Is The Light Shone Through A Complementary Color Mostly Transmitted Or Absorbed

Colour Measurement

During colour measurement the change in the intensity of electromagnetic radiation in the visible wavelength region of the spectrum after transmitting or reflecting by an object or solution is measured.

From: Principles of Colour and Advent Measurement , 2014

Colour Measurement

Doreen Becker , in Color Trends and Selection for Product Design, 2016

Abstract

Color Measurement is the quantitative expression of color and as indicated previously, there are a number of methods to quantify color. The all-time method of determining color is with the human eye. As mentioned previously, some humans run into colors more than distinctly and everyone sees and perceives color differently. Still, most colour scientists, engineers and manufacturers need to adhere numbers to their color assessments then at that place are many different types of tools available to place, quantify and differentiate colors. These analytical tools can help to provide direction in color matching, quality control in manufacturing and to develop new colors and color spaces. It too helps colour professionals and designers talk to each other about colour in a universal linguistic communication. At that place are two basic types of technology for the measurement and nomenclature of color: colorimetry and spectrophotometry.

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Instrumental color measurement

P.J. Clarke , in Full Color Management in Textiles, 2006

3.1 Introduction

Colour measurement instrumentation is very varied. It varies from large top of the range scanning spectrophotometers, maybe coupled with reflectance accessories through demote-top instruments, to hand-held small portable instruments. The instrumentation may be set up to brand a diversity of different colour measurements or to merely make measurements on one item color scale.

Colour measurements are essentially measurements of visible light shining through an object or visible calorie-free reflected from an object. There are many optical configurations to achieve the measurement of transmitted and reflected colour. There are standard or recommended geometries for making these measurements and classification for describing them and the variations that are possible. ¹ The pick of measurement geometry usually depends on the properties of the artefact to be measured, but may be due to historical use within a item industry or product area. There are colour measuring instruments bachelor that can measure transmitted color, reflected colour or both.

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Instrumental colourant formulation

A.1000. Roy Choudhury , in Principles of Color and Appearance Measurement, 2015

Accuracy of the instrument

Colour measurements are washed at two stages – once of the calibration dyed samples, and then of the sample to exist matched. By and large, the ii measurements are washed over long intervals of time. The instrument should have, therefore, long term repeatability and, more preferably, skilful absolute accuracy. The parameters determining the accuracy of the musical instrument are the 100% line, 0% line and the wavelength scale. If the boilerplate colour difference between the measured sample and the calculated match is smaller than 0.3 AN40 units, the instrumental error can be neglected.

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Colour quality evaluation

Grand.R. Luo , in Total Color Direction in Textiles, 2006

4.1 Introduction

Instrumental colour measurement systems have been widely used by color-using industries such as textiles, coatings, plastics, graphic arts and imaging. The most important awarding is undoubtedly colour quality control by ways of colour difference formulae, which are used to quantify color variations between pairs of specimens. Conventionally, this job was carried out by experienced colourists, but more than recently this was replaced by instrumental methods in club to reduce labour costs, save time and use a more scientific methodology. Some typical color quality control tasks include:

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setting the magnitude of tolerance for making instrumental laissez passer/fail decisions;

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evaluating fastness grades for assessing alter in colour and staining;

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predicting the metameric effect between a pair of specimens;

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determining the modify in colour appearance of a single specimen across unlike illuminants.

All the above tasks rely on the availability of a robust colour difference formula. This has long been eagerly sought past industry. This affiliate will briefly review the development of color difference formulae, including the CIE 2000 colour difference equation, CIEDE2000. ^{one , 2} An instance will exist given to illustrate the method for establishing a tolerance value for industrial applications. In addition, methods for calculating a metamerism alphabetize, relating to changes in illumination of a pair of samples, and a colour inconstancy index, recently proposed by the Colour Measurement Committee (CMC) of the Society of Dyers and Colourists (SDC), volition be introduced. Finally, a summary will be given of some new developments.

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Characterization of Impress Quality in Terms of Colorimetric Aspects

Michael Dattner , Daniel Bohn , in Printing on Polymers, 2016

20.1.1 Color Perception

Standardized frameworks for color measurement are based on the introduced specifications of color matching. Scientific discipline defines light equally the ring of electromagnetic radiation that is perceptible by the human center. The relevant wavelength range is λ   =   380–780   nm (1   nm   =   10^−ix  k). This range is responsible for the color stimulus and is located between the brusque-wavelength ultraviolet radiation and the infrared radiations, which is on the other side of the visible spectrum (cf. Figure xx.2).

Figure 20.2. Electromagnetic spectrum.

Color perception or in fact the color stimulus occurs because of the absorption of radiation power of the visible light in the cones of the eye. Cones are a type of photoreceptor cells that are responsible for the human color vision. From a physical bespeak of view, the radiation can be described by its spectral composition in the visible wavelength range. This limerick is in the context of colorimetry the spectral radiation distribution which defines the color stimulus function φ(λ) (Bergmann, Schaefer, & Lang, 1993).

In the case of a cocky-luminous object, φ(λ) is equal to its relative spectral power distribution Southward(λ). In the example of not–self-illuminant objects (in particular, printed products), the colour stimulus is equal to the product of the relative spectral power distribution of the used illumination South(λ) and the radiance factor β(λ) of the surface (Bergmann, et al., 1993; Richter, 1980; Urban, 2005). Therefore, φ(λ) of a so-called nonluminous colour is defined by the color stimulus office (cf. Eq. (20.i)):

(xx.1) $\phi \left(\lambda \right)\mathrm{:}=S\left(\lambda \right)·\beta \left(\lambda \right)\forall \lambda \in [380\mathrm{nm},\mathrm{...},780\text{nm}]\text{.}$

A closer look at the retina shows that the cones are mainly located inside of the fovea and within a ring of rods ("R") (cf. Figure xx.iii). This is important in the context of the "CIE standard observer" introduced in following department. Furthermore, rods are mainly responsible for the twilight vision, when the lite has not enough radiations energy to activate the cones (mesopic vision/scotopic vision).

Effigy xx.three. Distribution of cones and rods in the eye.

At that place are three types of cones: short-wavelength receptors ("S" with an absorption maximum at 420   nm), medium-wavelength receptors ("M" with an assimilation maximum at 534   nm), and long-wavelength receptors ("L" with an absorption maximum at 563   nm) (cf. Effigy 20.4; Bowmaker, 1981).

Figure 20.4. Normalized absorption characteristics of the rods (R) and the three types of cones: brusque-(South), medium-(Thou), and long (L)-wavelength receptors.

The normalized absorption curves of the cones describe how the individual cone types respond if these are stimulated past light with a specific intensity in an private wavelength range. But this on its own is no explanation for the separable perception of brightness or color: the stimulation of a cone increases in the same mode, if the intensity of the calorie-free increases, or if the maximum in the relative spectral power distribution of the incoming light S(λ) is shifted closer to the absorption maximum of the cone. Simply the combination of at least two cone types, which can be stimulated independently from each other with overlapping absorption ranges, allows the desired differentiation between a alter in brightness and in color (Funk, 2006).

For example, in the (weighted) difference of the G- and L-assimilation curves inducing the sensitivity bend of this 2-cone organization, the resulting values are positive likewise as negative and carve up, therefore, the full spectral range clearly into 2 dissimilar colour ranges (cf. Figure 20.v; Funk, 2006).

Effigy 20.five. Addition and subtraction of the Yard- and L absorption curves.

In this case, the complementary color areas bear witness their maximum in the green or in the carmine wavelength range, respectively. In the "white point" (cf. Figure 20.5), both cone types are stimulated with the aforementioned intensity. Just if the intensity of the incident lite is changed, the differential amount of both absorption curves stays the same, because both cone types are stimulated every bit. Just, if the wavelength of the incoming lite changes, the cone types are stimulated individually. Therefore, a color shift tin can be easily distinguished from a change in effulgence (Funk, 2006).

When taking all other cone-system combinations into account, information technology becomes obvious that the information regarding the absorbed radiation intensity of the iii dissimilar cone types can be transformed into 4 different and independent colour signals and one boosted effulgence betoken (Funk, 2006).

Even Leonardo da Vinci already ascribed the complementary color pairs red and green likewise equally xanthous and blue, supplemented by the achromatic pair white and black, for the brightness point for the description of the colour space of all colors (cf. Figure 20.6; Richter, 1996).

Figure twenty.six. Complementary colors.

Complementary colour pairs serve also for the CIE L^∗a^∗b^∗ color space with the color coordinate axes a^∗ and b^∗, supplemented by the brightness parameter 50^∗. For instance, it is possible to mix red with a yellow or blue with a carmine: This causes the impression of a yellowish ruddy or a reddish blue. Merely if blood-red is mixed with green or blueish with yellow, ane does not go the impression of a green cherry-red or yellowish blueish (Funk, 2006).

The weighted sum of the absorbed radiation power of all cones ("50   +   M   +   S") is interpreted equally effulgence. If the stimulus of all cone types is comparable ("L   ≈   M   ≈   S"), colors are perceived as white, gray, or black depending on the light intensity. The red–green differentiation is achieved by the complementary colors red and green ("L   −   G   +   S"), whereby the bluish–yellow differentiation is achieved by "L   +   Thousand   −   S" (Funk, 2006).

There is no conclusive clarification on which colour perception is actually motivated past the introduced color stimulus part. There are numerous and very complex furnishings interacting with each other: Identical colour stimuli can lead to dissimilar colour perceptions and vice versa (Bergmann et al., 1993).

For reproducible and comparable results generated by colour matching and spectral measurements, normative weather must be considered. Some classical examples for distorting effects are: simultaneous contrast, constants in perception of lightness, and lateral inhibition of the retina.

Example 20.1 (Simultaneous contrast): If a sheet of gray newspaper is cut into two pieces, and each piece is placed upon a yellowish and upon a blueish background, respectively, their visual advent differs. Against a yellow groundwork, the visual impression of gray will be blue; confronting the blue background information technology will be yellowish (Bach, 2008).

Instance xx.2 (Constants in the perception of lightness): The 2-dimensional prototype (Figure xx.7, left) is interpreted as a three-dimensional structure with a corresponding shadow. Two fields in this structure are marked with a circle. One circle is within and one is outside the shadow. The one within the shadow appears to be brighter than the other one. Really, the photometric effulgence of both fields is the same (Bach, 2008).

Figure 20.7. 2 examples for optical furnishings: constants in perception of lightness (left); Hermann grid (correct).

Example 20.iii (Lateral inhibition of the retina): When looking at the Hermann grid in Figure 20.7 (correct), grayness spots can be observed where the white lines cross, which disappear while focusing directly on the crossing (Bach, 2008).

In addition, the surrounding conditions and the illumination have to be taken into account for the measurement every bit well as the visual matching procedure:

Example 20.4 (Chromatic adaption of the heart): Both homo eyes tin can be chromatically adapted independently from each other. Dissimilar chromatic adaptions lead to a unlike color perception in spite of an identical color stimulus. Therefore, if a low-cal non-luminous colour is observed with a dark-green adjusted or a white adapted eye, respectively, the perception with the green adjusted centre appears temporarily cherry-red compared to the perception of the white adjusted center (Richter, 1980). A green adaption tin can exist realized by focusing on a stiff green cocky-luminous body for about 2   min.

This case also proves the demand for considering metamerism effects. According to DIN 5033, part 1, metamers are colors that have the aforementioned color stimulus values when observed under ane illumination (e.grand., daylight) and are dissimilar when observed under another illumination (e.g., incandescent light). This is acquired by the differing radiance factor β(λ) of the metamers. 2 isometric or identical colors take identical radiance factors β(λ) and, therefore, identical color stimulus values for all illuminants or standard observer (DIN, 1992).

To consider these and additional potential furnishings on the perception of color in the context of the characterization of print quality, fundamental basics of color measurement and visual color matching are introduced in the following section.

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Colour measurement of food: principles and practice

D.B Macdougall , in Color Measurement, 2010

13.6 Colour description: the CIE system

The CIE arrangement of colour measurement ( ASTM 2000; CIE 1986) transforms the reflection or transmission spectrum of the object into three-dimensional colour space using the spectral ability distribution of the illuminant and the colour-matching functions of the standard observers (CIE 1986). The mathematical procedures are given in any standard text on color, for exampleWright (1980), Judd and Wyszecki (1975), Hunt (2001) and Berns (2000). The system is based on the trichromatic principle but, instead of using 'real' carmine, green and blue primaries with their necessity for negative matching, information technology uses 'imaginary' positive primaries 10, Y, and Z. Primary Y, known every bit luminous reflectance or transmittance, contains the entire lightness stimulus. Every color can be located uniquely in the 1931 CIE colour space past Y and its chromaticity coordinates x = X/(X + Y + Z) and y = Y/(X + Y + Z), provided the illuminant and the observer are defined.

The original illuminant representative of daylight was defined by the CIE as source C, but is now superseded past D65, i.east., an illuminant which includes an ultraviolet component and has a colour temperature of 6500°K. The colour temperatures of lamps and daylight range from approximately 3000°G for tungsten filament lamps and 4000°Yard for warm white fluorescent to 5500°Thousand for sunlight and 6500°K for average overcast daylight to approximately 20000°One thousand for totally sunless blue sky. Because the original 2° colour-matching functions employ strictly only to small objects, i.eastward., equivalent to a 15   mm diameter circle viewed at a altitude of 45   cm, the CIE has added a 10° observer (Fig. 13.2) where the object bore is increased to 75   mm. Currently, the tendency in colour measurement is to use D65 and the 10° observer except for very pocket-sized objects. The 1986 CIE recommended procedures for colorimetry are included in the ASTM Standards (2000) and likewise in Hunt (2001) along with the weighting factors for several practical illuminants (Rigg 1987). These include representative fluorescent lamps, of which F2 is a typical lamp at 4230° K just with a low color-rendering index (R _a) of 64 (Fig. 13.3). The colour-rendering index R _a is a measure of the efficiency of a lamp at a given colour temperature to render the true appearance of Munsell colours. The broadband lamp F7 has the same colour temperature (6500°K) and chromaticity co-ordinates as D65 and, because of its flatter spectrum, information technology has a high R _a of 90. The triband lamp F11 (4000° K) likewise has a moderately high R _a of 80, but its main advantage is its much improved efficiency in free energy utilisation.

13.2. Colour matching functions of the CIE ten° standard observer.

thirteen.3. Relative spectral power distributions of preferred CIE representative fluorescent lamps.

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Visual and instrumental evaluation of whiteness and yellowness

R. Hirschler , in Colour Measurement, 2010

4.3.3 Measurement of white and nigh-white samples

The reflectance curves of some of the whitest non-fluorescent artefacts used as 'white standards' in spectrophotometry are illustrated in Fig. 4.seven.

4.7. Reflectance curves of four white artefacts used for the photometric scale adjustment of reflectance spectrophotometers.

Whiteness measurement, similar color measurement in general, is discipline to measurement uncertainties and errors, and to a great extent these are due to the differences in illumination and measurement geometry of different instruments. In a detailed study conducted in the textile industry ( Hardt et al., 2003), viii not-fluorescent and four fluorescent cloth samples were measured in 16 industrial laboratories, 5 public measuring laboratories and by iv instrument manufacturers, and the results were disastrous. The difference between some of the non-fluorescent samples was as loftier as 34 Berger whiteness units; for fluorescent samples this was just somewhat worse (36 Berger units). Even within the public measuring laboratories grouping differences of 15 to 20 units were institute. Willis (2002) reported differences of upwards to 20 CIE WI units between measurement results on the same samples on different instruments as 'not unusual'. These differences may exist reduced to a few CIE units with a proper calibration procedure. Co-ordinate to Hirschler et al. (2003) the differences between nominal values of a research constitute'south BAM-traceable measurements and the BAM data can be as large as 9 Ganz-Griesser units, only, under carefully controlled conditions, unlike instruments can measure with a difference of only a few CIE WI units as shown in Tabular array four.1. Using proper calibration and adjustment procedures in a comparative trial involving 24 different instruments the standard divergence of the different whiteness value results was 0,7 whiteness units (ISO, 2004).

Table 4.one. CIE WI measured on 4 dissimilar instruments and compared to the nominal values given by the Hohensteiner Institute for the four textile samples and past BAM for the Halon standard

		Textile samples
Instrument		T1	T2	T3	T4	Halon standard
Filter	Nominal	77.32	103.71	128.37	154.77	124.91
	SF500	77.4	102.iv	126.five	153.8	121.seven
	CM3720d	77.88	103.04	127	156.29	122.36
NUVC	CM3600d	78.54	105.08	129.71	154.97	125.75
	CM2600d	73.26	100.13	127.35	155.41	124.71

Source: Reproduced from Hirschler et al. (2003) by permission of the CIE Central Bureau, Vienna, Austria.

It has to exist emphasized hither that these differences are due only to measurement uncertainties (instrument geometry, illumination, calibration process) and the state of affairs becomes much worse when these are combined with the difficulties of translating measurement results into visually meaningful whiteness formulae.

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Colour management across the supply chain

R. Lawn , in Total Colour Management in Textiles, 2006

ten.3.4 ASP or not

The combination of digital color measurement and centralised information storage is now seen as the way frontward by about technology leaders in the apparel sector, and the growth of this method is rapid considering that only a few years ago the concept of broadband Internet connections to a dye mill in China would have seemed a long fashion off. One follow-on pick to be made once a digital centralised model is chosen is whether the centralised information-base and colour engine should be hosted past the specifier itself (internal) or by the software solution provider (the application service provider or ASP model). The pros and cons depend mostly on the size and complexity of the supply chain involved and the Information technology support skills of the specifier, but the ASP model has many advantages for the apparel industry.

This is because an clothes supply concatenation may have more than than 1000 parties involved, in many countries and time zones, and the actual parties may 'churn' (i.e. some are dropped, some added) continually. If the specifier Information technology team is responsible for managing this churn and supporting each party, the work load can exist huge. Also, such support generally includes colour scientific discipline instruction equally well every bit software help, and is typically in a language dissimilar from that of the specifier'southward home state. In that location are also serious IT security concerns if all parties are to be brought inside a specifier network. A useful analogy is with the mostly existing physical color communication systems, which are always handled by external parties – courier companies such as UPS, Fedex, and DHL. An dress supply chain should have its digital colour communication supported on a third-party platform for the aforementioned reasons as apparel specifiers use Fedex rather than starting their own courier company (Fig. ten.2).

10.2. An instance of the many parties involved in typical colour supply chain for the apparel industry.

In other industries this reasoning may be less valid: FMCG companies, for example, tend to run sophisticated global IT networks, and their supply chains accept fewer players and fewer layers, so internal hosting may be appropriate.

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Appearance qualities of paint — Basic concepts

T.R. Bullett , in Paint and Surface Coatings (2d Edition), 1999

17.7.4 Appreciation of colour differences

The CIE system of colour measurement in terms of X, Y, and Z can be looked upon every bit establishing a position in a color solid in which X, Y, and Z are measured along rectilinear axes. The distance between two colours represented by X ₁, Y _one, Z ₁ and X ₂, Y _two, Z _ii is thus:

(17.11) $\surd \left[{\left(X_1-X_2\right)}^2+{\left(Y_1-Y_{\mathrm{ii}}\right)}^2+{\left(Z_1-Z_2\right)}^{\mathrm{ii}}\right]$

Unfortunately, equal distances in this colour solid exercise not represent equally perceptible colour differences. This was shown by MacAdam [26] who studied the variation of colour matches, and thus of but perceptible colour differences, for different colours. Figure 17.13 shows MacAdam ellipses for colours of abiding lightness only varying x and y. Clearly, distances in this 10/y plot exaggerate colour differences in the greenish region of the field, and minimize those in the blue and orange/brown. Many attempts accept been fabricated to transform the XYZ colour space into ane giving more compatible correspondence with visual appreciation. A perfect reply is non possible considering visual appreciation varies with field size and colour of surrounding field and to some extent illumination levels, but much better approximations have been found. Thus the response of the centre to lightness change, represented past the luminance factor Yin the CIE system, is non a linear relationship; that is, if Yis 100 for white, the grey visually equidistant from black and white will exist considerably darker than that for which Y is 50. Again, x and y can be transformed by linear equations to new coordinates α and β which convert the MacAdam ellipses into something nearer circles of more than uniform size. Of the many transformations proposed the L* a* b* arrangement published by the CIE in 1976 has proved to be 1 of the most useful in do [16, 27], and its utilize is standardized in ISO 7724 Paints and Varnishes — Colorimetry. This organization is complicated, but basically employs cube root functions of Ten, Y, and Z for all light colours, and linear functions for dark colours. The colour difference is calculated equally √(Δ50*² + Δa*² + Δb*ⁱⁱ). It is recommended that for near-white specimens the colour difference should be described in terms of ΔL*, Δa*, and Δb*, but for colours the difference can exist analysed into ΔL, a chroma deviation ΔC* (representing a difference in depth of colour), and a hue difference ΔH*.

Fig. 17.13. MacAdam ellipses indicating preceptibility of chromaticity differences on the x/y diagram. The ellipses correspond in size to ten times the standard deviation of matches to a color represented past the central point.

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Color, Dyes, Dyeing, and Printing

Von Moody , Howard L. Needles Ph.D. , in Tufted Carpet, 2004

15.1.ii Additive and Subtractive Systems

Additive color systems used in color measurement determine the amount of 3 color main lights necessary to define a given color using a standard lite source and observer. Dyers and colorists use subtractive systems, since the net colour reflected from a dyebath or dyed fabric is more meaningful in matching dyeings and depends on the corporeality of the three subtractive primaries present. Color theory and colour measurement are complex and are further complicated by an private's response to concrete, physiological, and psychological aspects of color.

Nevertheless, color differences tin be finer measured using additive colour systems provided the light source, the observer, bending of viewing and degree of field observed is defined. In guild to clarify and standardize the additive colour system and color difference measurement, the Committee Internationale de 50'Eclairage (CIE) was formed in 1931. The CIE has provided the definitions and standards necessary for color measurement. The primaries defined by CIE are not real colors, merely are imaginary primaries used to ascertain all colors in the color space. The amount of each of these primaries (values X, Y, Z) in a given color is used to ascertain the shade and depth of shade for that color. Since these values are difficult to plot, the values are normalized and reduced to coefficients according to the following equations.

Then the shade of a sample is defined by x and y, and the relative lightness by the Y value which is equivalent to the total reflectance of the dyed textile every bit observed by the human heart. Color differences (ΔEast) between 2 samples are determined by Eq. (fifteen.3).

Eq. (15.iii) $\Delta E={\left(\Delta {\mathrm{10}}^2+\Delta y^{\mathrm{ii}}+\Delta y^{\mathrm{ii}}\right)}^{1/2}$

The colour space can be mathematically presented in a number of ways and numerous color departure formulas and systems exist.

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