CN105279486A - Optical fingerprint identification method - Google Patents

Abstract

The invention provides an optical fingerprint identification method suitable for improving the performance of optical fingerprint identification. The method comprises a transparent light guide substrate; light is subjected to a plurality of times of total reflection in the light guide substrate and is transmitted from the peripheral region of a fingerprint to the region of the fingerprint; a finger touches the light guide substrate, and the fingerprint comprises ridges and valleys; and as the reflection conditions of the ridges and the valleys are different, brightness difference of the ridges and the valleys are caused, and a fingerprint image is formed.

Description

Optical Fingerprint Recognition Method

technical field

The invention relates to the field of image processing, in particular to an optical fingerprint recognition method.

Background technique

The optical fingerprint sensor uses the principle of refraction and reflection of light. The light that hits the ridges (protrusions between the lines) on the surface of the finger will be totally reflected, and the reflected light will be projected onto the image sensor to form a black image, while the reflected light will be projected onto the image sensor to form a black image. The light on the valley line of the finger (the concave part between the lines) is absorbed by the finger to form a white image, so that the optical fingerprint sensor will capture a multi-grayscale fingerprint image with alternating light and dark. However, because the existing optical fingerprint sensor receives totally reflected light, it requires a long optical path and a large volume, so it is difficult to apply it to portable electronic devices such as mobile phones; way, but this way requires the finger to have a certain humidity to ensure the imaging quality, and the choice of the color of the film is also limited, which increases the cost of the sensor.

Existing optical fingerprint sensors mainly include three parts: LED light source, rectangular prism, and CMOS sensor. As shown in FIG. 1 , put finger 13 on rectangular prism 12 , under the illumination of LED light source 14 , the light shoots from the bottom to rectangular prism 12 , and reaches the upper surface of rectangular prism 12 , that is, the surface where finger 13 is placed. If the light beam arrives at the ridge of the finger, the light beam will form internal total reflection, transmit from the other side of the rectangular prism 12 , and reach the CMOS image sensor 11 . If the position where the light beam arrives is the valley line of the finger, the light beam will be absorbed by the skin of the finger 13 .

Contents of the invention

In view of the understanding of the technical issues in the background art.

The present invention provides a method for optical fingerprint recognition, which is suitable for improving the performance of optical fingerprint recognition. Fingerprint area: the finger is in contact with the light guide substrate, and the fingerprint of the finger includes: ridges and valleys. Due to the inconsistent reflection conditions of the ridges and valleys, the brightness of the ridges and valleys is different, forming a fingerprint image.

Preferably, the ridges of the fingerprint destroy the total reflection condition of light in the light guide substrate to form diffuse reflection, and the valleys maintain the total reflection condition; resulting in the brightness of the ridges being higher than that of the valleys, forming a fingerprint image.

Preferably, the thickness of the light guide substrate is less than or equal to 1 mm, and the dielectric constant n of the light guide substrate is: n=1.2 to n=1.8.

Preferably, the original energy of the light irradiating the ridge is 1, and the energy after being refracted and reflected by the skin of the finger is 0.15; the energy ratio of the diffuse reflection light irradiating the valley and the ridge is between 0.75 and 0.9, which increases the ridge image and The light energy contrast between valley images improves the resolution of recognition.

Preferably, when the light is transmitted from the light guide substrate to the first surface, the light and the normal form an angle, the angle is greater than or equal to the total reflection angle, and the total reflection angle is arcsin(1/n).

Preferably, the incident light is light that decays quickly in the skin of the finger, and the wavelength of the light is: 100nm to 380nm, 1100nm to 2000nm.

Preferably, an optical auxiliary element is further arranged under the light guide substrate, the optical auxiliary element is a triangular prism or a polygonal prism, and the material is glass or optical resin.

Preferably, the material of the light guide substrate is glass.

In the present invention, through the design of the light guide substrate, the total reflection conditions of the light on the ridges and valleys of the fingerprint are different, and the total reflection conditions of the ridges are destroyed while the total reflection conditions of the valleys are maintained, so that the contrast of the imaged images of the ridges and valleys is greater , the imaging effect is better; in addition, the present invention saves the composition and structure of the optical fingerprint recognition device and adopts a simple structure to achieve good imaging effect.

Description of drawings

Fig. 1 is the schematic diagram of the optical path of optical fingerprint identification in the prior art;

2 is a schematic diagram of the optical path of the optical fingerprint identification method in an embodiment of the present invention;

Fig. 3 is a schematic diagram of an optical path of an optical fingerprint identification method in another embodiment of the present invention.

detailed description

In order to improve the performance of optical fingerprint identification, reduce the cost, and reduce the thickness of the equipment using optical fingerprint identification, the present invention provides a method for optical fingerprint identification, providing a transparent light guide substrate; the light passes through multiple total reflections in the light guide substrate, From the area around the fingerprint to the fingerprint area; the finger touches the light guide substrate, and the fingerprint includes: ridges and valleys. Due to the inconsistent reflection conditions of the ridges and valleys, the brightness of the ridges and valleys is different, forming a fingerprint image.

For the detailed description of the specific embodiment of the present invention, Fig. 2 is a schematic diagram of the optical path of the optical fingerprint identification method in one embodiment of the present invention; Fig. 3 is a schematic diagram of the optical path of the optical fingerprint identification method in another embodiment of the present invention . Please refer to Fig. 2, the light 10' enters from the other two sides of the optical fingerprint recognition device. After entering the light guide substrate 11', the light 10' can undergo multiple total reflections in the light guide substrate 11', and the finger 12' presses On the first surface 110' of the light guide substrate 11', due to the factor of the finger 12', when the light 10' is transmitted to the base surface of the finger 12' and the light guide substrate 11', diffuse reflection may occur due to different total reflection conditions, The finger includes a ridge 121' and a valley 122'. The ridge 121' is close to the first surface 110' of the light guide substrate, and the valley 122' is far away from the first surface 110' of the light guide substrate. Since the reflection conditions of the ridge 121' and the valley 122' are inconsistent, The ridge 121' of the fingerprint destroys the total reflection condition of light in the light guide substrate, forming diffuse reflection, and the valley 122' maintains the total reflection condition; this will cause the brightness of the ridge 121' to be higher than that of the valley 122', forming a fingerprint image. The energy difference between the ridge 121 ′ and the valley 122 ′ of the fingerprint image formed at this time is larger and the image effect is better. For example: the original energy of the light irradiating the ridge 121' is 1, after refraction it is 0.9, the reflectance of the skin is 0.18, the energy after refraction and diffuse reflection by the ridge 121' of the finger skin is about 0.15; and at this time the valley 122' Still total reflection and little energy loss, the light energy difference between the light irradiating the valley 122' and the ridge 121' is very large, which increases the light energy contrast between the ridge image and the valley image, and improves the resolution of recognition. The material of the light guide substrate 11' is transparent light guide material such as glass, its thickness is less than or equal to 1 mm, and the dielectric constant of the light guide substrate is n=1.2 to 1.8. The original energy of the light 10' irradiating the ridge 121' is 1, and the energy after being refracted and reflected by the skin of the finger is 0.15; the energy ratio of the diffuse reflection light irradiating the valley and the ridge is between 0.75 and 0.9, in this embodiment In 13/15, the light energy contrast between the ridge image and the valley image is increased to improve the resolution of recognition. When the light 10' is transmitted to the first surface 110' from the light guide substrate 11', the light 10' forms a second angle A with the normal, the second angle A is greater than or equal to the total reflection angle, and the total reflection angle is arcsin(1/ n). In this embodiment, the incident light is light that attenuates quickly in the skin of the finger, and the wavelength of the light is: 100nm~380nm, 1100nm~2000nm. Please refer to Fig. 3 , an optical auxiliary element 14' is arranged under the light guide substrate 11' in Fig. 3, and the optical auxiliary element 14' is a triangular prism or a polygonal prism, and the material is glass or optical resin. In this embodiment, a triangular prism is used. Preferably, one side 141' of the triangular prism is in physical contact with the second surface 111' of the light guide substrate, and the other side of the triangular prism is the incident light plane 142', and the incident light plane 142' is arranged to be inclined. The plane ensures that the optical path of light entering the light guide substrate through the optical auxiliary component meets the requirements. In the present invention, through the design of the light guide substrate, the total reflection conditions of the light on the ridges and valleys of the fingerprint are different, and the total reflection conditions of the ridges are destroyed while the total reflection conditions of the valleys are maintained, so that the image contrast of the imaged ridges and valleys is greater. , the imaging effect is better; in addition, the present invention saves the composition and structure of the optical fingerprint recognition device and adopts a simple structure to achieve good imaging effect.

Other changes to the disclosed embodiments can be understood and effected by those skilled in the art by studying the specification, the disclosure, the drawings and the appended claims. In the practical application of the present invention, one component may perform the functions of multiple technical features cited in the claims. In the claims, the word "comprising" does not exclude other elements and steps, and the word "a" does not exclude a plurality. Any reference signs in the claims should not be construed as limiting the scope.

Claims (8)

1. A method for optical fingerprint identification, suitable for improving the performance of optical fingerprint identification, comprising: Provide a transparent light guide substrate; the light is transmitted from the area around the fingerprint to the fingerprint area through multiple total reflections in the light guide substrate; When the finger touches the light guide substrate, the fingerprint of the finger includes: ridges and valleys. Due to the inconsistent reflection conditions of the ridges and valleys, the brightness of the ridges and valleys is different, forming a fingerprint image. 2. the method for optical fingerprint identification according to claim 1, is characterized in that, The ridges of the fingerprint destroy the total reflection condition of the light in the light guide substrate to form diffuse reflection, and the valleys maintain the total reflection condition; the brightness of the ridges is higher than that of the valleys, forming a fingerprint image. 3. the method for optical fingerprint identification according to claim 1, is characterized in that, The thickness of the light guide substrate is less than or equal to 1 mm, and the dielectric constant n of the light guide substrate is: n=1.2 to n=1.8. 4. The method for optical fingerprint identification according to claim 2, characterized in that, the original energy of the light irradiating the ridge is 1, and the energy after refraction and reflection by the finger skin is 0.15; the diffuse energy of the light irradiating the valley and the ridge The reflected light energy ratio is between 0.75 and 0.9, which increases the light energy contrast between the ridge image and the valley image, and improves the resolution of recognition. 5. The method for optical fingerprint identification according to claim 1, wherein when the light is transmitted from the light guide substrate to the first surface, the light and the normal line form an angle, and the angle is greater than or equal to the total reflection angle, The total reflection angle is arcsin(1/n). 6. The method for optical fingerprint identification according to claim 1, characterized in that the incident light is light that decays quickly in the skin of the finger, and the wavelength of the light is: 100nm to 380nm, 1100nm to 2000nm. 7. The method for optical fingerprint identification according to claim 1, characterized in that, an optical auxiliary element is arranged under the light guide substrate, the optical auxiliary element is a triangular prism or a polygonal prism, and the material is glass or optical resin. 8. The optical fingerprint recognition method according to claim 1, wherein the material of the light guide substrate is glass.