Memory-saving fingerprint image generation method and device

Abstract

The present invention discloses a method and apparatus for generating a fingerprint image that saves memory. The method includes generating a first fingerprint image of an original data size based on a plurality of first analog sensing signals read from a fingerprint sensor array before the end of an exposure period. Then, the first fingerprint image represented by a first data size equal to or less than the original data size is stored. After generating the first fingerprint image of the original data size, a second fingerprint image of the original data size is generated based on a plurality of second analog sensing signals read from the fingerprint sensor array during the exposure period. Then, the second fingerprint image represented by a compressed data size smaller than the original data size is stored.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 124,103, filed on December 11, 2020. The entire content of the above - mentioned patent application is hereby incorporated by reference and made a part of this specification. Technical Field

[0003] The present invention relates to fingerprint image generation, and more particularly to a fingerprint image generation method and apparatus that save memory, reduce bandwidth, and improve fingerprint recognition processing efficiency. Background Art

[0004] Biometric data processing or biometric authentication is used to identify an individual's identity. Biometric features such as fingerprints are unique for each person.

[0005] To obtain better images, a fingerprint sensor array captures fingerprint images. For example, if the fingerprint sensor array has 270x270 sensing pixels and the data volume of each image is 270x270x12 bits. Thus, to capture six images, the size of the static random - access memory (SRAM) required to store the six images is 270x270x12 bits multiplied by 6, or 6 times 270x270x12 - bit data.

[0006] Unfortunately, this data volume results in slower fingerprint acquisition speed, excessive bandwidth requirements, and increased data transmission size.

[0007] Therefore, it is desirable to improve the fingerprint recognition system to enhance the efficiency of fingerprint image generation processing. Summary of the Invention

[0008] An object of the present invention is to provide a fingerprint image generation method and apparatus that save memory.

[0009] The fingerprint image generation method and apparatus include generating a first fingerprint image of an original data size based on a plurality of first analog sensing signals read from a fingerprint sensor array before the end of an exposure period; storing the first fingerprint image represented by a first data size equal to or less than the original data size; after generating the first fingerprint image of the original data size, generating a second fingerprint image of the original data size based on a plurality of second analog sensing signals read from the fingerprint sensor array during the exposure period; and storing the second fingerprint image represented by a compressed data size less than the original data size.

[0010] In a specific embodiment of the present invention, the fingerprint image generation method for saving memory further includes generating a third fingerprint image of the original data size according to a plurality of third analog sensing signals read from the fingerprint sensor array during the exposure period after generating the second fingerprint image of the original data size; and storing the third fingerprint image represented by the compressed data size smaller than the original data size.

[0011] In a specific embodiment of the present invention, the fingerprint image generation method for saving memory further includes generating the second fingerprint image represented by the compressed data size by calculating a difference image between the first fingerprint image of the original data size and the second fingerprint image of the original data size.

[0012] In a specific embodiment of the present invention, the method further includes storing the second fingerprint image of the original data size.

[0013] In a specific embodiment of the present invention, the method further includes generating a third fingerprint image of the original data size according to a plurality of third analog sensing signals read from the fingerprint sensor array during the exposure period after generating the second fingerprint image of the original data size; generating the third fingerprint image represented by the compressed data size smaller than the original data size by calculating a difference image between the second fingerprint image of the original data size and the third fingerprint image of the original data size; and storing the third fingerprint image represented by the compressed data size.

[0014] In a specific embodiment of the present invention, the method further includes storing the first fingerprint image of the original data size; obtaining a first reference pixel data in the first fingerprint image of the original data size, where the first reference pixel data is the minimum pixel data in the first fingerprint image of the original data size; and generating the first fingerprint image represented by the first data size smaller than the original data size by subtracting the first reference pixel data from the first fingerprint image of the original data size.

[0015] In a specific embodiment of the present invention, the method further includes storing the second fingerprint image of the original data size; obtaining a second reference pixel data in the second fingerprint image of the original data size, where the second reference pixel data is the minimum pixel data in the second fingerprint image of the original data size; and generating the second fingerprint image represented by the compressed data size by subtracting the second reference pixel data from the second fingerprint image of the original data size.

[0016] In a specific embodiment of the present invention, the method further includes generating the second fingerprint image represented by the compressed data size by subtracting the first reference pixel data from the second fingerprint image of the original data size.

[0017] In a specific embodiment of the present invention, the method further includes storing the first fingerprint image of the original data size; obtaining a first reference pixel data in the first fingerprint image of the original data size, where the first reference pixel data is the minimum pixel data in the first fingerprint image of the original data size; and generating the second fingerprint image represented by the compressed data size smaller than the original data size by subtracting the first reference pixel data from the second fingerprint image of the original data size.

[0018] In a specific embodiment of the present invention, the method further includes transmitting the first fingerprint image represented by the first data size and the second fingerprint image represented by the compressed data size to a backend processor.

[0019] In a specific embodiment of the present invention, the method further includes transmitting the "compressed" reference pixel data generated based on the minimum pixel data in the second fingerprint image of the original data size to the backend processor; and transmitting the "compressed" reference pixel data generated based on the minimum pixel data in the first fingerprint image of the original data size to the backend processor.

[0020] In a specific embodiment of the present invention, the fingerprint image generation method for saving memory further includes determining a touch position of a finger touch event occurring on a touch screen, where the touch screen includes a touch sensor array, the array includes a plurality of touch sensing electrodes, and a fingerprint sensor array, the array includes a plurality of fingerprint sensing pixels; finding positions of a plurality of touch sensing electrodes corresponding to a plurality of touch sensing data greater than or not less than a threshold value; generating a first fingerprint image corresponding to a fingerprint reading area determined based on the touch position; and storing a part of the first fingerprint image as a valid fingerprint image, where the area of the valid fingerprint image is determined according to the positions of the touch sensing electrodes corresponding to the touch sensing data greater than or not less than the threshold value.

[0021] In a specific embodiment of the present invention, the method further includes generating a first fingerprint image corresponding to a fingerprint reading area determined based on a touch position; and not storing a part of the first fingerprint image, which is a plurality of fingerprint sensing data not within a predetermined digital range.

[0022] In a specific embodiment of the present invention, the fingerprint image generation method for saving memory further includes storing other parts of the first fingerprint image, and these parts are a plurality of fingerprint sensing data within the predetermined digital range.

[0023] Another object of the present invention is to provide a fingerprint image generation method for saving memory, such as static random access memory (SRAM).

[0024] The fingerprint image generation method according to a specific embodiment of the present invention includes capturing a plurality of fingerprint images. The first fingerprint image is captured in the original data size. For example, the image is captured in the original data size of 270x270x12-bit data.

[0025] Then a second image is captured. In a specific embodiment, the second image data is subtracted from the first image data (subtracting at the same position) to obtain the difference between the first and second images. When the second image is subtracted from the first image, the difference between the first image data and the second image data will be a positive number. Then the difference value between the first image and the second image (also known as the difference image) is used to represent the second image and stored in the memory for the second image data, thereby saving memory.

[0026] Then a third image is captured. The third image data is subtracted from the second image data (subtracting at the same position) to obtain the difference between the second and third images. Since the exposure time of the third image is longer than that of the second image, when the third image is subtracted from the second image, the difference value between the second image and the third image will be a positive number.

[0027] This process is performed on a plurality of fingerprint images. For example, six fingerprint images.

[0028] The original data of the fingerprint images obtained with different exposure time lengths will be relatively close. The memory only stores the original data size of the first image, and all others only store the difference images.

[0029] In a specific embodiment of the present invention, the fingerprint image generation device for saving memory includes an analog-to-digital converter for generating a first fingerprint image in the original data size according to a plurality of first analog sensing signals read from a fingerprint sensor array before the end of the exposure period; a memory for storing the first fingerprint image represented by a first data size equal to or smaller than the original data size; after generating the first fingerprint image in the original data size, the analog-to-digital converter further generates a second fingerprint image in the original data size according to a plurality of second analog sensing signals read from the fingerprint sensor array during the exposure period; and the memory stores the second fingerprint image represented by a compressed data size smaller than the original data size.

[0030] In a specific embodiment of the present invention, a fingerprint image generating device for saving memory includes a touch controller for determining a touch position of a finger touch event occurring on a touch screen, where the touch screen includes a touch sensor array including a plurality of touch sensing electrodes, and a fingerprint sensor array including a plurality of fingerprint sensing pixels; the touch controller finds positions of the touch sensing electrodes corresponding to a plurality of touch sensing data greater than or not less than a threshold; a fingerprint reading circuit for generating a first fingerprint image corresponding to determining a fingerprint reading area based on the touch position; and storing a part of the first fingerprint image as a valid fingerprint image, where an area of the valid fingerprint image is determined according to positions of the touch sensing electrodes corresponding to the touch sensing data greater than or not less than the threshold.

[0031] In a specific embodiment of the present invention, a fingerprint image generating device for saving memory includes a fingerprint reading circuit for generating a first fingerprint image corresponding to determining a fingerprint reading area based on a touch position; the fingerprint reading circuit does not store a part of the first fingerprint image, and the part is a plurality of fingerprint sensing data not within a predetermined digital range.

[0032] The present invention can save memory, reduce transmission time and improve user experience.

[0033] To achieve the above object, the present invention provides a fingerprint image generating method and device for saving memory, reducing bandwidth and improving fingerprint recognition processing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1A A diagram illustrating a fingerprint recognition system according to a specific embodiment of the present invention;

[0035] Figure 1B A diagram illustrating a fingerprint reading circuit and a fingerprint recognition system according to a specific embodiment of the present invention;

[0036] Figure 2A A diagram illustrating a timing control diagram for a fingerprint image generating method according to a specific embodiment of the present invention, taking generating six images as an example;

[0037] Figure 2B A diagram illustrating Figure 2A an image data table of a first image among a total of six images in

[0038] Figure 2C A diagram illustrating Figure 2A a fingerprint image data table of a second image among a total of six images in

[0039] Figure 2D For illustrating the Figure 2A image data table obtained by subtracting the first image from the second image among a total of six images in

[0040] Figure 3A Same Figure 2A , a diagram for illustrating a timing control diagram of a fingerprint image generation method according to a specific embodiment of the present invention, Figure 3A marking the control timings of the second image and the third image;

[0041] Figure 3B For illustrating the Figure 3A image data table of the second image among a total of six images in

[0042] Figure 3C For illustrating the Figure 3A image data table of the third image among a total of six images in

[0043] Figure 3D For illustrating the Figure 3A image data table obtained by subtracting the second image from the third image among a total of six images in

[0044] Figure 3E , a diagram for illustrating the flow of a fingerprint image generation method according to a specific embodiment of the present invention;

[0045] Figure 3F For illustrating a fingerprint sensor circuit diagram according to a specific embodiment of the present invention;

[0046] Figure 3G For illustrating a diagram of a fingerprint gate driver array (GOA) circuit (labeled as FPR GOA scan circuit inside Figure 1A ) of a panel according to a specific embodiment of the present invention;

[0047] Figure 4A Including an image data table for illustrating a first image, a second image, a third image, the minimum pixel data value obtained by subtracting the first image from the first image, the minimum pixel data value obtained by subtracting the second image from the second image, and the minimum pixel data value obtained by subtracting the third image from the third image according to a specific embodiment of the present invention;

[0048] Figure 4B For illustrating a diagram of the flow of a fingerprint image generation method according to a specific embodiment of the present invention;

[0049] Figure 5AAn image data table including, for a first image, a second image, a third image, the minimum pixel data value of the first image subtracted from the first image, the minimum pixel data value of the second image subtracted from the second image, and the minimum pixel data value of the third image subtracted from the third image, as illustrated in a specific embodiment of the present invention;

[0050] Figure 5B A diagram illustrating a fingerprint image generation method flow according to a specific embodiment of the present invention;

[0051] Figure 6A A diagram illustrating a region where a fingerprint sensing signal is to be read out by a fingerprint reading circuit according to a specific embodiment of the present invention;

[0052] Figure 6B A diagram illustrating a touch electrode array according to a specific embodiment of the present invention;

[0053] Figure 6C Illustrating, according to a specific embodiment of the present invention, Figure 6B An enlarged view of the highlighted touch electrode;

[0054] Figure 7A A diagram illustrating a fingerprint image and an analog-to-digital converter (ADC) coding distribution according to a specific embodiment of the present invention;

[0055] Figure 7B A diagram illustrating a fingerprint and an ADC coding distribution according to a specific embodiment of the present invention.

[0056] Reference numerals

[0057] 100 Fingerprint reading circuit

[0058] 110 Analog front-end channel

[0059] 120 Analog-to-digital converter

[0060] 130 Digital circuit

[0061] 140 SRAM

[0062] 141 Buffer

[0063] 142 Buffer

[0064] 150 Interface

[0065] 210 Fingerprint sensor array

[0066] 220 Chip

[0067] 235 Touch controller

[0068] 240 Back-end processor

[0069] 300 Fingerprint Scanning Circuit Detailed Implementation Manner

[0070] To facilitate the understanding of the purpose, features, and effects of the present invention, specific embodiments of the implementation manner of the present invention and the accompanying drawings are provided. In the embodiments of the present invention, the fingerprint image generation method is performed by a fingerprint reading circuit or by a device including a fingerprint reading circuit. From the perspective of the fingerprint reading circuit, the first fingerprint image data (also referred to as the first image data) and the first fingerprint image (also referred to as the first image) in the description of the embodiments of the present invention are synonymous, or synonymous with the image data of the first fingerprint image (also referred to as the image data of the first image); the second fingerprint image data (also referred to as the second image data) and the second fingerprint image (also referred to as the second image) are synonymous, or synonymous with the image data of the second fingerprint image (also referred to as the image data of the second image), and so on.

[0071] Please refer to Figure 1A , which is a schematic diagram of a fingerprint identification system according to a specific embodiment of the present invention, and please refer to Figure 1B , which is a schematic diagram of a fingerprint reading circuit and a fingerprint identification system according to a specific embodiment of the present invention.

[0072] The fingerprint reading circuit 100 can be specifically implemented as a separate integrated circuit chip (IC), or integrated with a display driving circuit and a touch circuit into a single chip, namely a fingerprint, touch, and display integrated chip (FTDI) 220, for driving the touch screen of an electronic device, such as a mobile phone. The fingerprint reading circuit implemented as a single chip may include a memory such as SRAM and a microcontroller. The fingerprint sensor array 210 includes a plurality of fingerprint sensors, which can be embedded in the touch screen or used as an independent fingerprint sensing device and assembled on the touch screen. The fingerprint reading circuit 100 obtains fingerprint sensing signals regarding a fingerprint image from the fingerprint sensors, and converts the fingerprint sensing signals into digital fingerprint image data, and these data are transmitted to a backend processor 240, such as the system application processor of a mobile phone. The backend processor 240 performs image processing based on multiple images to obtain one or more clearer fingerprint images for fingerprint verification, that is, to verify whether the input fingerprint is the registered fingerprint of the user.

[0073] For example, assume that the image data of a fingerprint image has a data volume of 270 x 270 x 12 bits (based on a 270 x 270 pixel active fingerprint sensor array), and during a finger touch event (from when the finger is placed on the touch screen until the finger leaves the touch screen), the fingerprint is imaged six times. Then, the fingerprint reading circuit needs to reserve a space of 270 x 270 x 12 bits x 6 in the SRAM 140 to store these six images, resulting in a relatively large usage of the SRAM 140.

[0074] The fingerprint reading circuit (ROIC) 100 further includes an analog front end (AFE) channel 110, an analog-to-digital converter (ADC) 120, a digital circuit 130, and a serial peripheral interface 150 that connects the fingerprint reading circuit 100 to the back-end processor 240.

[0075] Please refer immediately to Figure 2A , which illustrates the timing control method for a fingerprint image generation method according to a specific embodiment of the present invention, used to generate, for example, six images; please refer immediately to Figure 2B , which illustrates according to a specific embodiment of the present invention Figure 2A the image data table of the first image among a total of six images; please refer immediately to Figure 2C , which illustrates according to a specific embodiment of the present invention Figure 2A the image data table of the second image among a total of six images; and please refer immediately to Figure 2D , which illustrates according to a specific embodiment of the present invention Figure 2A the image data table of the first image minus the second image among a total of six images. Additionally, please continue to refer to Figure 1A and Figure 1B .

[0076] In Figures 2A-2D the specific embodiment shown, the fingerprint reading circuit 100 acquires images multiple times during a continuous exposure period and uses value difference or compression techniques to store the image data to save SRAM space.

[0077] Although the fingerprint data is obtained at different exposure times, its data values should be very closely related. Therefore, for the other images obtained after the first image data, only the difference values from their respective previous image data are stored to save SRAM space and reduce the amount of data transmitted from the fingerprint sensor array 210 to the back-end processor 240 of an application processor (AP) such as a mobile phone, or in other words, to save the transmission bandwidth.

[0078] For example, when the storage data volume of the first image data is 270x270x12 bits, and the storage data volume of each of the second to sixth images is 270x270x10 bits, that is, only the difference value between each image and the previous image data is stored, and the space of the SRAM 140 can be saved.

[0079] When the fingerprint reading circuit 100 acquires the first image, it stores the complete 270x270x12-bit data of the first image in the SRAM 140.

[0080] When the fingerprint reading circuit 100 acquires the second image, it calculates the difference value between the second image and the first image row by row (that is, obtains the data difference at the same fingerprint pixel position of the two images), and only stores the difference value in the SRAM140. Since multiple images are acquired during a continuous exposure period, and the exposure time of the second image is longer than that of the first image, subtracting the first image from the second image results in a positive code. Please refer immediately to Figures 2B through 2D the table shown in. For the same pixel position, the image data of the upper left pixel of the second image actually stored in the SRAM is 279 instead of 1436.

[0081] In this specific embodiment, the longer the exposure time, the higher the digital value generated by the ADC (this is based on the situation that the analog voltage converted by the ADC is larger due to the longer exposure time). On the other hand, in a specific embodiment where the digital value is lower with a longer exposure time, the difference value is obtained by Image (N) - Image (N - 1).

[0082] The following is an example of an application. The fingerprint image generation method for saving memory in this example includes acquiring six fingerprint images with six different exposure time lengths.

[0083] The first image is captured with complete 270x270x12-bit data.

[0084] Then the second image is captured. Subtract the first image from the second image (subtract the image data at the same position) to obtain the difference between the first and second images. Since the exposure time of the second image is longer than that of the first image, when the first image is subtracted from the second image, the difference between the first image and the second image will be positive.

[0085] Then the method obtains the data difference at the same pixel position in the two images. As Figure 2B shown, the image data of the upper left pixel in the first image is 1157. As Figure 2C shown, the image data of the upper left pixel in the second image is 1436. As Figure 2DAs shown, the image data of the upper left pixel in the second image minus the image data of the upper left pixel in the first image is 279. Although the complete image data value 1157 of the first image is stored, only the difference value (279) between the first image and the second image is stored to represent the data of the upper left pixel of the second image. Compared with the data value 1436, the data value 279 is a value that can be represented with a lower data resolution and can consume less memory resources. The fingerprint reading circuit 100 can further perform an operation of subtracting two most significant bits (MSB), subtracting the two most significant bits of 279 represented by 12-bit data, resulting in 279 represented by 10-bit data. The data of each pixel of the second image (to the last image) is also processed in the same way. This greatly reduces the memory amount required by the fingerprint identification system, such as SRAM.

[0086] Please refer immediately to Figure 3A , which is an example showing the timing control method for the fingerprint image generation method according to a specific embodiment of the present invention, the same Figure 2A timing control method. In Figure 3A , the control timings of the second image and the third image are marked and highlighted. Please refer immediately to Figure 3B , which is an example showing Figure 3A the image data table of the second image among a total of six images according to a specific embodiment of the present invention; please refer immediately to Figure 3C , which is an example showing Figure 3A the image data table of the third image among a total of six images according to a specific embodiment of the present invention, please refer to Figure 3D , which is an example showing Figure 3A the image data table of the second image minus the third image among a total of six images according to a specific embodiment of the present invention; and please refer immediately to Figure 3E , which is an example showing the schematic diagram of the fingerprint image generation method flow according to a specific embodiment of the present invention. In addition, please continue to refer to Figure 1A and Figure 1B .

[0087] When the fingerprint reading circuit 100 acquires the third image data, it calculates row by row to obtain the difference value between the image data of the third image and the second image (that is, obtains the data difference at the same fingerprint sensing pixel position of the two images), and only stores the difference value in the SRAM 140. Since multiple images are collected during a continuous exposure period, and the exposure time of the third image is longer than the exposure time of the second image, subtracting the third image from the second image will obtain a positive code. Please refer immediately to Figures 2B through 2D the table shown in Figure 1A, 1B.

[0088] This image is obtained column by column from the fingerprint sensor array 210; that is, every time the fingerprint reading circuit 100 obtains the image data of one column of pixels, it stores one column of data in the buffer 141. Since there is no previous image for the first image, it is stored in the SRAM 140 in its original data size in its entirety.

[0089] The following is an example for application. The method for generating fingerprint images for saving memory in this example includes obtaining six fingerprint images with six different exposure time lengths.

[0090] In the example, the third image is obtained. Subtract the third image from the second image (subtracting at the same positions) to obtain the difference between the second and third images. Since the exposure time of the third image is longer than that of the second image, when the third image is subtracted from the second image, the difference between the second image and the third image will be a positive number.

[0091] This process is performed on all six images (image one, image two, image three, image four, image five, and image six).

[0092] As Figure 3B shown, the data of the upper left pixel in the second image is 1436. As Figure 3C shown, the data of the upper left pixel in the third image is 1716. As Figure 3D shown, subtracting the data of the upper left pixel in the second image from the data of the upper left pixel in the third image is 280. Since only the difference between the second and third images converted to a lower resolution (for example, 12 bits converted to 10 bits) (280 represented in 10 bits) is stored, the SRAM space required by the fingerprint identification system is significantly reduced.

[0093] Because the exposure times of the fingerprint images are different, the original data should be close. Therefore, only the differences are stored, which can save SRAM space and bandwidth (reduce the amount of data sent to the AP by SPI).

[0094] For example, the data size or the amount of data of the first image is 270 x 270 x 12 bits. The second image is 270 x 270 x 10 bits (storing the difference to save SRAM space). The third image is 270 x 270 x 10 bits (storing the difference to save SRAM space). The fourth image is 270 x 270 x 10 bits (storing the difference to save SRAM space). The fifth image is 270 x 270 x 10 bits (storing the difference to save SRAM space). The sixth image is 270 x 270 x 10 bits (storing the difference to save SRAM space).

[0095] The raw data of fingerprint images obtained with different exposure time lengths during an exposure time are relatively close. SRAM 140 only stores the size of the raw data of the first image, and for all other images, SRAM only stores the difference between each image and the previous image. Assuming incremental data, subtraction is used.

[0096] As previously described regarding Figures 2A through 3D The complete fingerprint image data (1157) of the first image is stored at the raw data resolution (12 bits), the second image minus the first image is stored as the fingerprint image data of the second image, and the fingerprint image data (280) of the third image minus the second image is stored as the fingerprint image data of the third image.

[0097] Please refer to Figures 3A through 3E , Figure 3F as an example of a fingerprint sensor circuit diagram according to a specific embodiment of the present invention.

[0098] When acquiring the second image, since the fingerprint sensing signal sensed ([ Figure 3F , Vout, also known as the sensing voltage) is lower than the voltage sensed when acquiring the first image, the digital number generated by the fingerprint reading circuit 100 according to the sensing voltage is less than the digital number of the same fingerprint pixel in the first image. Therefore, it is necessary to retrieve the memory, for example, a column of digital numbers corresponding to the first image data in SRAM 140, and then subtract a column of digital numbers corresponding to the second image data to obtain the difference value stored in SRAM 140.

[0099] Starting from the second image, only the difference value between any two corresponding columns of digital numbers in two consecutive images is stored in SRAM 140.

[0100] The fingerprint reading circuit 100 transmits the complete data of the first image and the difference values obtained from subsequent multiple images to the backend processor 240 (such as the AP of a mobile phone) via the serial peripheral interface (SPI interface) 150. As Figure 3F shown, a row of the fingerprint sensor array 210, or the fingerprint sensor array circuit, includes a plurality of fingerprint sensor circuits, which output the sensing voltage via the same sensing line. Vout is electrically connected to the fingerprint reading circuit 100.

[0101] The selection signal Sel at multiple rows in the fingerprint sensor array 210 is also Figure 2A and Figure 3A G1 - Gn in the timing diagram shown in.

[0102] Please immediately refer to Figure 3G which is an example of the fingerprint gate driver array (GOA) of the panel according to a specific embodiment of the present invention (in Figure 1AThe circuit diagram of the circuit marked as FPR GOA scanning circuit inside. The above panel is a touch display panel of a touch screen, and the FPR GOA scanning circuit is the fingerprint scanning circuit 300.

[0103] The FPR GOA scanning circuit receives the STV signal and the frequency signals Ck1 / Ck1b and Ck2 / Ck2b output by the fingerprint reading circuit 100. The STV signal is shifted according to the frequency signal Ck1 / Ck1b, and then the selection signals Sel at multiple rows of the fingerprint sensor array 210 are generated according to the frequency signal Ck2 / Ck2b, that is, Figure 2A and Figure 3A G1 - Gn in the timing diagram shown in.

[0104] Please refer immediately to Figure 4A , which includes an image data table for a first image, a second image, a third image, the minimum pixel data value of the first image minus the first image, the minimum pixel data value of the second image minus the second image, and the minimum pixel data value of the third image minus the third image according to a specific embodiment of the present invention; and please refer immediately to Figure 4B , which is a diagram illustrating the flowchart of the fingerprint image generation method. In addition, please continue to refer to Figure 1A and Figure 1B .

[0105] Since the background values of all images are very close, the minimum digital number can be subtracted from the data of each image before storing the image data in the SRAM 140. However, the minimum digital number of each image needs to be recorded correspondingly.

[0106] In this way, for each fingerprint pixel, the 12 - bit original data of each image data can be represented by 10 bits plus the minimum digital number of this image data, thus saving the usage space of the SRAM. In Figure 4A the table shown, the data in the lower table shows the actual stored image data of each image.

[0107] First, the current Image N is stored in a buffer 141, which can be an area for temporarily storing data in the SRAM 140. Before storing the next image data in the buffer 141, the minimum value (i.e., the minimum digital number or the minimum pixel data) of the current image pixel data is obtained. Then, before storing the current image data in the SRAM 140, the minimum pixel value is subtracted from each pixel data of the current image to reduce the required SRAM space.

[0108] The fingerprint reading circuit 100 transmits the minimum pixel data and the difference value data of all images to the AP via the serial peripheral interface 150, and the AP can restore the image data according to the stored minimum pixel data and the difference value.

[0109] The following takes an application as an example. In this example, the fingerprint image generation method for saving memory includes collecting a plurality of fingerprint images with different exposure time lengths.

[0110] In this example, the method includes the following. Since the background values of each image are relatively close, the minimum raw data value of each image is recorded before being stored in the SRAM 140, and the minimum raw data of each image is clipped.

[0111] For example, 2 to the 12th power of the original data can be expressed as 2 to the 10th power + the minimum raw data, which can reduce the required storage space of the SRAM, and the data can be restored after being sent to the application program (AP) through the serial peripheral interface (SPI) 150. The following table shown in bold in Figure 4 represents the actually stored data.

[0112] For example, capture the first image. In the first image, it is determined that the minimum pixel value is 716, which occurs at the middle - lower pixel. Then, 716 is subtracted from each pixel data of the first image and stored. Since 716 is the minimum pixel value, the result of subtracting this image data is 0.

[0113] Then, capture the second image. In the second image, it is determined that the minimum pixel value is 986, which still occurs at the middle - lower pixel. Then, 986 is subtracted from each pixel data of the second image and stored. For example, the original image data of the lower - right pixel is 1035, and the result of subtracting this image data is 49.

[0114] Then, capture the third image. In the third image, it is determined that the minimum pixel value is 1231, which still occurs at the middle - lower pixel. Then, 1231 is subtracted from each pixel data of the third image and stored. For example, the original image data of the upper - right pixel is 1403, and the result of subtracting this image data is 172.

[0115] This process is repeatedly executed for all the plurality of captured images.

[0116] Please refer immediately to Figure 5A , which includes a table of image data for a first image, a second image, a third image, the first image minus the minimum pixel data value of the first image, the second image minus the minimum pixel data value of the second image, and the third image minus the minimum pixel data value of the third image, illustrated according to a specific embodiment of the present invention; and please refer immediately to Figure 5B , which is a diagram illustrating the flow of the fingerprint image generation method. Additionally, please continue to refer to Figure 1A and Figure 1B .

[0117] In this specific embodiment, before storing multiple images (including the first image) into the SRAM 140, the method first subtracts the minimum pixel data of the first image from each image data.

[0118] Thus, for each fingerprint pixel, the 12-bit original data of each image can be represented by 10 bits plus the minimum pixel value of the first image, thereby saving the usage space of the SRAM. In Figure 5A the table shown, the data in the lower table shows the data of each image actually stored.

[0119] First, the complete first image is stored in a buffer 141, which can be an area for temporarily storing data in the SRAM 140. Before storing the second image into the buffer 142, the minimum pixel data value of the first image (i.e., the minimum pixel data) is obtained, and the minimum pixel data of the first image in the buffer 142 is stored in the SRAM 140. Then, the minimum pixel data of the first image is subtracted from each pixel data of the second image, and then the data resolution of this processed second image (i.e., the difference image) can be reduced to reduce the required SRAM space.

[0120] The fingerprint reading circuit 100 transmits the minimum pixel data of the first image and multiple difference images representing the second image to the last image to the AP through the serial peripheral interface 150, and the AP can restore the image data according to the stored minimum pixel data and difference images.

[0121] Please refer immediately to Figure 6A , which is a schematic diagram illustrating the sensing area of the fingerprint reading circuit 100; please refer immediately to Figure 6B , which is a schematic diagram illustrating the fingerprint sensor array 210; please refer immediately to Figure 6C , which is a Figure 6B close-up view of the highlighted touch electrodes in one specific embodiment of the present invention. Additionally, please continue to refer to Figure 1A and Figure 1B .

[0122] The area that the fingerprint reading circuit 100 can sense (i.e., Figure 6A the area enclosed by the solid line in) is generally larger than the fingerprint that can be clearly obtained. Since the fingerprint is not always fully imprinted, and the pressure applied at the periphery of the fingerprint is relatively smaller than the pressure applied at the central area of the fingerprint, the fingerprint imprint is usually not clear at its boundary.

[0123] In this specific embodiment, the fingerprint has an effective area determined according to the touch sensing value, as shown in Figure 6AThe area outlined by the dashed line has upper, lower, left, and right boundaries. The effective fingerprint area data is related to the fingerprint sensing line area and the fingerprint scanning line area. For example, the touch controller 235 determines which touch sensing electrode outputs a touch sensing value greater than the default value, and thus determines the effective fingerprint area. And the data of the effective fingerprint area is transmitted to the fingerprint reading circuit 100.

[0124] When sensing a fingerprint, the fingerprint reading circuit only stores the fingerprint image fingerprint data within the effective fingerprint area into the SRAM 140. The fingerprint image fingerprint data outside the effective fingerprint area (such as the area between the solid line and the dashed line in the above figure) is not stored in the SRAM 140 to save SRAM space. The data of the invalid fingerprint area is also not transmitted to the back-end processor 240 to save the SRAM in the fingerprint reading circuit and the time for transmitting data to the AP, thereby shortening the unlocking time and enhancing the user experience.

[0125] Figure 6B An example of an 18x32 touch electrode array with a pixel resolution of 1080*1920. In the touch sensing area corresponding to a touch electrode, there are 60 display pixels. When the resolution of the fingerprint sensor is the same as the display resolution, there are also 60 fingerprint sensing pixels in the corresponding touch sensing area on the touch electrode.

[0126] Figure 6B The highlighted touch electrode outputs a sensing value, which indicates that a touch has occurred. The highlighted block corresponds to the touch area. However, the maximum touch sensing value does not necessarily lie at the center of the touch area.

[0127] A larger touch sensing value indicates that the fingerprint image fingerprint sensed in that area is very clear. For the back-end processor 240, fingerprint verification can be performed based on a partial but relatively clear fingerprint image, and it is not necessarily a complete fingerprint image.

[0128] After obtaining the touch sensing value of the touch electrode from the touch sensing circuit, the touch controller 235 can determine which touch electrodes detect a touch based on the key value. For example, Figure 6B The multiple touch electrodes highlighted with a dot pattern background in [Figure] correspond to Figure 6C The touch sensing values highlighted with a dot pattern background in [Figure]. Since Figure 6C All the highlighted touch sensing values in [Figure] are greater than the key value of 60, it is determined that a touch has occurred.

[0129] In addition, the touch controller 235 determines which touch electrodes have touch sensing values greater than the default value, and takes the area corresponding to the touch electrodes with touch sensing values greater than the default value as the effective fingerprint area. The default value affects the area size of the effective fingerprint area. For example, when the default value is 150, Figure 6BThe area corresponding to the nine touch electrodes surrounded by the outer dashed line (coordinates X = 11 - 13, Y = 15 - 17) is the valid fingerprint area. Or, when the default value is 100, Figure 6B The area corresponding to the four touch electrodes surrounded by the inner dashed line (coordinates X = 11 - 12, Y = 15 - 16) is the valid fingerprint area.

[0130] Since the touch sensing area corresponding to a touch electrode includes 60 fingerprint sensing pixels, and if a relatively small valid fingerprint area is needed, the touch controller 235 can calculate to determine whether the valid fingerprint area extends horizontally from the 601st (= 10 * 60 + 1) fingerprint sensing line to the 720th (= 12 * 60) fingerprint sensing line to the right, and vertically from the 841st (14 * 60 + 1) fingerprint scanning line to the 960th (= 16 * 60) fingerprint scanning line, to have an area of 120 * 120 fingerprint sensing pixels, and transmit the information of the above valid fingerprint area to the fingerprint reading circuit. When sensing a fingerprint, even if the fingerprint reading circuit turns on 200 sensing channels (connecting 200 sensing lines) and 200 scanning lines (the quantity is for illustration only), it can only store the fingerprint data in the valid fingerprint area of the SRAM, and the fingerprint data outside the valid fingerprint area is not stored in the SRAM to save SRAM space. In another embodiment of the present invention, the fingerprint reading circuit can turn on only 120 sensing channels (connecting 120 sensing lines) corresponding to the relatively small valid fingerprint area, rather than turning on all the sensing channels, to receive the sensing signals.

[0131] Please refer to Figure 7A which is a schematic diagram illustrating the fingerprint capture area and the digital (code) distribution of the analog - to - digital converter (ADC) according to a specific embodiment of the present invention; and please immediately refer to Figure 7B which is a schematic diagram illustrating the fingerprint and the ADC coding distribution according to a specific embodiment of the present invention.

[0132] The valid numerical range of the fingerprint data is defined between a predetermined range above the middle code (such as code 2000) of the fingerprint data range and a predetermined range below the middle code of the fingerprint data range, as shown in Figure 7A the area of the solid - line frame shown in the ADC coding distribution diagram. Assuming that the 12 - bit ADC code has a full range of 0 - 4095, the ADC codes corresponding to the fingerprint ridges and fingerprint valleys will fall within the range of 1800 to 2200 (code 2000 + / - 200). That is to say, the codes 0 - 1800 and 2200 - 4095 corresponding to the areas outside the solid - line frame in the following ADC coding distribution diagram are not within the valid numerical range of the fingerprint data, which represents the negligible numerical range of the fingerprint image data.

[0133] The fingerprint reading circuit 100 calculates based on the received sensing voltage to obtain corresponding ADC digital codes. If the obtained ADC digital codes fall within the negligible value range, it will not store them in the SRAM 140 to save SRAM space. In this way, the fingerprint reading circuit only transmits the fingerprint image fingerprint data within the valid value range to the backend processor 240, and ignores the fingerprint image fingerprint data that is not transmitted, further saving the time required for data transmission and enhancing the user experience.

[0134] Taking the fingerprint image collected under strong light as an example, the valid value range of the fingerprint data is approximately between digital codes 1100 and 2400. This is because the valid value range of the fingerprint data is related to the light intensity during the exposure of the fingerprint sensor array. In fact, the valid value range of the fingerprint data does not distribute along with the middle value of the full range of the ADC digital codes (such as digital codes 0 to 4095 in a 12-bit ADC).

[0135] In a specific embodiment of the present invention, the method includes removing the two most significant bits (MSB) from the 270x270x12-bit original data size to generate a 270x270x10-bit compressed image data size.

[0136] In a specific embodiment of the present invention, a combination of multiple specific embodiments is used to implement the fingerprint image generation method for saving memory of the present invention.

[0137] Although the present invention has been described with reference to multiple specific embodiments, those skilled in the art can make various modifications and variations to it without departing from the scope and spirit of the present invention.

Claims

1. A fingerprint image generation method for saving memory, characterized in that, The method includes: Generating a first fingerprint image of an original data size based on a plurality of first analog sensing signals read from a fingerprint sensor array before the end of an exposure period, and storing the first fingerprint image of the original data size in a buffer; Obtaining a first reference pixel data in the first fingerprint image of the original data size, where the first reference pixel data is the minimum pixel data in the first fingerprint image of the original data size; Generating the first fingerprint image represented by a first data size smaller than the original data size by subtracting the first reference pixel data from the first fingerprint image of the original data size; Storing the first fingerprint image represented by a first data size equal to or smaller than the original data size in a memory; After generating the first fingerprint image of the original data size, generating a second fingerprint image of the original data size based on a plurality of second analog sensing signals read from the fingerprint sensor array during the exposure period; and Storing the second fingerprint image represented by a compressed data size smaller than the original data size in the memory.

2. The fingerprint image generation method for saving memory according to claim 1, wherein The method further includes: Storing the second fingerprint image of the original data size in the buffer; Obtaining a second reference pixel data in the second fingerprint image of the original data size, where the second reference pixel data is the minimum pixel data in the second fingerprint image of the original data size; And Generating the second fingerprint image represented by the compressed data size by subtracting the second reference pixel data from the second fingerprint image of the original data size.

3. The fingerprint image generation method for saving memory according to claim 1, wherein, The method further includes: Generating the second fingerprint image represented by the compressed data size by subtracting the first reference pixel data from the second fingerprint image of the original data size.

4. The fingerprint image generation method for saving memory according to claim 2, wherein The method further includes: Transmitting the first fingerprint image represented by the compressed data size and the second fingerprint image represented by the compressed data size to a backend processor.

5. The fingerprint image generation method for saving memory according to claim 4, wherein, The method further includes: Transmitting the first reference pixel data to the backend processor.

6. The fingerprint image generation method for saving memory according to claim 5, wherein, The method further includes: Transmitting the second reference pixel data to the backend processor.

7. A fingerprint image generating device for saving memory, characterized in that, The fingerprint image generating device includes a fingerprint reading circuit, and the fingerprint reading circuit includes: An analog-to-digital converter for generating a first fingerprint image of an original data size based on a plurality of first analog sensing signals read from a fingerprint sensor array before the end of an exposure period; and A memory including a buffer for storing the first fingerprint image of the original data size; Wherein the fingerprint reading circuit obtains a first reference pixel data in the first fingerprint image of the original data size, where the first reference pixel data is the minimum pixel data in the first fingerprint image of the original data size; The fingerprint reading circuit generates the first fingerprint image represented by a first data size smaller than the original data size by subtracting the first reference pixel data from the first fingerprint image of the original data size; After generating the first fingerprint image of the original data size, the analog-to-digital converter generates a second fingerprint image of the original data size based on a plurality of second analog sensing signals read from the fingerprint sensor array during the exposure period; and The internal memory stores the second fingerprint image represented by a compressed data size smaller than the original data size.

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