RU2484524C1 - System for recording papillary patterns - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: system has a light source, an element which sets the position of the reading surface, an optical system, a multi-element image receiver, electronic memory and a processing device, wherein the output electronic image of the system is associated, through combination in the processing device, with at least two intermediate images of lower resolution, which are associated with the optical image of the reading surface, the spectral composition of which is different for different intermediate images, wherein the position of elements of the optical image on the receiving surface of the image receiver is different for different spectral compositions of radiation.

EFFECT: high reliability, high image quality, small dimensions, faster operation and low power consumption of the system for recording papillary patterns.

8 cl, 4 dwg

Description

Technical field

The invention relates to the field of biometry, in particular to systems for automated registration of papillary patterns.

State of the art

A schematic diagram of a typical papillary pattern registration system is shown in FIG. The light source 1 emits in the direction of the element 2, which sets the position of the reading surface 3 of the registered object, such as, for example, papillary lines of a finger or palm of a hand. On the reading surface, due to the difference in reflection from the areas corresponding to the depressions and protrusions of the papillary pattern, the light flux from the light source becomes the image carrier of this papillary pattern. An optical system, as a rule, including a collective 4, a system of mirrors 5, a lens 6, a protective glass 7 and microlenses 8 above the image receiver, receives this stream and forms an image of a papillary pattern on the photosensitive surface 9 of the multi-element image receiver. The image receiver converts the image from optical to electronic digital in the form of an array of intensity values proportional to the radiation flux incident on the corresponding photosensitive element, and transfers it to electronic memory 10. Processing device 11 converts the scale of this electronic image to a standard one, thereby forming an output image of the system .

An element that sets the position of the registered object is usually made in the form of an optically transparent isosceles rectangular prism. However, there are options for constructing a registration scheme for papillary patterns in which the role of an element that sets the position of the reading surface is played by complex prisms, cylindrical elements, and plane-parallel plates. In more rare cases, the role of the element that sets the position of the reading surface is played by the housing element of the system.

The number of mirrors in an optical system can be different and determines the shape and overall dimensions of the system.

The radiation receiver, as a rule, is made in the form of a ruler or matrix based on metal-oxide-semiconductor transistors or charge-coupled devices.

A common drawback of these systems, due to extremely stringent requirements for image quality, is the need to use image receivers with relatively large sizes of photosensitive elements, which leads to significant overall dimensions of the working surface of the receivers and, as a consequence, the extremely high cost of systems built with their use.

The reason for the significant price of large-area receivers is the high cost of the silicon wafers from which they are made, and the low percentage of use of the area of such wafers.

Thus, FIG. 2 a shows the arrangement on a silicon wafer 12 with a diameter of 150 mm of crystals 13 of a typical image detector for a registration system for a papillary palm pattern with a resolution of 1000 dpi. Such a receiver has a photosensitive element size of 6.8 μm and contains 7216 elements horizontally and 5412 vertically. From the figure it can be seen that only 4 such crystals are placed on the plate. In addition, in this case, the useful area of the plate used for the manufacture of crystals is only about 50% of its total area. If, during the manufacturing process, only four critical manufacturing defects 14 are allowed, but located, for example, as shown in Fig. 2a, then no suitable crystal will be obtained from this plate.

If you build a receiver with the same number of photosensitive elements, but with a size of 1.4 microns, then the arrangement of crystals on the plate 15 with a diameter of 150 mm can be, for example, as shown in Fig.2B. In this case, 137 crystals 16 are placed on the plate, which already occupy 80% of the plate area. At the same time, if four critical manufacturing defects 17, located in the same manner as shown in Fig. 2a, are admitted during manufacture, then 133 suitable crystals will be obtained from this plate. Thus, due to defects, the losses will amount to only 3% of the total number of crystals on the plate.

However, despite the obvious advantages, the use of receivers with small sizes of photosensitive elements in registration systems of papillary patterns is constrained by insufficient quality of the image formed, in particular, noise and charge spreading between the elements to comply with current biometric standards. The main such standard for papillary pattern registration systems is currently the FBI EBTS Appendix F.

There are few options for constructing papillary pattern registration systems that implement the required resolution and size of the reading area when using relatively cheap image receivers.

So, in US patent 5859420 dated January 12, 1999 for IPC G01B 11/124, a system is shown in which the resolution of the registration system of papillary patterns is increased by dividing the system into several channels, each of which forms a separate image part of the registered object, after which the image parts are combined into output image.

US Pat. No. 6,928,195 of 08/09/2005 to IPC G06K 9/32 shows a system that can increase the resolution of a papillary pattern registration system without increasing the number of photosensitive elements of an image receiver by using a swinging mirror system to form several spatially spaced-apart intermediate images and generate an output image in which elements of intermediate images alternate.

This system is the closest analogue of the invention. Its main drawback is the presence of additional elements and procedures that, although they allow the use of a relatively inexpensive receiver, however, they themselves make an additional contribution to the high cost of the system and reduce its reliability. As a result, a significant reduction in the total cost of the system is not achieved, but at the same time reliability is reduced, dimensions are increased, energy consumption is increased and system performance is reduced.

Object of the invention

The objective of the present invention is the implementation of the registration system of papillary patterns with low cost, high reliability and at the same time providing high image quality, small overall dimensions, high speed and low power consumption.

SUMMARY OF THE INVENTION

This problem is solved due to the fact that the registration system of papillary patterns contains a light source that forms the working radiation, an element that sets the position of the reading surface of the papillary pattern, an optical system that reads the image of this surface at an angle i to its normal, a multi-element image receiver, electronic memory for image storage and processing device, and in electronic memory the output image of the reading surface of the papillary pattern is electrically connected with at least two intermediate images of lower resolution than the output, by combining, in the processing device, the intensity values between the elements of the intermediate images intersecting in the different intermediate images the same image area of the reading surface of the papillary pattern, and each of the intermediate images is electrically connected to the photosensitive elements of the image receiver which are connected optically to the radiation source and the reading surface of the papillary pattern through the formed e optical system image reading surface of the fingerprint, the spectral composition of which varies in different intermediate images, wherein the optical position of the image elements on the image receiving surface of the receiver differently for radiation of different spectral compositions.

The image receiver is preferably monochromatic.

Intermediate images are preferably associated with the photosensitive elements of the image receiver through the normalization of histograms in the processing device in order to compensate for the mismatch between the histograms of the intermediate images due to differences in the light flux from the light source, reflection coefficient from the recorded object, transmission of the optical system and the sensitivity of the image receiver for different spectral radiation compositions.

Between the reading surface and the image receiver, the system preferably comprises a refractive surface that is asymmetrical with respect to the optical beam connecting the centers of the subject and the image. In another embodiment, the part of the optical system that forms the actual image of the reading surface may have an increase in chromatism sufficient to effect the necessary mutual displacement of intermediate images of different spectral composition.

The spectral composition of the working radiation preferably lies in the range from 380 to 1200 nm.

The read angle i is preferably greater than the total internal reflection angle for the material from which the element defining the position of the read surface is made.

The processing device, the image receiver, and the light source are preferably electrically coupled to provide synchronization of the reading period of the intermediate images with the radiation period of the desired spectral composition.

Result of invention

The technical result provided by the given set of features is to reduce the cost, increase reliability, ensure high image quality, small overall dimensions, high speed and low power consumption of the registration system of papillary patterns.

The implementation of the invention

An example embodiment of the invention can be shown based on the circuit shown in figure 3. A light source, which is a light panel 1, capable of emitting in two spectral ranges due to the use of two types of LEDs with dominant radiation wavelengths of 470 and 525 nm, alternately and synchronously with flash pulses from a camera containing an image receiver, emits in one of these ranges direction of an isosceles rectangular prism 2 of optically transparent material. After passing the input side of the prism 21, light enters at the angle of total internal reflection on the hypotenuse face 3, which defines the reading surface of the papillary pattern. A registered object, such as, for example, papillary lines of a finger or palm of a hand, is placed on this surface. In places corresponding to the protrusions of the papillary pattern, the luminous flux from the light source is partially absorbed by the registered object, in other zones it is completely reflected by the hypotenuse face of the prism. Thus, the luminous flux becomes the image carrier of the registered papillary pattern. Next, the light passes through the output cathete face 22 of the prism, plane-parallel plate 30, collective 4, is reflected on the mirror 5 and enters the lens 6. The lens forms an image of the recorded object on the photosensitive surface 9 of the monochromatic camera built on a metal-oxide-semiconductor transistor matrix. Moreover, one photosensitive element accounts for 1.5 elements of the required resolution at the registered object, and the images for two emitted spectral ranges are mutually offset on the receiving surface by an amount corresponding to 0.5 of the size of the element of the required resolution. This displacement is achieved due to dispersion on a plane-parallel plate 30, inclined with respect to the optical axis. Rays of different wavelengths are refracted on the surface 31 at different angles and, as a result, reach the surface 32 at different points. After refraction on surface 32, the rays of different wavelengths are mutually parallel and mutually offset. The elements of the optical system and the image receiver are rigidly mounted on a single housing. The camera generates a digital image of the recorded object in the form of an array of intensity values associated with the light flux incident on the corresponding photosensitive element, and transfers it via USB to the memory 10 of the computer with the processor 11. Thus, two intermediate images are transmitted, and the first intermediate image is read camera during light emission with a dominant wavelength of 470 nm, and the second during radiation of light with a dominant wavelength of 525 nm. Further, the intensities of the elements of the second image are normalized by a computer program to ensure the mutual correspondence of the histograms of the first and second images. The deviation from this correspondence is caused by the difference in the luminous flux from the light source, the reflection coefficient from the detected object, the transmission of the optical system and the sensitivity of the image receiver for different spectral compositions of the radiation. From the obtained two intermediate images, one output image is formed. For this, a computer program combines the intensities of the elements intersecting the same area in the image of the registered object. The principle of this combination for the image area is shown in Fig.4. Let in order to obtain the output image of zone A on the registered object two vertical mutually displaced images with dominant wavelengths of 470 and 525 nm corresponding to zones B and C on the registered object, which coincide in the horizontal direction with zone A, are formed by marks A1, B1, C1, A2, B2, C2, etc. the elements of the registered object corresponding to the resolution elements of the corresponding image are indicated. It is easy to see that the intensity value of element B1 corresponds to the sum of the intensity value of element A1 and 0.5 of the intensity value of element A2. In addition, the intensity value of element C1 corresponds to a sum of 0.5 of the intensity value of element A1 and the intensity value of element A2. Those. we get a system of two equations with two unknowns:

A1 + 0.5A2 = B1

0.5 · A1 + A2 = C1.

Solving this system, we obtain the intensities A1 and A2 of the output image:

. $$\begin{array}{c}A\mathrm{one}=\frac{B\mathrm{one}-0.5\cdot C\mathrm{one}}{0.75}\\ \mathrm{<figure-callout\; id="2"\; label="A"\; filenames="00000003.png,00000005.png"\; state="\{\{state\}\}">A</figure-callout>}2=C\mathrm{one}-0.5\cdot A\mathrm{one}\end{array}$$

.

Further, A3 = B2-0.5 · A2.

In a similar way, intensity values for all elements of the output image can be calculated.

The applicant made samples of papillary pattern scanners that implement the present invention. The experimental data confirmed that when combining mutually offset images of different spectral composition, it is possible to build a papillary pattern registration system that meets the FBI EBTS Appendix F standard using an image receiver with less than the number of elements of the output image, the number of photosensitive elements.

The use of a small photosensitive pad has led to a relatively low cost of the image receiver and lower power consumption. The formation of the output image with increased resolution and the normalization of histograms of intermediate images made it possible to ensure high image quality. Also, due to the small size of the photosensitive surface, the focal length of the lens was significantly reduced compared to the closest analogue, which led to a decrease in the size of the system and the cost of the lens. There are no moving elements in the system, which leads to an increase, in comparison with the closest analogue, in the speed and reliability of the system.

Brief Description of the Drawings

The prior art and the invention is illustrated by drawings.

Figure 1 shows a typical diagram of the construction of the registration system of papillary patterns.

Figure 2 shows the location of the crystals of the image receiver with the number of photosensitive elements 7216 horizontally and 5412 vertically on a plate with a diameter of 150 mm for various sizes of photosensitive elements. Figure 2a shows crystals with an element size of 6.8 μm, and Figure 2b shows crystals with an element size of 1.4 μm.

Figure 3 shows a diagram of an implementation of the registration system of papillary patterns, built on a multi-band light source and using a combination of mutually offset intermediate images of different spectral composition to obtain a higher resolution output image.

Figure 4 shows a combination scheme of mutually offset intermediate images of different spectral composition to obtain a higher resolution output image.

Claims (8)

1. The registration system of papillary patterns, containing a light source that generates working radiation, an element that sets the position of the reading surface of the papillary pattern, an optical system that reads the image of this surface at an angle i to its normal, a multi-element image receiver, an electronic memory for storing images, and a processing device , characterized in that in electronic memory the output image of the reading surface of the papillary pattern is electrically connected with at least two intermediate images less resolution than the output resolution, by combining in the processing device the intensity values between the elements of the intermediate images intersecting in the different intermediate images the same region of the image of the reading surface, and each of the intermediate images is connected electrically to the photosensitive elements of the image receiver, which are optically connected the radiation source and the reading surface of the papillary pattern through the surface image formed by the optical system the reading angle, and the reading angle i and the spectral composition of the working radiation provide a difference in the light flux in the reading direction for the protrusions and depressions of the papillary pattern, the spectral composition of the radiation is not the same in different intermediate images, and the position of the optical image elements on the receiving surface of the image receiver is not the same for these different spectral radiation compositions. 2. The system according to claim 1, characterized in that the image receiver is monochromatic. 3. The system according to claim 1, characterized in that the intermediate images are connected with the photosensitive elements of the image receiver through the normalization of the histograms in the processing device in order to compensate for the mismatch between the histograms of the intermediate images due to differences in the luminous flux from the light source, reflection coefficient from the recorded object, transmission optical system and image detector sensitivity for various spectral compositions of radiation. 4. The system according to claim 1, characterized in that between the read surface and the image receiver, the system comprises a refractive surface that is asymmetric with respect to the optical beam connecting the centers of the object and the image. 5. The system according to claim 1, characterized in that the part of the optical system that forms the actual image of the reading surface has an increase in chromatism sufficient to effect the necessary mutual displacement of intermediate images of different spectral composition. 6. The system according to claim 1, characterized in that the spectral composition of the working radiation lies in the range from 380 to 1200 nm. 7. The system according to claim 1, characterized in that the reading angle i exceeds the angle of total internal reflection for the material from which the element specifying the position of the reading surface is made. 8. The system according to claim 1, characterized in that the processing device, the image receiver and the light source are electrically connected to ensure synchronization of the reading period of the intermediate images with the radiation period of the desired spectral composition.

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