Physical method for correcting LSC based on screen printing

Abstract

The invention relates to a physical method for correcting LSC based on screen printing, which belongs to the technical field of image processing, and comprises the following steps: constructing a relative illumination curve of a lens in vein recognition equipment; calculating a light intensity adjustment coefficient of each near-infrared lamp bead in the vein recognition equipment according to the relative illumination curve; screen printing is designed according to the light intensity adjustment coefficient; and covering a near-infrared optical filter above a near-infrared lamp bead of the vein recognition equipment with the silk screen. According to the method, the vein recognition speed is increased while the production efficiency of vein equipment is improved.

Description

Technical Field

[0001] This invention relates to the field of image processing technology, and in particular to a physical method for correcting LSC based on screen printing. Background Technology

[0002] Due to the physical characteristics of the lens, the amount of light it transmits gradually decreases from the center to the edges. As a result, the original image captured by the lens usually shows that the brightness of the central pixels is higher, and the brightness of the pixels decreases as they move towards the edges.

[0003] Current industry practices employ concentric circle and grid methods to perform lens shading correction (LSC) on the original image, increasing the grayscale around the edges of the image to align with the center and improve image quality. Traditional solutions require LSC correction for each module, increasing production time and reducing efficiency. Furthermore, using concentric circle and grid methods for lens shading correction in the ISP increases image optimization time, ultimately impacting finger vein recognition speed. Summary of the Invention

[0004] This invention provides a physical method for LSC correction based on screen printing. Screen printing is applied to the near-infrared filter above the near-infrared LED beads, which avoids LSC correction for each module and does not increase the image optimization time.

[0005] To achieve the above objectives, the present invention provides the following solution: This invention relates to a physical method for correcting LSCs based on screen printing, comprising the following steps: Construct the relative illumination curve of the lens in the vein recognition device; The light intensity adjustment coefficient of each near-infrared LED in the vein recognition device is calculated based on the relative illumination curve. The screen printing design is based on the light intensity adjustment coefficient; The silkscreen is applied to the near-infrared filter above the near-infrared LED beads of the vein recognition device.

[0006] Preferably, the calculation of the light intensity adjustment coefficient for each near-infrared LED in the vein recognition device based on the relative illuminance curve includes: The light intensity of each near-infrared LED in the vein recognition device at the lens imaging position is obtained based on the relative illumination curve. The light intensity adjustment coefficient for each near-infrared LED bead is calculated based on the light intensity at the location of each near-infrared LED bead in the vein recognition device.

[0007] Preferably, the light intensity of each near-infrared LED bead in the vein recognition device at the lens imaging position is obtained based on the relative illumination curve as follows: Obtain the relative illumination of each near-infrared LED in the vein recognition device at the lens imaging position; Calculate the light intensity of each near-infrared LED in the vein recognition device at the lens imaging position.

[0008] Preferably, the method for calculating the light intensity of each near-infrared LED at the lens imaging position in the vein recognition device is as follows: set the light intensity of each near-infrared LED as a, then the light intensity of each near-infrared LED at the lens imaging position is the product of a and the relative illuminance of that near-infrared LED at the lens imaging position.

[0009] Preferably, the step of calculating the light intensity adjustment coefficient of each near-infrared LED bead based on the illuminance at the location of each near-infrared LED bead in the vein recognition device includes: setting the standard light intensity of the near-infrared LED bead as b, and dividing the light intensity adjustment coefficient b by the light intensity of the near-infrared LED bead at the imaging position of the lens.

[0010] Preferably, the screen printing design based on the light intensity adjustment coefficient is as follows: Calculate the screen printing width coefficient corresponding to each near-infrared lamp bead, wherein the screen printing width coefficient is the difference between 1 and the light intensity adjustment coefficient of the corresponding near-infrared lamp bead; Calculate the screen printing width corresponding to each near-infrared LED bead. The screen printing width is the width of the near-infrared filter above the near-infrared LED bead multiplied by the screen printing width coefficient corresponding to that near-infrared LED bead.

[0011] Preferably, the relative illuminance curve of the lens in the vein recognition device is constructed by sequentially measuring the illuminance at each position of the lens field of view in the vein recognition device, and calculating the ratio of the illuminance at the center of the lens field of view to the illuminance at other positions.

[0012] Preferably, the screen printing is made of an opaque material.

[0013] Preferably, the screen printing is ink.

[0014] The physical method for LSC correction based on screen printing involved in this invention first calculates the light intensity adjustment coefficient of each LED bead, then designs the screen printing according to the light intensity adjustment coefficient, and then covers the near-infrared filter above the near-infrared LED bead of the vein recognition device with the screen printing. The LSC correction is performed physically, which avoids performing LSC correction on each module, thus improving production efficiency. It also eliminates the need to use the concentric circle method and grid method to correct lens shadows on the original image in the ISP, thus not increasing the image optimization time and improving the speed of finger vein recognition. Attached Figure Description

[0015] Appendix Figure 1 Add finger vein images captured before screen printing to vein recognition devices.

[0016] Appendix Figure 2 This invention relates to a flowchart of a physical method for correcting LSCs based on screen printing.

[0017] Appendix Figure 3 This refers to the relative illumination curve of the lens involved in this invention.

[0018] Appendix Figure 4 The image of a finger vein is captured after adding a silkscreen to the vein recognition device in this invention. Detailed Implementation

[0019] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be specifically described below in conjunction with embodiments and accompanying drawings, but the scope of protection of the present invention is not limited thereto.

[0020] Finger vein recognition technology is a biometric identification technology that uses images of veins in a person's finger to identify that person. The first step in finger vein recognition technology is to acquire an image of the user's finger veins using a finger vein recognition device. Depending on the application scenario, the arrangement of the near-infrared LEDs and the lighting method of the finger vein recognition device vary. In side-lit finger vein recognition devices, as described in the background section, due to the physical characteristics of the lens, the acquired image typically has high brightness in the center pixels and low brightness in the pixels around the edges. This can cause the light to hit the sides of the finger, resulting in an image like the one shown below. Figure 1 The uneven grayscale shown leads to an increase in overexposed areas and a decrease in the effective area, affecting the recognition rate of finger veins. Example 1:

[0021] To solve the above technical problems, refer to the appendix. Figure 2 As shown, this invention relates to a physical method for correcting LSCs based on screen printing, comprising the following steps: Step 101: Construct the relative illuminance curve of the lens in the vein recognition device; Illuminance is defined as the brightness of an object or surface illuminated by a light source, and relative illuminance is the ratio of the central illuminance to the peripheral illuminance.

[0022] In one embodiment, a uniform object is placed on the vein recognition device instead of a finger, an image of the uniform object is acquired, and then the illuminance at each position in the lens's field of view is measured sequentially. The ratio of the illuminance at the center of the lens's field of view to the illuminance at other positions is calculated to construct a relative illuminance curve for the lens. In this embodiment, since fingers are irregular, a uniform object is used to construct the relative illuminance curve to avoid the influence of finger irregularities.

[0023] Step 102: Calculate the light intensity adjustment coefficient of each near-infrared LED in the vein recognition device based on the relative illuminance curve, specifically including: Step 1021: Obtain the light intensity of each near-infrared LED bead in the vein recognition device at the lens imaging position based on the relative illumination curve. The specific steps are as follows: Step 10211: Obtain the relative illumination of each near-infrared LED bead in the vein recognition device at the lens imaging position; Step 10212: Calculate the light intensity of each near-infrared LED in the vein recognition device at the lens imaging position. The calculation method is as follows: set the light intensity of each near-infrared LED as a, then the light intensity of each near-infrared LED at the lens imaging position is the product of a and the relative illuminance of the near-infrared LED at the lens imaging position. Step 1022: Calculate the light intensity adjustment coefficient of each near-infrared LED bead based on the light intensity at the location of each near-infrared LED bead in the vein recognition device. The calculation method is as follows: set the standard light intensity of the near-infrared LED bead as b, and divide the light intensity adjustment coefficient b by the light intensity of the near-infrared LED bead at the imaging position of the lens.

[0024] Step 103: Design the silkscreen printing based on the light intensity adjustment coefficient. The specific steps are as follows: Step 1031: Calculate the screen printing width coefficient corresponding to each near-infrared lamp bead, wherein the screen printing width coefficient is the difference between 1 and the light intensity adjustment coefficient of the corresponding near-infrared lamp bead; Step 1032: Calculate the screen printing width corresponding to each near-infrared LED bead. The screen printing width is the width of the near-infrared filter above the near-infrared LED bead multiplied by the screen printing width coefficient corresponding to that near-infrared LED bead.

[0025] Step 104: Apply the silkscreen to the near-infrared filter above the near-infrared LED of the vein recognition device.

[0026] Each near-infrared LED emits near-infrared light that passes through a uniform object and enters the lens for imaging. Because of lens shading, the light intensity of each LED varies within the lens's field of view. In practical use, this results in uneven grayscale in the image on both sides of the finger. Therefore, a light intensity adjustment coefficient can be set according to the different light intensities, thus ensuring uniform imaging on both sides of the finger in actual use. Example 2:

[0027] In one embodiment, the vein recognition device uses a side-illumination method, with five near-infrared LEDs on each side.

[0028] Step 201: Construct the relative illumination curve of the lens in the vein recognition device, as shown in the attached figure. Figure 3 As shown, the horizontal axis represents image height, and the vertical axis represents relative illumination; Step 202: Obtain the relative illumination of the five near-infrared LEDs at the lens imaging position, which are 0.6, 0.8, 1, 0.8, and 0.6 respectively. Step 203: Assuming the light intensity of the near-infrared LED is 1, the light intensities of the 5 near-infrared LEDs at the lens imaging position are 0.6, 0.8, 1, 0.8, and 0.6, respectively. Step 204: To ensure that the light intensity values ​​of the five LEDs are consistent across the lens's field of view, calculate the light intensity adjustment coefficients for each of the five LEDs. Taking a standard light intensity of 0.5 as an example, the light intensity adjustment coefficients for the five LEDs are: 0.5 / 0.6, 0.5 / 0.8, 0.5 / 1, 0.5 / 0.8, and 0.5 / 0.6, which are equivalent to: 0.83, 0.625, 0.5, 0.625, and 0.83. Step 205: Calculate the screen printing width coefficient corresponding to each near-infrared lamp bead, which are 1-0.83, 1-0.625, 1-0.5, 1-0.625, 1-0.83, i.e. 0.17, 0.375, 0.5, 0.375, 0.17; Step 206: Calculate the screen printing width corresponding to each near-infrared LED bead, which is the width of the near-infrared filter multiplied by the screen printing width coefficient corresponding to that near-infrared LED bead. Step 207: The silkscreen is applied to the near-infrared filter above the near-infrared LED of the vein recognition device, thereby ensuring uniform imaging on both sides of the finger during actual use, as shown in the attached image. Figure 4 As shown. Example 3:

[0029] In one embodiment, the screen printing is made of an opaque material, preferably an opaque ink.

[0030] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A physical method for correcting LSCs based on screen printing, characterized in that, The method includes: Construct the relative illumination curve of the lens in the vein recognition device; The light intensity adjustment coefficient of each near-infrared LED in the vein recognition device is calculated based on the relative illumination curve. The screen printing design is based on the light intensity adjustment coefficient; The silkscreen is applied to the near-infrared filter above the near-infrared LED beads of the vein recognition device.

2. The physical method for correcting LSC based on screen printing according to claim 1, characterized in that, The calculation of the light intensity adjustment coefficient for each near-infrared LED in the vein recognition device based on the relative illuminance curve includes: The light intensity of each near-infrared LED in the vein recognition device at the lens imaging position is obtained based on the relative illumination curve. The light intensity adjustment coefficient for each near-infrared LED bead is calculated based on the light intensity at the location of each near-infrared LED bead in the vein recognition device.

3. The physical method for correcting LSC based on screen printing according to claim 2, characterized in that, The light intensity of each near-infrared LED bead in the vein recognition device at the lens imaging position is obtained according to the relative illumination curve: Obtain the relative illumination of each near-infrared LED in the vein recognition device at the lens imaging position; Calculate the light intensity of each near-infrared LED in the vein recognition device at the lens imaging position.

4. The physical method for correcting LSC based on screen printing according to claim 3, characterized in that, The method for calculating the light intensity of each near-infrared LED at the lens imaging position in the vein recognition device is as follows: set the light intensity of each near-infrared LED as a, then the light intensity of each near-infrared LED at the lens imaging position is the product of a and the relative illuminance of that near-infrared LED at the lens imaging position.

5. The physical method for correcting LSC based on screen printing according to claim 2, characterized in that, The calculation of the light intensity adjustment coefficient for each near-infrared LED bead based on the illuminance at the location of each near-infrared LED bead in the vein recognition device includes: setting the standard light intensity of the near-infrared LED bead as b, and dividing the light intensity adjustment coefficient b by the light intensity of the near-infrared LED bead at the imaging position of the lens.

6. The physical method for correcting LSC based on screen printing according to claim 1, characterized in that, The silkscreen design based on the light intensity adjustment coefficient is as follows: Calculate the screen printing width coefficient corresponding to each near-infrared lamp bead, wherein the screen printing width coefficient is the difference between 1 and the light intensity adjustment coefficient of the corresponding near-infrared lamp bead; Calculate the screen printing width corresponding to each near-infrared LED bead. The screen printing width is the width of the near-infrared filter above the near-infrared LED bead multiplied by the screen printing width coefficient corresponding to that near-infrared LED bead.

7. The physical method for correcting LSC based on screen printing according to claim 1, characterized in that, The relative illuminance curve of the lens in the vein recognition device is constructed as follows: the illuminance at each position of the lens field of view in the vein recognition device is measured sequentially, and the ratio of the illuminance at the center of the lens field of view to the illuminance at other positions is calculated.

8. The physical method for correcting LSC based on screen printing according to claim 1, characterized in that, The screen printing is made of an opaque material.

9. The physical method for correcting LSC based on screen printing according to claim 8, characterized in that, The screen printing is done with ink.

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