CN108982373A - A kind of label-free Stokes parameter polarization confocal micro imaging system and method for latent fingerprint - Google Patents

Abstract

The invention discloses a kind of label-free Stokes parameter of latent fingerprint polarization confocal micro imaging system and methods.The system comprises polarization generation module, cofocus scanning module, polarization measurement module and data to acquire image-forming module.The present invention is based on Stokes parameter measurements to carry out the imaging of fingerprint polarization scans, obtains single color plane polarised light and passes through the Stokes parameter and polarization parameter fingerprint image after being printed on the object of finger mark.The present invention can reduce the background luminance formed by the transmission of object such as mirror surface well, keep fingerprint obvious with background reflectance, and image background, which is interfered, to be weakened, and identification of fingerprint degree improves；The fingerprint image obtained through the invention, grain details are enriched, show the part three-level characteristic details being difficult to observe by clearly level-one feature, secondary characteristics and other fingerprint imaging methods；And operation of the present invention is simple, without processing fingerprint sample, avoids damaging fingerprint.

Description

A label-free Stokes parametric polarization confocal microscopy imaging system for latent fingerprints and method

technical field

The invention relates to the technical field of latent fingerprint detection, in particular to a marking-free Stokes parametric polarization confocal microscopic imaging system and method for latent fingerprints.

Background technique

Latent fingerprints are the sweat and sebum secreted by the sweat pores and fat glands on the fingers all the time. When the finger touches and exerts force on an object, the sweat and oil on the finger are reflected on the traces of the fingerprint pattern. Latent fingerprints are easily overlooked because they cannot be directly observed, but they contain information about each person's unique dermis lines. By analyzing the overall morphological information of the mastoid lines on the latent fingerprint and the detailed features formed by the deflection of the mastoid lines, the classification and identification can be compared with the database samples to realize fingerprint identification and individual identification. The display of latent fingerprints has important application value in the fields of criminal investigation science, identification, information security and so on.

At present, new latent fingerprint imaging technologies include fluorescence technology, nanoparticle method, immune technology, aptamer method, chemical (or hyperspectral) imaging method, etc. Xinxin Zhu et al. proposed to use polyethylenimine (PEI) to modify carbon dots (CDs) and fluorescein isothiocyanate (FITC) to conjugate CDs-FITC complexes for imaging fluorescent light fingerprints; Kim Young-Jae et al. Polyvinylpyrrolidone (PVP) was introduced to the surface of fluorescent silica nanoparticles (FSNP) for enhanced latent fingerprint detection on hydrophilic and hydrophobic substrates; Lam R et al. Evaluation of immunogenic reagents; ZhaoJ et al. used nucleic acid shell nanoparticle aptamers embedded in SERS records to visualize fingerprints; Tahtouh et al. conducted an infrared spectrum attempt to fumigate fingerprints with cyanoacrylate, using its presence in the infrared spectral region Imaging the strong absorption properties of fluorescence. These methods all use the fluorescence characteristics of the substance or the characteristics of the compound after adsorption, or combination, or reaction with the fingerprint components to detect and image, and then display the fingerprint papillae traces. However, there are problems such as background light interference, poor contrast, complex operation, long development time, high cost, and difficulty for operators to use. Some harmful reagents and dyes may cause damage to operators, and fingerprints and reagents may be compatible. The combination process such as body will cause irreversible damage to the fingerprint sample. Gao Shuhui and others proposed a new detection method using polarization imaging technology for latent fingerprints, and found that using polarization imaging technology can also better obtain fingerprint detail information. However, the general traditional polarization imaging method is complicated to operate, and the sample still needs to be treated with gold, silver and other metal powder before some experiments, which will inevitably cause damage to the fingerprint.

Contents of the invention

The object of the present invention is to overcome the disadvantages and deficiencies in the prior art, and provide a latent fingerprint-free Stokes parametric polarization confocal microscopic imaging system and method.

The present invention is achieved through the following technical solutions:

A label-free Stokes parametric polarization confocal microscopy imaging system for latent fingerprints, comprising:

A polarization generation module, which includes a laser and a polarizer; the laser light emitted by the laser generates polarized light through the polarizer;

A confocal scanning module, which includes a first objective lens, a displacement stage and a first lens; the polarized light generated from the polarization generation module is focused and incident on the fingerprint sample through the first objective lens, and the displacement stage is used to scan the fingerprint sample, After passing through the fingerprint sample, the outgoing light carrying fingerprint information is converted into parallel light by the first lens and transmitted;

Polarization measurement module, which includes three beam splitters and four-way Stokes polarized light collection optical path; the parallel light transmitted from the first lens of the confocal scanning module enters four-way Stokes polarized light collection optical path through three beam splitters , each Stokes polarized light collection optical path sequentially includes a polarizer, an objective lens and a photodetector along the light transmission direction;

The data acquisition imaging module includes a digital-to-analog converter and a processor; the signal output from the photodetector of the polarization measurement module is converted by the digital-to-analog converter and sent to the processor for processing, and finally outputs an image reflecting fingerprint features.

Compared with the prior art, the present invention uses a four-channel polarization confocal microscopic imaging system based on Stokes parameter measurement to perform fingerprint polarization scanning imaging, and measures the Stokes parameter and polarization parameter fingerprint image of monochromatic plane polarized light passing through the object with fingerprint imprints; The present invention can well reduce the background brightness formed by the transmission of objects such as mirrors, so that the contrast between the fingerprint and the background is obvious, the background interference of the image is weakened, and the fingerprint recognition degree is improved; the fingerprint image obtained by the present invention has rich texture details and presents Clear first-level features, second-level features, and some third-level feature details that are difficult to observe in other fingerprint imaging methods; and the invention is easy to operate and does not need to process fingerprint samples to avoid damage to fingerprints.

Further, the parallel light transmitted from the first lens of the confocal scanning module is vertically incident on the first beam splitter, and is divided into the first reflected light and the first transmitted light; the first reflected light is vertically incident on the second beam splitter. The beam mirror is divided into the second reflected light and the second transmitted light, which respectively enter the first Stokes polarized light collection optical path and the second Stokes polarized light collection optical path; the first transmitted light is vertically incident on the third beam splitter, and is divided into the first The third reflected light and the third transmitted light respectively enter the third Stokes polarized light collection optical path and the fourth Stokes polarized light collection optical path.

Further, the fourth Stokes polarized light collection optical path further includes a 1/4 wave plate, and the 1/4 wave plate is arranged between the third beam splitter and the polarizer of the fourth Stokes polarized light collection optical path.

Further, the orientation angle of the polarizer of the first Stokes polarized light collection optical path is 0°; the orientation angle of the polarizer of the second Stokes polarized light collection optical path is 45°; the third Stokes polarized light collection optical path has an orientation angle of 45°; The orientation angle of the polarizer in the polarized light collection optical path is 90°; the orientation angle of the 1/4 wave plate in the fourth Stokes polarized light collection optical path is 90°, and the orientation angle of the polarizer is 135°.

Further, the system also includes a normalization module, which includes a beam splitter, a second lens, and a second photodetector; the polarized light generated from the polarization generation module is reflected to the second lens by the beam splitter, and then After the second lens is focused, it enters the second photodetector to obtain a reference light signal.

Further, the reflection angle of the polarized light reflected by the beam splitter is less than 5°.

Further, the system further includes an aperture through which the parallel light transmitted from the first lens of the confocal scanning module enters the first beam splitter of the polarization measurement module.

Further, the polarized light generated by the polarization generation module enters the beam splitter of the normalization module after passing through the aperture.

The present invention also provides a marking-free Stokes parametric polarization confocal microscopic imaging method for latent fingerprints. The incident light is incident on the fingerprint sample, the incident light passes through the fingerprint sample and interacts with it, and the Stokes parameter of the outgoing light from the fingerprint sample is measured. Obtain the Stokes parameter image and the polarization parameter image reflecting the characteristics of the fingerprint.

Description of drawings

FIG. 1 is a schematic diagram of an imaging scanning experiment performed by a label-free Stokes parametric polarization confocal microscopy imaging system of a latent fingerprint in an embodiment.

FIG. 2 is a schematic diagram of a calibration experiment performed by a label-free Stokes parametric polarization confocal microscopy imaging system for latent fingerprints according to an embodiment.

Figure 3(a)～(h) respectively show the Stokes parameters S0, S1, S2, S3 of the latent fingerprint on the glass object, the polarization parameter amplitude ratio γ, and the phase difference The distribution image of the azimuth angle θ and the elliptic angle ε.

Figure 4(a) and Figure 4(b) are the light intensity imaging and Stokes parameter S1 imaging of the same finger, respectively.

Figure 5 shows the details of the edge of the mastoid stria line displayed in the Stokes parameter S1 imaging image.

Figure 6 shows the fingerprint sweat pores shown in the Stokes parameter S1 imaging image.

Figure 7 shows the double-line papillae in the polarization parameter amplitude ratio γ imaging map.

Fig. 8 is a Stokes parameter S1 imaging diagram of a latent fingerprint on a lens object.

Fig. 9 is the Stokes parameter S1 imaging diagram of the latent fingerprint on the book binder object.

Fig. 10 is a Stokes parameter S1 imaging diagram of a latent fingerprint on a transparent glue object.

Detailed ways

The present invention proposes a label-free Stokes parametric polarization confocal microscopic imaging system and method for latent fingerprints, which performs polarization scanning imaging based on Stokes parameter measurement, and studies and analyzes latent fingerprint images on different bearing objects. Because the object surface and the latent fingerprint carrying the skin surface substance have different polarization-maintaining ability to the active light source, in the fingerprint detection technology, the object carrying the fingerprint is generally an artificial object with strong polarization-maintaining ability, while the latent fingerprint has weak polarization-maintaining ability , so the difference in the polarization characteristics of the two can be used to extract the polarization image of the latent fingerprint that is different from the background.

Experimental principle of the present invention is as follows:

When the beam interacts with the sample, the optical anisotropy of the sample can be described by the Mueller matrix,

Correspondingly, the Stokes vector representation can be used to describe the polarization characteristics of the beam,

Denote the Stokes vector of the incident light as S,

Using the Stokes vector method, all polarization states of light can be described. For perfectly polarized light, the parameters of its Stokes vector satisfy If the light wave Stokes vector satisfies is partially polarized light. However, for natural light, that is, completely unpolarized light, S ₁ =0, S ₂ =0, and S ₃ =0 are satisfied.

Denote the Stokes vector of the outgoing light as S′,

The process of the beam passing through the sample and interacting with the sample can be expressed as the Stokes vector of the incident light being acted on by the Mueller matrix of the sample to obtain the Stokes vector of the outgoing light. The outgoing light after passing through the sample is another beam with different polarization characteristics.

Mathematically described as:

S'=MS or

It can be seen from formula (4) that when the polarization state S of the incident light is determined, the polarization state S' of the outgoing light will be uniquely determined by the Mueller matrix of the sample, so the polarization state S' of the outgoing light can characterize the optical anisotropy distribution of the sample.

The Stokes parametric imaging method uses the Stokes vector S' of the outgoing light to uniquely represent the optical anisotropy distribution of the sample presented by the Mueller matrix. Therefore, a beam of light with a known polarization state is incident, and the Stokes vector S' of the outgoing light is tested. , the optical anisotropy distribution of the sample can be obtained.

The present invention adopts the sub-amplitude confocal scanning system, which can obtain the four components I ₀ , I ₄₅ , I ₉₀ , and I _R of the four components of the Stokes vector S' of the sample exit light on the four optical paths at the same time. According to the formula (5), the output Incident light Stokes parametric imaging.

Among them, S ₀ ' is the sum of the light intensity of the horizontal and vertical polarization components of the light vector, indicating the total light intensity of the light; S ₁ ' is the light intensity difference between the horizontal and vertical polarization components; S ₂ ' is the light at π/4 The difference between the light intensity of the linearly polarized component and the -π/4 direction, combined with I ₄₅ +I _-45 = S ₀ ′, can be written as 2I ₄₅ -S ₀ ′; S ₃ ′ is the right-handed and left-handed circularly polarized components of light The difference in light intensity can be written as 2I _R -S ₀ ′ by combining I _R + _IL ＝ S ₀ ′ in the same way.

For better understanding and implementation, the present invention will be described in detail below in conjunction with the accompanying drawings.

Example 1

Please refer to FIG. 1 , which is a schematic diagram of an imaging scanning experiment performed by a label-free Stokes parametric polarization confocal microscopy imaging system for latent fingerprints in this embodiment. The system includes:

The polarization generation module 10 includes a laser 11 and a polarizer P5; the laser light emitted by the laser 11 generates polarized light through the polarizer P5. The laser 11 is preferably a helium-neon laser.

Confocal scanning module 20, it comprises objective lens L6, displacement stage 21 and lens L0; The polarized light that the polarizer P5 of polarization generation module 10 produces is incident on fingerprint sample Q through objective lens L6 focusing, and described displacement stage 21 is preferably precision displacement The station (PI, E664.S3) realizes XY scanning on the fingerprint sample Q, and after passing through the fingerprint sample Q, the outgoing light carrying the fingerprint information is converted into parallel light by the lens L0.

Polarization measurement module 30, which includes three beam splitters and four-way Stokes polarized light collection optical path; the parallel light transmitted from the lens L0 of the confocal scanning module 20 enters four-way Stokes polarized light collection through three beam splitters The optical path, and the conjugate of the object plane and the detection plane is guaranteed. Specifically, the parallel light transmitted from the lens L0 of the confocal scanning module 20 is vertically incident on the first beam splitter BS1, and is divided into the first reflected light and the first transmitted light; the first reflected light is vertically incident on the second beam splitter. The beam splitter BS2 is divided into the second reflected light and the second transmitted light, which respectively enter the first Stokes polarized light collection optical path and the second Stokes polarized light collection optical path; the first transmitted light is vertically incident on the third beam splitter BS3, Divided into the third reflected light and the third transmitted light, respectively enter the third Stokes polarized light collection optical path and the fourth Stokes polarized light collection optical path. The first Stokes polarized light collection optical path sequentially includes a polarizer P1, an objective lens L1 and a photodetector D1 along the light transmission direction, and the second Stokes polarized light collection optical path sequentially includes a polarizer P2 and an objective lens L2 along the light transmission direction and photodetector D2, the third Stokes polarized light collection optical path includes polarizer P3, objective lens L3 and photodetector D3 successively along the optical transmission direction, and the fourth Stokes polarized light collection optical path includes sequentially along the light transmission direction 1/4 wave plate W4, polarizer P4, objective lens L4 and photodetector D4. Therefore, the light entering each Stokes polarized light collection path is converted into a polarization state by the polarizer, then converged by the objective lens, and then receives an optical signal by the photodetector. The photodetector is preferably a highly sensitive silicon photomultiplier (SiPM, ASD-RGB3S-P).

Data collection imaging module 40, it comprises digital-to-analog converter 41 and processor 42; The signal that is output from the photodetector (D1, D2, D3, D4) of described polarization measurement module 30 is converted and transmitted through digital-to-analog converter 41 to the processor 42 for processing, and finally output a polarization image reflecting fingerprint features.

Please refer to FIG. 2 , which is a schematic diagram of a calibration experiment performed by the label-free Stokes parametric polarization confocal microscopy imaging system of the latent fingerprint in this embodiment. The system also includes:

A normalization module 50, which includes a beam splitter 51, a lens L5 and a photodetector D5. The laser light emitted by the laser 11 is modulated and polarized by the 1/4 wave plate W5 and the polarizer P6 into a specific polarized light. Before the Stokes parameter measurement, the system matrix A is measured by the Equator-Poles calibration method, and then the theoretical value Comparison with experimental values to determine the reliability of the Stokes parameter measurement system. Specifically, in order to reduce the calibration error caused by the light intensity jump of the laser 11, the beam splitter 51 made of a slide glass is used to reflect (the reflection angle is less than 5°) the polarized light, and after being focused by the lens L5, it enters the photodetector D5, obtain the reference optical signal i ₅ . Take the known polarization state beam as the incident light, and use the normalized light intensity matrix I=[i ₁ /i ₅ , i ₂ /i ₅ , i ₃ /i ₅ , i ₄ /i ₅ ] ^T to determine the system matrix a.

The system also includes an aperture G. When performing an imaging scanning experiment, the parallel light emitted from the lens L0 of the confocal scanning module 20 passes through the aperture G and enters the first beam splitter BS1 of the polarization measurement module 30; During the standard experiment, the polarized light generated from the polarizer P6 of the polarization generation module 10 passes through the aperture G and then enters the beam splitter S1 of the normalization module 50 .

This embodiment also provides a marking-free Stokes parametric polarization confocal microscopy imaging method for latent fingerprints. The incident light is incident on the fingerprint sample, the incident light passes through the fingerprint sample and interacts with it, and the Stokes parameter of the outgoing light from the fingerprint sample is measured. , to obtain the Stokes parameter image and the polarization parameter image reflecting the fingerprint characteristics.

Specifically, using the above-mentioned system, the four components I ₀ , I ₄₅ , I ₉₀ , and I _R of the four components of the Stokes vector S' of the outgoing light after passing through the fingerprint sample are obtained on the four-way Stokes polarized light collection optical path, according to the above formula ( 5), Stokes parametric imaging of the outgoing light. The Muller matrix theory is also applicable to the polarizing device. After the light wave passes through any Muller matrix as an M polarizing device, the role of the light wave and the polarizing device can be regarded as the Muller matrix of the light wave Stokes vector left multiplied by the polarizing device, which can also be described by S'=MS. Such as polarizing device Muller matrix, wave plate Muller matrix. If there is not only one polarizing device in the optical system, assuming that the process from the incident light entering the optical system to exiting has passed through n polarizing devices, and their respective Muller matrices are M _n .M ₃ .M ₂ .M ₁ , then the incident light polarization The state S and the polarization state S' of the outgoing light satisfy the following relationship: S'=M _i S, M _i =M _n . . . M ₃ M ₂ M ₁ .

Assuming that the parameters of the outgoing beam vector after passing through the fingerprint sample are S1, S2, S3, and S4, the Muller matrix composed of the components of the first path is M _I , and the Stokes vector of the light received by the first detector is S _I , then through the fingerprint After the sample, the outgoing beam passes through the first beam splitting path to the detector beam can be described as:

It can be obtained from the above that S ₁₀ =a ₁ S ₀₊ a ₂ S ₁₊ a ₃ S ₂₊ a ₄ S ₃ . S ₁₀ is the light intensity of the light received by the detector in the first channel. Similarly, the second, third and fourth channels have similar relationships:

Represented by a matrix:

make

A is the system matrix of the optical system, and its value is the combination of the first row of M _I , M _II , M _III , and M _IV of the optical elements of the four paths. In principle, the system matrix A is required to be an invertible matrix, so it is necessary to design different combinations of polarization elements on the four paths of light so that the first row of the specific Muller matrix for each path is different and linearly independent.

After the test, the following polarizing element combinations were placed under the four paths: the first path is the polarizer P1 with an orientation angle of 0°, and the first row of its Muller matrix is [1 1 0 0]; the second path is the orientation angle of 45° polarizer P2, the first behavior of its Muller matrix is [1 0 1 0]; the third path is polarizer P3 with an orientation angle of 90°, the first behavior of its Muller matrix is [1-1 0 0]; The fourth path is a 1/4 wave plate W4 with an orientation angle of 90° and a polarizer P4 with an orientation angle of 135°, the first row of the Muller matrix is [1 0 0 1]. Assuming that the beam splitters BS1, BS2, and BS3 do not change the polarization state, it can be considered that the system matrix after adding polarizing elements is:

It can be seen that the rows and columns in the system matrix are linearly independent at this time. However, it is impossible for system A to present an ideal estimated value in actual conditions, so calibration is required to determine the elements of system matrix A. Finally, for any incident light beam, as long as the corresponding electrical signal vectors I ₁ , I ₂ , I ₃ , and I ₄ are measured after it enters the system, the Stokes of the light emitted by the fingerprint sample can be calculated according to formula (8). vector and full polarization information.

Imaging Results and Analysis

Utilize the polarization confocal microscopic imaging system of the present invention, select different object materials to carry out experiment, obtain the Stokes parameter and polarization such as degree of polarization, phase difference, azimuth angle and elliptic angle of monochromatic plane polarized light after passing through the object printed with fingerprint imprint Parametric image, to explore the effectiveness of latent fingerprint imaging on different object materials, so as to investigate the feasibility of using Stokes parametric fingerprint imaging, in order to provide some reference for the study of improving the quality of latent fingerprint polarization imaging on various subject objects.

1. Polarization imaging results and analysis of latent fingerprints on glass objects

Polarization imaging is performed on the latent fingerprint on the glass slide object, as shown in Figure 3(a)~(h), and the Stokes parameters S0 (Figure 3(a)), S1 (Figure 3(b) ), S2 (Fig. 3(c)), S3 (Fig. 3(d)), polarization parameter amplitude ratio γ (Fig. 3(e)), phase difference (Fig. 3(f)), azimuth angle θ (Fig. 3(g)), and ellipticity angle ε (Fig. 3(h)). It can be seen that the four Stokes parametric maps all show fingerprint texture information. In addition to showing the first-level features of the overall shape composed of clear ridge lines and mastoid lines, they also include secondary features such as bifurcations and endpoints, which can be viewed as It is used for identification in criminal investigation and proves the feasibility of the fingerprint polarization imaging scheme.

Among them, S0 is the sum of the light intensity of the horizontal and vertical polarization components of the light vector, S1 is the light intensity difference between the horizontal and vertical polarization components, and S2 is the light intensity of the linear polarization components in the π/4 and -π/4 directions The difference, S3 is the difference between the right-handed and left-handed circular polarization components of light. Any one of S0, S1, S2, and S3 can clearly reflect the fingerprint information, but the physical meaning of S1 is more clear, which reflects the difference between two light intensity components in the vertical polarization direction. The technology using this polarization difference imaging principle can Improving the imaging contrast of shallow tissue embodies the idea of linear polarization difference imaging and reflects that the incident horizontal linearly polarized light maintains the original polarization ability after passing through the sample, which is more in line with the requirements of the guiding ideology of this technology. Therefore, the S1 parametric image was selected for analysis.

As shown in Figure 4(a) and Figure 4(b), they are the light intensity imaging map and the Stokes parameter S1 imaging map of the same finger respectively, both of which clearly present the characteristic image of the fingerprint. Comparing Figure 4(a) and Figure 4(b), it can be seen that the background of the three horizontal bars in the light intensity imaging image (Figure 4(a)) is obvious. In contrast, the Stokes parameter S1 imaging image (Figure 4(b) )) It can weaken the background, highlight the fingerprint features, improve the recognition of fingerprints, and make the fingerprint lines clearer. Specifically, in Fig. 4(b), the inner circle of the square is the terminal point in the secondary minutiae feature of the fingerprint, and the bifurcation point of the second-level minutiae feature of the fingerprint is circled in the inner circle.

In addition, in the Stokes parametric image, the third-level feature details of the ridge line that are difficult to observe in the ordinary light intensity image can be revealed: the detail features of the edge of the mastoid ridge line, the distribution of some fingerprint pores and the double-lined mastoid protrusion, As an auxiliary basis for the identification of incomplete and deformed fingerprints.

The edge details of the mastoid line refer to the convex-convex shape reflected by the edge of each mastoid line, which reflects the shape of the striae at the edge of the mastoid line, which belongs to the third-level feature and can be used as the edge shape Features, assisting fingerprint identification. As shown in Figure 5, it can be seen that in the Stokes parameter S1 imaging image, the bumps and depressions in the natural shape of the details of the mastoid line can be clearly observed. Specifically, the inner circle of the circle is the mastoid line depression Part, the inner circle of the square is the raised part of the mastoid line. Since the tertiary features are details that are difficult to observe by other fingerprint imaging methods, this reflects to a certain extent that the system of the present invention has better resolution, and the polarization imaging method of the present invention has certain advantages in fingerprint identification.

Fingerprint sweat pores are also a third-level feature in fingerprint recognition. Because of their stability and uniqueness, they have certain value in fingerprint recognition. The early sweat pore extraction algorithms are computationally intensive and require expensive equipment, but this experiment omits The sweat pore extraction algorithm is adopted, as shown in Figure 6, the inner circle of the circle is the sweat pore part of the three-level detail feature of the fingerprint, and the fingerprint sweat pore can be identified only from the naked eye, although the accuracy of the image obtained in the experiment is low, However, it is a great progress in fingerprint sweat pore extraction, and it has played a great practical value in fingerprint identification.

The mastoid protrusions of the double lines of human fingerprints are determined by the structure of the dermal papilla, as shown in Figure 7, the inner circle of the square is the papillae protrusions of the double lines of human fingerprints, from tanr (sample optical y axis and The amplitude ratio in the x-axis direction) images can be observed in the ordinary light intensity imaging, which is difficult to distinguish the texture details of the epidermis, which proves that the papillae skin of the epidermis reflects the papillae structure of the dermis.

2. Polarization imaging results and analysis of latent fingerprints on other objects

Experiments were carried out with more common transparent material objects in crime scenes. The common transparent material objects and their materials are shown in Table 1 below.

Table 1 Common transparent objects and their materials

object material lens resin book binder PP plastic (polyethylene) transparent glue OPP glue (vinyl and propylene monomer copolymer)

Polarized imaging of latent fingerprints with lenses, book folders and transparent glue as objects, the obtained Stokes parameter S1 diagrams are shown in Figures 8, 9 and 10, respectively. It can be seen from the figure that in the fingerprint imaging with the lens as the object, a relatively uniform double-line papillary protrusion can be observed along the edge of the ridge line. The lens is a concave lens, and the incident light is not perpendicular to the surface of some lenses, resulting in confocal imaging scanning. When the bottom of the image falls out of focus, the clarity and resolution of the lower half of the image will decrease. In the image formed by the fingerprint with the book folder as the object, the resolution is poor, and only the overall morphological lines formed by the mastoid lines can be observed, which has little reference value. In the image formed by the fingerprint with transparent glue as the object, the overall shape and texture formed by the lines can be clearly observed, and the secondary features such as the endpoints and bifurcations of the fingerprint can be seen. The resolution of the fingerprint image obtained on the mobile phone film is not good, which may be due to the high degree of mixing of the mobile phone film material, the transmission and depolarization characteristics are similar to the fingerprint, and the transmission degree is amplified by the anti-reflection film, making the fingerprint image blurred.

Experimental research results show that the method of the present invention can be applied to the fingerprint acquisition imaging research on most transparent objects, by analyzing 4 Stokes parameter diagrams (mainly S1 parameters containing polarization difference imaging significance) and polarization parameter diagrams of the probe light, It is found that the fingerprint polarization method can obtain clear and detailed images of fingerprints printed on some common transparent objects such as glass and lenses. background interference, highlight the fingerprint features, and improve the recognition of fingerprints. The present invention can observe the three-level feature details that are difficult to observe ridges in other fingerprint imaging methods, showing the good effect achieved by the latent fingerprint polarization imaging method. The experimental research on polarization imaging of fingerprints on other objects provided by the invention can provide partial reference for improving the research on the quality of polarization imaging of latent fingerprints on various bearing objects.

The above-mentioned embodiment only expresses one implementation mode of the present invention, and its description is relatively specific and detailed, but it should not be understood as limiting the patent scope of the invention. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Claims (9)

1. a kind of label-free Stokes parameter of latent fingerprint polarizes confocal micro imaging system, it is characterised in that: include:

Polarize generation module comprising laser and polarizing film；The laser that the laser issues generates polarised light through polarizing film；

Cofocus scanning module comprising the first object lens, displacement platform and the first lens；The polarization generated from the polarization generation module Light is incident to fingerprint sample through the focusing of the first object lens, and the displacement platform is for being scanned fingerprint sample, by fingerprint sample The emergent light for carrying finger print information afterwards is converted into directional light outflow through the first lens；

Polarization measurement module comprising three beam splitters and four road Stokes polarize light collection optical path；From the cofocus scanning mould The directional light of the first lens outflow of block enters four road Stokes through three beam splitters and polarizes light collection optical path, and every road Stokes is inclined Light collection optical path of shaking successively includes polarizing film, object lens and photodetector along optical transmission direction；

Data acquisition imaging module comprising digital analog converter and processor；From the photodetector of the polarization measurement module The signal of output converts through digital analog converter and reaches processor and handled, the image of finally output reflection fingerprint characteristic.

2. the label-free Stokes parameter of latent fingerprint according to claim 1 polarizes confocal micro imaging system, feature Be: the first beam splitter of directional light vertical incidence spread out of from the first lens of the cofocus scanning module is divided into the first reflection Light and the first transmitted light；The second beam splitter of the first reflected light vertical incidence, is divided into the second reflected light and the second transmitted light, point It Jin Ru not the first Stokes polarization light collection optical path and the 2nd Stokes polarization light collection optical path；First transmitted light vertically enters Third beam splitter is penetrated, third reflected light and third transmitted light are divided into, respectively enters the 3rd Stokes polarization light collection optical path and the Four Stokes polarize light collection optical path.

3. the label-free Stokes parameter of latent fingerprint according to claim 2 polarizes confocal micro imaging system, feature Be: the 4th Stokes polarization light collection optical path further includes quarter wave plate, and described includes that quarter wave plate is set to third beam splitter Between the polarizing film of the 4th Stokes polarization light collection optical path.

4. the label-free Stokes parameter of latent fingerprint according to claim 3 polarizes confocal micro imaging system, feature Be: the deflection of the polarizing film of the first Stokes polarization light collection optical path is 0 °；The 2nd Stokes polarization The deflection of the polarizing film of light collection optical path is 45 °；The side of the polarizing film of the 3rd Stokes polarization light collection optical path It is 90 ° to angle；The deflection of the quarter wave plate of the 4th Stokes polarization light collection optical path is 90 °, the deflection of polarizing film is 135°。

5. the label-free Stokes parameter of latent fingerprint according to claim 1 or 3 polarizes confocal micro imaging system, special Sign is: the system also includes normalization modules comprising beam splitter, the second lens and the second photodetector；From described The polarised light of generation module generation is polarized through beam splitter reflection to the second lens, enters the second photoelectricity after the second lens focus and visits Device is surveyed, reference optical signal is obtained.

6. the label-free Stokes parameter of latent fingerprint according to claim 5 polarizes confocal micro imaging system, feature Be: the polarised light is by the angle of reflection of beam splitter reflection less than 5 °.

7. the label-free Stokes parameter of latent fingerprint according to claim 6 polarizes confocal micro imaging system, feature Be: the system also includes diaphragm, the directional light spread out of from the first lens of cofocus scanning module enters by the diaphragm First beam splitter of polarization measurement module.

8. the label-free Stokes parameter of latent fingerprint according to claim 7 polarizes confocal micro imaging system, feature Be: the polarised light generated from polarization generation module enters the beam splitter of normalization module after the diaphragm.

9. a kind of label-free Stokes parameter of latent fingerprint polarizes confocal microscopic imaging method, it is characterised in that: use incident light It is incident to fingerprint sample, incident light is had an effect by fingerprint sample and with it, the emergent light that measurement comes out from fingerprint sample Stokes parameter obtains the Stokes parametric image and polarization parameter image of reflection fingerprint characteristic.