Abstract:
One embodiment of a method for aligning measurements taken by a plurality of color measurement instruments with measurements taken by an industry standard color measurement instrument includes receiving a first set of spectral data from the plurality of instruments, receiving a second set of spectral data from the industry standard instrument, generating initial profiles for the plurality of instruments (by producing, for each given instrument, a first correction that aligns the spectral data taken by the given instrument with the second set of spectral data), mathematically correcting the first set of spectral data using the initial profiles to produce a third set of spectral data, and generating new profiles for the plurality of instruments (by calculating a mean of the third set of spectral data, and producing, for each given instrument, a second correction that aligns the spectral data taken by the given instrument with the mean.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/670,353, filed Jul. 11, 2012, which is herein incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to the measurement of color, and more specifically relates to the coordination of multiple color measurement devices. 
       BACKGROUND 
       [0003]    Color-measurement instruments (e.g., spectrophotometers) can be characterized parametrically and corrected to measure like a reference or master instrument. The characterization and correction is based on instrument profiles. The “profile” of a first instrument relative to a second instrument is defined herein as a set of parameter values that mathematically map a first set of reflectance values of a set of specimens as measured by the first instrument to the best approximation of a second set of reflectance values of the same specimens as measured by the second instrument. The act of “profiling” is defined herein as the generation of these parameter values, and “profile-based correction” is defined herein as the act of implementing the mapping defined by these parameter values to correct subsequent reflectance measurements by the profiled instrument. Such profile-based correction compensates for small systematic differences between instruments. Profile-based correction typically starts from a model equation such as the following: 
         [0000]        R   ci   =A+BR   mi   +CR′   mi   DR″   mi−   +ER   mi (100− R   mi )  (EQN. 1)
 
         [0000]    Where R mi  is the i th  measured reflectance, R ci  is the i th  corrected reflectance, all variables A, B, C, D, and E implicitly depend on wavelength, and ′ and ″ refer to the first and second derivatives, respectively, of R mi  with respect to wavelength. The corrections in EQN. 1 are represented by the following parameters: offset (A), gain change (B), wavelength-scale change (C), bandwidth change (D), and some nonlinearities (E). EQN. 1 (or a similar equation, possibly with a different number of parameters) is used twice in profile-based correction. The first usage of EQN. 1 measures known specimens such as the British Ceramic Research Association (BCRA) tiles with parameters A-E (at each wavelength) in the solve state. In this first usage of EQN. 1, optimizing software is typically used to find the parameter values A-E that make the computed quantities R ci  closest to the quantities R mi  of the second instrument. The now-known quantities A-E (and possibly other parameters) comprise the profile of the first instrument relative to the second instrument. During the second usage of EQN. 1, the first instrument measures reflectances of test specimens, adopts the measured reflectances of the test specimens as the quantities R mi , substitutes the now-known parameters A-E into EQN. 1, and uses EQN. 1 to compute the corrected measurements Rd. Continued operation of the second usage of EQN. 1 constitutes the profile-based correction of the reflectance measurements. 
         [0004]    Profile-based correction of a fleet of spectrophotometers depends on the availability of a master instrument (to act as the second instrument described above) and at least one set of trustworthy color standards (i.e., reflecting specimens such as the BCRA tiles). Such correction also works best when the master instrument is very close in design to the instruments that are being corrected to it in the fleet. In some cases, the trusted master instrument may have a slightly different design than the instruments in the fleet; however, the master instrument must still be used as an initial anchor if no better standard exists. In such a case, one can improve the inter-instrument agreement by computing the average reflectance data from the fleet of instruments and correcting the fleet of instruments to this average. However, this introduces another problem: the use of the average reflectance data requires use of the same reflecting color standards for all of the profiling measurements. This is impractical, especially when the instruments in the fleet are not geographically co-located. One must have at hand either a real master instrument or a real set of standard color tiles that is used for all corrections. 
       SUMMARY OF THE INVENTION 
       [0005]    In one embodiment, the present invention includes a software program for aligning the measurements of a fleet of color measurement instruments with a master (or “industry standard”) color measurement instrument outside of the fleet. The software program includes four main sub-processes: (1) a process for generating initial profiles for the color measurement instruments in the fleet using an initial set of color tiles; (2) a process for generating new profiles for the color measurement instruments in the fleet based on the initial set of color tiles; (3) a process for generating a profile for a new device that is “similar” to the color measurement instruments in the fleet; and (4) a process for generating new profiles for the fleet of color measurement instruments based on a new set of color tiles. 
         [0006]    One embodiment of a method for aligning measurements taken by a plurality of color measurement instruments with measurements taken by an industry standard color measurement instrument includes receiving a first set of spectral data from the plurality of instruments, receiving a second set of spectral data from the industry standard instrument, generating initial profiles for the plurality of instruments (by producing, for each given instrument, a first correction that aligns the spectral data taken by the given instrument with the second set of spectral data), mathematically correcting the first set of spectral data using the initial profiles to produce a third set of spectral data, and generating new profiles for the plurality of instruments (by calculating a mean of the third set of spectral data, and producing, for each given instrument, a second correction that aligns the spectral data taken by the given instrument with the mean. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
           [0008]      FIG. 1  is a flow diagram illustrating one embodiment of a method for generating initial profiles for the color measurement instruments in a fleet of color measurement instruments, according to the present invention; 
           [0009]      FIG. 2  is a diagram further illustrating the improvement on color measurement performance according to the method illustrated in  FIG. 1 ; 
           [0010]      FIG. 3  is a flow diagram illustrating one embodiment of a method for generating new profiles for the color measurement instruments in the fleet based on the initial set of color standards, according to the present invention; 
           [0011]      FIG. 4  is a diagram further illustrating the improvement of color measurement performances by application of the method illustrated in  FIG. 3  to correct a fleet of instruments to the pre-determined virtual center; 
           [0012]      FIG. 5  is a flow diagram illustrating one embodiment of a method for generating a profile for a new color measurement instrument; 
           [0013]      FIG. 6  is a flow diagram illustrating one embodiment of a method  600  for generating new profiles for the fleet of color measurement instruments based on a new set of color standards, according to the present invention; and 
           [0014]      FIG. 7  is a high-level block diagram of the profiling method that is implemented using a general purpose computing device. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    In one embodiment, the present invention includes a method and apparatus for aligning the measurements of a fleet of color measurement instruments to a master (or “industry standard”) color measurement instrument outside of the fleet. The method includes four main sub-processes: (1) a process for generating initial profiles for the color measurement instruments in the fleet using an initial set of color tiles; (2) a process for generating new profiles for the color measurement instruments in the fleet based on the initial set of color tiles; (3) a process for generating a profile for a new device that is similar to (i.e., has the same specimen-illumination pattern and specimen-viewing geometry as) the color measurement instruments in the fleet; and (4) a process for generating new profiles for a new group of similar color measurement instruments based on a new set of color tiles. 
         [0016]    In one embodiment, sub-processes (2)-(4) are considered optional and may be performed in any combination and/or order once sub-process (1) is performed. However, a given color measurement instrument must be subjected to either sub-process (2) (if the color measurement instrument is a member of the fleet) or sub-process (3) (if the color measurement instrument is not a member of the fleet) if the color measurement instrument is to be able to measure color accurately. Moreover, if the initial set of color tiles is unavailable, a new color measurement device (not a member of the fleet) must be subjected to sub-process (4) in order to be able to measure color accurately. 
         [0017]    In practice, a certain type of color measurement instrument developed by a certain manufacturer may have systematic differences compared to some commonly used industry standard instrument. Furthermore, systematic differences may exist among instruments in a fleet of similar color measurement instruments, and thus the inter-instrument agreement among the fleet may be poor. 
         [0018]    For example, Table 1 shows the Commission internationale de l&#39;eclairage (CIE) 1976 (L*, a*, b*) color space (CIELAB) color difference ΔE (under illuminant D65) when using different instruments to measure the same set of color standards (in this case, reflecting tiles C1, . . . , C12). For each color standard, the color difference is calculated between the measured color from one instrument and the average of the same measured color (reflectance data) from all the instruments. As illustrated, ΔE ranges from 0.01 to 0.75. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Color difference between original instruments and the averages 
               
             
          
           
               
                   
                 Instr. 1 
                 Instr. 2 
                 Instr. 3 
                 Instr. 4 
                 Instr. 5 
                 Instr. 6 
                 Instr. 7 
                 Instr. 8 
               
               
                   
                   
               
             
          
           
               
                 C1 
                 0.0921 
                 0.0436 
                 0.0707 
                 0.0323 
                 0.0311 
                 0.023 
                 0.0274 
                 0.0206 
               
               
                 C2 
                 0.0987 
                 0.0722 
                 0.1186 
                 0.0425 
                 0.0101 
                 0.0485 
                 0.0546 
                 0.068 
               
               
                 C3 
                 0.0882 
                 0.0163 
                 0.0911 
                 0.0506 
                 0.0169 
                 0.0445 
                 0.0577 
                 0.071 
               
               
                 C4 
                 0.0713 
                 0.0428 
                 0.062 
                 0.0316 
                 0.0489 
                 0.0575 
                 0.0425 
                 0.074 
               
               
                 C5 
                 0.1484 
                 0.0366 
                 0.1047 
                 0.1039 
                 0.1013 
                 0.0398 
                 0.0902 
                 0.05 
               
               
                 C6 
                 0.1024 
                 0.1899 
                 0.0662 
                 0.2101 
                 0.1229 
                 0.0947 
                 0.4041 
                 0.0611 
               
               
                 C7 
                 0.0826 
                 0.3198 
                 0.2026 
                 0.4211 
                 0.0698 
                 0.2524 
                 0.6465 
                 0.1131 
               
               
                 C8 
                 0.1474 
                 0.4072 
                 0.3702 
                 0.3745 
                 0.1437 
                 0.3263 
                 0.7542 
                 0.0983 
               
               
                 C9 
                 0.0825 
                 0.2928 
                 0.171 
                 0.2946 
                 0.2225 
                 0.1322 
                 0.4587 
                 0.1299 
               
               
                 C10 
                 0.1545 
                 0.1739 
                 0.0996 
                 0.2364 
                 0.1109 
                 0.2094 
                 0.3914 
                 0.1277 
               
               
                 C11 
                 0.1653 
                 0.1499 
                 0.0811 
                 0.247 
                 0.1095 
                 0.239 
                 0.5375 
                 0.1012 
               
               
                 C12 
                 0.1221 
                 0.0987 
                 0.1185 
                 0.212 
                 0.1415 
                 0.0549 
                 0.2326 
                 0.0509 
               
               
                   
               
             
          
         
       
     
         [0019]    To reduce the systematic differences between a fleet of color measurement instruments and a widely accepted industry standard, and to improve the inter-instrument agreement performance among the fleet of color measurement instruments, the industry standard instrument can be used to measure the same set of color standards, to generate a profile for a given instrument in the fleet based on the difference between the given instrument and the industry standard, and to apply the profile to the given instrument. After each instrument in the fleet is profiled in this way, subsequent measurements by each instrument are corrected (or correlated) by using the respective profile. Compared to the uncorrected instruments (i.e., the instruments prior to application of the respective profiles), the corrected instruments perform more like the industry standard, and the inter-instrument agreement among the instruments in the fleet will be much tighter. 
         [0020]      FIG. 1  is a flow diagram illustrating one embodiment of a method  100  for generating initial profiles for the color measurement instruments in a fleet of color measurement instruments, according to the present invention. Thus, the method  100  corresponds to sub-process (1) discussed above. The method  100  may be performed, for example, by a centralized processor that communicates with the fleet of color measurement instruments. 
         [0021]    The method  100  begins in step  102 . In step  104 , an initial set of color standards (e.g., color tiles) is obtained. In step  106 , measurements are received from each instrument in the fleet of color measurement instruments. The measurements received in step  106  comprise a first set of spectral data measured from the initial set of color standards. 
         [0022]    In step  108 , measurements are received from an industry standard color measurement instrument, which is not a member of the fleet of color measurement instruments. The measurements received in step  108  comprise a second set of spectral data measured from the initial set of color standards. 
         [0023]    In step  110 , an initial profile is generated for each color measurement instrument in the fleet of color measurement instruments. A given color measurement instrument&#39;s initial profile is based on a comparison of the portion of the first set of spectral data that is received from the given color measurement instrument to the second set of spectral data (e.g., via an equation such as EQN. 1). 
         [0024]    In step  112 , a third set of spectral data is generated by applying the initial profiles to the respective color measurement instruments in the fleet. Application of the initial profiles in accordance with step  112  involves using the initial profile for a given color measurement instrument to mathematically correct the portion of the first set of spectral data that was measured by the given color measurement instrument. When the initial profiles have been applied in this way to each of the respective color measurement instruments in the fleet (i.e., such that all portions of the first set of spectral data have been mathematically corrected accordingly), the third set of spectral data is produced. The method  100  then ends in step  114 . 
         [0025]    The method  100  thus produces a “corrected” fleet of color measurement instruments. In other words, the initial profiles correct the measurements of the color measurement instruments in the fleet so that they are closer to what the industry standard color measurement instrument would have measured. Table 2 shows the CIELAB color difference when using different instruments in the corrected fleet to measure the same set of color standards. As illustrated, ΔE ranges from 0.01 to 0.2, which is much tighter when compared to the ranges in Table 1 for an “uncorrected” fleet. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Color differences between industry-standard-corrected 
               
               
                 instruments and the virtual center 
               
             
          
           
               
                   
                 Instr. 1 
                 Instr. 2 
                 Instr. 3 
                 Instr. 4 
                 Instr. 5 
                 Instr. 6 
                 Instr. 7 
                 Instr. 8 
               
               
                   
                   
               
             
          
           
               
                 C1 
                 0.054 
                 0.0604 
                 0.0914 
                 0.1045 
                 0.0988 
                 0.1221 
                 0.0213 
                 0.0911 
               
               
                 C2 
                 0.0668 
                 0.0828 
                 0.1876 
                 0.0834 
                 0.0888 
                 0.0584 
                 0.0764 
                 0.0567 
               
               
                 C3 
                 0.0624 
                 0.0724 
                 0.0966 
                 0.0586 
                 0.0098 
                 0.0707 
                 0.0448 
                 0.0204 
               
               
                 C4 
                 0.0968 
                 0.0365 
                 0.0425 
                 0.0345 
                 0.022 
                 0.0514 
                 0.0853 
                 0.0922 
               
               
                 C5 
                 0.1451 
                 0.1828 
                 0.107 
                 0.0477 
                 0.1726 
                 0.1181 
                 0.1538 
                 0.1042 
               
               
                 C6 
                 0.0202 
                 0.0808 
                 0.0748 
                 0.0141 
                 0.0203 
                 0.0792 
                 0.0415 
                 0.121 
               
               
                 C7 
                 0.2021 
                 0.0565 
                 0.1646 
                 0.0977 
                 0.0408 
                 0.0597 
                 0.0667 
                 0.0867 
               
               
                 C8 
                 0.1425 
                 0.0839 
                 0.1792 
                 0.0402 
                 0.0619 
                 0.0819 
                 0.0775 
                 0.0996 
               
               
                 C9 
                 0.0719 
                 0.0706 
                 0.0212 
                 0.0609 
                 0.1342 
                 0.0517 
                 0.0448 
                 0.0864 
               
               
                 C10 
                 0.0374 
                 0.0506 
                 0.0709 
                 0.0622 
                 0.1011 
                 0.1175 
                 0.0108 
                 0.0404 
               
               
                 C11 
                 0.0556 
                 0.057 
                 0.0563 
                 0.052 
                 0.0943 
                 0.1033 
                 0.0196 
                 0.0592 
               
               
                 C12 
                 0.1578 
                 0.1608 
                 0.1706 
                 0.0582 
                 0.0859 
                 0.0592 
                 0.0587 
                 0.0804 
               
               
                   
               
             
          
         
       
     
         [0026]      FIG. 2  is a diagram further illustrating the improvement on color measurement performance according to the method  100  illustrated in  FIG. 1 . For ease of illustration, the multi-dimensional color space (three dimensions of color×twelve color tiles) is represented as a plane. 
         [0027]    As can be seen in  FIG. 2 , after being corrected to the industry standard, not only do the individual color measurement instruments in the corrected fleet exhibit smaller differences from the industry standard color measurement instrument, but the color measurement instruments in the fleet also exhibit smaller differences among themselves (i.e., inter-instrument agreement among the fleet is improved). After being corrected to the industry standard color measurement instrument, the fleet of color measurement instruments as a whole shifts closer to the industry standard color measurement instrument, and the clustering is much tighter than that of the original, uncorrected fleet. 
         [0028]    Once a large enough population is obtained in the corrected fleet, the center of the fleet will be stable. Any color measurement instrument that is either part of the original fleet or is not part of the original fleet but is similar to the color measurement instruments in the original fleet (such as any color measurement instrument coming from the production line of the original fleet) can then be corrected to the virtual center of the corrected fleet. 
         [0029]      FIG. 3  is a flow diagram illustrating one embodiment of a method  300  for generating new profiles for the color measurement instruments in the fleet based on the initial set of color standards, according to the present invention. Thus, the method  300  corresponds to sub-process (2) discussed above. Like the method  100 , the method  300  may be performed, for example, by a centralized processor that communicates with the fleet of color measurement instruments. 
         [0030]    The method  300  begins in step  302 . In step  304 , the mean of the third set of spectral data (i.e., the measurements taken by the fleet of color measurement instruments that are mathematically corrected using the initial profiles) is calculated. As used herein, the term “mean” refers to the mean of a set of measurements taken by the fleet of color measurement instruments, rather than the mean of a set of measurements taken by a single color measurement instrument. The mean of the third set of spectral data represents the “virtual center” for the fleet of color measurement instruments. 
         [0031]    In step  306 , a new profile is generated for each color measurement instrument in the fleet. A given color measurement instrument&#39;s new profile is based on a comparison of the portion of the first set of spectral data that is received from the given color measurement instrument (i.e., the spectral data measured by the given color measurement instrument before application of the initial profile) to the virtual center (e.g., via an equation such as EQN. 1). 
         [0032]    In step  308 , the new profiles are applied to the respective color measurement instruments in the fleet. Application of the new profiles in accordance with step  308  involves using the new profile for a given color measurement instrument to mathematically correct subsequent measurements of spectral data by the given color measurement instrument. The method  300  then ends in step  310 . 
         [0033]    The method  300  thus refines the initial profiles generated for the fleet of color measurement instruments using the initial set of color tiles. After application of the new profiles, the inter-instrument agreement of the fleet of color measurement instruments is further improved, without using the industry standard color measurement instrument. 
         [0034]    To illustrate, Table 3 shows the CIELAB color difference when the original fleet of color measurement instruments is corrected to the virtual center directly, without using the industry standard color measurement instrument. The color difference is measured between the corrected color measurement instrument and the virtual center. As illustrated, most ΔE are below 0.1, with only a few exceptions going up to 0.19. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Color difference between the virtual center and the instruments that are 
               
               
                 directly corrected to the virtual center 
               
             
          
           
               
                   
                 Instr. 1 
                 Instr. 2 
                 Instr. 3 
                 Instr. 4 
                 Instr. 5 
                 Instr. 6 
                 Instr. 7 
                 Instr. 8 
               
               
                   
                   
               
             
          
           
               
                 C1 
                 0.004 
                 0.0072 
                 0.0219 
                 0.0083 
                 0.0059 
                 0.0036 
                 0.0043 
                 0.0122 
               
               
                 C2 
                 0.0238 
                 0.0505 
                 0.0975 
                 0.0311 
                 0.0599 
                 0.0516 
                 0.0513 
                 0.033 
               
               
                 C3 
                 0.0263 
                 0.0517 
                 0.0714 
                 0.0486 
                 0.0415 
                 0.0285 
                 0.0448 
                 0.0441 
               
               
                 C4 
                 0.0649 
                 0.0466 
                 0.045 
                 0.023 
                 0.0116 
                 0.0028 
                 0.0558 
                 0.0408 
               
               
                 C5 
                 0.011 
                 0.0112 
                 0.0193 
                 0.0205 
                 0.016 
                 0.0146 
                 0.0162 
                 0.0148 
               
               
                 C6 
                 0.0482 
                 0.0355 
                 0.036 
                 0.05 
                 0.015 
                 0.0317 
                 0.0325 
                 0.0609 
               
               
                 C7 
                 0.0426 
                 0.0366 
                 0.058 
                 0.0569 
                 0.0366 
                 0.0519 
                 0.0609 
                 0.0085 
               
               
                 C8 
                 0.0171 
                 0.059 
                 0.1863 
                 0.0446 
                 0.0305 
                 0.0283 
                 0.0446 
                 0.0324 
               
               
                 C9 
                 0.0227 
                 0.0506 
                 0.1323 
                 0.0454 
                 0.0322 
                 0.0188 
                 0.0508 
                 0.0825 
               
               
                 C10 
                 0.0351 
                 0.0222 
                 0.0707 
                 0.069 
                 0.0338 
                 0.0729 
                 0.0448 
                 0.0329 
               
               
                 C11 
                 0.0141 
                 0.048 
                 0.0577 
                 0.0497 
                 0.035 
                 0.011 
                 0.0114 
                 0.0371 
               
               
                 C12 
                 0.0294 
                 0.0195 
                 0.092 
                 0.0259 
                 0.0763 
                 0.0485 
                 0.0573 
                 0.0262 
               
               
                   
               
             
          
         
       
     
         [0035]      FIG. 4  is a diagram further illustrating the improvement of color measurement performances by application of the method  300  illustrated in  FIG. 3  to correct a fleet of instruments to the pre-determined virtual center. For ease of illustration, the multi-dimensional color space (three dimensions of color x twelve color tiles) is represented as a plane. 
         [0036]    As can be seen in  FIG. 4 , after being corrected to the virtual center directly, not only do the individual color measurement instruments in the corrected fleet exhibit smaller differences from the industry standard color measurement instrument, but the color measurement instruments in the fleet also exhibit smaller differences among themselves (i.e., inter-instrument agreement among the fleet is improved. After being corrected to the virtual center, the fleet of color measurement instruments as a whole shifts closer to the industry standard color measurement instrument, and the clustering is much tighter than that of the original, uncorrected fleet. Moreover, the clustering is tighter even than that of the fleet that has been corrected using the initial profiles (as illustrated in  FIG. 2 ). 
         [0037]      FIG. 5  is a flow diagram illustrating one embodiment of a method  500  for generating a profile for a new color measurement instrument. The new color measurement instrument is a color measurement instrument that is not part of the original fleet but is similar to the color measurement instruments in the original fleet (such as any color measurement instrument coming from the production line of the original fleet) Thus, the method  500  corresponds to sub-process (3) discussed above. The method  500  may be performed, for example, by a centralized processor that communicates with the fleet of color measurement instruments. 
         [0038]    The method  500  begins in step  502 . In step  504 , measurements from the new color measurement instrument are received. The measurements received in step  504  comprise a fourth set of spectral data measured from the initial set of color standards. 
         [0039]    In step  506 , a profile is generated for the new color measurement instrument. The new color measurement instrument&#39;s profile is based on a comparison of the fourth set of spectral data to the virtual center of the fleet of color measurement instruments. 
         [0040]    In step  508 , the profile is applied to the new color measurement instrument. Application of the profile in accordance with step  508  involves using the profile to mathematically correct subsequent measurements of spectral data by the new color measurement instrument. The method  500  then ends in step  510 . 
         [0041]    Thus, the method  500  creates a profile for a new color measurement instrument that is similar to the instruments in the fleet of color measurement instruments, using the virtual center and the initial set of color standards. 
         [0042]    At some point, it may be necessary to utilize a new set of color standards (e.g., due to unavailability of the initial set of color standards). In this case, the previously calculated virtual center of the fleet is no longer useful, since it is associated with the initial set of color standards. Thus, for similar instruments that are in current need of profiling (whether or not the similar instruments come from the original fleet) it will be necessary to generate new profiles using the new set of color standards. 
         [0043]      FIG. 6  is a flow diagram illustrating one embodiment of a method  600  for generating new profiles for the fleet of color measurement instruments based on a new set of color standards, according to the present invention. Thus, the method  600  correlates to sub-process (4) discussed above. The method  600  may be performed, for example, by a centralized processor that communicates with the fleet of color measurement instruments. 
         [0044]    The method  600  begins in step  602 . In step  604 , a new set of color standards (e.g., color tiles) is obtained. 
         [0045]    In step  606 , a secondary “master” color measurement instrument is selected either from the fleet of color measurement instruments or from a larger set of optically similar instruments. In one embodiment, the secondary master color measurement instrument is a color measurement instrument in this set whose measurements of the initial set of color standards are close to the virtual center. 
         [0046]    In step  608 , measurements are received from each instrument in the fleet of color measurement instruments. The measurements received in step  608  comprise a first set of spectral data measured from the new set of color standards. 
         [0047]    In step  610 , measurements are received from the secondary master color measurement instrument. The measurements received in step  610  comprise a second set of spectral data measured from the new set of color standards. 
         [0048]    In step  612 , a new profile is generated for each color measurement instrument in the fleet of color measurement instruments, relative to the new set of color standards. A given color measurement instrument&#39;s new profile is based on a comparison of the portion of the first set of spectral data that is received from the given color measurement instrument to the second set of spectral data (e.g., via an equation such as EQN. 1). 
         [0049]    In step  614 , the new profiles are applied to the respective color measurement instruments in the fleet. Application of the new profiles in accordance with step  614  involves using the new profile for a given color measurement instrument to mathematically correct the portion of the first set of spectral data that was measured by the given color measurement instrument. The method  100  then ends in step  616 . 
         [0050]    Thus, the method  600  is similar to the method  100 , except that the method  600  uses the new set of color standards in place of the initial set of color standards and uses the secondary master color measurement instrument in place of the industry standard color measurement instrument. In the case of the method  600 , the fleet is a set of color measurement instruments that are similar (but not necessarily identical) to the fleet of color measurement instruments deployed in accordance with the method  100 . A new set of profiles is then generated for the fleet of color measurement instruments, based on the new set of color standards. The method  600  ends in step  610 . 
         [0051]    Thus, the secondary master instrument is used, along with the new color standards, to generate new profiles for a newly defined fleet of color measurement instruments according to the process described above in connection with  FIG. 1 . 
         [0052]      FIG. 7  is a high-level block diagram of the profiling method that is implemented using a general purpose computing device  700 . In one embodiment, a general purpose computing device  700  comprises a processor  702 , a memory  704 , a profiling module  705  and various input/output (I/O) devices  706  such as a display, a keyboard, a mouse, a stylus, a wireless network access card, an Ethernet interface, and the like. In one embodiment, at least one I/O device is a storage device (e.g., a disk drive, an optical disk drive, a floppy disk drive). It should be understood that the profiling module  705  can be implemented as a physical device or subsystem that is coupled to a processor through a communication channel. 
         [0053]    Alternatively, the profiling module  705  can be represented by one or more software applications (or even a combination of software and hardware, e.g., using Application Specific Integrated Circuits (ASIC)), where the software is loaded from a storage medium (e.g., I/O devices  706 ) and operated by the processor  702  in the memory  704  of the general purpose computing device  700 . Thus, in one embodiment, the profiling module  705  for aligning the measurements of a fleet of color measurement instruments to a master (or “industry standard”) color measurement instrument outside of the fleet, as described herein with reference to the preceding figures, can be stored on a tangible or physical computer readable storage medium (e.g., RAM, magnetic or optical drive or diskette, and the like). 
         [0054]    It should be noted that although not explicitly specified, one or more steps of the methods described herein may include a storing, displaying and/or outputting step as required for a particular application. In other words, any data, records, fields, and/or intermediate results discussed in the methods can be stored, displayed, and/or outputted to another device as required for a particular application. Furthermore, steps or blocks in the accompanying figures that recite a determining operation or involve a decision, do not necessarily require that both branches of the determining operation be practiced. In other words, one of the branches of the determining operation can be deemed as an optional step. 
         [0055]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. Various embodiments presented herein, or portions thereof, may be combined to create further embodiments. Furthermore, terms such as top, side, bottom, front, back, and the like are relative or positional terms and are used with respect to the exemplary embodiments illustrated in the figures, and as such these terms may be interchangeable.