise to the term COLOUR TEMPERATURE.
Leads to colloquial terms such as “red hot” but unlike psychological colours red is a cold colour and blue is a hot colour.
© Huw Owens - University of Manchester : 10/11/2018

22. Colour Temperature
© Huw Owens - University of Manchester : 10/11/2018

23. NEON lights – red line is prominent. Used in advertising.
Line Sources
Low pressure gas discharge lamps: pass electric current through a vapour of various elements.
SODIUM vapour gives sodium ‘D’ lines at 589nm and 589.6nm (almost monochromatic), used for street lighting
MERCURY vapour is used in fluorescent lamps, 4 peaks in the visible, one in the UV. The phosphors coating the glass spreads the light to other wavelengths including red.
TRIPHOSPHOR lamps – Phillips TL84, F11. Have three main peaks one in each of the red, green and blue.
NEON lights – red line is prominent. Used in advertising.
© Huw Owens - University of Manchester : 10/11/2018

24. Fluorescent Lights
Fluorescent lights are low pressure mercury lamps with a coating of phosphors on the inside of a glass tube that spreads the light, and in particular enhances the light at the red end of the spectrum.
SPD of Fluorescent Lamp
SPD of Triphosphor Lamp (TL84)
Mercury lines
© Huw Owens - University of Manchester : 10/11/2018

25. Reflectance
The colour of a surface depends on how much is absorbed by the material and how much is scattered, transmitted and reflected.
The reflectance properties of a surface are specified by its surface spectral reflectance (SSR) curve.
The SSR curve is a plot of the percentage (or proportion) of reflectance against wavelength across the visible spectrum.
Note the shapes and heights of the SSRs.
Yellow and red do not peak like green and blue.
Freshly fallen snow is close to 97% reflectance.
Black velvet fabric is approx 0.5%. Perfect white
And perfect black are theoretical. Our perception
Of the grey scale (even visual steps between
Black and white) is non-linear. A mid-grey has a
Reflectance of ~20% at all wavelengths.
© Huw Owens - University of Manchester : 10/11/2018

26. Surface Spectral Reflectance (SSR)
The SSR of a surface does not change when the light source is changed.
If two samples have identical SSR curves then they will be a visual match under different light sources.
Therefore a SSR curve may be thought of as the “fingerprint” of a colour.
© Huw Owens - University of Manchester : 10/11/2018

27. The converse is called colour inconstancy.
Colour Constancy
Definition: This is when a coloured surface appears not to change when the light source is changed.
The converse is called colour inconstancy.
Colour standards should be colour constant.
© Huw Owens - University of Manchester : 10/11/2018

28. Four types of metamerism are recognised:- Illuminant
Metamerism is the phenomenon of two colours that match under one set of conditions but fail to match under a different set.
Four types of metamerism are recognised:-
Illuminant
Observer (matches for one person and not another)
Field size (2° to 10°)
Geometric (eg Metallic paints)
© Huw Owens - University of Manchester : 10/11/2018

29. Metamerism (Illuminant)
When a standard and a batch match under one light source but do not match under a different light source they are said to be metameric and exhibit metamerism.
A perfect non-metameric match can only be achieved when the SSR curve of the batch is identical to that of the standard.
To achieve a metameric match the SSR curves of the standard and the batch must cross at least three times across the visible spectrum (at least once in each third of the spectrum).
© Huw Owens - University of Manchester : 10/11/2018

30. Metamerism
© Huw Owens - University of Manchester : 10/11/2018