Glossary

Home Measuring Instruments Learning Centre Glossary
 
Term Definition Link 
∆E Measure of perceived colour difference.  
Achromatic colour Colour that can be described only by its lightness.  
Absorption spectrum Spectrum after transmission through a medium.  
Additive colour mixing Combination of spectrally different visible radiation. The colour stimuli are incident on the retina if they are projected continuously or periodically changing onto the same spot, or if smallest dots printed next to each other cannot be resolved by the eye. In any case, the spectral composition of the colour stimuli involved is not changed.  
Backing White or black area on which the sample is placed for colour matching. The XY-stage CSA+ is shipped with both ISO conforming backings.  
Basic colorimetry System of techniques defined by the CIE to evaluate colour stimuli in respect to their sameness. Tristimulus values are measured to numerically describe colour stimuli in a given system of observance (i.e. under a given CIE standard illuminant, observed by one of the CIE standard colorimetric oberservers and using a given measurement geometry.   
Black CMYK primary used for black generation and greyscale images.  
Black generation Colour separation methods in four-colour process printing that determine the ration of black to cyan, magenta and yellow. Depending on the software the user can influence the black generation parameters. learn more
Brightness 1) Sensation of light created by observing a self-luminous area and whose intensity is represented by the absolute quantity luminance.
2) Value used to quantify optical paper characteristics		 learn more
Candela SI unit of luminous intensity.1 cd = lm/sr learn more
Chroma The colourfulness of a non-luminous colour that is compared to a similarly illuminated area that appears white or highly transmitting. learn more
Chromatic colour Colour that can be described by its hue.  
Chromaticity Discernible property of a surface of a certain shape, structure, size and brightness or lightness when that surface is compared to another one of the same shape, structure, size and brightness or lightness. Hue and saturation, both properties of a colour, form the chromaticity of a colour. It can be plotted in the chromaticity diagram using chromaticity coordinates. learn more
Chromaticity coordinates Tristimulus values that are normalised to sum up to 1, the scale of the CIE x,y chromaticity diagram. learn more
CIE 1931 standard colorimetric observer also known as 2° observer Ideal observer who perceives colours in a 2° field according to the spectral luminous efficiency function for photopic vision and on whom the x(λ), y(λ), z(λ) colour-matching functions are based. Basis of the CIE 1931 standard colorimetric system. learn more
CIE 1931 standard colorimetric system Internationally agreed upon colorimetric system of objective colour description using three virtual primary colours (X, Y, Z) to form a colour space, and the tristimulus values derived from them. learn more
CIE 1964 standard colorimetric observer also known as 10° observer Ideal observer who perceives colours in a 10° field according to the spectral luminous efficiency function for photopic vision and on whom the x10(λ), y10(λ), z10(λ) colour-matching functions are based. Basis of the CIE 1964 standard colorimetric system. learn more
CIE 1974 general colour rendering index Mean of the CIE 1974 special colour rendering indices for a specified set of colour samples.  learn more
CIE 1974 special colour rendering index Colour rendering index calculated for one colour out of a specified set of colour samples.  learn more
CIE 1976 L*a*b* colour space Approximately perceptually uniform colour space presented in a three-dimensional rectangular coordinate system. The coordinates a* and b* form a plane to which the lightness axis L* is perpendicular. The positive a* axis approximates red, the negative a* axis approximates green. The positive b* axis approximates yellow and the negative b* axis approximates blue. Colours plotted on the outer circle around the achromatic stimulus have the same chroma. Colours plotted on a radius have the same hue. learn more
CIE 1976 L*u*v* colour space Approximately perceptually uniform colour space presented as a transformed CIE xy chromaticity diagram, i.e. in a two-dimensional rectangular coordiante system. The u'v' plane shows more purplish hues and a compressed green area. Lightness L* is perpendicular to the u'v' plane. Coordinates L*u*v* allow for determining chroma, saturation, hue angle and hue difference. learn more
CIE xy chromaticity diagram Chromaticity diagram in which all spectral colours and the chromaticities derived by additive colour mixing are plotted. learn more
CIE illuminant Lightsource whose spectral power distribution is defined by CIE to be the measurement standard. learn more
Colorimetry System of techniques defined by the CIE to evaluate colour stimuli in respect to their sameness, to evaluate the perceived difference of colour stimuli and to evaluate colour appearances. Colorimetry can be divided into basic and advanced colorimetry.  
Colour Visual sensation defined by a colour stimulus having a certain chromaticity and brightness or lightness. A colour can be described by the tristimulus values.  
Colour cast Imbalance in neutral colours caused by the preponderance of one primary colour. Can be judged by a spectrophotometer.  
Colour constancy Almost total physiological compensation for the illuminant colour shift by the adaptive colour shift. As a result, a colour is perceived to be almost the same under different illuminants.   
Colour density Value of the lightness of a printed substrate area that is determined by the negative logarithm to base ten of the reflection factor or transmission factor of this area. Can be measured with a spectrodensitometer.  
Colour difference Geometrical distance between colours that are plotted in a two- or three-dimensional colour space. This metric should be designed to correlate with the magnitude of the perceived colour difference. Its measure is ∆E. Spectrophotometers can show the colour differnence between reference and sample diretly.  
Colour difference formula Mathematical expression, often as Euclidean distance, of colour difference. Spectrophotometers can often make use of different formulas.  
Colour gamut Amount of all colours present in a scene or an image, or that can be generated by an imaging device under specified circumstances by mixing its primary colours. This amount of colours is, when graphically represented in a three-dimensional colour space, also called colour solid. Note that an input device can be characterized colorimetrically but does not have a colour gamut.  
Colour gamut boundary Graphic representation of colour space coordinates of the primary colours and their highest saturated secondary colours that form the surface of a colour gamut.  
Colour gamut mapping Transformation of the colour gamut of the source medium or source image that compensates for differences in the source and destination medium colour gamuts. Some profilers allow to influence the gamut mapping strategy.  
Colour management Workflow with a varying number of processes and  data communication via spectral measurement data.  
Colour match Intentional or accidental result of colour matching. Can be controlled objectively using a spectrophotometer.   
Colour matching Process of mixing colours so as to produce a colour that is indisitinguishable from a reference colour. CCM software is used in various industries to assure a colour match for products.  
Colour rendering index Measure of colour rendering. ∆E is calculated using the tristimulus values of the sample that is first illuminated by a reference illuminant and then by the test light source. ∆E is then transformed into the special or the general colour rendering index.
Can be displayed directly using a KM CL-500A. 		 learn more
Colour separation Action of creating monochrome colourant values and storing them in the corresponding colour channel of the image file. ICC-Profilers differ in strategy and quality of colour separation.  
Colour space Spatial representation of colours that can be numerically described by tristimulus values in two or three dimensions.   
Colour stimulus Visible radiation that causes colour perception as soon as it is incident onto the retina.   
Colour temperature Measure for describing the chromaticity of a light source. Temperature of the Planckian radiator having the same chromaticity as a given light source, but usually not the same spectral power distribution. learn more
Colourant Portion of printing ink that gives it ist characteristic hue. Can be dye or pigment. CCM software uses calibrations of colourants to calculate colour recipes.  
Colourfulness Property of an area that is perceived to be more or less chromatic.  
Commission Internationale de l'Éclairage Non-profit organisation that conducts research on the topics of lighting and colorimetry.    
Complementary wavelength Helmholtz coordinate that can be used to specify the hue and saturation of a colour that is plotted in the CIE xy chromaticity diagram between the chromatic stimulus and the purple boundary. The complementary wavelength is the point where an elongated straight line from the point of the given colour through the achromatic stimulus intersects the spectrum locus (e.g. λc = c530 nm).  
Continuous spectrum Visible spectrum that can be plotted having radiant flux at all wavelengths.  
Contrast Difference between two visual items with one common property, e.g. print contrast.  
Correlated colour temperature Measure for describing the chromaticity of a light source if it cannot be allocated a distribution temperature. Temperature of the Planckian radiator having its chromaticity coordinates on the isotemperature lines defined by Judd. learn more
Cyan One of the primary colours in four-colour process printing that defines the CMYK colour space.   
Device characterisation Part of the profiling process that consists of measuring the device-dependent values produced and listing them in a table together with the device-independent CIEXYZ or CIEL*a*b* tristimulus values. This can be done using automatic test chart readers.  
Device-dependent colour space Any colour space that is defined by the colour rendering characteristics of a real or virtual imaging device. A device-dependent colour space can be a colorimetric colour space.  
Device-independent colour space Any colour space that is defined by CIE XYZ tristimulus values or their derivatives, usually CIE 1976 L*a*b* colour space.  
DeviceLink profile Profile format developed by the International Color Consortium that is used to directly combine two imaging devices without performing colour space transformations via the Profile Connection Space.  
Diffraction grating Component of spectral measurement equipment to split polychromatic light into separate wavelengths  learn more
Diffuse Evenly in all directions, not glossy. (e.g. diffuse reflection)  
Diffuse reflection Type of reflection where, ideally, the efflux beam is all-directional.  
Distribution temperature Measure for describing the chromaticity of a light source. Temperature of the Planckian radiator having the same spectral power distribution as the light source to be described. learn more
Dominant wavelength Helmholtz coordinate that can be used to specifiy the hue and saturation of a colour in the CIE xy chromaticity diagram. The dominant wavelength can be plotted on the spectrum locus as the point intersected by an elongated straight line from the achromatic stimulus through the point of the given colour.  
Fluorescent Whitening Agent Substance that absorbs UV-energy and emits this energy as visible blue light. Used to compensate for yellowish casts of various materials such as paper, textiles and plastics rsp. to increase the impression of "white". learn more

learn more
Fluorescent Whitening Intensity Index to quantify the amount of optical brighteners in paper.  
G7 Method of calibration of printing systems. With spectrophotometers it's possible to conduct a G7 certification.  
Green One of the CIE-defined additive primary colours that define the RGB colour space.  
Grey Colour that possesses all wavelenghts of visible radiation in equal amounts and has therefore no hue.  
Grey balance Colour values for a certain combination of process colours in four-colour process printing or for RGB colours that appears as an achromatic colour under specified output and viewing conditions.
Can be controlled using Spectrophotometers.		  
Helmholtz coordinate Numerical value that separately specifies a colour stimulus regarding its hue and its saturation. Helmholtz coordinates are dominant wavelength, complementary wavelength and excitation purity.  
Hue Property of a colour that distinguishes a chromatic colour from an achromatic colour. The hue can be specified by the chromaticity coordinates of a colour or the dominant wavelength (or complementary wavelength) in the CIE x,y chromaticity diagram. learn more
Illuminance Photometric quantity. Quotient of the luminous flux incident on a surface by the area of that surface. learn more
Illuminant Visible radiation whose relative spectral power distribution is known. learn more
Irradiance Radiometric quantity. Quotient of the incident radiant flux by the area delimited by its solid angle. learn more
Isotemperature line Connection line between the chromaticity coordinates of constant correlated colour temperatures intersecting the Planckian locus.  
Light scattering Heterogenous media cause incident photons to deviate from a straight trajectory. The part of the incident radiation or light that is absorbed into the medium is diffusely reflected within the medium.  
Light source Source of visible radiation, including ultraviolet and infrared radiation. learn more
Light stimulus Visible radiation incident on the retina and thus causing the perception of light.  
Lightness Sensation of light created by observing an illuminated area in comparison to another, similarly illuminated white or transmitting area and whose intensity is represented by the relative quantities luminance factor or reflecting factor.  
Local contrast Difference between two neighboring visual items with one common property, e.g. pixel brightness.  
Lumen SI unit of luminous flux. Luminous flux emitted within one steradian by a point source that has a constant luminous intensity of one candela. learn more
Luminance factor Fotometric correlate of the radiance factor that states the relative lightness of an object colour by giving the ratio of luminance L of the illuminated object and luminance Lw of the equally illuminated perfect reflecting diffusor. learn more
Luminous colour Colour that is attributed to a self-luminous object or to a specularly reflecting object. learn more
Luminous flux Photometric quantity. Radiant flux weighted by the spectral luminous efficiency function V(λ) of the CIE standard photometric observer. learn more
Luminous intensity Photometric quantity. Quotient of the emitted luminous flux by its solid angle. Unit: candela. learn more
Lux Unit of illuminance. learn more
M0 Measurement mode of ISO 13655:2009 reflecting instruments using a tungsten lamp as light source. The UV-content is not specified. Thus this mode should not be used when papers with optical brighteners are used.  
M1 Measurement mode of ISO 13655:2009. The UV-content of the used light source excites optical brighteners equal to CIE D50. Thanks to the VFS the KM FDs were the first M1-capable instruments.  
M2 Measurement mode of ISO 13655:2009 with a limited UV-content of the light source. Often realized using a UV-Cut filter. The KM VFS allows measurements according to M2.  
M3 Measurement mode of ISO 13655:2009 using polarized light and a polarization filter in front of the sensor. Is used to minimize the difference between wet and dried offset prints.    
MacAdam ellipse Ellipsoid area in the CIE xy chromaticity diagram. These areas represent all colours that are perceptually indistinguishable from a specified reference colour. MacAdam ellipses are differently shaped and have different directions.  
Magenta One of the primary colours in four-colour process printing that defines the CMYK colour space.   
Metameric colour metamer/ Colour stimuli that are spectrally different but have the same tristimulus values for a given illuminant and observer. A metmarism index describes the effects of such an illuminant colorimetric shift.  
Monitor black point Minimum of the red, green and blue intensities of an RGB display mapped by CIE chromaticity coordinates x and y as well as the luminance coordinate Y. This minimum is R=0, G=0, B=0. learn more
Monitor white point Maximum of the red, green and blue intensities of an RGB display mapped by CIE chromaticity coordinates x and y as well as the luminance coordinate Y. This maximum is R=255, G=255, B=255. learn more
Monochromatic Pertaining to a single wavelength, or an infinitesimal wavelength interval.  
Monochromatic light Visible radiation of a single wavelength.  
Monochromator Device for dispersing polychromatic radiation into its spectrum (2) in the form of slit images of monochromatic light. learn more
Non-luminous colour Colour that is attributed to a secondary light source.  
Normalisation A quantity is scaled so as to fall within a specified range (often a scale between 0 and 1).  
Optical brightening agent Substance that absorbs UV-energy and emits this energy as visible blue light. Used to compensate for yellowish casts of various materials such as paper, textiles and plastics rsp. to increase the impression of "white".  
Optical radiation Electromagnetic radiation comprising the ultraviolet (UV) spectrum, the visible spectrum and the infrared spectrum. (wavelength range approx. 10 nm - 10.000 nm)  
Out-of-gamut colour Tristimulus values in the source colour space that do not have a colorimetric equivalent in the destination colour space and therefore cannot be displayed on the output medium unless the gamut mapping methods gamut clipping or gamut compression are performed.  
Output profile ICC profile that describes an output device.  
Perfect reflecting diffuser Ideal object that reflects any incident optical radiation without loss and regardless of the incident angle (reflectance ρ = 1). Its colour is always called white. Implemented only as reflectance standard. Reference standard of reflectance.  
Planckian locus Chromaticity coordinates of the Planckian radiation.  
Planckian radiator Ideal object which absorbs all incident radiation and is also an ideal thermal radiator.  
Point of the specified achromatic stimulus Point of the illuminant when non-luminous colours are to be displayed in the CIE xy chromaticity diagram.  
Polychromatic light Visible radiation of multiple wavelengths.  
Primary colour Any colour that is not the result of colour mixing and that can define a colour space in combination with other primary colours.  
Primary light source Object that emits light.   
Print substrate Material on which the ink is applied. Often contains optical brightening agents. For measurements mode M1 is needed.  
Printing ink Substance that is applied to the print substrate. Can be formulated for colour matching using CCM software.  
Prism Transmitting body that disperses incident radiation. Dispersion of an continuous spectrum into monochromatic slit images. learn more
Process colour Primary colour in multi-colour process printing.  
Profile Connection Space Connection colour space defined by the International Color Consortium based on the CIE XYZ colour space or the CIE 1976 L*a*b* colour space. It provides a device-independent interface for colour communication from source to destination colour spaces via colour profiles.  
Profiling Act of compiling and storing the transfer functions derived from device calibration and device characterisation in a device colour profile.   
Process Standard Digital Printing® Handbook containing best practices for Digital Printing. Catch QC can be used to test a print for conformance against Fogra PSD®  
Process Standard Offset Handbook containing best practices for Offset Printing. The KM FD Spectrodensitometers and the software Catch QC can be used to test a print for conformance against PSO  
Purkinje effect Change of the maximum light sensitivity from long wavelenghts to short wavenlengths induced by a decrease in luminance. Represented by the curves of the spectral luminous efficiency for photopic vision V(λ) and scotopic vision V'(λ) respectively.  
Radiance Radiometric quantity. Incident radiant flux per point of surface per solid angle of the incident radiant flux. learn more
Radiance factor Ratio of the radiance of the sample to that of the perfect reflecting diffuser when the solid angle  = 0°.  learn more
Radiant emittance Radiometric quantity. Quotient of the emitted radiant flux and the irradiated point of surface. learn more
Radiant energy Energy in the form of electromagnetic waves and particles. learn more
Radiant flux Radiation quantity. Quotient of radiant flux and a given time interval. learn more
Radiant intensity Radiometric quantity. Quotient of the emitted radiant flux and its solid angle. learn more
Radiation source Any source of electromagnetic radiation. learn more
Red One of the CIE-defined additive primary colours that define the RGB colour space.  
Reference illuminant Illuminant to which other illuminants are compared. learn more
Reflectance Ratio of the reflected radiant flux to the incident radiant flux measured as specular reflectance, diffuse reflectance or both.  
Reflectance factor    
Reflectance standard Materials calibrated in terms of the perfect reflecting diffuser.   
Reflection Phenomenon of thrown back incident radiation. Reflection can be specular, diffuse or both (= mixed) and can be measured in terms of reflectance, reflectance factor and radiance factor.  
Reflection factor Measure of lightness that is used in colorimetry instead of the luminance factor (and transmittance factor). The reflection factor corresponds to the tristimulus value Y, the parameter of lightness in the CIEXYZ system.  
Retina Back part of the inner eye that contains photoreceptors.  
RGB colour space Colorimetric, device-dependent colour space that is modelled after the principles of additive colour mixing using the CIE-defined primary colours red, green and blue.  
Saturated Property of a colour that is only minimally or not at all mixed with the achromatic stimulus.  
Saturation Chroma of a colour, determined by the added portion of achromatic colour and its lightness.  
Scattering    
Secondary colour Colour that is additively or subtractively mixed  from at least two primary colours.  
Secondary light source Transparent or reflecting object that only becomes visible and has the quality of lightness when being illuminated.  
Selective radiator Thermal radiator whose emissivity is wavelength-dependent.  
Self-luminous The quality of emitting light.   
Sichtbare Strahlung Optical radiation (wavelength range approx. 360 nm - 830 nm) that can stimulate the human eye and thus produce a visual sensation.   
Single-line spectrum Noncontinuous (discrete) spectrum of radiation (not having radiant flux for each wavelength).  
Software calibration Monitor calibration that is effected in the graphics board, e.g. the setting of colour temperature or the output values of the three colour channels R, G, and B.  
Solid area An area of the print substrate that is fully and evenly covered by one type of printing ink.   
Special metamerism index Colour difference between two metameric colour stimuli (original and reproduction in most cases) that is caused by changes in illuminant or observer. The "special metamerism index: change in illuminant" is used to describe light sources. The "special metamerism index: change in observer" compares samples observed by the 2° or 10° standard colorimetric observer respectively. Normally, the special metamerism index is computed using the CIELAB colour difference formula.  
Spectral Quality of wavelength dependency of a radiometric quantity.  
Spectral colour Colour of monochromatic radiation.  
Spectral density Quotient of a radiometric or photmetric quantity measured for a given wavelength or wavelength interval and that wavelength or wavelength interval.  
Spectral line Discrete slit image that is produced by dispersing a continuous spectrum.   
Spectral power distribution Variation of the radiant flux of each wavelength or wavelength interval.  
Spectral range Any part of the visible spectrum.  
Spectral sensitivity    
Spectrum Distribution of the intensity of any electromagnetic radiation for each wavelength in a given wavelength range.  
Specular reflection Type of reflection where the efflux beam exits the sample at an angle of 90° (= perpendicular) to the incident beam.  
Spot colour Printing ink that is not one of the usual primary colours used in four-colour process printing, i.e. cyan, magenta, yellow and black.  
Standard light source Light source whose relative spectral power distribution corresponds to a CIE standard illuminant (e.g. a tungsten lamp). learn more
Stimulus Physical or chemical change in the environment  that causes a reaction of the corresponding sensory cells.  
Subtractive colour mixing The wavelengths of visible radiation incident on a surface of specific texture, e.g. a colour filter or printing inks on a print substrate, are absorbed, scattered and reflected and, hence, have changed once they enter the eye.  
Tertiary colour Colour that is additively or subtractively mixed  from at least two colours, only one of those being a primary colour.  
Thermal radiator Ideal or real source that emits light by transforming electric energy into thermal radiation (e.g. Planckian radiator).  
Tonal range Number of tones of a colour  that can be stored in a colour channel. The corresponding parameter is bit depth.  
Tone value 1) In a data file: CMYK colour value that controls the output on a specified print substrate area. 2) On a print: percentage of the print substrate that appears to be covered by printing ink.   
Tone value increase Difference between the tone value on the print and the corresponding tone value in the digital data or on the half-tone film; in percent.  
Tone value sum Tone values of all process colours added up at a specified spot in the digital image or the half-tone film.  
Transmission Phenomenon of passing incident radiation. Transmission can be specular, diffuse or both (= mixed) and can be measured in terms of transmittance transmittance factor and radiance factor.  
Transmittance Ratio of the transmitted radiant flux to the incident radiant flux measured as specular transmittance, diffuse transmittance or both.  
Transmittance factor Ratio of the transmitted radiant flux to the incident radiant flux when the solid angle > 0°.  
Trichromacy Property of the human visual system that enables colour perception via three types of photoreceptors, and their accessory organic structures, that differ in their visual pigments and spectral sensitivities.  
Trichromatic system Any system dedicated to colour specification that is based on three primary colours.  
Virtual Fluorescence Standard Patented method to obtain spectral data from a print on brightened paper for any given illuminant. Used in the KM FD-series spectrophotometers.  
Wave Result of a periodically changing electric and magnetic field (i.e. electromagnetic radiation).  
White (1) RGB colour that is produced when each  colour channel contains the maximum colour value.  
White (2) Area of the print substrate that is not covered with ink when none of the four colour channels contains colour values after the colour separation to CMYK.   
White (3) Term used for the by comparison highest luminance level perceived in a system.  
White balance The adjustment of the colour channels of a digital still camera so that the colours in a scene or an original are rendered relative to the white point of the scene or original. This white point is also called adopted white.  
White point Highest luminance neutral of an imaging medium or a print substrate and therefore a determinant of its dynamic range. Also a grey line determinant.  
Yellow One of the primary colours in four-colour process printing that defines the CMYK colour space.   
Yule-Nielsen effect Impression of tone value increase. This impression is caused by light scattering within the print substrate. A part of the light is caught under an area covered with ink which in turn appears greater.  
Yule-Nielsen factor Modification of the Murray-Davies equation. Can be used to separate the optical from the geometrical tone value increase. Can also be used to adjust the reading of a spectrodensitometer on printing plates to match the readings of a digital microscope.