Apparatus and method for color measurement and color grading of diamonds, gemstones, and the like

Abstract

The present invention discloses method for color measurement and color grading of faceted gemstones, diamonds and the like. A novel three-step calibration insures an accurate spectral measurement of the sample inside the measurement integrating sphere. Using the method of the present invention, a computer provides measurement parameters calculated from the physical parameters of the measured sample, including, but not limited to, shape, dimensions, refractive index, intensity of fluorescence and cut grade. By means of the present invention, a computer then calculates the spectral reflectance and colorimetric data, and determines an average color grade by checking a look-up-table that represents the relationship between the CIELAB coordinate and the average color grade, and it also determines a true color grade based upon the average color grade and the physical parameters, using mathematical analyses and algorithms.

1 - 12 . (canceled) 
   
   
       13 . A method for determining average color grade and true color grade, comprising the steps of:
 inputting the physical parameters of a sample into a computer;   calculating measurement parameters for measuring spectral reflectance of the sample;   measuring the spectral reflectance of the sample;   calculating colorimetric data, based upon, among other things, measured spectral reflectance;   determining the average color grade using the colorimetric data; and   determining the true color grade using the average color grade and physical parameters.   
   
   
       14 . The method according to  claim 13  wherein the physical parameters of the sample include, but are not limited to, shape, length, width, depth, refractive index, intensity of fluorescence, and cut grade. 
   
   
       15 . The method according to  claim 13  wherein said step of calculating the measurement parameters includes using the computer to calculate the measurement parameters, which measurement parameters include, but are not limited to, measurement time, samples for average, width of the slit, voltage of the detector and range of wavelength. 
   
   
       16 . The method according to  claim 13  wherein the step of calculating the measurement parameters includes using one or more algorithms selected from the group consisting of complex numerical function, matrix transfer, finite element analysis, numerical analysis, artificial neural network, optimization, fuzzy logic, regression, possibility, and statistics. 
   
   
       17 . The method according to  claim 13  wherein the step of measuring the spectral reflectance of the sample includes using a measuring means configured to receive light of spectral reflectance from the sample, separate said light into spectrum, convert the intensity of the spectrum into digital counts, and output digital counts to said computer. 
   
   
       18 . The method according to  claim 13 , wherein said measuring means is selected from the group consisting of a spectrometer, spectrophotometer, spectral imaging system, spectral graphic system and spectroradiometer. 
   
   
       19 . The method according to  claim 13 , wherein said measuring means is a colorimeter with R, G and B detectors. 
   
   
       20 . The method according to  claim 13  wherein the step of calculating colorimetric data includes the steps of calculating the spectral reflectance of the sample and then using the spectral reflectance to calculate colorimetric data in a color space. 
   
   
       21 . The method according to  claim 20 , wherein the step of calculating the spectral reflectance of the sample is by the following equation: 
     
       
         
           
             
               R 
                
               
                 ( 
                 λ 
                 ) 
               
             
             = 
             
               
                 
                   S 
                    
                   
                     ( 
                     λ 
                     ) 
                   
                 
                 - 
                 
                   α 
                    
                   
                       
                   
                    
                   
                     
                       C 
                       2 
                     
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                    
                   
                     B 
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                 
                 - 
                 
                   κ 
                    
                   
                       
                   
                    
                   
                     IS 
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                 
               
               
                 
                   
                     
                       C 
                       1 
                     
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                    
                   
                     W 
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                 
                 - 
                 
                   
                     
                       C 
                       2 
                     
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                    
                   
                     B 
                      
                     
                       ( 
                       λ 
                       ) 
                     
                   
                 
               
             
           
         
       
       where is wavelength in nanometers, R(λ) is the spectral reflectance of the sample, S(λ) is a measured digital count of the sample, W(λ) is a digital count of white calibration, B(λ) is a digital count of black calibration, IS(λ) is a digital count of integrating sphere calibration parameter, α is a black calibration correction parameter, κ is an integrating sphere calibration correction parameter, C 1 (λ) is a white standard tile spectral correction parameter and C 2 (λ) is a black standard tile spectral correction parameter. 
     
   
   
       22 . The method according to  claim 13  wherein the step of determining the average color grade includes checking a look-up-table to find a color grade corresponding to the colorimetric data in a color space and assigning said color grade as the average color grade. 
   
   
       23 . The method according to  claim 13  wherein the step of determining the true color grade includes assigning a true color grade based upon the colorimetric data in a color space of the average color grade, the physical parameters, and mathematic analyses and algorithms including, but not limited to, matrix transfer, finite element analysis, numerical analysis, artificial neural network, optimization, fuzzy logic, regression, possibility, and statistics. 
   
   
       24 . The method according to  claim 20  or  claim 22  or  claim 23  wherein the color space is selected from the group consisting of a CIELAB color space including colorimetric data L*, a*, b*, C* ab  and h ab , a CIELUV color space including colorimetric data L*, u*, v*, Suv and huv, and a CIE(x, y)color space including colorimetric data x, y and Y.