METHOD AND SYSTEM FOR QUANTIFYING A SPECTRAL SIMILARITY BETWEEN A SAMPLE COLOR AND A TARGET COLOR

Abstract

Described herein is a computer-implemented method and a system for providing a match metric for quantifying a spectral similarity of a target coating and at least one sample coating, the system including a computing device that performs a computing process, the computing process including: receiving reflectance values of the target coating and the sample coating; normalizing each of the reflectance values; generating a normalized reflectance curve for the target coating and for the sample coating; producing derivative values of the normalized reflectance curve of the target coating and derivative values of the normalized reflectance curve of the sample coating with respect to the wavelength; producing difference values between the derivative values of the target coating and the derivative values of the sample coating; and producing a match metric for a similarity between the normalized reflectance curves of the target coating and the sample coating.

Claims

1. A computer-implemented method for providing a match metric for quantifying a spectral similarity between a target coating and at least one sample coating, the method comprising at least the steps of: a) obtaining, for a number of wavelength values, reflectance values of the target coating and reflectance values of the sample coating, wherein the reflectance values of the target coating are determined at one or more measurement geometries, and the reflectance values of the sample coating are determined at the one or more measurement geometries; and by using one or more processors: b) normalizing each of the reflectance values of the target coating determined at the respective one of the one or more measurement geometries and the reflectance values of the sample coating determined at the respective one of the one or more measurement geometries by using a scaling function; c) generating a normalized reflectance curve for the target coating based on the normalized reflectance values of the target coating for each wavelength value, and a normalized reflectance curve for the sample coating based on the normalized reflectance values of the sample coating for each wavelength value; d) producing, for the number of wavelength values, normalized first derivative values of the normalized reflectance curve of the target coating with respect to the wavelength and normalized first derivative values of the normalized reflectance curve of the sample coating with respect to the wavelength; e) producing, for each wavelength value of the number of wavelength values, difference values between the normalized first derivative values of the normalized reflectance curve of the target coating and the normalized first derivative values of the normalized reflectance curve of the sample coating; f) producing a match metric for a similarity between the normalized reflectance curves of the target coating and the sample coating based at least on the difference values for all of the number of wavelength values; and g) outputting, using an output device, the produced match metric for a user.

2. The method according to claim 1, the method further comprising the step of: h) retrieving from a formulation database which comprises formulas for coating compositions and interrelated colorimetric characteristics, one or more preliminary matching formulas based on reflectance values of the sample coating and/or further pre-determined color characteristics of the sample coating or a combination thereof.

3. The method according to claim 1, the method further comprising the step of: i) modifying an initial formulation of the sample coating, so as to minimize the match metric for the similarity of the normalized reflectance curves of the target coating and the sample coating as additional constraint beside existing color difference metric(s).

4. The method according to claim 1, wherein step d) further comprises: d2) transforming the normalized first derivative values of the normalized reflectance curve of the target coating and the normalized first derivative values of the normalized reflectance curve of the sample coating, respectively, with respect to the wavelength, into an angular representation.

5. The method according to claim 4, wherein the normalized first derivative values of the normalized reflectance curve of the target coating and the normalized first derivative values of the normalized reflectance curve of the sample coating, respectively, are represented, for each wavelength value as a two-dimensional vector according to the following formulas: $u_{{\lambda }_i}=\left(\begin{array}{c}{k}_1.Math.\Delta {\lambda }_i\\ \Delta R_{\mathrm{ref},{\lambda }_i}^{\mathrm{norm}}\end{array}\right)$ $v_{{\lambda }_i}=\left(\begin{array}{c}{k}_1.Math.\Delta {\lambda }_i\\ \Delta R_{\mathrm{smp},{\lambda }_i}^{\mathrm{norm}}\end{array}\right)$ ${\theta }_{{\lambda }_i}={\cos }^{-1}\left(\frac{u_{{\lambda }_i}.Math.v_{{\lambda }_i}}{.Math.u_{{\lambda }_i}.Math..Math..Math.v_{{\lambda }_i}.Math.}\right)$ with
ΔR.sub.ref,λ.sub.i.sup.norm=R.sub.ref,λ.sub.i.sub.+Δλ.sub.i.sup.norm−R.sub.ref,λ.sub.i.sup.norm, and
ΔR.sub.smp,λ.sub.i.sup.norm=R.sub.smp,λ.sub.i.sub.+Δλ.sub.i.sup.norm−R.sub.smp,λ.sub.i.sup.norm, and
Δλ.sub.i=λ.sub.i+1−λ.sub.i, wherein R.sub.ref,λ.sub.i.sup.norm indicates a normalized reflectance value for the target coating at the wavelength value, λ.sub.i, R.sub.ref,λ.sub.i.sub.+Δλ.sub.i.sup.norm indicates a normalized reflectance value for the target coating at the wavelength value, λ.sub.i+1, R.sub.smp,λ.sub.i.sup.norm indicates a normalized reflectance value for the sample coating at the wavelength value, λ.sub.i, R.sub.smp,λ.sub.i+1.sup.norm indicates a normalized reflectance value for the sample coating at the wavelength value, λ.sub.i+1, k.sub.1 is a non-linear damping parameter with k.sub.1=0.005 and θ.sub.λ.sub.i indicates the angle between the two normalized vectors u.sub.λ.sub.i and v.sub.λ.sub.i, the vector u.sub.λ.sub.i indicating a normalized gradient of the reflectance curve of the target coating at λ.sub.i, and the vector v.sub.λ.sub.i indicating a normalized gradient of the reflectance curve of the sample coating at λ.sub.i.

6. The method according to claim 1, wherein the wavelength values of the number of wavelength values are chosen from an interval from a minimum wavelength value to a maximum wavelength value, with the minimum wavelength value being about 420 nm and the maximum wavelength value being about 680 nm.

7. The method according to claim 1, wherein the scaling function is chosen as a non-linear scaling function ƒ.

8. The method according to claim 7, wherein the non-linear scaling function ƒ.sub.ref,smp is chosen as follows: $f_{ref/smp}=\frac{1}{Nor{m}_{R_{ref/smp}}}$ $\mathrm{with}$ ${\mathrm{Norm}}_{R_{\mathrm{ref}/\mathrm{smp}}}=\frac{116.Math.x_{ref/smp}-16}{100}$ $\mathrm{with}$ $x_{\frac{\mathrm{ref}}{\mathrm{smp}}}=\{\begin{array}{c}\sqrt[3]{R_{\frac{\mathrm{ref}}{\mathrm{smp}},\mathrm{center}}},R_{\frac{\mathrm{ref}}{\mathrm{smp}},\mathrm{center}}>\frac{216}{24389}\\ \frac{\frac{24389}{27}{R}_{\frac{\mathrm{ref}}{\mathrm{smp}},\mathrm{center}}+16}{116},\mathrm{otherwise}\end{array}$ wherein R.sub.ref,/smp,center is given by: $R_{ref/smp,\mathrm{center}}=R_{ref/\mathrm{sm}p,\min }+\frac{R_{\mathrm{ref}/\mathrm{smp},\max }-R_{\mathrm{ref}/\mathrm{smp},\min }}{2}$ $\mathrm{with}$ $R_{ref/\mathrm{smp},\max }=R_{ref/\mathrm{smp},\max }\mathrm{and}{R}_{ref/\mathrm{smp},\min }=\mathrm{Min}\left(R_{ref/\mathrm{smp},{\lambda }_i}\right)$

9. The method according to claim 4, wherein the match metric is chosen as follows: $\mathrm{dShape}=k_2.Math.\frac{31}{n}.Math.\underset{i=0}{\overset{n-2}{.Math.}}{\theta }_{{\lambda }_i}$ wherein n is an integer and k.sub.2 is a linear scaling factor with k.sub.2=0.65.

10. The method according to claim 4, wherein the match metric is chosen as follows: $dShap{e}^{*}=k_2^{*}.Math.\frac{31}{n}.Math.\underset{i=0}{\overset{n-2}{.Math.}}\frac{.Math.\Delta R_{smp,{\lambda }_i}^{norm}-\Delta R_{\mathrm{ref},{\lambda }_i}^{\mathrm{norm}}.Math.}{k_1.Math.{\mathrm{\Delta \lambda }}_i}$ wherein n is an integer and k.sub.2* is a linear scaling factor with k.sub.2*=100.

11. A system for providing a match metric for quantifying a spectral similarity of a target coating and at least one sample coating, the system comprising: A) a computing device; and B) a computer program product, the computer program product comprises computer executable codes stored on a computer readable storage medium functionally coupled to the computing device and causes the computing device to perform a computing process when in operation, the computing process comprises the steps of: B1) receiving, for a number of wavelength values, reflectance values of the target coating and reflectance values of the sample coating, wherein the reflectance values of the target coating are determined at one or more measurement geometries, and the reflectance values of the sample coating are determined at the one or more measurement geometries; B2) normalizing each of the reflectance values of the target coating determined at the respective one of the one or more measurement geometries and the reflectance values of the sample coating determined at the respective one of the one or more measurement geometries by using a non-linear scaling function; B3) generating a normalized reflectance curve for the target coating based on the normalized reflectance values of the target coating for each wavelength value, and a normalized reflectance curve for the sample coating based on the normalized reflectance values of the sample coating for each wavelength value; B4) producing, for the number of wavelength values, normalized first derivative values of the normalized reflectance curve of the target coating with respect to the wavelength and normalized first derivative values of the normalized reflectance curve of the sample coating with respect to the wavelength; B5) producing, for each wavelength value of the number of wavelength values, difference values between the normalized first derivative values of the normalized reflectance curve of the target coating and the normalized first derivative values of the normalized reflectance curve of the sample coating; and B6) producing a match metric for a similarity between the normalized reflectance curves of the target coating and the sample coating based at least on the difference values for all of the number of wavelength values.

12. The system according to claim 11, further comprising: C) a color measuring device; and D) a formulation database comprising formulas for coating compositions and interrelated colorimetric data; wherein the computing device is functionally coupled to the color measuring device and the formulation database.

13. The system according to claim 11, wherein the computing process further comprises a matching process for matching the color of the target coating and the at least one sample coating, the matching process comprises at least the steps of: B7) retrieving from the formulation database one or more preliminary matching formulas based on the sample colorimetric data; and B8) selecting at least one from the one or more preliminary matching formulas so as to minimize the match metric beside other colorimetric metrics.

14. The system according to claim 11, wherein the computing process further comprises the step of: B9) modifying a formula for the sample coating so as to minimize the match metric beside other colorimetric metrics.

15. The method according to claim 2, the method further comprises the step of: i) modifying one of the one or more preliminary matching formulas retrieved from the database, so as to minimize the match metric for the similarity of the normalized reflectance curves of the target coating and the sample coating as additional constraint beside existing color difference metric(s).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0087] FIG. 1 shows a diagram of spectral reflectance curves of a target coating and a sample coating;

[0088] FIG. 2 shows a diagram of the spectral reflectance curves of the target coating of FIG. 1 and, for each spectral reflectance curve, an average reflectance value of the target coating;

[0089] FIG. 3a shows a diagram of the spectral reflectance curves of FIG. 1 wherein a specific region is encircled;

[0090] FIG. 3b shows the encircled region of FIG. 3a in an enlarged representation;

[0091] FIG. 3c shows a vector indicating a gradient of the reflectance curve of the target coating in the encircled region of FIG. 3b;

[0092] FIG. 3d shows a vector indicating a gradient of the reflectance curve of the sample coating in the encircled region of FIG. 3b;

[0093] FIG. 3e shows an angle between the vector of FIG. 3c and the vector of FIG. 3d;

[0094] FIG. 4 shows in the FIGS. 4a to 4k examples of values of a match metric as provided by an embodiment of the proposed method.

[0095] FIG. 5 schematically shows an embodiment of the proposed system.

DETAILED DESCRIPTION OF THE DRAWINGS

[0096] FIG. 1 shows normalized spectral measurements, i.e. normalized spectral reflectance curves of a target coating and a sample coating at different viewing angles. The in-plane bidirectional reflectance of a metallic pigmented sample coating was measured using a multi-angle spectrometer, e. g. a Byk-Mac® I or a spectrometer of the XRite MA®-T-family. Reflectance of the sample coating is measured from several geometries, namely with a given illumination angle of 45° measured relative to the surface normal of the coating and viewing angles of −15°, 15°, 25°, 45°, 75°, 110°, each measured relative to the specular angle.

[0097] The wavelength of an incident light flux is plotted along a horizontal axis 110. The normalized reflectance of the sample coating and of the target coating is plotted along a vertical axis 120. The measured reflectance values are normalized using a scaling function ƒ.sub.ref/smp:

[00006]$f_{ref/smp}=\frac{1}{Nor{m}_{R_{ref/smp}}}$$\mathrm{with}$${\mathrm{Norm}}_{R_{\mathrm{ref}/\mathrm{smp}}}=\frac{116.Math.x_{ref/smp}-16}{100}$$\mathrm{with}$$x_{ref/smp}=\{\begin{array}{c}\sqrt[3]{R_{ref/smp,\mathrm{center}}},R_{ref/smp,center}>\frac{216}{24389}\\ \frac{\frac{24389}{27}{R}_{ref/smp,center}+16}{116},\mathrm{otherwise}\end{array}$

[0098] wherein R.sub.ref,/smp,center is given by:

[00007]$R_{ref/smp,\mathrm{center}}=R_{ref/\mathrm{sm}p,\min }+\frac{R_{\mathrm{ref}/\mathrm{smp},\max }-R_{\mathrm{ref}/\mathrm{smp},\min }}{2}$$\mathrm{with}$$R_{ref/\mathrm{sm}p,\max }=\mathrm{Max}\left(R_{ref/\mathrm{sm}p,{\lambda }_i}\right)\mathrm{and}{R}_{ref/\mathrm{sm}p,\min }=\mathrm{Min}\left(R_{ref/\mathrm{sm}p,{\lambda }_i}\right)$

[0099] The curve 130 indicates the reflectance of the target coating measured at a viewing angle of −15°, the curve 135 indicates the reflectance of the sample coating measured at the viewing angle of −15°. The curve 140 indicates the reflectance of the target coating and the curve 145 indicates the reflectance of the sample coating measured at a viewing angle of 15°, respectively. The curve 150 indicates the reflectance of the target coating and the curve 155 indicates the reflectance of the sample coating measured at a viewing angle of 25°, respectively. The curve 160 indicates the reflectance of the target coating and the curve 165 indicates the reflectance of the sample coating measured at a viewing angle of 45°, respectively. The curve 170 indicates the reflectance of the target coating and the curve 175 indicates the sample coating measured at a viewing angle of 75°, respectively. The reflectance curve of the target coating and the reflectance curve of the sample coating measured at a viewing angle of 110°, respectively, can not be differentiated in the representation here from the reflectance curves 170, 175, respectively, as at the flop angles 45°, 75° and 110°, only small reflectance values are measured, respectively. Further, only small variances of shape of the respective curves dependent on the wavelength are observed.

[0100] The wavelength values of the number of wavelength values for which reflectance is analyzed, are chosen from an interval from a minimum wavelength value to a maximum wavelength value, with the minimum wavelength value being about 420 nm and the maximum wavelength value being about 680 nm, i.e.:

λ.sub.i=λ.sub.min, . . . ,λ.sub.max

λ.sub.min≈420 nm

λ.sub.max≈680 nm

wherein the number of analyzed reflectance values between λ.sub.min and λ.sub.max is n and the index of the respective reflectance values i∈[0, . . . (n−1)].

[0101] FIG. 2 shows a diagram of the spectral reflectance curves of the target coating of FIG. 1 and, for each spectral reflectance curve, an average reflectance value 131, 141, 151, 161, 171 of the target coating, each indicated as dashed line.

[0102] FIG. 3a shows the diagram of the normalized spectral reflectance curves of FIG. 1 wherein a specific region 133 is encircled.

[0103] FIG. 3b shows the encircled region 133 of FIG. 3a in an enlarged representation. The crossing point 134 of the two reflectance curves 130 and 135 is considered in the following.

[0104] FIG. 3c shows a vector indicating a normalized gradient (=normalized derivative value) of the reflectance curve of the target coating in the encircled region 133 of FIG. 3b, particularly at the crossing point 134. Therefore, only an enlarged section 110′ of the horizontal axis 110 is shown which reaches from λ.sub.i≈605.3 nm to λ.sub.i+Δλ.sub.i and only an enlarged section 120′ of the vertical axis 120 is shown which embraces reflectance values from R.sub.ref,λ.sub.i.sup.norm to R.sub.ref,λ.sub.i.sub.+Δλ.sub.i.sup.norm. By means of the vector representation of the normalized first derivative value of the reflectance curve of the target coating and the normalized first derivative value of the reflectance curve of the sample coating, respectively, a difference value between the normalized first derivative value of the reflectance curve of the target coating and the normalized first derivative value of the reflectance curve of the sample coating can be indicated as an angle θ.sub.λ.sub.i (see FIG. 3e).

[0105] As shown in FIG. 3c, the normalized first derivative value of the reflectance curve of the target coating at the crossing point 134 is represented for λ.sub.i≈605.3 nm as a two-dimensional vector u.sub.λ.sub.i according to the following formula:

[00008]$u_{{\lambda }_i}=\left(\begin{array}{c}{k}_1.Math.\Delta {\lambda }_i\\ \Delta R_{\mathrm{ref},{\lambda }_i}^{\mathrm{norm}}\end{array}\right)$

[0106] with

ΔR.sub.ref,λ.sub.i.sup.norm=R.sub.ref,λ.sub.i.sub.+Δλ.sub.i.sup.norm−R.sub.ref,λ.sub.i.sup.norm, and

Δλ.sub.i=λ.sub.i+1−λ.sub.i,

wherein R.sub.ref,λ.sub.i.sup.norm indicates a normalized reflectance value of the target coating at the wavelength value λ.sub.i, R.sub.ref,λ.sub.i.sub.+Δλ.sub.i.sup.norm indicates the normalized reflectance value of the target coating at the wavelength value λ.sub.i+1=λ.sub.i+Δλ.sub.i. k.sub.1 is a non-linear damping parameter with k.sub.1=0.005.

[0107] FIG. 3d shows a normalized vector indicating a gradient of the reflectance curve of the sample coating in the encircled region of FIG. 3b, particularly at the crossing point 134. Again, only the enlarged section of the horizontal axis 110′ is shown which reaches from λ.sub.i≈605.3 nm to λ.sub.i+Δλ.sub.i. Furthermore, only an enlarged section 120′ of the vertical axis 120 is shown which embraces reflectance values from R.sub.smp,λ.sub.i.sup.norm to R.sub.smp,λ.sub.i.sub.+Δλ.sub.i.sup.norm.

[0108] As shown in FIG. 3d, the normalized first derivative value of the reflectance curve of the sample coating at the crossing point 134 is represented for λ.sub.i≈605.3 nm as a two-dimensional vector according to the following formula:

[00009]$v_{{\lambda }_i}=\left(\begin{array}{c}{k}_1.Math.\Delta {\lambda }_i\\ \Delta R_{\mathrm{smp},{\lambda }_i}^{\mathrm{norm}}\end{array}\right)$
ΔR.sub.smp,λ.sub.i.sup.norm=R.sub.smp,λ.sub.i.sub.+Δλ.sub.i.sup.norm−R.sub.smp,λ.sub.i.sup.norm, and

Δλ.sub.i=λ.sub.i+1−λ.sub.i,

[0109] R.sub.smp,λ.sub.i.sup.norm indicates a normalized reflectance value of the sample coating at the wavelength value λ.sub.i, R.sub.smp,λ.sub.i+1.sup.norm indicates a normalized reflectance value of the sample coating at the wavelength value λ.sub.i+1=λ.sub.i+Δλ.sub.i. k.sub.1 is the non-linear damping parameter.

[0110] FIG. 3e shows the angle θ.sub.λ.sub.i between the vector u.sub.λ.sub.i of FIG. 3c and the vector v.sub.λ.sub.i of FIG. 3d, thus indicating a difference value of the gradient (=normalized derivative value) of the reflectance curve 130 of the target coating and of the gradient (=normalized derivative value) of the reflectance curve 135 of the sample coating at this crossing point 134, i.e. at the wavelength value λ.sub.i≈605.3 nm. θ.sub.λ.sub.i indicates the angle between the two normalized vectors u.sub.λ.sub.i and v.sub.λ.sub.i, the vector u.sub.λ.sub.i indicating a gradient of the reflectance curve of the target coating at λ.sub.i and the vector v.sub.λ.sub.i indicating a gradient of the reflectance curve of the sample coating at λ.sub.i. Thus, θ.sub.λ.sub.i indicates a kind of difference angle/value and is determined according to the following formula (cosine theorem):

[00010]${\theta }_{{\lambda }_i}={\cos }^{-1}\left(\frac{u_{{\lambda }_i}.Math.v_{{\lambda }_i}}{.Math.u_{{\lambda }_i}.Math..Math..Math.v_{{\lambda }_i}.Math.}\right)$${\theta }_{{\lambda }_i}\in \left[0,\frac{\pi }{2}\right]$

[0111] FIG. 4 shows in the FIGS. 4a to 4k examples of values of the match metric dShape as provided by an embodiment of the proposed method.

[0112] FIGS. 4a to 4k, each show a diagram of a normalized spectral curve of a target coating and a normalized spectral curve of a sample coating. The wavelength values are plotted along a horizontal axis 410 and are chosen from an interval from a minimum wavelength value to a maximum wavelength value, with the minimum wavelength value being 420 nm and the maximum wavelength value being 680 nm. The normalized reflectance values of the target coating and the sample coating, respectively, are plotted along a vertical axis 420 which ranges from 0.0 to 0.5.

[0113] Above each diagram, the respective value of the match metric dShape, the minimum wavelength value wlmin, the maximum wavelength value wlmax, the non-linear damping parameter k.sub.1 and the linear scaling-factor k.sub.2 are stated.

[0114] FIG. 5 schematically illustrates an embodiment of the proposed system. The system 500 shown here comprises a computing device 510, a formulation database 520, a color measurement device 530, an output device 540, an input device 550 and a computer readable storage medium 560. The system further comprises a computer program product which comprises computer executable codes stored on the computer readable storage medium 560. In the example shown here, the computer readable storage medium 560 is loaded in an internal memory of the computing device 510. Thus, the computer readable storage medium 560 is functionally coupled to the computing device 510. Any other functional coupling of the computer readable storage medium 560 and the computing device 510 is possible. The computer readable storage medium 560 causes the computing device 510 to perform a computing process when in operation, the computing process comprises the steps of: [0115] B1) receiving, via a communications interface, for a number of wavelength values, reflectance values of the target coating and reflectance values of the sample coating, wherein the reflectance values of the target coating are determined, particularly measured, at one or more measurement geometries, and the reflectance values of the sample coating are determined, particularly measured, at the one or more measurement geometries; [0116] B2) normalizing each of the reflectance values of the target coating determined at the respective one or more measurement geometries and the reflectance values of the sample coating determined at the respective one or more measurement geometries by using a non-linear scaling function; [0117] B3) generating a normalized reflectance curve for the target coating based on the normalized reflectance values of the target coating for each wavelength value, and a normalized reflectance curve for the sample coating based on the normalized reflectance values of the sample coating for each wavelength value; [0118] B4) producing, for the number of wavelength values, normalized first derivative values of the normalized reflectance curve of the target coating with respect to the wavelength and normalized first derivative values of the normalized reflectance curve of the sample coating with respect to the wavelength; [0119] B5) producing, for each wavelength value of the number of wavelength values, difference values between the normalized first derivative values of the normalized reflectance curve of the target coating and the normalized first derivative values of the normalized reflectance curve of the sample coating; [0120] B6) producing a match metric for the similarity of the normalized reflectance curves of the target coating and the sample coating based at least on the difference values for all of the number of wavelength values, and [0121] B7) outputting, using the output device 540, the produced match metric to a user.

[0122] The formulation database 520 comprises formulas for coating compositions and interrelated colorimetric data and is functionally coupled to the computing device 510.

[0123] Generally, the color measuring device 530 which is also functionally coupled to the computing device 510, is a spectrometer, particularly a multi-angle spectrometer, such as a Byk-Mac® I or a spectrometer of the XRite-MA®-T-family.

[0124] The computing process may further comprise a color retrieval process for matching the color of the target coating and the at least one sample coating, the matching process comprises at least the steps of: [0125] B8) retrieving from the formulation database 520 one or more preliminary matching formulas based on the sample colorimetric data; [0126] B9) selecting at least one from the one or more preliminary matching formulas so as to minimize the match metric beside other colorimetric metrics like color differences (color difference metric) and texture differences (texture difference metric).

[0127] Additionally, the computing process may further comprise the step of [0128] B10) modifying an initial formula, particularly the selected at least one preliminary matching formula, for the sample coating so as to minimize the match metric beside other colorimetric metrics like color differences and optionally texture differences.

[0129] Generally, at least the color measuring device 530, the computing device 510 and the formulation database 520 are networked among each other via respective communicative connections. Further, the input device 550 and the output device 540 are part of the computing device 510 or at least functionally coupled with the computing device 510. It is possible to illustrate on the output device 540 simultaneously, both, the target coating, i.e. the spectral curve of the target coating, and the sample coating, i.e. the spectral curve of the sample coating, so as to allow a visual comparison “on the fly”, i.e. during operation of the matching process.

LIST OF REFERENCES

[0130] 110 horizontal axis [0131] 120 vertical axis [0132] 130 reflectance curve at −15° [0133] 135 reflectance curve at −15° [0134] 140 reflectance curve at 15° [0135] 145 reflectance curve at 15° [0136] 150 reflectance curve at 25° [0137] 155 reflectance curve at 25° [0138] 160 reflectance curve at 45° [0139] 165 reflectance curve at 45° [0140] 170 reflectance curve at 75° [0141] 175 reflectance curve at 75° [0142] 131 average reflectance value at −15° [0143] 141 average reflectance value at 15° [0144] 151 average reflectance value at 25° [0145] 161 average reflectance value at 45° [0146] 171 average reflectance value at 75° [0147] 133 specific region [0148] 134 crossing point [0149] 110′ enlarged section of horizontal axis 110 [0150] 120′ enlarged section of vertical axis 120 [0151] 410 horizontal axis [0152] 420 vertical axis [0153] 500 system [0154] 510 computing device [0155] 520 formulation database [0156] 530 color measurement device [0157] 540 output device [0158] 550 input device [0159] 560 computer readable storage medium