Fundamentals of spectroradiometry and colorimetry

János Schanda

SpectroradiometrySpectroradiometry

Publication CIE 63-1984:The spectroradiometric measurement of light sources– The spectroradiometer– Basic principles of measurement– Bandwidth considerations

Colorimetry - Division 1Colorimetry - Division 1

Publication CIE 15.2-1986: Colorimetry– Standard illuminants– Standard observers– Calculation of tristimulus values– Uniform colour spacing

TC 1-36: New chromaticity diagram TC 1-38: Tabulation of spectral data Report on Improved Colorimetry

Colorimetry - Division 2Colorimetry - Division 2

TC 2-04: Secondary standard sources TC 2-16: Characterization of the

performance of tristimulus colorimeters TC 2-33, -35: Standard illuminants and

V() & V’() TC 2-39: Geometric tolerances for

colorimetry

Spectroradiometry of LEDsSpectroradiometry of LEDs

Spectral irradiance measurement Spectral radiance and flux measurement The spectroradiometer Measurement principles Practical measurements

Colorimetry of LEDsColorimetry of LEDs

Fundamentals of CIE colorimetry Light source colorimetry A new system of colorimetry?

Reportership: Improved colorimetry Work in CIE TC 1-36: Fundamental

chromaticity diagram with physiologically significant axes

The spectroradiometer systemThe spectroradiometer system

Input optical arrangement-1Input optical arrangement-1

Input optical arrangement-2Input optical arrangement-2

Monochromators - 1

Light grasp or etendu, throughput, efficiency:

Double monochromator: – Two gratings (additive, subtractive dispersion)– grating + prism

Zh A

f( )

( ).

d

d

Monochromators - 2

Stray radiationDetermination with– Interference filter:– Sharp cut-off filters– Lasers

Wavelength accuracy: +/- 0,1 nm– stability– temperature dependence: 0,1 - 0,5 nm/C°

s

( )

( )

R T

R2

11

Detector and measuring systemDetector and measuring system

Irradiation of detector - homogeneity Type of detector: photomultiplier, Si-cell

– linearity (superposition)– temperature dependence– high voltage stability

Standard sources Method of measurement

Method of measurementMethod of measurement

Sequence: test - standard Transmittance function - Bandwidth

Bandwidth & samplingBandwidth & sampling

Continuous scan methodContinuous scan method

Practical measurements - ErrorsPractical measurements - Errors

Stray light Wavelength error Bandwidth - interpolation, extrapolation Polarization Detector system Reference standard

Colorimetry

Additive colour mixture

Laws of additive colour matching

Symmetry law:

Transitivity law:

Proportionality law:

Additivity law:

If thenA B B A

If and thenA B B C A C

If thenA B A B

If or

then

A B C D A C B D

A D B C

, ,

Grassmann’s lawsGrassmann’s laws

To specify a colour match three independent variables are necessary and sufficient

For additive mixture of colour stimuli, only their tristimulus values are relevant, not their spectral composition

In additive mixtures of colour stimuli, if one or more components are gradually changed, the resulting tristimulus values also change gradually

Colour equation - 1

Positive additivity C R G B B R G

Colour equation - 2

External colour mix - negative additivity C R G B R G B

Colour equation - 3

Two spectral lights:

Many spectral lights:

C C R R G G B B( ) ( ) 1 2 1 2 1 2 1 2 R G B

R k P r

G k P g

B k P b

( ) ( )

( ) ( )

( ) ( )

380 nm

780 nm

380 nm

780 nm

380 nm

780 nm

Colour equation - 4

Integral form:

with three t values Three real primaries with

L = 1,000R + 4,5907G + 0,601B

T k ti i e

nm

780nm

d 380

( ) ,

R, G, B colour space

RGB - XYZ transformation

wavelength, nm

rel.

sen

s.

0,00

0,20

0,40

0,60

0,80

1,00

1,20

1,40

1,60

1,80

350 400 450 500 550 600 650 700 750 800 850

x2(lambda)

y2(lambda)

z2(lambda)

A new system of colorimetry?

TC 1-36: Physiologically significant ...

-8

-7

-6

-5

-4

-3

-2

-1

0

1

350 450 550 650 750

wavelength, nm

log

co

ne

ac

tio

n s

en

sit

ivit

y

L-cone

M-cone

S-cone

Improved colorimetry?Improved colorimetry?

Luminance-brightness discrepancy Additivity problems New colour matching functions? Individual variations Highly metameric matches Colour appearance models

TC 1-36: Physiologically significant ...

L, M, S primaries based on psychophysical measurements:

König hypothesis - congenital dichromats Photopigment spectral absorbance Selective absorption by the lens Selective absorption by the macular

pigment

Thanks for your attention