Diamond screening method and apparatus based on characteristic spectra

Abstract

The feature spectrum-based diamond screening method of the present application utilizes the reflection of a diamond on an irradiation light source, acquires the image of the diamond to be measured under the irradiation of the light source filtered by a band-pass filter through a camera; uses a histogram equalization algorithm to improve the contrast of the image; uses a YOLO algorithm for image calibration according to the different brightness of different grades of diamonds in the image to determine the diamond grade. It uses narrow-band filtering technology, utilizes the transmission and reflection of diamonds, and combines the contrast properties of the image, so that the contrast of a specific type of diamond in a certain specific waveband reaches the highest, realizing high-precision rapid screening of diamonds. For different types of diamonds, only the band-pass filter needs to be replaced, the whole device is low in cost and simple in operation. The technology realizes the automatic screening of diamonds on the basis of simple operation, provides strong technical support for diamond production units and diamond identification units, and has strong practicality and wide applicability.

Description

Technical Field

[0001] This invention relates to a diamond screening device, and more specifically to a diamond screening method and device based on characteristic spectra. Background Technology

[0002] Diamonds, as an ideal optical and semiconductor material, have wide applications in industry and high-tech fields. With decreasing diamond supply and persistent demand, synthetic diamonds play a vital role as a substitute for natural diamonds, and the penetration rate of lab-grown diamonds is rapidly increasing.

[0003] In recent years, with the rapid development of diamond synthesis technology, a number of synthetic diamonds of varying quality have gradually entered the market, posing a significant challenge to gemological laboratories. Traditional identification techniques rely on visual judgment based on color, luster, and transparency, which is clearly insufficiently objective. To ensure more accurate identification and grading of synthetic diamonds, further testing using relevant instruments is necessary to provide a basis for judgment. Common testing instruments include microscopes, spectroscopes, ultraviolet fluorescence spectrometers, and infrared absorption spectrometers; however, most of these instruments are medium to large-sized scientific research instruments, resulting in slow screening speeds that cannot meet the efficiency requirements of production units.

[0004] Patent CN202110438435.4 discloses an "Identification Device for Distinguishing Natural Diamonds, Synthetic Diamonds, and Moissanite Based on Reflection Method." This scheme uses a test setup based on the reflection of diamonds to identify natural diamonds, moissanite, and synthetic diamonds through the absorption spectra of different types at different wavelengths. However, this device uses a fiber optic spectrometer, requires additional control circuitry for the processor, and can only identify diamond types, not perform batch testing and screening.

[0005] Patent CN201821263163.9 discloses a "rapid batch screening and testing instrument for diamonds." This solution uses an X-ray source and an ultraviolet source, and utilizes X-ray imaging technology to achieve batch testing of diamonds. However, this instrument requires the construction, design, and use of a high-voltage power supply to start and control the X-ray source, making operation complex and unsuitable for low-cost, rapid, and efficient screening, thus limiting the device's application scope.

[0006] In their article "A Brief Description of the Identification of HPHT and CVD-grown Diamonds and the Latest Market Analysis" published in the journal Gem and Gemology (Chinese and English) [J]. 2021, 23(6):40-50, Yuan Zhizhong et al. listed and explained the identification characteristics of various existing instruments or methods, illustrating that synthetic diamonds currently require the use of multiple methods in combination for identification and differentiation. However, these methods are only used by research institutions and universities for diamond identification and cannot achieve large-scale screening, nor can they meet the requirements of production units for low cost, high efficiency, and suitable application scenarios.

[0007] Currently, there are national and industry standards for gem identification. Due to the small size of diamonds, integrating national standards into online testing during production while overcoming the shortcomings of existing technologies, such as high cost and cumbersome operation, is an urgent and challenging task. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a high-precision, low-cost diamond screening device with characteristic spectra.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] The diamond screening method based on characteristic spectra includes the following steps;

[0011] S1. By utilizing the reflection of the light source by the diamond, an image of the diamond under test is obtained by a camera under the illumination of the light source filtered by a bandpass filter.

[0012] S2. Use histogram equalization algorithm to process the image to improve image contrast;

[0013] S3. Based on the different brightness levels of diamonds of different grades in the image, the YOLO algorithm is used to calibrate the image and determine the diamond grade.

[0014] The aforementioned light sources include ultraviolet light sources in the UVA or UVB bands.

[0015] The above image is a black and white image.

[0016] Determining the center wavelength of the aforementioned bandpass filter includes the following steps:

[0017] A1. Convolve the characteristic spectral curves of each standard diamond with the camera's sensing curve and the light source's emission curve to calculate the wavelength-reflection intensity relationship of each standard diamond.

[0018] A2. Using the interval enumeration algorithm, the convolution results of the above standard diamonds are compared in each interval to obtain the wavelength interval with the best contrast for each standard diamond.

[0019] A3. Determine the center wavelength of the bandpass filter based on the wavelength range.

[0020] Furthermore, it also includes refitting the characteristic spectral curves of each standard diamond, the camera's sensing curve, and the light source's emission curve using a cubic spline interpolation algorithm beforehand.

[0021] A diamond screening device based on characteristic spectra includes a camera, a bandpass filter, a light source, and a stage.

[0022] The platform is used to hold the diamonds;

[0023] The light source is used to illuminate the diamonds on the stage;

[0024] The bandpass filter is located at the lens of the camera, which is used to acquire an image of the diamond illuminated by a light source on the stage.

[0025] The camera mentioned above is a CCD monochrome camera, positioned vertically directly facing the diamond.

[0026] The light source mentioned above uses ultraviolet LEDs in the UVA or UVB band.

[0027] The optical path of the aforementioned light source is based on a longitudinal tilt angle of 45°.

[0028] The aforementioned diamond screening device also includes a control device that connects the camera and the ultraviolet light source, the control device including a computer with a built-in MATLAB system;

[0029] The computer is used to process images using a histogram equalization algorithm to improve image contrast, and uses the YOLO algorithm to calibrate images based on the different brightness levels of different types of diamonds in the image, thereby determining the diamond's grade.

[0030] The advantages of this invention are:

[0031] The diamond screening method and apparatus based on characteristic spectrum of the present invention adopts narrowband filtering technology, utilizes the transmission and reflection of diamonds, and combines the contrast properties of images to make the contrast of specific types of diamonds reach the highest in a specific band, thereby achieving high-precision and rapid diamond screening.

[0032] This invention starts with the transmission and reflection of diamonds. Diamonds have a stable structure and can be considered to absorb virtually no light. The sum of the transmission and reflection of a diamond equals the total light intensity. Therefore, the reflection intensity of different types of diamonds can be obtained by convolution fitting the characteristic spectrum of the diamond, the light source curve, and the detector curve. By comparing the ratios of different grades of diamonds within different wavelength ranges, the range with the most obvious contrast can be obtained, which is the optimal filtering range. The bandpass filter is also customized based on this. For different types of diamonds, only the bandpass filter needs to be replaced. The entire device is low-cost, simple to operate, and convenient.

[0033] The diamond screening method and apparatus based on characteristic spectra of this invention effectively solves the contradiction between large-scale, automated diamond screening and simple operation and easy control in existing technologies, realizing large-area, automated diamond screening technology with simple operation. It provides strong technical support for diamond production and identification units; and has strong practicality and wide applicability. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the diamond screening device of the present invention.

[0035] Figure 2 This is the characteristic spectral curve of a standard diamond.

[0036] Figure 3 This is the sensing curve of a CCD camera.

[0037] Figure 4 This is the emission curve of an ultraviolet light source.

[0038] Figure 5 The curves are the emission curves of the light source and the sensing curve of the camera, which are then refitted using a cubic spline interpolation algorithm (Figure a is the light source, and Figure b is the CCD camera).

[0039] Figure 6 An image of the diamond being tested, taken by a CCD camera.

[0040] Figure 7 This is the image after processing with a histogram equalization algorithm.

[0041] The labels in the attached diagram have the following meanings: 1. Computer, 2. CCD camera, 3. Lens, 4. Bandpass filter, 5. Stage, 6. Ultraviolet light source. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0043] The standard diamonds and the diamond to be tested used in this invention were provided by Shenzhen Zhongtian Yinhe Technology Co., Ltd. The standard diamonds were classified as D (since the manufacturer listed it as Class II, but it's not part of the standard classification; during our experiments, we found this diamond to be among the brightest and likely a natural diamond, so we tentatively classified it as Class D), G, H, M, and Z. The grading standards were based on the "Diamond Grading" published in 2017 and the "Synthetic Diamond Identification and Quality Evaluation" published in 2020 (in the 1950s, the Gemological Institute of America (GIA) classified diamonds into 23 grades from D to Z according to color, ranging from colorless to light yellow; China uses 11 grades from D to N). The diamond to be tested was grade G.

[0044] The characteristic (reflectance) spectral curve of a standard diamond is provided by the manufacturer or obtained using a spectrometer, such as... Figure 2 As shown.

[0045] The CCD camera uses a monochrome industrial digital camera with a resolution of 768×494 and a pixel size of 8.4×9.8um; the lens uses an ultraviolet camera lens or a lens created through 3D printing using an uncoated lens. The CCD camera's sensing curve is provided by the manufacturer (Sony), such as... Figure 3 As shown.

[0046] The light source uses UVA or UVB band ultraviolet LEDs, or deuterium lamps. The emission curve of the ultraviolet light source is provided by the manufacturer (Sorebo deuterium lamps), such as... Figure 4 As shown.

[0047] The stage should be a flat plate that does not absorb or can reflect ultraviolet light.

[0048] like Figure 1 As shown, the diamond screening device based on characteristic spectra consists of a CCD camera, a bandpass filter, an ultraviolet light source, a stage, and a computer.

[0049] A stage is used to hold the diamond. A bandpass filter is positioned at the lens of a CCD camera. The CCD camera captures images of the diamond on the stage illuminated by an ultraviolet light source along its longitudinal direction. The ultraviolet light source illuminates the diamond on the stage at a 45° angle away from the longitudinal direction. A computer is connected to and controls the on / off state of the CCD camera and the ultraviolet light source, acquiring and processing the images captured by the CCD camera to determine the grade of the diamond in the captured images.

[0050] When using,

[0051] When the ultraviolet light source is turned on, the light emitted by the ultraviolet light source shines on the diamond at a 45° angle. The reflected light is filtered by a bandpass filter and then converged by the lens before entering the CCD camera to form an image. In other words, the CCD camera takes a picture and records the image of the diamond at this moment.

[0052] The selection of a bandpass filter, i.e., the determination of the center wavelength:

[0053] A0. Simulation using a computer with built-in MATLAB system: Import characteristic spectral curve data of each standard diamond, emission curve data of ultraviolet light source and sensing curve data of CCD camera;

[0054] The characteristic spectral curves of each standard diamond, the camera's sensing curve, and the light source's emission curve were refitted using a cubic spline interpolation algorithm; for example... Figure 5 As shown, Figure a is the curve after fitting the light source, and Figure b is the curve after fitting the camera.

[0055] A1. Convolve the characteristic spectral curves of each standard diamond with the camera's sensing curve and the light source's emission curve to calculate the wavelength-reflection intensity relationship of each standard diamond.

[0056] A2. Using a 20nm wavelength range, the range enumeration algorithm is used to compare the data of the convolution results of the above standard diamonds in each range. The wavelength range with the best contrast for each standard diamond is 300-320nm. The data ratios in the 300-320nm wavelength range are shown in Table 1 below. That is, within this wavelength range, the light reflection intensity (brightness, contrast) of each standard diamond can be distinguished and determined.

[0057]

[0058] Table 1. Ratio of Category G diamonds to other types of diamonds within the range

[0059] A3. Based on the wavelength range, the center wavelength of the bandpass filter is determined to be 310nm, and the bandwidth is 20nm, i.e., 310±10nm.

[0060] A4. Customize bandpass filters based on center wavelength and bandwidth.

[0061] Diamond screening methods based on characteristic spectra:

[0062] S1. Based on a custom bandpass filter, the computer acquires an image of the diamond to be tested captured by a CCD camera, such as... Figure 6 As shown;

[0063] S2. Use histogram equalization algorithms to process the image to improve its contrast, such as... Figure 7 As shown;

[0064] S3. Based on the different brightness of diamonds of different grades in the image, the YOLO algorithm is used for image calibration, and the contrast properties of the image are used for differentiation to determine the grade of the diamond, thereby enabling the screening of diamonds of different types and qualities.

[0065] The diamond was tested and classified as Grade G. This result is consistent with the manufacturer's assessment, indicating that the test results are accurate.

[0066] The image shows the measurement results of this invention: the contrast between the tested diamond and other types of diamonds reached its maximum value, as indicated by the image. Figure 7 It is evident that diamond types can be distinguished even with the naked eye, achieving satisfactory application results.

[0067] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method of diamond screening based on characteristic spectra, characterised in that, The method comprises the following steps: S1, using the reflection of the diamond on the irradiation light source, obtaining the black and white image of the diamond under the irradiation of the light source filtered by the band-pass filter through the camera; the light source is an ultraviolet light source in UVA or UVB band; S2, processing the image using the histogram equalization algorithm to improve the contrast of the image; S3, according to the different brightness of the different grades of diamonds in the image, using the YOLO algorithm to calibrate the image to determine the grade of the diamond; The determination of the center wavelength of the band-pass filter comprises the following steps: A0, using the cubic spline interpolation algorithm to re-fit the characteristic spectral curve of each standard diamond, the sensing curve of the camera and the light-emitting curve of the light source in advance; A1, convoluting the characteristic spectral curve of each standard diamond with the sensing curve of the camera and the light-emitting curve of the light source respectively to fit the wavelength-reflection intensity relationship of the standard diamond; A2, using the interval enumeration algorithm to calculate the ratio of the convolution results of each standard diamond in each interval to obtain the wavelength interval with the best contrast of each standard diamond; A3, determining the center wavelength of the band-pass filter according to the wavelength interval.

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