Biometric image acquisition methods, chips, terminals, and storage media

Abstract

This invention relates to the field of biometric detection technology, and discloses a method, chip, terminal, and storage medium for acquiring biometric images. The method for acquiring biometric images includes: determining a vertical synchronization (VSYNC) period; calculating a target exposure time based on the VSYNC period and a pre-stored calibration exposure time; wherein the target exposure time is the exposure time that differs least from the calibration exposure time among exposure times that are integer multiples of the VSYNC period; and acquiring a biometric image based on the target exposure time, thereby avoiding horizontal stripes in the acquired biometric image and improving the accuracy of subsequent biometric identification or registration.

Description

Technical Field

[0001] This invention relates to the field of biometric detection technology, and in particular to a method for acquiring biometric images, a chip, a terminal, and a storage medium. Background Technology

[0002] Biometric technology has emerged as a new interactive technology in terminal unlocking solutions, with optical fingerprint recognition becoming a particularly convenient and fast option. Optical fingerprint recognition uses an under-screen fingerprint design; simply press the fingerprint icon area displayed on the screen to unlock. More and more mobile phone manufacturers are supporting optical fingerprint recognition, and are also incorporating screens from different manufacturers, resulting in significant differences between these screens.

[0003] Currently, during the overall device calibration phase, a fixed exposure time is used to calibrate the biometric acquisition chip within the device; this fixed exposure time can be called the calibration exposure time. After the device leaves the factory, biometric image acquisition is performed based on this calibration exposure time. However, consistently using this calibration exposure time for biometric image acquisition under all circumstances can easily result in horizontal stripes appearing in the acquired biometric images, reducing the accuracy of subsequent biometric recognition or registration. Summary of the Invention

[0004] The purpose of this invention is to provide a method, chip, terminal, and storage medium for acquiring biometric images, which can avoid horizontal stripes in the acquired biometric images and improve the accuracy of subsequent biometric identification or registration.

[0005] To address the aforementioned technical problems, embodiments of the present invention provide a method for acquiring biometric images, comprising: determining a vertical synchronization (VSYNC) period; calculating a target exposure time based on the VSYNC period and a pre-stored calibration exposure time; wherein the target exposure time is the exposure time that differs least from the calibration exposure time among exposure times that are integer multiples of the VSYNC period; and acquiring a biometric image based on the target exposure time.

[0006] To address the aforementioned technical problems, embodiments of the present invention provide a chip located within a terminal and connected to a memory within the terminal. The memory stores instructions executable by the chip, which are then executed by the chip to enable the chip to perform the aforementioned biometric image acquisition method.

[0007] To address the aforementioned technical problems, embodiments of the present invention provide a terminal that includes a display screen and the aforementioned chip.

[0008] To address the aforementioned technical problems, embodiments of the present invention provide a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the aforementioned method for acquiring biometric images.

[0009] In this embodiment of the invention, a target exposure time is calculated based on a determined VSYNC period and a pre-stored calibration exposure time. The target exposure time is the exposure time that differs least from the calibration exposure time among exposure times that are integer multiples of the VSYNC period. Biometric images are acquired based on the target exposure time. Since the target exposure time is an integer multiple of the VSYNC period, the biometric images acquired based on this target exposure time can eliminate horizontal lines. The calibration exposure time is a fixed exposure time obtained during the overall device calibration phase, considering various factors. Under the calibration exposure time, relatively effective biometric images can be acquired. Therefore, the target exposure time being the exposure time that differs least from the calibration exposure time among exposure times that are integer multiples of the VSYNC period is beneficial for acquiring relatively effective biometric images while eliminating horizontal lines. It also helps to avoid the situation where the biometric image cannot be acquired if the target exposure time is too small, and it also helps to avoid the situation where the biometric image is overexposed due to the target exposure time being too large. Attached Figure Description

[0010] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, and these illustrative descriptions do not constitute a limitation on the embodiments.

[0011] Figure 1 This is a schematic diagram of horizontal lines appearing in the fingerprint image mentioned in the embodiments of this application;

[0012] Figure 2 This is a schematic diagram illustrating that the closer the exposure time T is to an integer multiple of the PWM cycle, the finer the horizontal lines will be, as mentioned in the embodiments of this application.

[0013] Figure 3 This is a schematic diagram illustrating that the further the exposure time T is from the integer multiple of the PWM cycle mentioned in the embodiments of this application, the thicker the horizontal lines will be;

[0014] Figure 4 This is a schematic flowchart of a biometric image acquisition method mentioned in the embodiments of this application;

[0015] Figure 5 This is another flowchart illustrating the biometric image acquisition method mentioned in the embodiments of this application;

[0016] Figure 6 This is a schematic diagram showing that the horizontal lines in the fingerprint image mentioned in the embodiments of this application have been completely eliminated;

[0017] Figure 7This is a schematic diagram of the chip structure mentioned in the embodiments of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details are presented in the various embodiments of the present invention to facilitate a better understanding of this application. However, the technical solutions claimed in this application can be implemented even without these technical details and various changes and modifications based on the following embodiments. The division of the various embodiments below is for ease of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined with and referenced by each other without contradiction.

[0019] Organic Light-Emitting Diode (OLED) screens use Pulse Width Modulation (PWM) dimming. This method adjusts brightness not by changing power, but by alternating between on and off states. For example, when the screen is on, it doesn't emit light continuously; it constantly turns on and off. When the on / off cycle is fast enough, the human eye perceives the screen as constantly lit. The longer the off state lasts, the lower the perceived brightness. Conversely, a longer on-time corresponds to a shorter off-time, making the screen appear brighter. PWM dimming inherently involves periodic brightness drops. When the chip collects data, it uses line exposure, which is an integral process. When each line is captured with varying brightness, alternating bright and dark stripes are produced. Since biometric image acquisition is always based on calibrated exposure time, variations in brightness across lines can easily occur, leading to horizontal stripes in the acquired biometric images. For example, refer to... Figure 1 , Figure 1 The fingerprint image was captured by the chip, and horizontal lines appeared in the fingerprint image.

[0020] To solve the aforementioned technical problems, the inventors of this application discovered through experimental research that the width of the horizontal stripes also changes regularly with each millisecond increment of the exposure time T: (See reference...) Figure 2 , Figure 2 From left to right, the images are six fingerprint images acquired over six exposure durations T. The six exposure durations T progressively approach or even equal integer multiples of the PWM cycle. Figure 2 It can be seen that the closer the exposure time T is to an integer multiple of the PWM cycle, the finer the horizontal lines become, sometimes even almost non-existent. (Reference) Figure 3 , Figure 3From left to right, the images are six fingerprint images acquired over six exposure durations T. The six exposure durations T progressively move further away from integer multiples of the PWM cycle. Figure 3 It can be seen that the further the exposure time T deviates from an integer multiple of the PWM period, the thicker and more obvious the horizontal lines become. This indicates that the horizontal lines are related to the PWM period, and setting the exposure time to an integer multiple of the PWM period can eliminate the horizontal lines. Furthermore, the inventors of this application have discovered that in practical implementations, the screen's PWM period is difficult to obtain, and the PWM period dynamically changes according to the screen brightness. Currently, neither screen manufacturers nor terminal operating systems provide an interface for obtaining the screen's PWM period, making it difficult to acquire. Based on this, the inventors of this application conducted further experimental research, using a photosensor to measure the relationship between the vertical synchronization (VSYNC) period and the PWM period under various brightness conditions. The research found that the VSYNC period and the PWM period exhibit an integer multiple relationship under various brightness conditions. Therefore, it can be concluded that setting the exposure time to an integer multiple of the VSYNC period can also eliminate the horizontal lines, and the VSYNC period is easier to obtain than the PWM period, as the VSYNC period can be the same as the screen refresh period. Therefore, the study concludes that setting the exposure time to an integer multiple of the VSYNC cycle or the screen refresh cycle can also eliminate horizontal lines.

[0021] Based on the experimental research results of the inventors of this application, one embodiment of this application provides a method for acquiring biometric images, applied to a chip, which can also be called a biometric acquisition chip, such as a fingerprint chip. The chip can be installed in a terminal, such as a mobile phone or tablet computer. Specifically, the chip installed in the terminal can be a chip located under the screen of the terminal; for example, a fingerprint chip can be an under-display fingerprint chip. The implementation details of the biometric image acquisition method of this embodiment are described below. The following content is only for ease of understanding and is not essential for implementing this solution.

[0022] The biometric image acquisition method in this embodiment is as follows: Figure 4 As shown, it includes:

[0023] Step 401: Determine the vertical synchronization VSYNC period;

[0024] Step 402: Calculate the target exposure time based on the VSYNC cycle and the pre-stored calibration exposure time;

[0025] Step 403: Acquire biometric images based on the target exposure duration;

[0026] The target exposure duration is the exposure duration that differs the least from the calibrated exposure duration among the exposure durations that are integer multiples of the VSYNC period.

[0027] In this embodiment, since the target exposure time is an integer multiple of the VSYNC period, the biometric image acquired based on this target exposure time can eliminate horizontal lines. The calibrated exposure time is a fixed exposure time obtained by calibrating the entire device, including the chip, at the factory, taking into account various factors. Under the calibrated exposure time, relatively effective and high-quality biometric images can be acquired. Therefore, the target exposure time is the exposure time that differs the least from the calibrated exposure time among the exposure times that are integer multiples of the VSYNC period. This is beneficial for acquiring relatively effective biometric images while eliminating horizontal lines, avoiding the situation where the biometric information cannot be acquired due to an insufficient target exposure time, and also avoiding the situation where the acquired biometric image is overexposed due to an excessively long target exposure time.

[0028] In step 401, the VSYNC cycle can also be understood as the screen refresh cycle, or as the screen's VSYNC cycle, the terminal's operating system (such as Android), the VSYNC cycle of the vertical synchronization signal, etc. Assume the screen contains 1080*1920 pixels, that is, 1080 pixels per row and 1920 pixels per column. The process of the display drawing 1080 pixels in one row is called a row scan, and drawing all 1920 rows is called a field scan. The physical signal that begins scanning one row is called the horizontal synchronization (Hsync) signal, and the physical signal that begins scanning one field is called the vertical synchronization (VSYNC) signal. The interval between the generation times of two consecutive VSYNC signals can be understood as the VSYNC cycle.

[0029] In one example, the chip can be located in a terminal, which includes a display screen. The VSYNC cycle can be considered the display screen's content refresh cycle. When the display screen is understood as a screen, its content refresh cycle can also be understood as the screen refresh cycle.

[0030] In one example, the VSYNC period can be determined as follows: the chip acquires the timestamps of two consecutive VSYNC signals; the difference between the two timestamps is calculated, and this difference is used as the VSYNC period. For instance, if the timestamps of the two consecutive VSYNC signals are Tx1 and Tx2, then the VSYNC period Tv = Tx2 - Tx1. Since timestamps are typically in the nanosecond range and are highly precise, the VSYNC period obtained from the difference between the timestamps of the two consecutive VSYNC signals is more accurate.

[0031] In one example, the timestamps of two consecutive VSYNC signals are obtained separately, including obtaining the timestamps of the two consecutive VSYNC signals through the requestNextVSYNC interface. The requestNextVSYNC interface is the requestNextVSYNC interface of the Android system's DisplayService. The requestNextVSYNC interface is one of the standard interfaces of the current Android system, and it is convenient to directly obtain the timestamps of the VSYNC signals by utilizing existing interfaces of the Android system.

[0032] In one example, obtaining the timestamps of two consecutive VSYNC signals is performed by: obtaining the timestamps of two consecutive VSYNC signals through a custom first interface. The first interface can be used to obtain the timestamps of the VSYNC signals. The first interface can be configured according to actual needs; this embodiment does not impose specific limitations on it.

[0033] In another example, the VSYNC period can be determined by acquiring the VSYNC frequency and then determining the VSYNC period based on that frequency. For instance, if the VSYNC frequency is denoted as Fv (in Hz), then the VSYNC period Tv = 1 / Fv. Determining the VSYNC period based on the acquired VSYNC frequency provides a more convenient and faster method for determining the VSYNC period.

[0034] In one example, obtaining the VSYNC frequency includes using the `AChoreographer_registerRefreshRateCallback` interface. The `AChoreographer_registerRefreshRateCallback` interface is one of the standard interfaces in the current Android system, and is an interface within the Android NDK. This interface facilitates the direct acquisition of the VSYNC frequency using existing Android system interfaces, making the VSYNC frequency determination simpler and more direct.

[0035] In one example, obtaining the VSYNC frequency includes: obtaining the VSYNC frequency through a custom second interface; wherein, the second interface can be used to obtain the VSYNC frequency. The second interface can be configured according to actual needs, and this embodiment does not impose specific limitations on it.

[0036] In one example, the chip can determine the VSYNC period in real time, and then combine the real-time determined VSYNC period to calculate the target exposure time in real time. This allows the target exposure time to adapt to the VSYNC period, which may change, thereby more accurately eliminating horizontal stripes in biometric images.

[0037] In step 402, the pre-stored calibration exposure time can be a fixed exposure time calibrated during the whole-device calibration stage. The calibration exposure time is affected by chip characteristics, overall screen brightness, screen structure, and image quality. The calibration exposure time is typically a fixed exposure time obtained by considering various factors under specific brightness conditions (e.g., high brightness, medium brightness, low brightness, or the desired operating brightness for the chip); these factors can include the aforementioned: chip characteristics, overall screen brightness, screen structure, and image quality. Because the calibration exposure time is obtained by calibrating multiple factors, relatively effective biometric images can be acquired based on the calibration exposure time. The calibrated exposure time can be pre-stored in a preset file in the whole device. This preset file can be set according to actual needs; this embodiment does not specifically limit this. The chip can read the calibration exposure time from the preset file in the whole device, which can be understood as a terminal such as a mobile phone or tablet computer.

[0038] In one example, the chip can multiply multiple preset integers by the VSYNC period, obtaining products for each integer. These products are then compared to the calibration exposure time to determine a target integer. The product of the target integer and the VSYNC period is closest to the calibration exposure time compared to the other integers. Finally, the product of the target integer and the VSYNC period is taken as the target exposure time. In other words, the target exposure time can be the exposure time closest to the calibration exposure time among multiple candidate exposure times that are integer multiples of the VSYNC period; where the multiple candidate exposure times can be the products of the aforementioned integers.

[0039] In practical implementation, if the calibration exposure time is on the order of tens of milliseconds and the VSYNC period is on the order of less than 10 milliseconds, then the preset integers can include, for example, 1 to 10. For instance, if the VSYNC period is 1 / 120Hz ≈ 8.33ms and the calibration exposure time is 36ms, then 8.33ms × 4 = 33.32ms and 8.33ms × 5 = 41.65ms. Since 33.32ms is closer to 36ms, the target integer can be 4, corresponding to a target exposure time of 33.32ms. In other words, in this embodiment, the target exposure time can be set to an integer multiple of the VSYNC period, and the target exposure time can be taken around the calibration exposure time (closest to the calibration exposure time). This minimizes the impact on the system's anti-counterfeiting and biometric image acquisition performance.

[0040] In step 403, the chip acquires a biometric image based on the target exposure time. Specifically, the chip can expose its photosensitive area to the target exposure time and obtain the photosensitive value of the photosensitive area, and then obtain the biometric image based on the photosensitive value. In a practical implementation, the target exposure time can be understood as the exposure time for the chip to acquire the biometric image, that is, the exposure time used by the chip when acquiring the biometric image is the target exposure time.

[0041] In one example, the biometric image can be a fingerprint image, and the corresponding chip can be a fingerprint chip. Optionally, in a specific implementation, the biometric image can also be a palm print image, an iris image, etc., and the corresponding chip can be a palm print recognition chip, an iris recognition chip, etc.

[0042] In practical implementation, after the chip acquires biometric images, it can perform biometric identification or registration as needed. For example, after acquiring a fingerprint image, the chip can perform fingerprint identification or registration as needed.

[0043] In one embodiment, the method for acquiring biometric images is as follows: Figure 5 As shown, it includes:

[0044] Step 501: Determine the vertical synchronization VSYNC period;

[0045] Step 502: Calculate the ratio of the pre-stored calibration exposure time to the VSYNC cycle;

[0046] Step 503: Determine if the ratio is an integer; if yes, proceed to step 305; otherwise, proceed to step 306.

[0047] Step 504: Round the comparison values ​​to the nearest integer to obtain the integer ratio;

[0048] Step 505: Calculate the product of the integer ratio and the VSYNC period, and use the product as the target exposure duration;

[0049] Step 506: Calculate the product of the ratio and the VSYNC period, and use the product as the target exposure duration;

[0050] Step 507: Collect biometric images based on the target exposure time.

[0051] Steps 501 and 507 are largely the same as steps 401 and 403 in the above embodiments, and will not be repeated here to avoid repetition. The main difference between this embodiment and the above embodiments lies in the method of calculating the target exposure time.

[0052] The following mainly explains the calculation method of the target exposure time in this embodiment, namely steps 502 to 506:

[0053] In step 502, the pre-stored calibration exposure time is denoted as Te, and the VSYNC period is denoted as Tv. Then, the ratio n of the calibration exposure time to the VSYNC period calculated by the chip is:

[0054] In step 504, if the chip determines that n is not an integer, it can round n to obtain an integer ratio. In a specific implementation, if n is an integer, the product of n and the VSYNC period can be directly used as the target exposure time.

[0055] In step 505, the chip can calculate the product of the integer ratio and the VSYNC period Tv, and use this product as the target exposure time. By rounding, it ensures that the final target exposure time is both an integer multiple of the VSYNC period Tv and deviates minimally from the calibration exposure time Te, thereby eliminating horizontal stripes in the biometric image while maintaining system performance. Maintaining system performance can be understood as ensuring that the chip can acquire relatively effective and high-quality biometric images.

[0056] In step 506, if the chip determines that the ratio n of the pre-stored calibration exposure time and VSYNC period is an integer, the product of the ratio and the VSYNC period can be directly calculated, and the product is used as the target exposure time. Calculating the ratio directly yields an integer multiple of the VSYNC period, which is beneficial for quickly calculating a reasonable target exposure time.

[0057] In one example, the chip is an under-display fingerprint chip, and the biometric image acquired based on the target exposure time is a fingerprint image, which can be referenced. Figure 6 , Figure 6This is an image captured by the under-display fingerprint chip based on the actual exposure time of the target. (The last sentence appears to be incomplete and possibly refers to a different image.) Figure 6 As can be seen, the horizontal lines in the fingerprint image are completely eliminated. This verifies that the conclusion reached by the inventors of this application, namely that "setting the exposure time to an integer multiple of the VSYNC cycle or the screen refresh cycle can also eliminate horizontal lines," is valid in practical applications.

[0058] In this embodiment, the ratio of the calibration exposure time to the VSYNC period is calculated. When the ratio is not an integer, it is rounded to the nearest integer. The integer ratio is then used as the integer multiple that the VSYNC period needs to be multiplied to calculate the target exposure time. This allows for the rapid calculation of the target exposure time, which is close to the calibration exposure time after multiplication by the VSYNC period. This speeds up the acquisition of biometric images.

[0059] It should be noted that the examples described above in this embodiment are merely illustrative for ease of understanding and do not constitute a limitation on the technical solution of the present invention.

[0060] The steps of the various methods described above are only for clarity. In practice, they can be combined into one step or some steps can be split into multiple steps. As long as they include the same logical relationship, they are all within the scope of protection of this patent. Adding insignificant modifications or introducing insignificant designs to the algorithm or process, but without changing the core design of the algorithm and process, are also within the scope of protection of this patent.

[0061] One embodiment of the present invention relates to a chip such as Figure 7 As shown, it includes a processing unit 701 and a storage unit 702 connected to the processing unit 701. The storage unit 702 stores instructions that can be executed by the processing unit 701. The instructions are executed by the processing unit 701 so that the processing unit 701 can perform the biometric image acquisition method in any of the above embodiments.

[0062] Embodiments of this application also relate to a terminal, which includes a display screen and further includes, as well as, Figure 7 The chip shown above, the VSYNC cycle mentioned above can be the refresh cycle of the display screen in the terminal.

[0063] Embodiments of this application also relate to a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, it implements the above-described method embodiments.

[0064] That is, those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a device (which may be a microcontroller, chip, etc.) or processor to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0065] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of the present invention.

Claims

1. A method for acquiring biometric images, characterized in that, include: Determine the vertical synchronization VSYNC period; The target exposure time is calculated based on the VSYNC period and the pre-stored calibration exposure time; wherein, the target exposure time is the exposure time that differs from the calibration exposure time the least among the exposure times that are integer multiples of the VSYNC period; the ratio of the calibration exposure time to the VSYNC period is calculated, and the target exposure time is calculated based on the ratio and the VSYNC period; Based on the target exposure duration, biometric images are acquired.

2. The method for acquiring biometric images according to claim 1, characterized in that, The determination of the vertical synchronization VSYNC period includes: Obtain the timestamps of the two consecutive VSYNC signals generated; Calculate the difference between the timestamps when the two consecutive VSYNC signals are generated, and determine the difference as the VSYNC period.

3. The method for acquiring biometric images according to claim 2, characterized in that, The step of obtaining the timestamps of the generation of the two consecutive VSYNC signals includes: The timestamps of the two consecutive VSYNC signals are obtained through the requestNextVSYNC interface.

4. The method for acquiring biometric images according to claim 1, characterized in that, The determination of the vertical synchronization VSYNC period includes: Obtain the VSYNC frequency and determine the VSYNC period based on the VSYNC frequency.

5. The method for acquiring biometric images according to claim 4, characterized in that, The acquisition of the VSYNC frequency includes: The VSYNC frequency is obtained through the AChoreographer_registerRefresh RateCallback interface.

6. The method for acquiring biometric images according to any one of claims 1 to 5, characterized in that, The step of calculating the target exposure time based on the VSYNC period and the pre-stored calibration exposure time includes: Calculate the ratio of the calibration exposure duration to the VSYNC period; When the ratio is not an integer, the ratio is rounded to the nearest integer to obtain an integer ratio. Calculate the product of the integer ratio and the VSYNC period, and use the product as the target exposure duration.

7. The method for acquiring biometric images according to any one of claims 1 to 5, characterized in that, The step of calculating the target exposure time based on the VSYNC period and the pre-stored calibration exposure time includes: Calculate the ratio of the calibration exposure duration to the VSYNC period; When the ratio is an integer, the product of the ratio and the VSYNC period is calculated, and the product is used as the target exposure duration.

8. The method for acquiring biometric images according to any one of claims 1 to 5, characterized in that, The biometric image is a fingerprint image.

9. A chip, characterized in that, The device includes a processing unit and a storage unit connected to the processing unit. The storage unit stores instructions that can be executed by the processing unit, which are executed by the processing unit to enable the processing unit to perform the biometric image acquisition method as described in any one of claims 1 to 8.

10. The chip according to claim 9, characterized in that, The target exposure time refers to the exposure time for the chip to acquire biometric images.

11. A terminal comprising a display screen, characterized in that, include: The chip as described in claim 9.

12. The terminal according to claim 11, characterized in that, The VSYNC cycle is the content refresh cycle of the display screen.

13. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the biometric image acquisition method according to any one of claims 1 to 8.

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