A method for detecting the glossiness of freshwater pearls based on double-illumination collaborative imaging

Abstract

The application provides a detection method for freshwater pearl glossiness based on double-illumination collaborative imaging, relates to the technical field of pearl quality detection, and discloses a double-illumination mode collaborative design and protection: through the combination of a ring light source and a surface light source, three core components of high light intensity, high light definition, and volume scattering or haze of pearl glossiness are accurately separated and quantified, and the problem of single index in the prior art is solved; the ring light source is used to detect high light intensity and definition, the surface light source is used to detect volume scattering or haze, the distance of the surface light source is greater than the distance of the ring light source, an exclusive quantification method is formed, based on the physical mechanism of positive contribution of high light and negative contribution of volume scattering, a 0-1 normalized comprehensive gloss index (PLI) is constructed, the glossiness grade is intuitively divided, the weight can be optimized through data regression, the scientificity and practicability are considered, the detection is performed every 15° of the pearl, and after the detection, the PLI mean ±PLI std is output, the stability of multi-directional detection is ensured, and the problem of poor repeatability in the prior art is solved.

Description

Technical Field

[0001] This application relates to the field of pearl quality testing technology, and more specifically, to a method for detecting the luster of freshwater pearls based on dual-illumination synergistic imaging. Background Technology

[0002] Pearl luster is a core indicator for evaluating pearl quality, directly determining its commercial value and grading. However, traditional methods of pearl luster testing rely heavily on subjective sensory evaluation, which is influenced by the operator's own circumstances and environmental factors. This results in low consistency of judgments, lack of specific quantitative representation, and insufficient scientific explanation, making it impossible to establish a connection between the evaluation results and the underlying physical and optical mechanisms of luster.

[0003] To overcome the above-mentioned shortcomings, existing technology 1 (Chinese patent publication number CN112288722A, publication date 2021-01-29) proposes a method for testing pearl luster. The method includes: first, acquiring images of the pearl surface using a data acquisition device; second, preprocessing the acquired images; third, performing multi-threshold binarization on the images processed in the second step; fourth, performing particle statistics on the multiple binarized images obtained in the third step to generate a multi-element count array; fifth, calculating the mean and standard deviation of the count array; sixth, rotating the pearl and performing m repeated measurements to generate m means and m standard deviations; seventh, calculating the mean and standard deviation again for the m means to obtain a and b; and calculating the mean and standard deviation again for the m standard deviations. The beneficial effects of this invention are: it can simply and effectively identify the grade of pearl luster, establish a more objective digital standard method for detecting pearl luster, reduce the influence of subjective sensory bias, and efficiently classify and grade pearl luster.

[0004] Prior art 2 (Chinese patent CN221714980U, published on 2024-09-17) discloses a pearl grading device based on luster, relating to the field of pearl processing technology. It includes a loading seat and a storage seat. A turntable is rotatably mounted on the top of the loading seat, and a feeding mechanism is provided on the turntable. A sorting pre-set slot is formed on the loading seat and inside the feeding mechanism. Multiple sorting mechanisms are arranged on the sorting pre-set slot. A central platform is fixedly mounted on the loading seat and inside the sorting pre-set slot. A luster detector is fixedly mounted on the top of the central platform, and multiple connecting components are arranged on the central platform. Pearls are moved to the inside of the sorting pre-set slot by the turntable and enter the sorting mechanism for sorting. The connecting mechanism transports the pearls to the storage seat during sorting, thereby achieving fast and accurate automatic classification and screening of pearls, improving the pearl sorting efficiency.

[0005] While existing mass-produced technologies attempt to detect pearl luster using optical instruments, they still suffer from four major limitations: some schemes focus only on a single luster indicator, such as high light reflectance intensity, ignoring core luster components such as high light clarity and volume scattering, leading to a one-sided evaluation; some schemes fail to fix key instrument parameters, resulting in poor repeatability of results under different testing scenarios; some schemes do not establish a unified comprehensive evaluation index, failing to intuitively reflect the overall luster level of pearls; and most schemes do not clearly define the correspondence between quantitative indicators and physical optical mechanisms, resulting in results lacking scientific explanatory power. Summary of the Invention

[0006] This application provides a method for detecting the luster of freshwater pearls based on dual-illumination collaborative imaging, which can realize standardized quantitative detection of pearl luster, clarify the relationship between quantitative indicators and optical physical mechanisms, and construct a unified detection standard and comprehensive evaluation index system.

[0007] In a first aspect, this application provides a method for detecting the luster of freshwater pearls based on dual-illumination co-imaging, the method comprising the following steps:

[0008] S1. Invention Objectives: Based on the physical principles of pearly luster and industry testing needs, this invention aims to achieve three core objectives. S2. Instruments and Fixed Parameters: The instruments include an integrated luminance and colorimetry camera, an electric rotating stage, spot metering light sources, high-brightness light sources, medium-brightness light sources, low-brightness light sources, a ring LED light source, and a matte black velvet background. S3. Detection of volume scattering or haze and gloss uniformity indicators through a dual-illumination collaborative mode. S4. Exposure and Quality Control Standards. S5. Calculation Method for Gloss Quantification Indicators: Indicator values ​​include high-brightness intensity, high-brightness clarity, and volume scattering or haze. S6. Comprehensive Gloss Index Calculation and Grading: This includes the index calculation logic and gloss grading standards. S7. Repeatability Assurance Mechanism.

[0009] In this embodiment, the core objective of the invention objective S1 includes:

[0010] S1-1, Accuracy and Repeatability Targets.

[0011] S1-2, Scientific and Comparable Objectives.

[0012] S1-3, Practicality and Economy Objectives.

[0013] In this embodiment, the main function of S1-1 is to establish a standardized quantitative system to ensure that the standard deviation of the detection results is ≤0.02, so as to achieve consistent and repeatable results under different operators and different detection scenarios. The main function of S1-2 is to clarify the correspondence between each quantitative indicator and the optical physical mechanism, construct a unified detection standard and comprehensive evaluation index, and solve the pain points of subjective and incomparable traditional detection. S1-3, through the multiple imaging scheme, overcomes the problem of synchronous acquisition without increasing hardware costs and ensuring system stability, and takes into account both detection accuracy and industrial scenario adaptability efficiency, providing a precise, efficient and scalable technical solution for pearl quality grading.

[0014] In this embodiment, the dual illumination coordination mode in S3 includes a highlight detection mode and a diffuse detection mode, wherein the highlight detection mode is mode A and the diffuse detection mode is mode B.

[0015] In this embodiment, mode A uses a ring light source, with the light source and lens arranged nearly coaxially (coaxiality deviation ≤ ±5°). The light source brightness is set based on the core principle of "saturated pixels within ROI = 0". If saturated pixels appear, the exposure time or light source brightness needs to be adjusted. This mode is used to accurately detect highlight intensity and highlight clarity indicators.

[0016] In this embodiment, mode B uses a surface light source with a diffuser plate, achieving a light transmittance uniformity of ≥95%. The distance between the surface light source and the pearl sample is ≥ the distance between the ring light source and the sample. This mode is used to accurately detect volume scattering or haze and gloss uniformity indicators.

[0017] In this embodiment, the high light intensity value is derived from the fact that high light intensity reflects the specular reflectivity of the pearl surface. The mean value calculation can reduce the influence of random noise. The average brightness data of 24 point metering light sources are extracted from mode A, and the mean value of the average brightness of the 24 point metering light sources is used for calculation.

[0018] 8. The method for detecting the luster of freshwater pearls based on dual illumination co-imaging as described in claim 7, characterized in that the ratio of the high-brightness sharpness value to the average brightness can normalize the sharpness feature because the standard deviation reflects the degree of brightness dispersion, thus eliminating the influence of the absolute value of brightness. The standard deviation and average brightness data of 24 point metering light sources are extracted from mode A, and the mean of the ratio of the standard deviation and average brightness of the point metering light sources is used.

[0019] In this embodiment, the volume scattering or haze value is extracted from Mode B and calculated using the median of the average brightness of the spot metering light source in the non-high-brightness area. The higher the volume scattering or haze value, the stronger the volume scattering and the heavier the haze inside the pearl; the lower the volume scattering or haze value, the better the transparency of the pearl.

[0020] In this embodiment, the gloss level classification standard is as follows:

[0021] High gloss grade: Overall gloss index > 0.7;

[0022] Medium gloss level: 0.4 ≤ Overall gloss index ≤ 0.7;

[0023] Low gloss level: Overall gloss index < 0.4.

[0024] The technical solutions provided by the embodiments disclosed in this application have the following beneficial effects:

[0025] 1. Dual-lighting mode collaborative design and protection: By combining ring light source and surface light source, the three core components of pearly luster—high light intensity, high light clarity, and volume scattering or fogging—are accurately separated and quantified, solving the problem of single indicators in existing solutions. Its innovation lies in: using ring light source to detect high light intensity and clarity, and surface light source to detect volume scattering or fogging, and clearly defining that the distance of surface light source is ≥ the distance of ring light source, forming a unique quantification method.

[0026] 2. PLI Index Construction Logic and Protection: Based on the physical mechanism of positive contribution from specular highlights and negative contribution from volume scattering, a 0-1 normalized comprehensive gloss index (PLI) is constructed to achieve intuitive classification of gloss levels. The weights can be optimized through data regression, taking into account both scientific validity and practicality. Its innovation lies in the fact that after normalizing specular highlights (G), specular highlights (S), and volume scattering or haze (H) to 0-1, PLI is calculated as PLI = 0.45 × G + 0.45 × (1-S) - 0.1 × H, and high, medium, and low gloss levels are classified based on PLI.

[0027] 3. Repeatability assurance design and protection: Detection is performed every 15° rotation of the pearl, and the result is output via PLI. mean ±PLI std This ensures the stability of multi-directional detection and solves the problem of poor repeatability in existing solutions. Its innovation lies in the formation of a dedicated repeatability assurance method, which improves detection reliability through angle marking and multi-directional data integration.

[0028] Therefore, this application demonstrates that the luster of freshwater pearls can be detected. First, by detecting various data of freshwater pearls, a standardized quantitative system is established to ensure the accuracy of the test results. A comprehensive luster index integrating multiple indicators is constructed to achieve an intuitive classification of pearl luster grades, thereby improving the practicality and industrial adaptability of the testing method.

[0029] In summary, the technical solution adopted in this application can achieve the detection of the luster of freshwater pearls. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are only for this embodiment of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a flowchart of a method for detecting the luster of freshwater pearls based on dual-illumination co-imaging, as provided in this application.

[0032] Figure 2 It is based on the brightness intensity distribution curve of the high-gloss pearl provided in this application;

[0033] Figure 3 It is based on the brightness intensity distribution curve of medium-luster pearl provided in this application;

[0034] Figure 4 It is based on the brightness intensity distribution curve of the low-luster pearl provided in this application;

[0035] Figure 5 This is based on the specific objectives of the invention in this application. Detailed Implementation

[0036] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0037] This application provides a method for detecting the luster of freshwater pearls based on dual-illumination co-imaging. Its core is to construct a scientific, objective and repeatable evaluation system for pearl luster by combining dual-illumination co-imaging technology with standardized instrument parameter control and multi-dimensional luster index quantification.

[0038] Example 1: To better understand the above technical solution, the following will provide a detailed description of the technical solution in conjunction with the accompanying drawings and specific implementation methods. (Refer to...) Figure 1 As shown in the figure, this is an exemplary flowchart of a method for detecting the luster of freshwater pearls based on dual-illumination co-imaging according to this embodiment of the present application. The method for detecting the luster of freshwater pearls based on dual-illumination co-imaging includes the following steps:

[0039] The method for detecting the luster of freshwater pearls includes the following steps:

[0040] S1. Invention Objectives: Based on the physical principles of pearly luster and industry testing needs, this invention aims to achieve three core objectives. S2. Instruments and Fixed Parameters: The instruments include an integrated luminance and colorimetry camera, an electric rotating stage, spot metering light sources, high-brightness light sources, medium-brightness light sources, low-brightness light sources, a ring LED light source, and a matte black velvet background. S3. Detection of volume scattering or haze and gloss uniformity indicators through a dual-illumination collaborative mode. S4. Exposure and Quality Control Standards. S5. Calculation Method for Gloss Quantification Indicators: Indicator values ​​include high-brightness intensity, high-brightness clarity, and volume scattering or haze. S6. Comprehensive Gloss Index Calculation and Grading: This includes the index calculation logic and gloss grading standards. S7. Repeatability Assurance Mechanism.

[0041] The core objectives of the invention described in S1 include: S1-1, accuracy and repeatability objectives; S1-2, scientific validity and comparability objectives; and S1-3, practicality and economy objectives.

[0042] The main function of S1-1 is to establish a standardized quantitative system to ensure that the standard deviation of the test results is ≤0.02, and to achieve consistent and repeatable results under different operators and different test scenarios. The main function of S1-2 is to clarify the correspondence between each quantitative indicator and the optical physical mechanism, construct a unified test standard and comprehensive evaluation index, and solve the pain points of subjective and incomparable traditional test. S1-3, through a multiple imaging scheme, overcomes the problem of synchronous acquisition without increasing hardware costs and ensuring system stability, and balances test accuracy with industrial scenario adaptability, providing a precise, efficient and scalable technical solution for pearl quality grading.

[0043] It should be noted that the following parameters must be strictly maintained throughout the entire testing process and must not be changed:

[0044] Camera model: LumiCam1300, integrated brightness and colorimetry camera, spectral response range 400-700nm; lens specification: Nikon 50mm; aperture parameter: f / 2.8; working distance: 0.5m, the vertical distance from the camera lens to the center of the pearl sample.

[0045] Darkroom and lighting geometry design, sample placement specifications: Pearl samples are placed on non-reflective supports to avoid interference from support reflections on the test results; the test background is made of matte black velvet cloth with a reflectivity ≤0.5% and a size of not less than 50cm×50cm to ensure that there is no ambient light reflection interference around the sample, in order to eliminate stray light interference on gloss detection and ensure signal purity.

[0046] In this embodiment, a dual-lighting collaborative mode is required for various data detections. Both modes must be executed simultaneously during the detection process; neither can be omitted.

[0047] Mode A, Highlight Detection Mode: Uses a ring light source, with the light source and lens arranged nearly coaxially (coaxiality deviation ≤ ±5°). The light source brightness setting is based on the core principle that the number of saturated pixels within the ROI = 0. If saturated pixels appear, it is necessary to adjust the exposure time or the light source brightness. This mode is used to accurately detect highlight intensity and highlight clarity indicators.

[0048] Mode B Diffuse Illumination Detection Mode: Uses a surface light source with a diffuser plate, with a light transmittance uniformity ≥95%. The distance between the surface light source and the pearl sample is ≥ the distance between the ring light source and the sample. This mode is used to accurately detect indicators such as volume scattering, haze, and gloss uniformity.

[0049] For exposure and quality control standards, the CIE1931Y channel, i.e. the brightness channel, should be used first for exposure adjustment, with the initial exposure time set to 10ms. If the brightness of the highlight area is ≥90% of the sensor saturation value, the exposure time should be reduced in 1ms increments to avoid signal saturation.

[0050] Qualification criteria: ① Maximum brightness value (Max cd / m²) within the ROI < sensor saturation value (read in real time by camera software); ② The highlight area is a single main connected region, judged by image connected region analysis algorithm. If multiple bright spots appear, the sample surface must be cleaned with a lint-free cloth soaked in anhydrous ethanol and the image must be retaken.

[0051] It should be noted that in this embodiment, the spot metering light source layout process is as follows: the pearl sample is placed on an electric rotary table with an accuracy of ±0.5°. Every 15° of rotation, the ring light source image and the area light source image are captured simultaneously, for a total of 24 sets of images, covering the entire 360° angle, to avoid timing errors caused by separate time-sharing acquisition; in each image, in the ROI (Region of Interest), a circular area with the pearl outline contracted inward by 5% is set, and the point with the highest brightness within the area is automatically identified as the spot metering light source detection point at that angle. The 24 detection points evenly cover the three areas: the highlight center, the highlight edge, and the non-highlight background area;

[0052] Output parameters: comprehensively characterize the brightness distribution features of the detection points, providing basic data for subsequent index calculations. The output parameters for each point are the average brightness (Avg, unit cd / m²) and standard deviation (Std). Dev (Unit: cd / m²), minimum value (Min, unit: cd / m²), maximum value (Max, unit: cd / m²), absolute value of brightness (unit: cd / m²).

[0053] It should be noted that in this embodiment, the method for calculating the gloss quantification index is as follows:

[0054] High light intensity (G):

[0055] Since high light intensity reflects the specular reflectivity of the pearl surface, mean value calculation can reduce the influence of random noise. The average brightness data of 24 point metering sources are extracted from the ring light source image (Mode A), and the mean brightness of these 24 point metering sources is used for calculation, as shown in the following formula:

[0056] G mean =(Avg1+Avg2+...+Avg 24 ) / twenty four

[0057] Among them, Avg1~Avg 24 The average brightness (unit: cd / m²) of the light source was measured at 24 points, and the average value was taken to avoid interference from outliers at single points.

[0058] Highlight sharpness (S):

[0059] Because the standard deviation reflects the degree of brightness dispersion, its ratio to the average brightness can normalize the sharpness feature and eliminate the influence of the absolute value of brightness. The standard deviation (StdDev) and average brightness (Avg) data of 24 point metering sources are extracted from the ring light source image (Mode A). The calculation is based on the mean of the ratios of the standard deviation and the average brightness of the point metering sources, as shown in the following formula:

[0060] S=(StdDev1 / Avg1+StdDev2 / Avg2+...+StdDev 24 / Avg 24 ) / twenty four

[0061] The smaller the S value, the more concentrated the brightness distribution in the highlight area of ​​the pearl, and the sharper the highlight; the larger the S value, the more obvious the brightness diffusion in the highlight area, and the more blurred the highlight.

[0062] Volume scattering or fog perception (H):

[0063] Data is extracted from the surface light source image (Mode B) and calculated using the "median of the average brightness of the spot metering light source in the non-highlight area". The higher the H value, the stronger the internal volume scattering of the pearl and the heavier the fogging effect; the lower the H value, the better the transparency of the pearl.

[0064] Comprehensive Gloss Index (PLI) Calculation and Grading:

[0065] Exponent calculation logic:

[0066] First, the three indicators G (highlight intensity), S (highlight sharpness), and H (volume scattering / haze) are normalized to 0-1: a linear normalization method is used for G. mean (Highlight intensity), S (highlight clarity), and H (volume scattering / haze) are normalized respectively:

[0067] G norm=(G mean -G min ) / (G max -G min ), where G min =500cd / m², G max =4000cd / m²;

[0068] S norm =(SS min ) / (S max -S min ), where S min =0.05, S max =0.3;

[0069] H norm =(HH min ) / (H max -H min ), where H min =100cd / m², H max =1500cd / m²;

[0070] Fusion Calculation: PLI is calculated using the following weighting formula:

[0071] PLI=0.45×G norm +0.45×(1-S norm )-0.1×H norm

[0072] Weighting logic: Highlight intensity and highlight sharpness (in 1-S) norm The higher the clarity, the greater the contribution value (which aligns with the core characteristics of high-quality pearl luster); volume scattering / haze is a negative correction indicator (heavy haze reduces luster quality), and the weights can be optimized and adjusted through regression analysis using larger-scale sample data.

[0073] Gloss grade classification standard:

[0074] High gloss level: PLI > 0.7;

[0075] Medium gloss grade: 0.4≤PLI≤0.7;

[0076] Low gloss rating: PLI < 0.4.

[0077] It should be noted that the repeatability assurance mechanism involves taking photos of each individual pearl sample at 15° intervals and calculating the average PLI value from 24 angles. mean ) and standard deviation (PLI) std The final output is PLI mean ±PLI std PLIstd ≤0.02, to ensure the stability and reliability of the test results.

[0078] In practice:

[0079] First, experimental preparation:

[0080] Three freshwater pearls with a diameter of 6-7mm were selected and pre-labeled as A (high gloss), B (medium gloss), and C (low gloss). A LumiCam1300 was used with an aperture of f / 2.8, a working distance of 0.5m, a ring LED light source, a surface light source (frosted acrylic diffuser), an electric rotating stage (accuracy ±1°), and a matte black velvet background. All testing equipment was set up.

[0081] Experimental procedure:

[0082] Darkroom environment calibration: Turn off ambient light and ensure background reflectivity ≤ 0.5%;

[0083] Light source alignment: Calibrate the coaxiality of the ring light source and the lens using an optical alignment instrument, with a deviation ≤ ±5°; measure and fix the distance between the surface light source and the sample, ensuring that it is ≥ the distance between the ring light source and the sample (difference = 5cm).

[0084] Synchronous imaging acquisition: The pearl is placed on an electric rotating stage, and one ring light source image (mode A) and one area light source image (mode B) are captured simultaneously every 15° of rotation, for a total of 24 sets of images;

[0085] Data extraction: Based on the point metering light source layout rules, parameters such as Avg and StdDev of 24 detection points were extracted, and G was calculated. mean S, H;

[0086] Exponent calculation: for G mean Normalize S and H to 0-1, substitute them into the PLI formula to calculate the PLI values ​​for 24 angles, and finally output the PLI. mean ±PLI std .

[0087] Experimental results, such as Figures 2-4 As shown.

[0088] like Figure 2 As shown, Sample A (highlight): PLI mean ≈0.75, PLI std ≤0.02, classified as high gloss level;

[0089] like Figure 3 As shown, Sample B (medium brightness): PLI mean ≈0.55, PLI std ≤0.02, classified as medium gloss level;

[0090] like Figure 4 As shown, sample C (low light): PLI mean ≈0.36, PLI std If the value is ≤0.02, it is classified as a low gloss level.

[0091] In other gemstone testing, this method can be extended to the quality testing of gemstones with strong anisotropic luster, such as saltwater pearls, opals, and obsidian.

[0092] Industrial surface inspection: It can be used for online quantitative quality inspection of coating gloss uniformity and "haze" on automotive paint, high-gloss plastic parts, and 3C product casings.

[0093] In the field of cultural relic appraisal: it is used for the objective assessment of the weathering degree of glazed pottery and lacquerware surfaces.

[0094] In summary, the technical solution adopted in this application can achieve the detection of the luster of freshwater pearls.

[0095] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0096] Those skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, including read-only memory (ROM), random access memory (RAM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), one-time programmable read-only memory (OTPROM), electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM) or other optical disc storage, disk storage, magnetic tape storage, or any other computer-readable medium capable of carrying or storing data.

[0097] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

Claims

1. A method for detecting the luster of freshwater pearls based on dual-illumination co-imaging, characterized in that, The method for detecting the luster of freshwater pearls includes the following steps: S1. Invention Objectives: Based on the physical principles of pearly luster and the needs of industry testing, three core objectives are to be achieved. S2. Instruments and fixed parameters: The instruments include: a luminance and chromaticity integrated camera, an electric rotary stage and spot metering light source, a high light source, a medium light source, a low light source, a ring LED light source and a matte black velvet background. S3. Detect volume scattering or fog sensation and gloss uniformity indicators through dual illumination collaborative mode; S4, Exposure and Quality Control Standards; S5. Gloss quantification index calculation method, the index values ​​include: high gloss intensity, high gloss clarity, volume scattering or haze. S6. Comprehensive gloss index calculation and grading, including index calculation logic and gloss grading standards; S7, Repetitiveness Guarantee Mechanism.

2. The method for detecting the luster of freshwater pearls based on dual-illumination co-imaging as described in claim 1, characterized in that, The core objectives of the invention described in S1 include: S1-1, Accuracy and Repeatability Targets; S1-2, Scientific Rigor and Comparability Objectives; S1-3, Practicality and Economy Objectives.

3. The method for detecting the luster of freshwater pearls based on dual-illumination co-imaging as described in claim 2, characterized in that, The main function of S1-1 is to establish a standardized quantitative system to ensure that the standard deviation of the test results is ≤0.02, and to achieve consistent and repeatable results under different operators and different test scenarios. The main function of S1-2 is to clarify the correspondence between each quantitative indicator and the optical physical mechanism, construct a unified test standard and comprehensive evaluation index, and solve the pain points of subjective and incomparable traditional test. S1-3, through a multiple imaging scheme, overcomes the problem of synchronous acquisition without increasing hardware costs and ensuring system stability, and balances test accuracy with industrial scenario adaptability, providing a precise, efficient and scalable technical solution for pearl quality grading.

4. The method for detecting the luster of freshwater pearls based on dual-illumination co-imaging as described in claim 3, characterized in that, The dual illumination co-processing mode in S3 includes a highlight detection mode and a diffuse detection mode. The highlight detection mode is mode A, and the diffuse detection mode is mode B.

5. The method for detecting the luster of freshwater pearls based on dual-illumination co-imaging as described in claim 4, characterized in that, Mode A uses a ring light source, with the light source and lens arranged nearly coaxially (coaxiality deviation ≤ ±5°). The light source brightness is set based on the core principle of "saturated pixels within the ROI = 0". If saturated pixels appear, the exposure time or light source brightness needs to be reduced. This mode is used to accurately detect highlight intensity and highlight clarity indicators.

6. The method for detecting the luster of freshwater pearls based on dual-illumination co-imaging as described in claim 5, characterized in that, Mode B uses a surface light source with a diffuser plate, achieving a light transmittance uniformity of ≥95%. The distance between the surface light source and the pearl sample is ≥ the distance between the ring light source and the sample. This mode is used to accurately detect volume scattering or haze and gloss uniformity indicators.

7. The method for detecting the luster of freshwater pearls based on dual-illumination co-imaging as described in claim 6, characterized in that, The high light intensity value is derived from the fact that high light intensity reflects the specular reflectivity of the pearl surface. The mean value calculation can reduce the influence of random noise. The average brightness data of 24 point photometers are extracted from mode A, and the mean value of the average brightness of the 24 point photometers is used for calculation.

8. The method for detecting the luster of freshwater pearls based on dual-illumination co-imaging as described in claim 7, characterized in that, The high-brightness sharpness value is normalized by the ratio of the standard deviation, which reflects the degree of brightness dispersion, to the average brightness, thus eliminating the influence of the absolute brightness value. The standard deviation and average brightness data of 24 spot metering sources are extracted from mode A, and the mean of the ratio of the standard deviation and average brightness of the spot metering sources is used.

9. The method for detecting the luster of freshwater pearls based on dual-illumination co-imaging as described in claim 8, characterized in that, The volume scattering or haze value is extracted from Mode B and calculated using the median of the average brightness of the spot metering light source in the non-high-gloss area. The higher the volume scattering or haze value, the stronger the volume scattering and the heavier the haze inside the pearl; the lower the volume scattering or haze value, the better the transparency of the pearl.

10. The method for detecting the luster of freshwater pearls based on dual-illumination co-imaging as described in claim 9, characterized in that, The gloss level classification standard is as follows: High gloss grade: Overall gloss index > 0.7; Medium gloss level: 0.4 ≤ Overall gloss index ≤ 0.7; Low gloss level: Overall gloss index < 0.4.

Images