WO2020199500A1 - 防复制的二维码及二维码的防伪认证方法 - Google Patents

防复制的二维码及二维码的防伪认证方法 Download PDF

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WO2020199500A1
WO2020199500A1 PCT/CN2019/104598 CN2019104598W WO2020199500A1 WO 2020199500 A1 WO2020199500 A1 WO 2020199500A1 CN 2019104598 W CN2019104598 W CN 2019104598W WO 2020199500 A1 WO2020199500 A1 WO 2020199500A1
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Prior art keywords
dimensional code
code
data area
peak value
image
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PCT/CN2019/104598
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English (en)
French (fr)
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陈昌盛
李沐霖
黄继武
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深圳大学
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/06009—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code with optically detectable marking
    • G06K19/06037—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code with optically detectable marking multi-dimensional coding
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
    • G06K7/14—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation using light without selection of wavelength, e.g. sensing reflected white light
    • G06K7/1404—Methods for optical code recognition
    • G06K7/1408—Methods for optical code recognition the method being specifically adapted for the type of code
    • G06K7/1417—2D bar codes

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  • the present disclosure relates to the field of information technology, and in particular to a method and system for modeling illegal duplication of two-dimensional codes.
  • the methods of preventing copying of QR codes mainly include: (1) using special printing materials or processes to prevent copying; (2) using encryption algorithms and security protocols to control the generation and reading of QR codes; (3) using numbers Watermark technology to prevent copying; (4) Use physical unclonable features to prevent copying.
  • the two-dimensional code uses a copy detection pattern and a physical unclonable function, or the aforementioned security (encryption and digital watermark) algorithm, it is difficult to prevent counterfeiters from copying the two-dimensional code under the framework of the Internet of Things system.
  • the image features extracted based on the physical unclonable function relate to the details in the printed output image.
  • the comprehensive performance of these methods in ensuring the uniqueness of the two-dimensional code, that is, resisting illegal copying still needs to be further improved.
  • an illegal copy channel modeling method and system that can obtain an illegal copy channel closer to the actual scene and can be used to prevent copying of an optimized two-dimensional code is proposed.
  • the first aspect of the present disclosure provides a copy-proof two-dimensional code, which is a two-dimensional code in which a pixel dot matrix represented by a binary code is arranged on a two-dimensional plane, and is characterized by having: a data area, which Stored with information; and a position detection pattern, which is arranged around the data area, wherein, in the data area, the pixel dot matrix undergoes halftone processing to form a multi-level gray scale.
  • the pixel matrix of the two-dimensional code is subjected to halftone processing to form a multi-level gray scale, thereby making the frequency of the two-dimensional code in the frequency domain closer to scanning -The sampling frequency of the printing device to increase the signal aliasing during the copying process, so as to improve the anti-duplication ability of the two-dimensional code while increasing the versatility of the two-dimensional code.
  • the pixel dot matrix has a reference peak value related to the parameter of the halftone processing in the frequency spectrum. In this case, the complexity of generating a two-dimensional code can be reduced.
  • the reference peak value is also related to at least one of the resolution and the rotation angle of the imaging device that captures the two-dimensional code.
  • the anti-copy capability of the two-dimensional code can be further improved.
  • the pixel dot matrix has a predetermined number of reference peaks located at a predetermined position on the frequency spectrum. Therefore, the legitimacy of the two-dimensional code can be easily judged by comparing the reference peak value.
  • the second aspect of the present disclosure discloses an anti-counterfeiting authentication method for a two-dimensional code, which is a method for anti-counterfeiting authentication of the above-mentioned two-dimensional code, which is characterized in that an image of the two-dimensional code is captured; Perform recognition; obtain the data area based on the position detection pattern; analyze the data area, and calculate the data area based on the resolution and rotation angle of the data area and the imaging device capturing the two-dimensional code Whether there is a corresponding frequency domain peak in the frequency domain; and judging whether the two-dimensional code is legal according to the calculated frequency domain peak.
  • whether the data area has a corresponding frequency domain peak in the frequency domain is calculated based on the data area and the resolution and rotation angle of the imaging device that captures the two-dimensional code, and according to the The calculated frequency domain peak value is used to determine whether the two-dimensional code is legal, so that it can be easily determined whether the two-dimensional code is legal.
  • the captured two-dimensional code is regarded as a legal two-dimensional code, and if it is determined that the calculated frequency domain peak value does not match the distribution of the reference peak value of the pixel lattice, the captured two-dimensional code is regarded as an illegally copied two-dimensional code. Therefore, the legitimacy of the two-dimensional code can be easily judged by comparing the reference peak value.
  • the anti-counterfeiting authentication method of the two-dimensional code involved in the second aspect of the present disclosure optionally, it further includes evaluating the quality of the captured two-dimensional code image, and if the two-dimensional code image does not reach the predetermined quality, then Recapture the two-dimensional code. As a result, the user can be prompted whether to obtain a two-dimensional code image that meets the predetermined quality requirements, and the accuracy of the two-dimensional code anti-counterfeiting authentication can be improved.
  • the anti-counterfeiting authentication method of the two-dimensional code involved in the second aspect of the present disclosure optionally, if it is impossible to determine whether the calculated frequency domain peak value matches the distribution of the reference peak value of the pixel lattice, it is based on the Halftone processing performs authentication feature extraction on the two-dimensional code image in the time domain. In this case, it is possible to conveniently extract the authentication feature of the two-dimensional code image in the time domain based on the halftone processing, so that the complexity of anti-counterfeiting authentication can be suppressed.
  • the two-dimensional code image is corrected so that the two-dimensional code image is The code image is presented as a standard two-dimensional code. Therefore, by presenting the two-dimensional code image as a standard two-dimensional code, the accuracy of the two-dimensional code anti-counterfeiting authentication can be further improved.
  • a local binary mode descriptor is used in the authentication feature extraction.
  • an anti-copy two-dimensional code capable of improving the anti-copy capability of the two-dimensional code while improving the versatility of the two-dimensional code, and an anti-counterfeiting authentication method for the two-dimensional code.
  • FIG. 1 is a diagram showing an actual scene of a two-dimensional code for preventing copying involved in an example of the present disclosure.
  • Fig. 2 is a schematic diagram showing a two-dimensional code involved in an example of the present disclosure.
  • FIG. 3 is a partial enlarged schematic diagram showing a legal two-dimensional code and a copied two-dimensional code image involved in an example of the present disclosure.
  • Fig. 4 shows an example of image distortion of the copied two-dimensional code.
  • FIG. 5 is a schematic diagram showing the frequency spectrum of the halftone multi-level two-dimensional code of the two-dimensional code involved in the example of the present disclosure.
  • FIG. 6 is a schematic diagram showing the anti-counterfeiting authentication of the anti-copy two-dimensional code involved in the example of the present disclosure.
  • FIG. 7 is a schematic diagram showing the flow of anti-counterfeiting authentication of a two-dimensional code involved in an example of the present disclosure.
  • FIG. 1 is a diagram showing an actual scene of a two-dimensional code for preventing copying involved in an example of the present disclosure.
  • Fig. 2 is a schematic diagram showing a two-dimensional code involved in an example of the present disclosure.
  • FIG. 3 is a partial enlarged schematic diagram showing a legal two-dimensional code and a copied two-dimensional code image involved in an example of the present disclosure.
  • the two-dimensional code image obtained by the original two-dimensional code through the "print-shoot" channel (PC) is a real two-dimensional code.
  • the original two-dimensional code (designed two-dimensional code) passes through the printing device Print, and then capture (photograph) by the imaging device to obtain a real two-dimensional code.
  • the two-dimensional code image obtained through the "print-scan-print-shoot" channel (PSPC) is a copied two-dimensional code (illegal captured two-dimensional code), specifically, an electronic two-dimensional code (designed two-dimensional code) ) Print through a printing device, then scan and acquire through a scanning device, and then print and capture.
  • the PSPC channel adds a "scan-print" process, which is not a real two-dimensional code and belongs to a copied two-dimensional code.
  • the printing device, scanning scanner, imaging device, etc. shown in FIG. 1 may all be commercially available.
  • the anti-copy two-dimensional code 1 involved in the present disclosure is a two-dimensional code in which a pixel dot matrix represented by a binary code is arranged on a two-dimensional plane (see FIG. 2(b)), and includes: a data area 10, which stores Information; and a position detection pattern 20, which is arranged around the data area, wherein, in the data area 10, the pixel dot matrix undergoes halftone processing to form a multi-level gray scale.
  • the pixel matrix of the two-dimensional code is subjected to halftone processing to form a multi-level gray scale, thereby making the frequency of the two-dimensional code in the frequency domain closer to scanning -The sampling frequency of the printing device to increase the signal aliasing during the copying process, so as to improve the anti-duplication ability of the two-dimensional code while increasing the versatility of the two-dimensional code.
  • the conventional two-dimensional code 1A composed of black and white block (low-frequency square wave) structure (for example, as shown in Figure 2(a)), its frequency is very different from the sampling frequency of the scanning-printing device, and the signal generated after resampling The aliasing phenomenon is not obvious.
  • the two-dimensional code with halftone processed pixel dot matrix of the present disclosure has multi-level grayscale, and the signal aliasing phenomenon generated after resampling is obvious, which can increase the reproduction of two-dimensional The difficulty of the code.
  • the original two-dimensional code may be the electronic two-dimensional code shown in FIG. 1.
  • the original QR code can be obtained based on the original information and authentication information.
  • the original information may be the information that the user wants to transmit, that is, the original information may be the information input by the user, such as a character string.
  • the authentication information may be the parameters of halftone processing, the resolution of commonly used imaging devices, the angle of rotation during shooting, and the like. The authentication information can be used to authenticate the authenticity of the original two-dimensional code to verify the authenticity of the original two-dimensional code.
  • the position detection pattern 20 may be a plurality of corner points, such as 3 corner points, located in the data area 10. In this case, by capturing the two-dimensional code 1 including the position detection pattern 20 using an imaging device, the data area 10 can be accurately acquired.
  • the position detection pattern 20 may be a dot matrix (not shown) surrounding the data area 10. In this case, the data area 10 may also be captured in preparation by capturing the two-dimensional code 1 including the position detection pattern 20.
  • the encoding method of the original two-dimensional code is not particularly limited.
  • a multi-system error correction encoding method may be used.
  • Reed-Solomon (RS) encoding method is a kind of channel coding.
  • RS coding has forward error correction capability, and it is effective for polynomials generated by correcting oversampling data.
  • RS coding has strong anti-interference, anti-noise and error correction capabilities.
  • the encoded information may be a binary bit stream composed of "0" and "1".
  • the encoding method of the original two-dimensional code can also adopt a binary error correction encoding method.
  • a binary error correction encoding method For example, BCH (Bose, Ray-Chaudhuri Hocquenghem) coding method.
  • the BCH code is a linear block code in a finite field.
  • the BCH code has the ability to correct multiple random errors, and is usually used for error correction in the communication and storage fields.
  • BCH coding can be used for multi-level phase shift keying of prime numbers or power levels of prime numbers. Compared with RS coding, BCH coding has weaker anti-interference, anti-noise and error correction capabilities.
  • authentication information when encoding the original two-dimensional code, authentication information can also be added.
  • the information length of the authentication information can be much smaller than the information length of the original information of the QR code.
  • the authentication information may be less than 30% of the original information.
  • the length of the authentication information is 100 bits
  • the length of the original information is 1000 bits
  • the length of the target bit stream finally obtained is between 1000 bits and 1100 bits.
  • the original QR code is obtained based on the original information and authentication information.
  • the authentication information is embedded in the original information to obtain a target bit stream; the target bit stream is converted into a gray value according to a preset modulation method, and halftone processing is performed to generate the original two-dimensional code.
  • the original two-dimensional code with strong encryption capability and multi-level grayscale.
  • the preset modulation method may adopt any one of a quadrature amplitude modulation (Quadrature Amplitude Modulation, QAM) method, a quadrature phase shift keying (Quadrature Phase-Shift Keying, QPSK) method, or a pulse modulation method.
  • QAM Quadrature Amplitude Modulation
  • QPSK Quadrature Phase shift keying
  • the pulse modulation method may be a pulse amplitude modulation (Pulse Amplitude Modulation, PAM) modulation method.
  • PAM modulation method can convert the target bit stream into a gray value, and undergo halftone processing to generate the original two-dimensional code.
  • the target bit stream can be composed of "0" and "1".
  • the adjacent two binary numbers as a group there are 4 situations in each group, such as “00", “01", “10” and “11".
  • the PAM modulation method can be used to modulate different groups to different gray values.
  • the gray values corresponding to the above four situations can be "40", "100", “160” and "220”.
  • the original two-dimensional code can be obtained based on the above four gray values.
  • the positional relationship of each group of adjacent two binary numbers in the target bit stream corresponds to the positional relationship of pixels with corresponding gray values in the original two-dimensional code.
  • the pulse amplitude modulation method can convert the target bit stream into a gray value and undergo halftone processing to generate the original two-dimensional code.
  • the examples of the present disclosure are not limited to this.
  • the adjacent three or more binary numbers of the target bit stream can be regarded as a group, and different groups can be modulated into different gray values by using the PAM modulation method. , And get the original QR code.
  • the legal two-dimensional code may be obtained by printing the original two-dimensional code of FIG. 1 through a printer into a real two-dimensional code and then using an imaging device such as a mobile terminal. .
  • an imaging device such as a mobile terminal.
  • the illegal party may use a scanning device to capture the real two-dimensional code, print the real two-dimensional code again, and then use the imaging device to capture it.
  • the captured two-dimensional code image belongs to Copy the QR code.
  • Figure 3 shows the image of the real two-dimensional code
  • Figure 3(b) shows the image of the copied two-dimensional code. It can be seen from Figure 3 that there is obvious image distortion when copying the QR code.
  • Fig. 4 shows an example of image distortion of the copied two-dimensional code.
  • the distortion of the two-dimensional code image in the PSPC channel is described as an example of the image distortion of the copied two-dimensional code in FIG. 4.
  • the original two-dimensional code becomes a real two-dimensional code after being printed. If the real two-dimensional code is scanned again, the scanned two-dimensional code image will introduce noise, etc., which will cause it to be printed again.
  • the distortion in the image structure changes, for example, from circular dots to directional dots.
  • the pixel dot matrix has a reference peak value related to the parameter of the halftone processing in the frequency spectrum.
  • the complexity of generating a two-dimensional code can be reduced.
  • the frequency representations of the original two-dimensional code and the copied two-dimensional code are peaks distributed in the entire frequency spectrum. The difference between the two is reflected in the number and position of peaks, which are mainly determined by the parameters of halftone processing. Therefore, through halftone processing, the original two-dimensional code can be effectively distinguished from the copied two-dimensional code.
  • the reference peak value is also related to at least one of the resolution and the rotation angle of the imaging device that captures the two-dimensional code.
  • the anti-copy capability of the two-dimensional code can be further improved.
  • the pixel dot matrix has a predetermined number of reference peaks located at a predetermined position on the frequency spectrum. Therefore, the legitimacy of the two-dimensional code can be easily judged by comparing the reference peak value.
  • the QR code is considered to be real, otherwise it is considered to be a duplicate.
  • FIG. 6 is a schematic diagram showing the anti-counterfeiting authentication of the anti-copy two-dimensional code involved in the example of the present disclosure.
  • FIG. 7 is a schematic diagram showing the flow of anti-counterfeiting authentication of a two-dimensional code involved in an example of the present disclosure.
  • FIG. 6 and FIG. 7 the anti-counterfeiting authentication method of the two-dimensional code involved in the present disclosure will be described in detail.
  • step S100 an image of the two-dimensional code is captured (step S100).
  • step S200 the position detection pattern of the two-dimensional code is recognized (step S200).
  • step S300 a data area is acquired based on the position detection pattern 10 (step S300).
  • step S400 analyze the data area, and calculate whether the data area has a corresponding frequency domain peak in the frequency domain according to the resolution and rotation angle of the data area and the imaging device capturing the two-dimensional code.
  • step S500 it is judged whether the two-dimensional code is legal (step S500).
  • step S100 it may also include quality evaluation of the captured two-dimensional code image, and if the two-dimensional code image does not reach a predetermined quality, the two-dimensional code is captured again (step S110). As a result, the user can be prompted whether to obtain a two-dimensional code image that meets the predetermined quality requirements, and the accuracy of the two-dimensional code anti-counterfeiting authentication can be improved.
  • the position detection pattern of the two-dimensional code can be recognized.
  • the position detection pattern is the corner point of the two-dimensional code.
  • the position of the QR code can be identified by the corner points of the QR code.
  • step S300 the data area 10 can be acquired based on the position detection pattern 20 based on the position of the identified two-dimensional code (see FIG. 2(b)), so that the data area 10 can be processed and decoded.
  • step S400 calculate whether the data area has a corresponding frequency domain peak in the frequency domain according to the resolution and rotation angle of the data area 10 and the imaging device that captures the two-dimensional code, and judge according to the calculated frequency domain peak Whether the two-dimensional code is legal, it can be easily judged whether the two-dimensional code is legal.
  • preprocessing is performed in the captured two-dimensional code image spectrum to remove some noise.
  • Gaussian filtering is performed on the spectrum image.
  • a spot detector such as LOG filter
  • the peak point of the DFT spectrogram is used to detect the local peak, and the detected peak is marked with a white circle.
  • the QR code image passing through the PC channel can be expressed by the following formula (1):
  • I G (x) represents the printed two-dimensional code image
  • ⁇ x c is the error between the printing and shooting process
  • F lp represents a low-pass filter.
  • the approximation process (a) is by modeling the imaging process as a convolution step.
  • the resampling process is formed by convolution of a two-dimensional Dirac function array and a low-pass filter.
  • the vectors d and e specify the sampling direction and frequency in the resampling process.
  • the vectors s and t are the frequency domain representations of the vectors d and e.
  • the QR code image passing through the PSPC channel can be expressed by the following formula (3):
  • the approximate process (a) represents the assumption of a perfect calibration and high enough resolution in the printing process.
  • Approximation process (b) means that it is assumed that both scanning and recovery processes produce unambiguous barcode images.
  • 3 features in the frequency domain are proposed to describe the difference between the original QR code and the copied QR code: 1) The number of peak points around each reference point 2) The number of all points around the 9 reference points; 3) The average distance between the calculated reference point and the observed reference point.
  • step S500 optionally, if it is determined that the calculated frequency domain peak value matches the distribution of the reference peak value of the pixel lattice, the captured two-dimensional code is regarded as a legal two-dimensional code. If the distribution of the domain peak value and the reference peak value of the pixel lattice does not match, the captured two-dimensional code is regarded as an illegally copied two-dimensional code. Therefore, the legitimacy of the two-dimensional code can be easily judged by comparing the reference peak value.
  • step S500 optionally, if it is impossible to determine whether the calculated frequency domain peak value matches the distribution of the reference peak value of the pixel lattice, then the two-dimensional code image is extracted in the time domain based on halftone processing. . In this case, it is convenient to extract the authentication feature of the two-dimensional code image in the time domain based on halftone processing, so that the complexity of anti-counterfeiting authentication can be suppressed.
  • the quality of the authenticated two-dimensional code image is first evaluated. If the quality of the two-dimensional code does not meet the requirements, the user will be prompted to take another shot, thereby improving the reliability of the authentication process.
  • the extracted frequency domain features are input into a certain probability SVM, and the probability value p is output, which represents the probability that the two-dimensional code is true.
  • Set the probability interval to (p1, p2).
  • the p value is in this interval (p1, p2), it is uncertain whether it is a real QR code, and then it is transferred to the second stage for further evaluation.
  • the second stage firstly, the two-dimensional code image is deformed and corrected to make the two-dimensional code appear as a standard square, so that the two-dimensional code module can be accurately extracted and described in the time domain. Finally, the time domain feature vector is input into the standard SVM for authentication, and the result is obtained.
  • the two-dimensional code image before performing the step of restoring the two-dimensional code image, may be corrected so that the two-dimensional code image appears as a standard two-dimensional code. Therefore, by presenting the two-dimensional code image as a standard two-dimensional code, the accuracy of the two-dimensional code anti-counterfeiting authentication can be further improved.
  • a local binary mode descriptor is used.
  • This embodiment discloses a computer-readable storage medium.
  • the program (instruction) can be stored in a computer-readable memory (storage medium), the memory can include: flash disk, read-only memory (English: Read-Only Memory, abbreviated as: ROM), Random access device (English: Random Access Memory, abbreviated as: RAM), magnetic disk or optical disk, etc.

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Abstract

一种防复制的二维码（1）和一种针对上述防复制二维码（1）的二维码防伪认证方法。该二维码（1）是在二维平面上配置利用二进制代码表示的像素点阵的二维码，其特征在于，具备：数据区域（10），其存储有信息；以及位置检测图案（20），其设置在数据区域（10）周围，其中，在数据区域（10）内，像素点阵经过半色调处理而形成有多级灰阶。该二维码（1）能够在保持二维码通用性的情况下提高二维码的防复制能力。

Description

防复制的二维码及二维码的防伪认证方法 技术领域
本公开涉及信息技术领域，具体涉及一种二维码的非法复制信道建模方法及系统。
背景技术
传统的二维码在打印出来之后，容易被非法用户复制。目前，二维码的防复制方法主要包括：(1)使用特殊的打印材料或工艺防复制；(2)使用加密算法与安全协议，控制二维码的生成与读取；(3)使用数字水印技术来防复制；(4)使用物理不可克隆特征防复制。
尽管上述方法在一定程度上能够起到防复制的作用，但也存在明显的局限性。例如，以特殊的打印材料或工艺制作二维码，可加强对生成过程的控制以抵御对二维码的非法复制，但却无可避免地降低了二维码的通用性，增加了二维码的生产成本及对特殊设备的依赖性。此外，引入基于加密与数字水印等算法或安全协议的方案可控制二维码未经授权的生成以及对当中数据的非法篡改，但却增加了系统的复杂度。而且，即使二维码应用了拷贝检测图案与物理不可克隆函数，或者是上述安全(加密与数字水印)算法，也难以在物联网的系统框架下防止伪造者复制该二维码。基于物理不可克隆函数所提取的图像特征涉及打印输出图像中的细节。上述这些方法在保证二维码的唯一性，即抵御非法复制方面的综合表现仍有待进一步提高。面对日益严重的产品仿冒以及相对初步的二维码溯源防伪系统框架，需要积极探索提高二维码安全性以抵御非法复制的新理论与技术方案。
发明内容
为了解决上述问题，提出了一种能够获得更加接近于实际场景的非法复制信道，可用于防复制二维码的优化的二维码的非法复制信道建模方法及系统。
为此，本公开的第一方面提供了一种防复制的二维码，是在二维平面上配置利用二进制代码表示的像素点阵的二维码，其特征在于，具备：数据区域，其存储有信息；以及位置检测图案，其设置在所述数据区域周围，其中，在所述数据区域内，所述像素点阵经过半色调处理而形成有多级灰阶。
在本公开的第一方面中，在生成二维码时将二维码的像素点阵进行半色调处理以形成多级灰阶，由此能够使二维码在频域上的频率更加接近扫描-打印设备的采样频率以提高复制过程中的信号混叠，从而能够在提高二维码通用性的情况下改善二维码的防复制能力。
在本公开的第一方面所涉及的防复制的二维码中，可选地，所述像素点阵在频谱上具有与所述半色调处理的参数相关的参考峰值。在这种情况下，能够降低生成二维码时的复杂度。
在本公开的第一方面所涉及的防复制的二维码中，可选地，所述参考峰值还与捕获所述二维码的成像装置的分辨率、旋转角度中的至少一个相关。由此，能够进一步提高二维码的防复制能力。
在本公开的第一方面所涉及的防复制的二维码中，可选地，所述像素点阵在频谱上具有预定数量且位于预定位置的参考峰值。由此，能够方便地通过比较参考峰值来判断二维码的合法性。
本公开的第二方面公开了一种二维码的防伪认证方法，是对上述的二维码进行防伪认证的方法，其特征在于，捕获二维码的图像；对二维码的位置检测图案进行识别；基于所述位置检测图案获取所述数据区域；对所述数据区域进行分析，并根据数据区域和捕获所述二维码的成像装置的分辨率和旋转角度来计算所述数据区域在频域上是否具有相应的频域峰值；并且根据所计算的频域峰值来判断所述二维码是否合法。
在本公开的第二方面中，通过根据数据区域和捕获所述二维码的成像装置的分辨率和旋转角度来计算所述数据区域在频域上是否具有相应的频域峰值，并且根据所计算的频域峰值来判断所述二维码是否合法，由此能够方便地判断二维码是否合法。
在本公开的第二方面所涉及的二维码的防伪认证方法中，可选地，如果判断所计算的频域峰值与所述像素点阵的参考峰值的分布匹配， 则将所被捕获的二维码视为合法二维码，如果判断所计算的频域峰值与所述像素点阵的参考峰值的分布不匹配，则将所被捕获的二维码视为非法复制的二维码。由此，能够方便地通过比较参考峰值来判断二维码的合法性。
在本公开的第二方面所涉及的二维码的防伪认证方法中，可选地，还包括对所捕获的二维码图像进行质量评估，如果所述二维码图像未达到预定质量，则重新捕获所述二维码。由此，能够提示用户是否获得符合预定质量要求的二维码图像，提高二维码防伪认证的准确性。
在本公开的第二方面所涉及的二维码的防伪认证方法中，可选地，如果无法判断所计算的频域峰值与所述像素点阵的参考峰值的分布是否匹配，则基于所述半色调处理对所述二维码图像在时域上进行认证特征提取。在这种情况下，能够方便地基于半色调处理对二维码图像在时域上进行认证特征提取，从而能够抑制防伪认证的复杂性。
在本公开的第二方面所涉及的二维码的防伪认证方法中，可选地，在对所述二维码图像进行恢复之前，对所述二维码图像进行修正以使所述二维码图像呈现为标准的二维码。由此，通过将二维码图像呈现为标准的二维码，从而能够进一步提高二维码防伪认证的准确性。
在本公开的第二方面所涉及的二维码的防伪认证方法中，可选地，在所述认证特征提取中，使用局部二值化模式描述符。由此，能够方便地通过使用局部二值化模式描述符来进行认证特征提取，提高认证效率。
根据本公开，能够提供一种能够在提高二维码通用性的情况下改善二维码的防复制能力的防复制的二维码以及该二维码的防伪认证方法。
附图说明
现在将仅通过参考附图的例子进一步详细地解释本公开的实施例，其中：
图1是示出了本公开的示例所涉及的防复制的二维码的实际场景图。
图2是示出了本公开的示例所涉及的二维码的示意图。
图3是示出了本公开的示例所涉及的合法二维码和复制二维码图像的局部放大示意图。
图4是示出复制二维码的图像畸变一个示例。
图5是示出了本公开的示例所涉及的二维码的半色调多级二维码的频谱的示意图。
图6是示出了本公开的示例所涉及的防复制的二维码的防伪认证的示意图。
图7是示出了本公开的示例所涉及的二维码的防伪认证的流程示意图。
具体实施方式
以下，参考附图，详细地说明本公开的优选实施方式。在下面的说明中，对于相同的部件赋予相同的符号，省略重复的说明。另外，附图只是示意性的图。
需要说明的是，本公开的说明书和权利要求书及上述附图中的术语“第一”、“第二”、“第三”和“第四”等是用于区别不同对象，而不是用于描述特定顺序。此外，术语“包括”和“具有”以及它们任何变形，意图在于覆盖不排他的包含。例如包含了一系列步骤或单元的过程、方法、系统、产品或设备没有限定于已列出的步骤或单元，而是可选地还包括没有列出的步骤或单元，或可选地还包括对于这些过程、方法、产品或设备固有的其它步骤或单元。
图1是示出了本公开的示例所涉及的防复制的二维码的实际场景图。图2是示出了本公开的示例所涉及的二维码的示意图。图3是示出了本公开的示例所涉及的合法二维码和复制二维码图像的局部放大示意图。
如图1所示，原始二维码通过“打印-拍摄”信道(PC)得到的二维码图像为真实二维码，具体而言，原始二维码(设计的二维码)通过打印设备打印，接着通过成像装置进行捕获(拍摄)，从而获得真实的二维码。另外，通过“打印-扫描-打印-拍摄”信道(PSPC)得到的二维码图像为复制二维码(非法捕获的二维码)，具体而言，电子二维码(设计的二维码)通过打印设备打印，接着通过扫描装置进行扫描 获取，然后进行打印和捕获，由于与PC通道相比，PSPC通道增加了“扫描-打印”过程，并非真实二维码，属于复制二维码。另外，图1所示的打印设备、扫描扫描、成像装置等均可以是市售的。
本公开所涉及的防复制的二维码1，是在二维平面上配置利用二进制代码表示的像素点阵的二维码(参见图2(b))，具备：数据区域10，其存储有信息；以及位置检测图案20，其设置在数据区域周围，其中，在数据区域10内，像素点阵经过半色调处理而形成有多级灰阶。在本公开中，如上所述，在生成二维码时将二维码的像素点阵进行半色调处理以形成多级灰阶，由此能够使二维码在频域上的频率更加接近扫描-打印设备的采样频率以提高复制过程中的信号混叠，从而能够在提高二维码通用性的情况下改善二维码的防复制能力。
常规的由黑白块状(低频方波)结构组成的二维码1A(例如图2(a)所示)，其频率与扫描-打印设备的采样频率相差甚远，重采样后所产生的信号混叠现象不明显，相比而言，本公开具有经过半色调处理的像素点阵的二维码具有多级的灰阶，重采样后所产生的信号混叠现象明显，能够增加复制二维码的难度。
在本公开的实施方式中，原始二维码可以是图1所示的电子二维码。原始二维码可以基于原始信息和认证信息获得。其中，原始信息可以是用户所要传递的信息，也即原始信息可以是用户所输入的信息，如字符串等。认证信息可以是半色调处理的参数、常用的成像装置的分辨率、拍摄时旋转角度等。认证信息可以用于对原始二维码的真伪进行认证，以验证原始二维码的真实性。
在一些示例中，位置检测图案20可以是位于数据区域10的多个角点例如3个角点。在这种情况下，通过利用成像装置捕获包含位置检测图案20的二维码1，由此能够准确地获取数据区域10。另外，位置检测图案20可以是包围数据区域10的点阵(未图示)，在这种情况下，同样可以通过捕获包含位置检测图案20的二维码1来准备地捕获数据区域10。
在一些示例中，原始二维码的编码方式没有特别限定，例如可以采用多进制纠错编码方式。例如里德所罗门(Reed-solomon，RS)编码方式。RS编码是一种信道编码。RS编码具有前向纠错能力，且其 对由校正过采样数据所产生的多项式有效。RS编码具有较强的抗干扰、抗噪声能力和纠错能力。另外，编码信息可以是一段由“0”和“1”组成的二进制比特流。
另外，原始二维码的编码方式还可以采用二进制纠错编码方式。例如BCH(Bose、Ray-Chaudhuri Hocquenghem)编码方式。BCH码是一种有限域中的线性分组码。BCH码具有纠正多个随机错误的能力，通常用于通信和存储领域中的纠错。BCH编码可以用于质数级或者质数的幂级的多级相移键控。与RS编码相比，BCH编码的抗干扰、抗噪声能力和纠错能力较弱。
此外，在一些示例中，在对原始二维码进行编码时，还可以添加认证信息。认证信息的信息长度可以远小于二维码原始信息的信息长度。例如，认证信息可以小于原始信息的30％。例如，认证信息的长度为100bits，原始信息的长度为1000bits，最终得到的目标比特流的长度为1000bits～1100bits之间。
在一些示例中，基于原始信息和认证信息获得原始二维码。具体而言，将认证信息嵌入原始信息，获得目标比特流；按照预设调制方式将目标比特流转换为灰度值，并且进行半色调处理，进而生成原始二维码。由此，能够进一步获得加密能力较强且多级灰阶的原始二维码。
在一些示例中，预设调制方式可以采用正交振幅调制(Quadrature Amplitude Modulation，QAM)方式、正交相移键控(Quadrature Phase-Shift Keying，QPSK)方式或脉冲调制方式中的任一种。
在一些示例中，脉冲调制方式可以是脉冲幅度调制(Pulse Amplitude Modulation，PAM)调制方式。采用PAM调制方式可以将目标比特流转换为灰度值，并经过半色调处理，进而生成原始二维码。
具体而言，目标比特流可以由“0”和“1”组成。将相邻的两位二进制数看做一组，则每组存在4种情况，例如“00”、“01”、“10”和“11”。采用PAM调制方式可以将不同组调制为不同的灰度值，例如上述四种情况对应的灰度值可以为“40”、“100”、“160”和“220”。基于上述的四种灰度值可以获得原始二维码。其中，每组相邻两位二进制数在目标比特流的位置关系与具有相应的灰度值的像素 在原始二维码的位置关系一一对应。由此，采用脉冲幅度调制方式能够将目标比特流转换为灰度值，并经过半色调处理，进而生成原始二维码。本公开的示例不限于此，在另一些示例中，可以将目标比特流的相邻的三位及以上的二进制数看做一组，采用PAM调制方式可以将不同组调制为不同的灰度值，并获得原始二维码。
在一些示例中，如上所述，基于上述图1的实际场景图，合法二维码可以是由图1的原始二维码经过打印机打印成真实二维码，再经过成像装置例如移动终端得到的。由此，可以获得合法二维码图像。另外，例如非法方可能会利用扫描设备等捕获真实二维码，并将真实二维码再次进行打印，然后再利用成像装置进行捕获，在这种情况下，其所捕获的二维码图像属于复制二维码。
如图3所示，真实二维码与复制二维码在图像上存在明显区别。其中，图3(a)表示的是真实二维码的图像，图3(b)表示的是复制二维码的图像。从图3中可以看出，复制二维码存在明显的图像畸变。
图4是示出复制二维码的图像畸变一个示例。以下，以图4的复制二维码的图像畸变为例说明书在PSPC信道中二维码图像的畸变。如图4所示，原始二维码经打印后成为真实的二维码，如果再次对该真实二维码进行扫描，则扫描后的二维码图像会引入噪点等，导致在再次打印时产生图像结构上的畸变例如从圆形的点变成了方向的点。
在本公开的实施方式所涉及的防复制的二维码中，可选地，像素点阵在频谱上具有与半色调处理的参数相关的参考峰值。在这种情况下，能够降低生成二维码时的复杂度。具体而言，原始二维码和复制二维码的频率表现形式都是分布在整个频谱上的峰值。两者的不同体现在峰值的数量和位置，其主要是由半色调处理的参数决定的。因此，通过半色调处理，能够有效地区分原始二维码与复制二维码。
在本公开的实施方式所涉及的防复制的二维码中，可选地，参考峰值还与捕获二维码的成像装置的分辨率、旋转角度中的至少一个相关。由此，能够进一步提高二维码的防复制能力。具体而言，参见稍后描述的图5，在复制二维码中也有一些额外的频谱峰值。这些峰值的位置是由扫描操作中的成像参数(分辨率和旋转角度)所决定的。
在本公开的实施方式所涉及的防复制的二维码中，可选地，像素 点阵在频谱上具有预定数量且位于预定位置的参考峰值。由此，能够方便地通过比较参考峰值来判断二维码的合法性。
作为一个示例，选择原始二维码的频谱中的9个点作为参照，而白色圆圈则表示干扰(参见图5(b))。在计算二维码图像的峰值位置时，半色调和相机参数是由使用者提供。因此，如果被计算的参考点的数量和位置与观察到的匹配，则这个二维码就被认为是真实的，否则就被认为是复制的。
图6是示出了本公开的示例所涉及的防复制的二维码的防伪认证的示意图。图7是示出了本公开的示例所涉及的二维码的防伪认证的流程示意图。以下，参照图6和图7，对本公开的所涉及的二维码的防伪认证方法进行详细描述。
在本公开的所涉及的二维码的防伪认证方法中，首先，捕获二维码的图像(步骤S100)。接着，对二维码的位置检测图案进行识别(步骤S200)。然后，基于位置检测图案10获取数据区域(步骤S300)。获取数据区域20后，对数据区域进行分析，并根据数据区域和捕获二维码的成像装置的分辨率和旋转角度来计算数据区域在频域上是否具有相应的频域峰值(步骤S400)。最后，根据所计算的频域峰值来判断二维码是否合法(步骤S500)。根据本公开，能够提供一种能够在提高二维码通用性的情况下改善二维码的防复制能力的防复制的二维码以及该二维码的防伪认证方法。
在步骤S100中，还可以包括对所捕获的二维码图像进行质量评估，如果二维码图像未达到预定质量，则重新捕获二维码(S110步骤)。由此，能够提示用户是否获得符合预定质量要求的二维码图像，提高二维码防伪认证的准确性。
在步骤S200中，可以对二维码的位置检测图案进行识别。例如，在一些示例中，位置检测图案为二维码的角点。通过二维码的角点可以识别出二维码的位置。
接着，在步骤S300中，通过识别出的二维码的位置，可以基于位置检测图案20获取数据区域10(参见图2(b))，由此能够对数据区域10进行处理和解码。
在步骤S400中，通过根据数据区域10和捕获二维码的成像装置 的分辨率和旋转角度来计算数据区域在频域上是否具有相应的频域峰值，并且根据所计算的频域峰值来判断二维码是否合法，由此能够方便地判断二维码是否合法。
在上述步骤中，为了提高频域特征提取的效果，在所捕获的二维码图像频谱中进行预处理来去除了一些噪声。首先对频谱图像进行高斯滤波处理。然后利用用于检测DFT频谱图峰值点的斑点检测器(例如LOG滤波)检测局部峰值，并将检测到的峰值用白色圆圈标记。
经过PC信道的二维码图像可以用如下公式(1)表示：
Figure PCTCN2019104598-appb-000001
其中c表示拍摄过程，I G(x)表示打印后的二维码图像，Δx c是打印和拍摄过程之间的误差，F lp表示一个低通滤波器。近似过程(a)是通过对成像过程建模为一个卷积步骤。重采样过程是由二维狄拉克函数数组与低通滤波器卷积构成的，向量d,e指定了重采样过程中的采样方向和频率。
其频谱可以用公式(2)表示：
Figure PCTCN2019104598-appb-000002
其中
Figure PCTCN2019104598-appb-000003
表示二维傅里叶变换，
Figure PCTCN2019104598-appb-000004
表示经过PC信道的真实二维码图像，
Figure PCTCN2019104598-appb-000005
为经过信道之前的半色调多级二维码的频域表示，
Figure PCTCN2019104598-appb-000006
为低通滤波器的频域表示。向量s,t为向量d,e的频域表示。
经过PSPC信道的二维码图像可以用如下公式(3)表示：
Figure PCTCN2019104598-appb-000007
其中近似过程(a)表示假设比较完美的校准和打印过程中足够高的分辨率。近似过程(b)表示假设扫描和恢复过程均产生无模糊条码图像。
其频谱可以用公式(4)表示：
Figure PCTCN2019104598-appb-000008
通过频域信道模型的比较，公式(2)和公式(4)，可以看出，原始二维码和复制二维码的频率表现形式都是分布在整个频谱上的峰值。两者的不同体现在峰值的数量和位置。
根据公式(1)的频谱模型，9个参照点的位置(如图5所示)可以由以下公式计算得到：
P 0＝(0，0)；
P 2＝s c；P 4＝t c；
P 6＝-t c；P 8＝-s c；
P 1＝s c-t c；P 5＝-s c+t c；
P 3＝s c+t c；P 7＝-s c-t c.    (5)
基于公式(5)所计算的9个参考点，提出了频域中的3种特征用来描述原始二维码和复制二维码的区别：1)每个参考点周围的峰值点数量2)9个参考点周围所有点的数量；3)计算所得参考点和观察所得参考点之间的平均距离。
这些特征均可以推广到几何畸变的情况，如旋转。根据二维DFT旋转的性质，空间上的旋转会导致频域中旋转相同的角度。给出空间上旋转角度就可以准确的估算出图像四个边角以及二维码的模式，频域中的旋转角度就可以根据这些进行计算。
在步骤S500中，可选地，如果判断所计算的频域峰值与像素点阵的参考峰值的分布匹配，则将所被捕获的二维码视为合法二维码，如果判断所计算的频域峰值与像素点阵的参考峰值的分布不匹配，则将所被捕获的二维码视为非法复制的二维码。由此，能够方便地通过比较参考峰值来判断二维码的合法性。
另外，在步骤S500中，可选地，如果无法判断所计算的频域峰值与像素点阵的参考峰值的分布是否匹配，则基于半色调处理对二维码图像在时域上进行认证特征提取。在这种情况下，能够方便地基于半 色调处理对二维码图像在时域上进行认证特征提取，从而能够抑制防伪认证的复杂性。
如图6所示，首先会对被认证的二维码图像进行质量评估，如果二维码的质量没达到要求，则使用者会被提示重新拍摄，由此能够提高认证过程的可靠性。
另外，在认证过程中，将提取的频域特征输入某个概率SVM，输出概率值p，该值表示二维码为真实的概率大小。设定概率区间为(p1,p2)，当p值处于这个区间(p1,p2)时，会不确定是否为真实二维码，接着被转到第二阶段进行进一步评估。在第二阶段中，首先会对二维码图像进行形变修正以使得二维码呈现为标准的正方形，这样二维码模块才可以保证被准确提取出并进行时域特征描述。最终将时域特征向量输入标准SVM进行认证，得出结果。
在一些示例中，在进行步骤，即对二维码图像进行恢复之前，可以对二维码图像进行修正以使二维码图像呈现为标准的二维码。由此，通过将二维码图像呈现为标准的二维码，从而能够进一步提高二维码防伪认证的准确性。
在一些示例所涉及的二维码的防伪认证方法中，可选地，在认证特征提取中，使用局部二值化模式描述符。由此，能够方便地通过使用局部二值化模式描述符来进行认证特征提取，提高认证效率。
本实施方式公开一种计算机可读存储介质，本领域普通技术人员可以理解上述公开的各种防复制的二维码及二维码的防伪认证方法中的全部或部分步骤是可以通过程序(指令)来指令相关的硬件来完成，该程序(指令)可以存储于计算机可读存储器(存储介质)中，存储器可以包括：闪存盘、只读存储器(英文：Read-Only Memory，简称：ROM)、随机存取器(英文：Random Access Memory，简称：RAM)、磁盘或光盘等。
虽然以上结合附图和实施例对本发明进行了具体说明，但是可以理解，上述说明不以任何形式限制本发明。本领域技术人员在不偏离本发明的实质精神和范围的情况下可以根据需要对本发明进行变形和变化，这些变形和变化均落入本发明的范围内。

Claims (10)

  1. 一种防复制的二维码，是在二维平面上配置利用二进制代码表示的像素点阵的二维码，其特征在于，
    具备：
    数据区域，其存储有信息；以及
    位置检测图案，其设置在所述数据区域周围，
    其中，在所述数据区域内，所述像素点阵经过半色调处理而形成有多级灰阶。
  2. 根据权利要求1所述的二维码，其特征在于，
    所述像素点阵在频谱上具有与所述半色调处理的参数相关的参考峰值。
  3. 根据权利要求1所述的二维码，其特征在于，
    所述参考峰值还与捕获所述二维码的成像装置的分辨率、旋转角度中的至少一个相关。
  4. 根据权利要求2所述的二维码，其特征在于，
    所述像素点阵在频谱上具有预定数量且位于预定位置的参考峰值。
  5. 一种二维码的防伪认证方法，是对权利要求1所述的二维码进行防伪认证的方法，其特征在于，
    捕获二维码的图像；
    对二维码的位置检测图案进行识别；
    基于所述位置检测图案获取所述数据区域；
    对所述数据区域进行分析，并根据数据区域和捕获所述二维码的成像装置的分辨率和旋转角度来计算所述数据区域在频域上是否具有相应的频域峰值；并且
    根据所计算的频域峰值来判断所述二维码是否合法。
  6. 根据权利要求5所述的防伪认证方法，其特征在于，
    如果判断所计算的频域峰值与所述像素点阵的参考峰值的分布匹配，则将所被捕获的二维码视为合法二维码，如果判断所计算的频域峰值与所述像素点阵的参考峰值的分布不匹配，则将所被捕获的二维码视为非法复制的二维码。
  7. 根据权利要求5所述的二维码的防伪认证方法，其特征在于，
    还包括对所捕获的二维码图像进行质量评估，如果所述二维码图像未达到预定质量，则要求重新捕获所述二维码。
  8. 根据权利要求5所述的二维码的防伪认证方法，其特征在于，
    如果无法判断所计算的频域峰值与所述像素点阵的参考峰值的分布是否匹配，则基于所述半色调处理对所述二维码图像在时域上进行认证特征提取。
  9. 根据权利要求8所述的二维码的防伪认证方法，其特征在于，
    在对所述二维码图像进行认证特征提取之前，对所述二维码图像进行修正以使所述二维码图像呈现为标准的二维码。
  10. 根据权利要求8所述的二维码的防伪认证方法，其特征在于，
    在所述认证特征提取中，使用局部二值化模式描述符。
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