Method for grading colors of white blanks by using colorimetric parameters

Abstract

The invention discloses a method for carrying out color grading on a white blank by using colorimetric parameters, and belongs to the field of diamond blank color grading. Comprising the following steps: S1, placing a diamond blank as a to-be-measured sample on an objective table of spectral measurement equipment; s2, spectral measurement equipment is started, and light rays with the wavelength of lambda emitted by a light source enter the diamond crystal and then enter a spectrograph through an optical fiber; s3, converting the received optical signal into an electric signal by the spectrograph to form spectral data R (lambda); and S4, reading spectral data R (lambda), converting the spectral data into L * a * b * and L * c * h data in a D65, 2-degree illumination environment, and then performing color grading. The accuracy of color grading can be improved, and the efficiency of color grading can also be improved.

Description

Technical Field

[0001] The invention belongs to the field of diamond blank color grading, and in particular relates to a method for color grading of white blanks using colorimetric parameters. Background Art

[0002] Artificially grown gem-quality diamonds have very high color requirements. During the cultivation process, the growth environment is controlled, which in turn affects the color quality of the finished diamond rough. Cultivated colorless diamonds are required to match the color of natural diamonds, with the whiter the better. Therefore, color grading of diamond roughs is necessary. The current grading method is based on the national standard GB / T 16554-2017, which uses a color classification scale of DZ (white to yellow). Grading is performed visually using selected or calibrated master stones or rough diamonds, relying heavily on human perception and experience. Because the grades are divided into several levels within a color range that is difficult for the human eye to distinguish, visual grading places high demands on both the human eye and the reference sample. Currently, color grading using selected or calibrated master stones or rough diamonds is generally performed, relying heavily on human perception and experience, which can lead to a wide and unstable color range and low grading efficiency.

[0003] Furthermore, compared with the mature grading system for rough stones, the color grading of rough stones is prone to unstable final results due to factors such as the appearance of the rough stones to be graded, the thickness of the rough stones, and the color of the rough stones that are not the final finished products. Its non-quantifiable nature also means that this grading cannot be assisted by machines, affecting production efficiency.

[0004] Gem-grade diamonds grown by CVD are generally graded before color treatment (high-temperature and high-pressure treatment of the raw rough diamonds to whiten their color), which further increases the difficulty and uncertainty of color grading. Summary of the Invention

[0005] To address the above-mentioned problems, the present invention aims to provide a method for color grading white blanks using colorimetric parameters, scientifically quantifying the subjective color perceived by the naked eye. Based on the CIE L*a*b* or L*c*h* color system, the method simulates the human visual system, converts sample transmittance data into color data, selects the parameters that have the greatest impact on color grading, and compares them with the parameters of a standard sample to perform color grading. This method can improve both the accuracy and efficiency of color grading.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] The present invention provides a method for color grading of white blanks using colorimetric parameters, comprising the following steps:

[0008] S1: Place the diamond blank as the sample to be tested on the stage of the spectrum measurement equipment;

[0009] S2: Turn on the spectrum measurement device, and the light source emits light with a wavelength of λ into the diamond crystal, and then enters the spectrometer through the optical fiber;

[0010] S3: The spectrometer converts the received optical signal into an electrical signal, forming spectral data R(λ) which is displayed on the spectrum analysis software;

[0011] S4: Read the spectral data R(λ), and use the conversion method in the CIE color system to convert the spectral data into L*a*b* and L*c*h data under the D65, 2° lighting environment. Then, quantify the color grade of the original blank based on the L* and c* values.

[0012] Furthermore, in step S2, the light source is a halogen lamp or a xenon lamp. The light from the light source enters the collimator through the optical fiber to form a light spot with a diameter of 5 mm. The light spot is incident on the sample to be tested. The integrating sphere under the sample to be tested receives and evenly diffusely reflects the light spot, and then enters the spectrometer through the optical fiber.

[0013] Furthermore, the spectral data R(λ) in step S4 is one of the transmittance, absorptivity, and reflectivity of the spectrum, and needs to be aligned with the wavelength of the light source and the observer data during detection.

[0014] Furthermore, step S4 includes:

[0015] S41: reading the spectrum data R(λ) of the sample to be tested;

[0016] S42: performing spectrum thickness normalization processing on the spectrum data R(λ);

[0017] S43: Read data S(λ), xˉ(λ), yˉ(λ), and zˉ(λ) from the CIE data table and calculate the values of the spectrum conversion color parameters X, Y, and Z;

[0018] S44: Calculate the L*a*b* value of the CIE L*a*b* color system by spectrally converting the color parameters X, Y, and Z;

[0019] S45: Calculate the L*c*h* value of the CIE L*a*b* color system;

[0020] S46: Calculate the value of whiteness A by the formula A=c*(100-L*), and then perform color grading of the white blank according to the whiteness A.

[0021] Furthermore, in step S42, when the difference between the thickness of the sample to be tested and the thickness of the standard sample is ≥1.0 mm, the spectrum data R(λ) is subjected to spectrum thickness normalization processing, and then the process proceeds to S43; when the difference between the thickness of the sample to be tested and the thickness of the standard sample is <1.0 mm, the process proceeds directly to S43;

[0022] Furthermore, in step S42, since the absorbance is proportional to the thickness of the sample to be tested, the relationship between absorbance and transmittance is: Therefore, the normalized formula of the corresponding wavelength spectrum data R(λ) of each sample is: T 归一 (λ) is the normalized spectral data R(λ), and T(λ) is the read spectral data R(λ).

[0023] Furthermore, in step S43, the calculation formulas of the color parameters X, Y, and Z are respectively:

[0024]

[0025] Among them, k≈0.00944;

[0026] S(λ) is the relative spectral power distribution of the D65 illuminant (normalized to Y = 100), read from the CIE 15:2004 table or the ASTM E308-17 appendix;

[0027] is the color matching function X component of the CIE 19312° standard observer, is the Y component of the color matching function (i.e., luminosity function) of the CIE 19312° standard observer; is the Z component of the color matching function of the CIE 19312° standard observer. The above three data are read through CIE 15:2004 Table 1 or ASTM E308-17 Table 5;

[0028] Furthermore, in step S44, the calculation formula of the L*a*b* value is:

[0029] L * =116·f(Y / Y n )-16

[0030] a * =500·[f(X / X n )-f(Y / Y n )]

[0031] b * =200·[f(Y / Y n )-f(Z / Z n )]

[0032] in,

[0033]

[0034] δ=6 / 29, solves the nonlinear perception problem in low-brightness areas;

[0035] Reference white point: Take the tristimulus values Xn, Yn, and Zn under the light source. For D65 light source, Xn=95.047, Yn=100, and Zn=108.883.

[0036] Furthermore, in step S45, L*c*h* is converted according to L*a*b*:

[0037] The L* values are the same.

[0038] Further, in step S46, whiteness A == c*(100-L*);

[0039] The color grading method for white blanks is:

[0040] When A F When A<0.636A F When it is level D, A∈[0.636A F , 0.773A F ), it is E grade; A∈[0.773A F , A F ) is F grade;

[0041] When A∈[A F , 1.818A F ), is GH level, where A=[A F , 1.364A F ), it is G level, A∈[1.364A F , 1.818A F ), it is H level;

[0042] When A∈[1.818A F , 20A F ), it is <H level;

[0043] Among them, A F The A value of the blank of standard sample F color.

[0044] ​The beneficial effects of the present invention are as follows: compared with the prior art, the present application scientifically quantifies the subjective color of the naked eye, simulates the human visual system based on the CIE L*a*b* or L*c*h* color system, converts sample transmittance data into color data, selects the parameters that have the greatest impact on color grading and compares them with the parameters of the standard sample, thereby performing color grading, thereby improving both the accuracy and efficiency of color grading; the method is simple to operate, easy to master, and can reduce human eye errors, and the color parameters of the color reference sample or grading boundary can be adjusted at any time to adapt to changes in market standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 4 is a flowchart of the method for color grading of white blanks in this embodiment.

[0046] Figure 2 Schematic diagram of the white blank color grading device in this embodiment.

[0047] Figure 3 : is the spectrum data diagram of the transmittance R(λ) of this embodiment.

[0048] Figure 4 Graph showing the calculation results of this embodiment.

[0049] Figure 5 is a data table of data S(λ).

[0050] Figure 6 It is a data table of xˉ(λ), yˉ(λ), and zˉ(λ). DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0052] To achieve the above object, the technical solution of the present invention is as follows:

[0053] See also Figure 1-4 This embodiment provides a method for color grading of white blanks using colorimetric parameters, such as Figure 1 As shown, the following steps are included:

[0054] S1: Figure 2 In the process, a diamond blank is placed on the stage of a spectrum measurement device as a sample to be measured;

[0055] S2: Turn on the spectrum measurement device, and the light source emits light with a wavelength of λ into the diamond crystal, and then enters the spectrometer through the optical fiber;

[0056] S3: Figure 3 In the spectrometer, the received light signal is converted into an electrical signal, forming the transmittance R(λ) which is displayed on the spectrum analysis software;

[0057] S4: Figure 4 In the process, the transmittance R(λ) is read and the conversion method in the CIE color system is used to convert the spectral data into L*a*b* and L*c*h data under the lighting environment of D65, 2°. The color grade of the original blank is then quantified based on the L* and c* values.

[0058] Furthermore, in step S2, the light source is a halogen lamp or a xenon lamp. The light from the light source enters the collimator through the optical fiber to form a light spot with a diameter of 5 mm. The light spot is incident on the sample to be tested. The integrating sphere under the sample to be tested receives and evenly diffusely reflects the light spot, and then enters the spectrometer through the optical fiber.

[0059] Furthermore, the transmittance R(λ) in step S4 needs to be aligned with the wavelength of the light source and the observer data during detection.

[0060] Furthermore, step S4 includes:

[0061] S41: Reading the transmittance R(λ) of the sample to be tested;

[0062] S42: performing spectral thickness normalization processing on the transmittance R(λ);

[0063] S43: See Figure 5-6 , read the data S(λ), xˉ(λ), yˉ(λ), zˉ(λ) through the CIE data table, and calculate the values of the spectrum conversion color parameters X, Y, Z;

[0064] S44: Calculate the L*a*b* value of the CIE L*a*b* color system by spectrally converting the color parameters X, Y, and Z;

[0065] S45: Calculate the L*c*h* value of the CIE L*a*b* color system;

[0066] S46: Calculate the value of whiteness A by the formula A=c*(100-L*), and then perform color grading of the white blank according to the whiteness A.

[0067] Furthermore, in step S42, when the difference between the thickness of the sample to be tested and the thickness of the standard sample is ≥1.0 mm, the transmittance R(λ) is subjected to spectral thickness normalization, and then the process proceeds to S43; when the difference between the thickness of the sample to be tested and the thickness of the standard sample is <1.0 mm, the process proceeds directly to S43;

[0068] Furthermore, in step S42, since the absorbance is proportional to the thickness of the sample to be tested, the relationship between absorbance and transmittance is: Therefore, the normalized formula for the corresponding wavelength transmittance R(λ) of each sample is: T 归一 (λ) is the normalized transmittance R(λ), and T(λ) is the read transmittance R(λ).

[0069] Furthermore, in step S43: Since the above-mentioned S(λ), xˉ(λ), yˉ(λ), and zˉ(λ) are all values at 5 nm intervals, actual integration cannot be performed. The continuous spectrum integral of the visible light band (380–780 nm) is approximated by discrete wavelength intervals. In accordance with CIE 15:2004 and ASTM E308-17 standards, 5 nm interval data points are used for summation to effectively balance calculation accuracy and practicality. The approximate calculation formulas for color parameters X, Y, and Z are designed as follows:

[0070]

[0071] Among them, k≈0.00944;

[0072] S(λ) is the relative spectral power distribution of the D65 light source (normalized to Y=100), see Figure 5 , read from CIE 15:2004 table or ASTM E308-17 appendix;

[0073] is the color matching function X component of the CIE 19312° standard observer, is the Y component of the color matching function (i.e., luminosity function) of the CIE 19312° standard observer; is the Z component of the color matching function for the CIE 19312° standard observer, see Figure 6 , the above three data are read through CIE 15:2004 Table 1 or ASTM E308-17 Table 5;

[0074] For example, if the transmittance of a material at a wavelength of λ = 500nm is R(500) = 0.8, then the contribution of this wavelength point when calculating X is:

[0075] X contribution = k*S(500)*0.8*xˉ(500)*5 = 0.00944*109.35*0.8*0.004900*5 = 0.0202. The total X value is the cumulative contribution of all wavelength points. Similarly, the Y and Z values can be obtained.

[0076] Furthermore, in step S44, the calculation formula of the L*a*b* value is:

[0077] L * =116·f(Y / Y n )-16

[0078] a * =500·[f(X / X n )-f(Y / Y n )]

[0079] b * =200·[f(Y / Y n )-f(Z / Z n )]

[0080] in,

[0081]

[0082] δ=6 / 29, solves the nonlinear perception problem in low-brightness areas;

[0083] Reference white point: Take the tristimulus values Xn, Yn, and Zn under the light source. For D65 light source, Xn=95.047, Yn=100, and Zn=108.883.

[0084] Furthermore, in step S45, L*c*h* is converted according to L*a*b*:

[0085] The L* values are the same.

[0086] Further, in step S46, whiteness A == c*(100-L*);

[0087] In this embodiment, through a large amount of data research, it was found that the c* value and L* value of the sample (two main parameters of CIE L*c*h) have a strong correlation with the actual color of the white blank. For samples of different thicknesses, the absorbance can be proportional to the thickness. The absorbance can be multiplied by the thickness coefficient (test sample h to be tested / standard sample thickness h standard) and then converted into a transmittance spectrum to obtain a normalized spectrum value and then a normalized color parameter (normalization is not required when the height difference between the thickness and the standard sample is less than 1.0mm). The sample color can then be distinguished by the c* (saturation) value or the whiteness A value (A value = c* (100-L*)). The white blank can be distinguished between DEF, GH, and <H with an accuracy of >95%, and a subdivision reference classification of D-<H can be given according to the D value range. The classification method is:

[0088] When A F When A<0.636A F When it is level D, A∈[0.636A F , 0.773A F ), it is E grade; A∈[0.773A F , A F ​) is F grade;

[0089] When A∈[A F , 1.818A F ), is GH level, where A=[A F , 1.364A F ), it is G level, A∈[1.364A F , 1.818A F ), it is H level;

[0090] When A∈[1.818A F , 20A F ), it is <H level;

[0091] Among them, A F The A value of the blank of standard sample F color.

[0092] Among them, in the existing color grading system, grade D represents completely colorless; grade E belongs to the colorless level, but trace amounts of color can be detected; grade F belongs to the colorless level, and a small amount of color can be detected; grade G is close to colorless with a slight color; grade H is close to colorless with some color.

[0093] This embodiment scientifically quantifies the subjective color perception of the naked eye, simulating the human visual system based on the CIE L*a*b* or L*c*h* color system, converts sample transmittance data into color data, selects the parameters that have the greatest impact on color grading, and compares them with the parameters of standard samples to perform color grading. This method can improve both the accuracy and efficiency of color grading. This method is simple to operate and easy to master, reduces human visual error, and allows the color parameters of color reference samples or grading boundaries to be adjusted at any time to adapt to changes in market standards.

[0094] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for color grading of white blanks using colorimetric parameters, characterized in that: The following steps are involved: S1: Place the diamond blank as the sample to be tested on the stage of the spectrum measurement equipment; S2: Turn on the spectrum measurement equipment. The light source emits a continuous spectrum of light with a wavelength of λ, which enters the diamond crystal and then enters the spectrometer through the optical fiber. S3: The spectrometer converts the received optical signal into an electrical signal, forming spectral data R(λ) which is displayed on the spectrum analysis software; S4: Read the spectral data R(λ), and use the conversion method in the CIE color system to convert the spectral data R(λ) into L*a*b* and L*c*h data under the D65, 2° lighting environment. Then, quantify the color grade of the original blank based on the L* and c* values.

2. The method for color grading of white blanks using colorimetric parameters according to claim 1, wherein: In step S2, the light source is a halogen lamp or a xenon lamp with a wavelength λ ranging from 380nm to 780nm. The light from the light source enters the collimator through the optical fiber to form a light spot with a diameter of 5mm. The light spot is incident on the sample to be tested. The integrating sphere below the sample to be tested receives and evenly diffusely reflects the light spot, and then enters the spectrometer through the optical fiber.

3. The method for color grading of white blanks using colorimetric parameters according to claim 1, wherein: The spectrum data R(λ) in step S4 is one of the transmittance, absorptivity, and reflectivity of the spectrum.

4. The method for color grading of white blanks using colorimetric parameters according to claim 1, wherein: Step S4 includes: S41: reading the spectrum data R(λ) of the sample to be tested; S42: performing spectrum thickness normalization processing on the spectrum data R(λ); S43: Read data S(λ), xˉ(λ), yˉ(λ), and zˉ(λ) from the CIE data table and calculate the values of the spectrum conversion color parameters X, Y, and Z; S44: Calculate the L*a*b* value of the CIE L*a*b* color system by spectrally converting the color parameters X, Y, and Z; S45: Calculate the L*c*h* value of the CIE L*a*b* color system; S46: Calculate the value of whiteness A by the formula A=c*(100-L*), and then perform color grading of the white blank according to the whiteness A.

5. The method for color grading of white blanks using colorimetric parameters according to claim 4, wherein: In step S42, when the difference between the thickness of the sample to be tested and the thickness of the standard sample is ≥1.0 mm, the spectral data R(λ) is subjected to spectral thickness normalization processing, and then enters S43; when the difference between the thickness of the sample to be tested and the thickness of the standard sample is <1.0 mm, directly enter S43.

6. A method for color grading of white blanks using colorimetric parameters according to claim 5, characterized in that: In step S42, since the absorbance is proportional to the thickness of the sample to be tested, the relationship between absorbance and transmittance is: Therefore, the normalized formula of the corresponding wavelength spectrum data R(λ) of each sample is: T 归一 (λ) is the normalized spectral data R(λ), and T(λ) is the read spectral data R(λ).

7. The method for color grading of white blanks using colorimetric parameters according to claim 4, wherein: In step S43: the calculation formulas of color parameters X, Y, and Z are respectively: Among them, k≈0.00944; S(λ) is the relative spectral power distribution of the D65 illuminant (normalized to Y=100), read from the CIE 15:2004 table or the ASTM E308-17 appendix; is the X component of the color matching function for the CIE 1931 2° standard observer, is the Y component of the color matching function (i.e., luminosity function) of the CIE 193 1 2° standard observer; is the Z component of the color matching function for the CIE 1931 2° standard observer. The above data can be read using Table 1 of CIE 15:2004 or Table 5 of ASTM E308-17.

8. The method for color grading of white blanks using colorimetric parameters according to claim 7, wherein: In step S44, the calculation formula of the L*a*b* value is: L * =116·f(Y / Y n )-16 a * =500·[f(X / X n )-f(Y / Y n )] b * =200·[f(Y / Y n )-f(Z / Z n )] in, δ=6 / 29, solves the nonlinear perception problem in low-brightness areas; Reference white point: Take the tristimulus values Xn, Yn, and Zn under the light source. For D65 light source, Xn=95.047, Yn=100, and Zn=108.

883.

9. A method for color grading of white blanks using colorimetric parameters according to claim 8, characterized in that: In step S45, L*c*h* is converted according to L*a*b*: The L* values are the same.

10. The method for color grading of white blanks using colorimetric parameters according to claim 9, characterized in that: In step S46, whiteness A=c*(100-L*); The color grading method of white blanks by whiteness A is: When A F When A<0.636A F When it is level D, A∈[0.636A F , 0.773A F ), it is E grade; A∈[0.773A F , A F ) is F grade;​ When A∈[A F , 1.818A F ), is GH level, where A=[A F , 1.364A F ), it is G level, A∈[1.364A F , 1.818A F ), it is H level; When A∈[1.818A F , 20A F ), it is <H level; Wherein, AF is the A value of the blank of the standard sample F color.

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