Colour Measurement

How colour is measured with instruments rather than eyes: colorimeters, spectrophotometers, measurement geometry, standard observers and illuminants, and what a ΔE number does and does not tell you.

Describes measurement principles and published standards in summary. Instrument brand recommendations are out of scope.

18 topics · 80 evidence-labelled claims · 45 sources

Tools

ΔE colour difference calculator Spectral explorer

Instruments

What each kind of instrument measures.

What is the difference between a colorimeter and a spectrophotometer?A colorimeter measures colour through three filters shaped like the eye's colour-matching functions and reports tristimulus value…What does a spectroradiometer measure that a spectrophotometer does not?A spectroradiometer measures light itself — the spectral power emitted by a lamp, a display or the sky, in absolute radiometric u…How is colour measured for opaque, translucent and transparent materials?Opaque materials are measured in reflectance: the instrument lights the surface and reports the fraction reflected at each wavele…What does the shape of a reflectance curve tell you about a colour?The height of the curve sets lightness, where it is high sets hue, and how sharply it rises or falls sets how saturated the colou…How do you measure the colour of something that lets light through?Decide first whether the sample is to be judged by reflected or by transmitted light, then control where the rest of the light go…Why does a display colorimeter need a correction for each type of screen?Because its three filters only approximate the colour-matching functions, and the size of the resulting error depends on the spec…

Conditions

Geometry, observers, illuminants and calibration.

What do 45°/0° and d/8° mean, and why do they give different readings?Measurement geometry is the angle at which an instrument lights the sample and the angle at which it collects the reflected light.What is the difference between SCI and SCE measurement?SCI (specular component included) measures all the light a sample reflects, including the mirror-like gloss reflection; SCE (spec…What are the 2° and 10° standard observers, and which should I use?A standard observer is a set of three colour-matching functions describing an average person's colour vision, from which XYZ and…What are CIE standard illuminants, and why do D50 and D65 both exist?A CIE illuminant is a table of relative spectral power — a defined 'light' for calculating colour — not a physical lamp.How accurate is a colour measurement, and how do I know?Three different numbers describe it.How much do colour values change between the 2° and 10° observers?For a neutral, almost nothing; for a saturated blue or green, several CIELAB units.How is a colour calculated from a reflectance spectrum?Multiply the light's power by the surface's reflectance at each wavelength, weight the product by each of the observer's three co…Why does a spectrophotometer's UV setting change the colour of white samples?Because many whites fluoresce.

Colour difference

ΔE formulas, tolerances and their limits.

What is ΔE, and why do ΔE76, ΔE94 and CIEDE2000 give different numbers?ΔE is a single number for the difference between two colours, calculated from their CIELAB values.What ΔE tolerance is acceptable, and how do industries set one?There is no universal acceptable ΔE.Why does the 'nearest' colour by ΔE sometimes look like the wrong match?Because ΔE formulas model average judgements of two large, flat, adjacent samples on a neutral background under standard light.What is a metamerism index, and what does the number mean?A metamerism index is a colour difference with a condition attached: how far apart two samples are under a test light, given that…