introduction
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ISO 11664-1-2019 Colorimetric method – Part 1: CIE Standard Colorimetric Observer

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This document has been prepared by the International Commission on Lighting (CIE) in collaboration with ISO/TC 274 Technical Committee (Light and Lighting).

The first edition of ISO/CIE 11664-1 cancels and replaces ISO 11664-1:2007 |CIE S 014-1:2006, which constitutes a minor revision including minor editorial updates.

A list of all parts in the ISO 11664 and ISO/CIE 11664 series can be found on the ISO website.

Any feedback or questions regarding this document should be directed to the user’s national standards body. A complete list of these institutions can be found at iso.org/members.html.

ISO 11664-1-2019 Colorimetric method – Part 1: CIE Standard Colorimetric Observer

introduce
Colors with different spectral components may look similar. An important function of colorimetry is to determine whether a pair of such heterochromatic color stimuli look similar. The use of visual colorimeters for this purpose is hampered by variations in color matching between observers classified as having normal color vision. Visual colorimetry also tends to be time-consuming. For these reasons, colorimetry has long used a set of color matching functions to calculate the tristimulus value of a color: Equal tristimulus value of a pair of colors indicates that the color appearance of the two colors matches, when an observer applying the color matching function observes them under the same conditions. Using the standard set of color matching functions, it is possible to compare the tristimulus values obtained at different times and places.

1 Range
This document specifies the color matching function for colorimetry. Two sets of color matching functions are specified.

a) Color matching function of CIE 1931 standard colorimetric viewer.

This set of color matching functions represents the color matching properties of an observer with normal color vision, with a field of view size of about 1° to about 4° angular subtension, for vision at the level of clear vision adaptation.

b) Color matching function of CIE 1964 standard colorimetric viewer.

This set of color matching functions represents the color matching properties of observers with normal color vision, for field sizes with angular subtension greater than about 4°, and for visual and spectral power distributions with sufficiently high clear vision levels that no rod receptors of the retina are required to participate.

ISO 11664-1-2019 Colorimetric method – Part 1: CIE Standard Colorimetric Observer

2 Normative references
The following files are referenced in text in a manner that constitutes part or all of the requirements of this document. For dated references, only the cited version applies. For undated references, a new version of the reference (including any revisions) applies.

CIE S 017: –, 1 ILV: International lighting vocabulary

3 Terms and definitions
For the purposes of this document, the terms and definitions given in CIE S 017 and the following apply.

ISO and IEC maintain terminology databases for standardization at the following addresses:

– ISO Online browsing platform: available at iso.org/obp

– IEC electronic encyclopedia: available at electropedia.org/

ISO 11664-1-2019 Colorimetric method – Part 1: CIE Standard Colorimetric Observer

3.1 Color stimulation function F l (l)

Describes the function of the spectral distribution of color stimuli

Note 1: The color stimulus function is generated by the spectral distribution of the amount of radiation, such as radiosity or radiant flux.

Note 2: For object color, the color stimulus function φλ (λ) is equal to the product of the relative spectral distribution S (λ) and the spectral reflectance ρ (λ) or spectral radiation coefficient β (λ) or spectral transmittance τ (λ), depending on the application.

[Source: CIE S 017: -, entry 17-23-003, revised – Definitions have been completely revised and entry notes have been added.

3.2 Heterochromatic color stimulus, PL

Isomer, PL

Spectral stimuli of different colors having the same tri-stimulus value in a specified colorimetric system

Note 1: The corresponding property is called “metamerism”.

[Source: CIE S 017: -, article 17-23-008]

3.3 Monochromatic stimulus

Spectral stimulation

A stimulus consisting of monochromatic radiation

[Source: CIE S 017: -, article 17-23-011]

3.4 isoenergy spectrum

Radiation spectrum, the spectral distribution of the amount of radiation as a function of wavelength is constant throughout the visible region

ISO 11664-1-2019 Colorimetric method – Part 1: CIE Standard Colorimetric Observer

Note 1: Radiation in the equal-energy spectrum is sometimes treated as a light source, in which case it is represented by the symbol E.

[Source: CIE S 017: -, entry 17-23-023, modified – “(φλ (λ) = constant)” omitted at end of definition.

3.5 Additive Mixture

< Color stimulus > Stimuli, which combine the effects of various color stimuli on the retina in a way that cannot be perceived individually

[Source: CIE S 017: -, article 17-23-030]

3.6 Color Matching

The effect of a color stimulus on a color identical to that of a given color stimulus

[Source: CIE S 017: -, article 17-23-031]

ISO 11664-1-2019 Colorimetric method – Part 1: CIE Standard Colorimetric Observer

3.7 Trichromatic system

A system that specifies a color stimulus according to a tristimulus value, based on matching colors by adding a mixture of three suitably selected reference color stimuli

[Source: CIE S 017: -, article 17-23-036]

3.8 Reference Color stimulus, PL

The three-color stimulus on which the three-color system is based

Note 1: These stimuli are either real color stimuli or theoretical stimuli defined by linear combinations of real color stimuli.

Note 2: In the CIE standard colorimetric system, the reference color stimulus is represented by symbols [R], [G], [B]; [X], [Y], [Z]; [R 10], [G 10], [B 10] or [X 10], [Y 10], [Z 10].

[Source: CIE S 017: -, entry 17-23-037, modified – “three-piece set” has been changed to “three”, and “and” in note 2 has been changed to “or”.

ISO 11664-1-2019 Colorimetric method – Part 1: CIE Standard Colorimetric Observer

3.9 tristimulus value, PL

< Color stimulus > In a given three-color system, the amount of reference color stimulus is needed to match the color of the stimulus under consideration

Note 1: In the CIE standard colorimetric system, the tristimulus values are represented by symbols R, G, B; X, Y, Z; R 10, G 10, B 10 or X 10, Y 10, Z 10.

[Source: CIE S 017: -, entry 17-23-038, amended – “The amount of three references” has been changed to “the amount of reference”.

3.10 Color matching function, PL

< Three color System > The tristimulus value of a monochromatic stimulus of equal radiative flux

[Source: CIE S 017: -, entry 17-23-039, amended – Entry notes omitted.

3.11CIE 1931 standard colorimetric system

X, Y, Z

Use a set of reference color stimuli [X], [Y], [Z] and three CIE color matching functions adopted by CIE in 1931

mml_m1

ISO 11664-1-2019 Colorimetric method – Part 1: CIE Standard Colorimetric Observer

A system that determines the tristimulus values of any spectral power distribution

Note 1: Same as V (λ), so the tristimulus value Y is proportional to the brightness value.

mml_m2

Note 2: The CIE 1931 standard colorimetric system is suitable for central observation fields with angular subtension between about 1° and about 4° (0,017 rad and 0,07 rad).

Note 3: The CIE 1931 standard colorimetric system can be derived from the CIE 1931 RGB colorimetric system using a transformation based on a set of three linear equations. The CIE 1931 RGB system is based on three real monochromatic reference stimuli.

Note 4: See also CIE 15, Colorimetry.

[Source: CIE S 017: -, article 17-23-045]

3.12 CIE 1964 standard colorimetric system

X 10, Y 10, Z 10

Use a set of reference color stimuli [X 10], [Y 10], [Z10] and the three CIE color matching functions adopted by CIE in 1964

mml_m3

A system to determine the tristimulus value of any spectral power distribution

Note 1: The CIE 1964 standard colorimetric system is suitable for central observation fields with angular subtension greater than about 4° (0,07 rad).

Note 2: When using the CIE 1964 standard colorimetric system, all symbols representing colorimetric measurements are distinguished by the use of the subindex 10.

ISO 11664-1-2019 Colorimetric method – Part 1: CIE Standard Colorimetric Observer

Note 3 See also CIE 15, Colorimetry.

[Source: CIE S 017: -, articles 17-23-046]

3.13 CIE color matching function, PL

The CIE 1931 standard colorimetric system or

mml_m5

Functions in the CIE 1964 standard colorimetric system

mml_m4

[Source: CIE S 017: -, article 17-23-047]

3.14 CIE 1931 standard colorimetric viewer

For the professional observer, its color matching characteristics correspond to the CIE color matching function adopted by CIE in 1931

mml_m6

[Source: CIE S 017: -, articles 17-23-049]

3.15 CIE 1964 standard colorimetric Observer

For the professional observer, the color matching characteristics correspond to the CIE color matching function adopted by CIE in 1964

mml_m7

[Source: CIE S 017: -, article 17-23-050, modified – Article note 1 omitted.

3.16 Chrominance coordinates, pl

Coordinates representing the quotient and sum of each value in a set of three tristimulus values

ISO 11664-1-2019 Colorimetric method – Part 1: CIE Standard Colorimetric Observer

Note 1: Since the sum of the three chromaticity coordinates equals 1, two of them are sufficient to define chromaticity.

Note 2: In the CIE standard colorimetric system, chrominance coordinates are represented by the symbols x, y, z or x 10, y 10, z 10.

Note 3: Chromaticity coordinates are quantities in unit one.

[Source: CIE S 017: -, entry 17-23-053, amended – “ratio” has been changed to “quotient”.

3.17 Spectral chromaticity coordinates, PL

r (λ), g (λ), b (λ); x (λ), y (λ), z (λ); R 10 (λ), g 10 (λ), b 10 (λ); x 10 (λ), y 10 (λ), z 10 (λ)

Chromaticity coordinates of monochromatic stimuli

[Source: CIE S 017: -, article 17-23-055]

3.18 Spectral luminous efficiency

ISO 11664-1-2019 Colorimetric method – Part 1: CIE Standard Colorimetric Observer

V (λ) For bright vision > V ‘(λ), < For dark vision > Vmes; m (λ) For medium vision >; V10 (λ), < For CIE 10° brightness observer >; VM (λ), < Improved luminous 2° spectral luminescence efficiency function for CIE 1988 >

< For specified luminosity conditions > The quotient of the radiant flux at wavelength λm and the radiant flux at wavelength λ such that both produce an equally strong luminous sensation under the specified luminosity condition, and λm is chosen so that the maximum value of this quotient is equal to 1

[Source: CIE S 017: -, entry 17-21-035, amended – Entry notes omitted.

3.19 Reflection diffuser

An ideal isotropic diffuser whose reflectivity is equal to the unit

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