Short answer
A standard observer is a set of three colour-matching functions describing an average person's colour vision, from which XYZ and CIELAB are computed. The CIE 1931 observer was derived for a small 2° field; the 1964 supplementary observer for a 10° field, where more of the retina outside the fovea is involved. Use 2° for small samples and the graphic arts, 10° for larger samples such as paint, textiles and plastics — and never mix them in one comparison.
In colour-matching experiments, observers adjust three primary lights until their mixture matches a test wavelength. Averaged over observers and converted to the CIE's X, Y, Z primaries, the results are the colour-matching functions: how much of each tristimulus value one unit of power at each wavelength contributes. The CIE adopted the first set in 1931, based on experiments using a field about 2° across — the size of a thumbnail at arm's length — which falls mostly on the fovea. Every CIELAB, ΔE or CCT value is calculated through one of these sets.
Colour sensitivity changes with field size. The fovea is covered by a yellowish macular pigment and has a different cone mix from the surrounding retina, so a large field is matched differently from a small one. In 1964 the CIE added a supplementary standard observer for a 10° field, which at 50 cm is a circle about 8.8 cm across, against 1.7 cm for 2°. The 10° functions are more sensitive in the blue and differ enough that the same sample gives noticeably different XYZ values under each. Instrument makers advise the 2° observer for viewing angles of about 1–4° and the 10° observer above 4°.
The graphic arts use the 2° observer: ISO 13655 and every Fogra characterisation data set specify D50 and 2°, reflecting print viewed as small detail. Paint, plastics and textile industries mostly use D65 with the 10° observer, reflecting large painted areas and garments; the CMC textile formula was designed around that combination. Display and lighting work largely uses 2°, because CCT, sRGB and most video standards are defined with it. None of these is more correct; the requirement is to state the observer with every number and use the same one for the reference and the sample.
Both standard observers are averages, and real people differ — in lens yellowing with age, macular pigment density and cone sensitivity — so two people can disagree about a match that an instrument reports as exact (observer metamerism). The CIE has since published physiologically based cone-fundamental colour-matching functions (CIE 170-1:2006) that can be computed for different field sizes and ages. They are used in research and some display work, but industrial colour specification still runs on the 1931 and 1964 observers, which CIE 15:2018 continues to recommend.
| Observer | Field of view | Size at 50 cm | Typical industries |
|---|---|---|---|
| CIE 1931 standard observer | 2° | ≈ 1.7 cm circle | Graphic arts, displays, lighting (CCT) |
| CIE 1964 supplementary observer | 10° | ≈ 8.8 cm circle | Paint, plastics, textiles |
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactStrong evidence
The CIE defined the standard observer in 1931 using a 2° field of view and a supplementary standard observer in 1964 using a 10° field; at 50 cm a 2° field is a circle about 1.7 cm across and a 10° field about 8.8 cm.
Source: Precise Color Communication; CIE 015:2018 Colorimetry, 4th edition
ConventionModerate evidence
The 2° standard observer is recommended for viewing angles of about 1° to 4° and the 10° supplementary observer for viewing angles above 4°.
Caveat: Instrument maker's guidance summarising CIE practice.
Source: Precise Color Communication
StandardStrong evidence
Graphic-arts measurement to ISO 13655 and the Fogra offset characterisation data use illuminant D50 with the 2° observer.
Source: ISO 13655:2017 Graphic technology — Spectral measurement and colorimetric computation for graphic arts images; FOGRA51 characterization data (premium coated offset, ISO 12647-2:2013)
ConventionLimited evidence
In textile practice the CMC(l:c) colour-difference formula is commonly applied with illuminant D65 and the 10° supplementary observer.
Caveat: A common practice described in secondary summaries; the 1984 paper's published abstract does not state viewing conditions.
Source: Modification to the JPC79 colour-difference formula; Color difference (Wikipedia)
FactStrong evidence
The CIE has published cone-fundamental-based colour-matching functions (CIE 170-1:2006) that can be computed for different field sizes and observer ages.
Source: CIE 170-1:2006 Fundamental Chromaticity Diagram with Physiological Axes – Part 1
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.