Glossary Of Terms For Colour Measurement | HunterLab
Glossary of Terms
A
Absolute Reflectance Value
Reflectance value relative to the perfectly reflecting and perfectly diffusing surface, which is assigned a value of 1.0.
Absorption
Process by which light or other electromagnetic radiation is converted into heat or other radiation when incident on or passing through material.
Accuracy
Conformity of a measured result to an accepted reference value or scale.
Achromatic Colour
A neutral colour, such as white, gray or black, that has no hue. Also termed nonchromatic.
Angle of Incidence
The angle between the axis of an impinging light beam and the perpendicular to the specimen surface.
Angle of View
The angle between the axis of observation and the perpendicular to the specimen surface.
Attribute
Distinguishing characteristic of a sensation, perception or mode of appearance. Distinction is made between chromatic and geometric appearance attributes.
B
Brightness
The attribute of visual sensation by which an observer is made aware of differences in luminance.
C
Calibration
The graphical or mathematical relationship of a desired property to an instrument's output.
Chromatic
Perceived as having a hue - not white, gray or black.
Chromatic Attributes
Those attributes associated with the spectral distribution of light, hue and saturation.
Chromaticity
That part of a colour specification which does not involve luminance.
CIE 1976 L*a*b* Colour Space
A uniform-colour space utilizing an Adams-Nickerson cube root formula, suggested in 1976 for adoption by the CIE in 1976 for use in measurement of small colour differences.
CIE Chromaticity Coordinates (Trichromatic Coefficients)
The ratios of each of the tristimulus values of a colour to the sum of the tristimulus values. In the CIE system they are designated by x, y and z.
CIE Luminosity Function
A plot of the relative magnitude of the visual response as a function of wavelength from about 380 nm to 770 nm, adopted by CIE in 1924.
CIE Standard Observer
A hypothetical observer having the tristimulus colour-mixture data recommended in 1931 by the CIE for a 2° field of vision (x, y, z or x2, y2, z2). A supplementary observer for a larger 10° field (x10, y10, z10) was adopted in 1964.
CIE Tristimulus Values
The amounts of the three reference or matching stimuli required to give a match, with the colour stimulus considered, in a given trichromatic system.
CIE, Commission Internationale de l'Eclairage
In English, the International Commission on Illumination; the main international organization concerned with colour and colour measurement.
Clarity
The characteristic of a transparent material whereby distinct images may be observed through it.
CMC
Colour difference based on the CIELAB colour scale which can automatically generate tolerances for perceptible or acceptable differences.
Colour Attribute
A three-dimensional characteristic of the appearance of an object, light source or aperture. One dimension usually defines the lightness and the other two together define the chromaticity.
Colour Constancy
Substantial invariance of object-colour perceptions in the presence of changes in illumination or viewing conditions.
Colour Difference
The magnitude and character of the difference between two object colours under specified conditions.
Colour Measurement Scale
A system of specifying numerically the perceived attributes of colour.
Colour Perceived
The visual sensation produced by light of different wavelengths throughout the visible region of the spectrum. By such perception an observer may distinguish differences between two objects of the same size, shape, and structure.
Colour Specifications
Tristimulus values, chromaticity coordinates and luminance value, or other colour-scale values, used to designate a colour numerically in a specified colour system.
Colorimeter
Instrument which senses tristimulus values and converts them to chromaticity components of colour.
Contrast Ratio
A measure of opacity; the ratio of the luminous reflectance of a specimen backed with black material of specified reflectance to the reflectance of the same specimen backed with white material of specified reflectance.
D
Delta Descriptor
A comparison of a sample to a standard in words. It is based on colour difference data. When the selected colour scale is L, a, b or L*a*b*, the delta descriptors are lighter/darker, redder/greener, or yellower/bluer. When the selected colour scale is LCh, the descriptors are lighter/darker, less saturated/more saturated and less chromatic/more chromatic.
Diffuse Reflection
Process by which incident light is redirected over a range of angles from the surface on which it is incident.
Diffuse Transmission
Process by which incident light, while being transmitted through an object, is redirected or scattered over a range of angles.
H
Haze
The scattering of light within or at the surface of a nearly clear specimen, responsible for cloudy appearance seen in transmission.
Hitch Standards
Standards close in colour to the specimens being measured. These are the same as transfer standards.
Hue
The attribute of colour perception by means of which an object is judged to be red, yellow, green, blue or purple.
Hunter L,a,b Scale
A uniform colour scale devised by Hunter in 1958 for use in a colour difference meter. It is based on Hering's opponent-colours theory of vision.
I
Illuminant
A table of spectral distribution as close as possible to that of the natural light source, usually daylight, to be duplicated.
Instrument Standards
Secondary standards which are only used with a particular instrument for maintaining the calibration of the instrument.
L
Light
Electromagnetic radiation in the spectral range (approximately 380 nm to 780 nm) detectable by the normal human eye.
Light Source
That element in an instrument or in the visual observing situation that furnishes radiant energy in the form of light.
Lightness
Perception by which white objects are distinguished from gray objects and light objects from dark colour objects.
M
Metamerism
The phenomenon whereby colours of specimens match when illuminated by light of one spectral composition despite differences in spectral reflectance of the specimens, and that consequently may not match in light of some other spectral composition.
Metamerism Index
A measure of the degree of metamerism. A general index of metamerism is derived from two metameric spectral distribution curves without regard to the illuminant. A special index of metamerism is specified to two different illuminants.
Munsell Colour System
The colour identification of a specimen by its Munsell hue, value and chroma as visually estimated by comparison with the Munsell Book of Colour.
N
Nanometer (nm)
Unit of length equal to 10-9 of a meter.
O
Object Colour
The aspect of the appearance of an object dependent upon the spectral composition of the incident light, the spectral reflectance or transmittance of the object, and the spectral response of an observer.
Observing Conditions
The geometric and spectral conditions of illuminating and viewing a specimen for visual or instrumental evaluation. In visual observations, the conditions include the surroundings and the state of adaptation of the observer.
Opacity
The degree to which a sheet or film obscures a pattern beneath it.
Opponent-Colours System
A colour system based on Hering's opponent-colours theory which states that there are six independent colour dimensions which are perceived by three opponent-colour systems: black-white, red-green and yellow-blue.
P
Perception
The combination of different sensations and the utilization of past experience in recognizing the objects from which the stimulation comes.
Perfect Diffuse Reflector
An ideal uniform diffuser with zero absorbance and zero transmittance.
Perfect Diffuse Transmitter
An ideal uniform diffuser with zero absorbance and zero reflectance.
Polychromator
A device for isolating narrow portions of the spectrum by dispersing light into its component wavelengths.
Precision
The degree of agreement of repeated measurements of the same property.
Primary Light
Any one of three lights in terms of which a colour is specified by giving the amounts required to duplicate it by additive combination.
Primary Standard
A standard whose calibration is determined by the measurement of parameters usually different from the parameter for which it will be used as a standard.
R
Reflectance
The ratio of reflected to incident radiation.
Reflection
Process by which incident light leaves a surface or medium from the side on which it is incident.
Refraction
The bending of light rays as they pass from one medium into another having a different index of refraction.
Regular Transmittance
Process by which incident light is transmitted through an object in a rectilinear, straight-through manner, without diffusion.
Repeatability
The degree to which a single instrument gives the same reading on the same specimen.
Reproducibility
The agreement attainable between measurements performed by different instruments in different laboratories.
Restandardize
To set the top of the standardization scale only.
S
Saturation
The attribute of colour perception that expresses the degree of departure from the gray of the same lightness.
Scattering
The process by which light passing through granular, fibrous or rough surface matter is redirected throughout a range of angles.
Secondary Standards
All standards other than primary standards.
Shade Sorting
The grouping together of similarly-colored materials so that the materials within each group may be used together in a finished product.
Spectrocolorimeter
Visible spectrum-sensing full-scanning or abridged spectrophotometer with either an integral microprocessor or a personal computer programmed to perform tristimulus integrations, normally with a broad bandpass of 10 nm to 20 nm.
Spectrophotometer
An instrument used for measuring the transmittance and/or reflectance of specimens as a function of wavelength.
Spectrum
Spatial arrangement of electromagnetic energy in order of wavelength. For visible radiation, the spectrum is a band of colour produced by breaking white light into its component colours.
Specular
Having the qualities of a speculum or mirror; having a smooth reflecting surface.
Specular Reflectance
Process by which incident light is redirected at the specular angle, as from a mirror, without diffusion.
Standard
A reference against which instrumental measurements are made.
Standardization
Process by which a given method, procedure or protocol is made to conform to prescribed conditions. Standardization can only follow calibration.
T
Tolerance
Limits that determine how far a sample can deviate from a standard. Tolerances can be set for any colour scale or index parameter.
Total Reflection
Diffuse plus specular reflection.
Total Transmission
Diffuse plus regular transmission.
Transfer Standards
Standards close to the colour of the specimens being measured. These are the same as hitch standards.
Translucency
The property of a material by which a major portion of the transmitted light undergoes scattering.
Transmission
Process by which incident light is transmitted through an object.
Transparency
The property of a material by which a negligible portion of the transmitted light undergoes scattering.
U
Uniform Colour Scale
A colour scale or colour solid in which the differences between points correspond to the perceptual visual differences between the colours represented by these points.
W
Wavelength
The distance, measured along the line of propagation, between two points that are in phase or on adjacent waves. Wavelength distribution determines the colour of light. Wavelengths of visible light range from about 380 nm to about 780 nm.
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