1.  physics  measurement  norm  perception
Glossiness & colour of a transparent glass:
 physics  measurement  norm  perception
Claudio Oleari Università degli Studi di Parma Dipartimento di Fisica

2. Light TRANSMISSION and REFLECTION are considered in relation to the perception in order to open a debate useful to define the most meaningful specification of the APPEARANCE of a transparent glass.

3. In practice: How to judge visually the appearance of a glass?
Transmitted and reflected lights are present at the same time in a glass object.
In practice: How to judge visually the appearance of a glass?
In science: How to specify and measure the appearance of a glass?

4. 1) Optics For an optical characterization of a non scattering glass
i) appearance characterization
spectral transmittance t(l)
spectral reflectance r(l)
ii) optical characterization spectral refraction index n(l) absorption coefficient k(l)

5. Colour stimulus VISIBILE SPECTRUM violet blue green yellow orange rednm
gamma X radio
ray ray UV IR microwave wave long radio wave l m
Colour stimulus

6. Refraction index  reflection & refraction
n(l) 1 l
- Snell laws (geometrical properties of light)
Fresnel laws (energetic properties of light)
reflectance & transmittance

7. Snell laws
geometrical optics
From Wikipedia

8. Fresnel laws
Surface reflectance

9. What geometry for illumination and light collection?
Biconical Transmittance and Reflectance spectral Distribution Function (BTDF) (BRDF) wi w ji j Ji J

10. 2) CIE norm (Commission Internationale de l’Éclairage) for transmittance measurement
(a standard reflectance measurement of a transparent medium is not defined)
Norms for light-modulation measurement
CIE publication No. 15:2004, Colorimetry, 3rd Ed.

11. specimen
10° W
to the spectrometer
CIE geometry (0°:0°)

12. specimen
10° W 2°
to the spectrometer
CIE geometry (di:0°), (de:0°)

13. specimen
W =2p
to the spectrometer
CIE geometry (d:d)

14. absorption Incident light CIE geometry (0°:0°) Transparent glass
reflected light
refracted light
absorption
Transparent glass
CIE geometry (0°:0°)

15. Absorption and Internal transmittance Lambert-Bouguer and Beer laws
F,l(s=0)
F,l(s) s

16. Fi Ft Fr Physical quantities directly related to the perception
nair(l)
nglass(l)
a ≈ 0 Fi Ft Fr
Measured by spectrophotometer
Total spectral transmittance
Total spectral reflectance

17. For an (approximate) complete optical characterization
n(l), k(l)
t(l), r(l)

18. Transmittance for orthogonal incidence
Approximate equation
Zero-thickness transmittance

19. For a complete optical (approximate) characterization
From measures of transmittance for two different thicknesses
absorption coefficient
refraction index

20. For an (approximate) complete characterization of appearance
t(l), r(l)

21. For an (approximate) complete characterization of appearance
Total transmittance is measured
Total reflectance is function of n(l) and k(l), obtained by approximation from two transmittance measurements
refraction index

22. 3) Colour perception & specification of transmitted and reflected lights
CIE observers
CIE colorimetric systems
CIE colorimetric computation

23. Macular absorbance [a. u.]
MACULA LUTEA
Macula lutea
Fovea
Blind point nm
lunghezza d’onda
Macular absorbance [a. u.]
CIE 1931
CIE 1964
CIE observers

24. typical of the psycho-physical and psycho-metric colorimetry
aperture mode
typical of the psycho-physical and psycho-metric colorimetry

25. CIE colorimetric systems:
(X, Y, Z) linear vector space (tristimulus space)
Luminance factor, ld dominant wavelength, purity
CIELAB metric space (L*,a*,b*), (L*, hab, C*ab) colour-difference formulae
CIELUV metric space (L*,u*,v*), (L*, huv, C*uv)
Luminance factor, whiteness, tint

26. L* b* a* C*ab hab CIELAB – CIELUV
A colour specification close to the perception
unique hues (red, yellow, green, blue)
binary hues
colour opponency
Binary hues L* a* b*
hab
C*ab

27. Colorimetric computation:
Colour specification depends on
 the observer (CIE 1931 or CIE 1964)  the spectral transmittance/reflectance  the illuminant (A, D65, F11)
(X, Y, Z)

28. Few warnings

29. TRISTIMULS COMPUTATION according to CIE[1] and ASTM [2]
RAW SPECTRAL DATA
IF Dl  1 nm THEN
ELSE OR
CHOICES
observer (CIE 1931, CIE 1964,., …)
illuminant (A, B, C, D65,…, F11, …)
deconvolution
interpolation
ASTM 1996
Weighting
Functions
ASTM 1985
1 nm CIE
TRISTIMULUS VALUES (X, Y, Z)
[1]Publication CIE N° 15:2004, Colorimetry, 3rd edition, Central Bureau of the CIE, A-1033 Vienna, P.O. BOX 169 Austria.
[2] ASTM E Standard Practice for Computing the Colors of Objects by Using the CIE System, Annual book of ASTM Standard, American Society for Testing and Materials, Philadelphia, USA.

30. ? What means “COLOR CALCULATION ACCORDING TO CIE
RECOMMENDATION (D65/10° - CIE 15:2004)” ?

31. RECOMMENDATIONS CONCERNING THE CALCULATION OF TRISTIMULUS VALUES AND CHROMATICITY COORDINATES
The CIE Standard (CIE, 1986) on standard colorimetric observers recommends that the CIE tristimulus values of a colour stimulus be obtained by multiplying at each wavelength the value of the colour stimulus function () by that of each of the CIE colour-matching functions and integrating each set of products over the wavelength range corresponding to the entire visible spectrum, 360 nm to 830 nm. The integration can be carried out by numerical summation at wavelength intervals, , equal to 1 nm.
(7.1)
In the above equations () denotes the spectral distribution of the colour stimulus function, i.e. () = d()/d, see CIE International Lighting Vocabulary item (CIE,1987). X, Y, Z are tristimulus values, X(), Y(), Z() (or ) are colour-matching functions of a standard colorimetric observer, and k is a normalising constant defined below. Each of these may be specified for the CIE 1931 standard colorimetric system by being written without a subscript, or for the CIE 1964 standard colorimetric system by the use of the subscript 10.
The fundamental colorimetric tables are the 1 nm tables in CIE standards. All rigorous calculations should use these 1 nm tables. For most practical purposes, the summation may be approximated by using wavelength intervals,  equal to 5 nm over the wavelength range 380 nm to 780 nm. Values of the CIE colour-matching functions at 5 nm intervals suitable for use in summation over this range of wavelengths are given in Tables T.4 and T.5. In case measurement have been made at smaller intervals than 5 nm, the appropriate values from the tables in the standards should be used.

32. What about
“WHITENESS and TINT ” ?

33. The evaluation of whiteness
To promote uniformity of practice in the evaluation of whiteness of surface colours, it is recommended that the formulae for whiteness, W or W10, and for tint, Tw or Tw,10, given below, be used for comparisons of the whiteness of samples evaluated for CIE standard illuminant D65. The application of the formulae is restricted to samples that are called "white" commercially, that do not differ much in colour and fluorescence, and that are measured on the same instrument at nearly the same time. Within these restrictions, the formulae provide relative, but not absolute, evaluations of whiteness, that are adequate for commercial use, when employing measuring instruments having suitable modern and commercially available facilities.
W = Y + 800(xn – x) (yn – y)
W10 = Y (xn,10 – x10) (yn,10 – y10) (9. 11)
Tw = 1000(xn – x) – 650(yn – y)
Tw,10 = 900(xn,10 – x10) – 650(yn,10 – y10)
where Y is the Y-tristimulus value of the sample, x and y are the x, y chromaticity coordinates of the sample, and xn, yn are the chromaticity coordinates of the perfect diffuser, all for the CIE 1931 standard colorimetric observer; Y10, x10 , y10, xn,10 and yn,10 are similar values for the CIE 1964 standard colorimetric observer.

34. Conclusion:
 deep physical specification refraction index n(l) {measured, approximate from 2 transmittances} absorption coefficient k(l) {approximate from 2 transmittances}  appearance physical specification spectral transmittance t(l,s) {measured by spectrophotometer} spectral reflectance r(l,s) {measurement?} {approximate from 2 transmittances}  Colorimetric specification of the appearance- physical specification observer: CIE illuminants: A, D65, F colorimetric system: CIELAB (L*, C*ab, hab)

35. About the VISUAL JUDGEMENT of the appearance?

37. Thank you for your attention
Claudio Oleari