CN117115868A - Under-screen fingerprint acquisition device, adjusting method thereof and electronic equipment - Google Patents

Abstract

The application discloses an under-screen fingerprint acquisition device, an adjusting method thereof and electronic equipment, wherein the under-screen fingerprint acquisition device is arranged in the electronic equipment with a screen and comprises an image sensor and a lens assembly formed by a lens box and a lens group, and the adjusting method comprises the following steps: calculating to obtain theoretical optimal parameters according to an equivalent optical model of the under-screen fingerprint acquisition device; traversing the vicinity of the theoretical optimal parameters according to the selected step length to obtain a plurality of intermediate parameters, adjusting the under-screen fingerprint acquisition device by using the intermediate parameters, and acquiring a stripe card to obtain a plurality of test images; calculating the pixel number per inch of the test image and a modulation transfer function to evaluate the acquisition quality of each test image, wherein the intermediate parameter corresponding to the test image with the acquisition quality within a selected range is the actual optimal parameter.

Description

Under-screen fingerprint acquisition device, adjusting method thereof and electronic equipment

Technical Field

The application relates to the technical field of biological feature recognition, in particular to an under-screen fingerprint acquisition device, an adjusting method thereof and electronic equipment.

Background

With the rapid development of the mobile phone industry, fingerprint identification technology is more and more paid attention to, and the practical application of the under-screen fingerprint identification technology is required by the public.

The technology for identifying the fingerprints under the optical screen is that the optical fingerprint sensor collects reflected light formed by reflecting light rays emitted by the light source on the fingers, and fingerprint information of the fingers is carried in the reflected light, so that the fingerprint identification under the screen is realized. The fingerprint identification device can guide the light signals returned by the finger through the lens system, and the reflected light needs to pass through the lens system and then reach the optical fingerprint sensor. In order to obtain more fingerprint information, it is necessary to enlarge the field of view of the lens system as much as possible to acquire a fingerprint image of a larger area, but this results in a longer lens system being designed, which occupies a somewhat small longitudinal space of the electronic device itself. Therefore, how to obtain a suitable field of view without increasing the length of the lens system is a problem to be solved.

An improved under-screen fingerprint acquisition device and method of adjusting the same is desired to address the above-mentioned problems.

Disclosure of Invention

In view of the above problems, an object of the present application is to provide an under-screen fingerprint identification device, a parameter adjustment method thereof, and an electronic device, which can adjust a distance between a lens assembly and a screen and between the lens assembly and an image sensor, thereby improving quality of a captured fingerprint image.

According to an aspect of the present application, there is provided a method of adjusting an under-screen fingerprint acquisition device provided in an electronic apparatus having a screen, including an image sensor, and a lens assembly composed of a lens box and a lens group, the method comprising: calculating to obtain theoretical optimal parameters according to an equivalent optical model of the under-screen fingerprint acquisition device; traversing the vicinity of the theoretical optimal parameters according to the selected step length to obtain a plurality of intermediate parameters, adjusting the under-screen fingerprint acquisition device by using the intermediate parameters, and acquiring a stripe card to obtain a plurality of test images; calculating the pixel number per inch of the test image and a modulation transfer function to evaluate the acquisition quality of each test image, wherein the intermediate parameter corresponding to the test image with the acquisition quality within a selected range is the actual optimal parameter.

Optionally, the parameters include a module height equal to a distance between the lens box and a surface of the image sensor opposite the lens box; the air space is equal to a distance between the opposite surfaces of the lens case and the screen.

Optionally, the calculating the theoretical optimal parameter according to the equivalent optical model of the under-screen fingerprint acquisition device includes: calculating to obtain an equivalent object distance according to the air space, the equivalent distance of the screen and a first distance, wherein the first distance is equal to the distance between the object side main surface of the lens group and the upper surface of the lens box; the equivalent distance is reached according to the height of the module, the first distance, the second distance and the third distance, wherein the second distance is equal to the thickness of the lens group, and the third distance is equal to the thickness of the image sensor; and according to the equivalent object distance, the equivalent distance and the equivalent focal length of the lens group, combining an imaging formula to obtain the mapping relation between the air distance and the module height so as to calculate and obtain the theoretical optimal parameter.

Optionally, the calculating the equivalent distance according to the air space, the equivalent distance of the screen and the first distance includes: and calculating the sum of the air space, the equivalent distance of the screen and the first distance to obtain the equivalent distance.

Optionally, the equivalent distance according to the module height, the first distance, the second distance, the third distance, and the like includes: subtracting the first distance, the second distance and the third distance from the module height to obtain the equivalent distance.

Optionally, traversing around the theoretical optimal parameter according to the selected step size to obtain a plurality of intermediate parameters includes: traversing the theoretical optimal module height by a first selected step length to obtain a plurality of middle module heights; traversing the vicinity of the theoretical optimal air spacing with a second selected step size to obtain a plurality of intermediate air spacing; and combining the heights of the plurality of intermediate modules with the plurality of intermediate air spaces in pairs to obtain the plurality of intermediate parameters.

Optionally, said calculating the number of pixels per inch of the test image comprises: obtaining a corresponding gray scale/pixel curve graph according to the test image; calculating to obtain the average pixel distance between the wave peaks according to the pixel distances between the wave peaks; 8. according to the adjusting method, the intermediate parameters corresponding to the test images with the acquisition quality within the selected range are actual optimal parameters, and the method comprises the following steps: and selecting the intermediate parameter of which the pixel number per inch is in a selected range and the transmission modulation function is larger than a selected threshold value, namely the actual optimal parameter.

According to another aspect of the present application, there is provided an under-screen fingerprint acquisition apparatus provided in an electronic device having a screen, comprising: an image sensor, and a lens assembly composed of a lens box and a lens group, the lens assembly guiding the off-screen fingerprint reflection light to the image sensor to collect fingerprint images; and the lifting rail is connected with the lens assembly and can enable the lens assembly to move along the direction vertical to the screen so as to change the distance between the lens assembly and the screen as well as between the lens assembly and the sensor.

Optionally, the method further comprises: the camera box is arranged in the camera box, and the part of the camera box opposite to the image sensor comprises a through hole; the lifting rail is connected with the darkroom box at the through hole.

Optionally, the lens group comprises at least two lenses; the lens close to the screen is an object principal surface, and the lens close to the image sensor is a phase principal surface.

According to another aspect of the present application, there is provided an electronic apparatus including a base and a stand provided on the base, the stand configured to support the screen; and the under-screen fingerprint acquisition device is characterized in that the darkroom box is arranged on the base, and the image sensor is arranged on the surface of the darkroom box, which is close to the base.

The under-screen fingerprint acquisition device provided by the application comprises the lifting track connected with the lens assembly, the lifting track can drive the lens assembly to move along the direction vertical to the screen, so that the distance between the lens assembly and the screen as well as between the lens assembly and the image sensor is adjusted, the mapping relation between the air space A and the module height H is established by utilizing the equivalent optical model in cooperation with the adjusting method provided by the application, the theoretical optimal air space a0 and the theoretical optimal module height H0 are calculated, and therefore, the position of the lens assembly in the under-screen fingerprint acquisition device is adjusted according to the theoretical optimal parameter, high-quality fingerprint images can be acquired, and powerful help is provided for subsequent fingerprint identification analysis.

Optionally, the application also traverses around the theoretical optimal air space a0 and the theoretical optimal module height h0 according to the selected step length to obtain a plurality of intermediate parameters, applies the plurality of intermediate parameters to the under-screen fingerprint acquisition device, evaluates the acquisition quality according to the test image obtained by the acquisition stripe card, takes the intermediate parameters corresponding to the test image with DPI falling in the selected range and MTF larger than the selected threshold value as the actual optimal parameters, and further improves the quality of the acquired fingerprint image.

Drawings

The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic block diagram of an electronic device of the present application;

fig. 2 shows a schematic cross-sectional view of the electronic device of fig. 1;

FIG. 3 shows a partial enlarged view of region A of FIG. 2;

FIG. 4 illustrates a method of adjusting an off-screen fingerprint acquisition device in accordance with an embodiment of the present application;

FIG. 5 shows an equivalent optical model of an off-screen fingerprint acquisition device according to an embodiment of the present application;

FIG. 6 shows a schematic diagram of a striped card;

fig. 7 shows a gray scale/pixel plot of the test image.

Detailed Description

Various embodiments of the present application will be described in more detail below with reference to the accompanying drawings. The same elements or modules are denoted by the same or similar reference numerals in the various figures. For clarity, the various features of the drawings are not drawn to scale.

It should be appreciated that in the following description, a "circuit" may include a single or multiple combined hardware circuits, programmable circuits, state machine circuits, and/or elements capable of storing instructions for execution by the programmable circuits. When an element or circuit is referred to as being "connected to" another element or circuit is "connected between" two nodes, it can be directly coupled or connected to the other element or intervening elements may be present, the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled to" or "directly connected to" another element, it means that there are no intervening elements present between the two.

Also, certain terms are used throughout the description and claims to refer to particular components. It will be appreciated by those of ordinary skill in the art that a hardware manufacturer may refer to the same component by different names. The present patent specification and claims do not take the form of an element or components as a functional element or components as a rule.

Furthermore, it should be noted that relational terms such as first and second are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.

Fig. 1 shows a schematic block diagram of an electronic device according to the application, and fig. 2 shows a schematic cross-sectional view of the electronic device of fig. 1. As can be seen in fig. 1 and 2, the electronic device 100 comprises a screen 120 and an off-screen fingerprint acquisition device 200, wherein the off-screen fingerprint acquisition device 200 is arranged below the screen 120. The off-screen fingerprint acquisition device 200 comprises, for example, a sensing array having a plurality of optical sensing units, the sensing array being, for example, selected from image sensors. The optical sensing area of the sensing array is the acquisition area 102 of the off-screen fingerprint acquisition device 200. As can be seen from fig. 1, the acquisition area 102 is located in the display area 101 of the screen 120, and a user only needs to press a finger on the acquisition area 102 when the user needs to unlock the electronic device 100 or perform other verification by using the fingerprint.

In one possible embodiment, the screen 120 is selected from a screen including a self-luminous unit, for example, any one selected from an Organic Light-Emitting Diode (OLED) screen, a Light-Emitting Diode (LED) screen, an Active-matrix Light-Emitting Diode (AMOLED) screen, a Micro Light-Emitting Diode (Micro LED) screen, or a sub-millimeter Light-Emitting Diode (Mini LED) screen. When the electronic device 100 is selected from a terminal device such as a mobile phone and a tablet computer, the electronic device 100 further includes a touch device, for example, disposed on the surface of the screen 120, or partially or fully integrated inside the screen 120 to form a touch display screen, which not only can display a picture and collect fingerprints, but also can detect operations such as touching and pressing by a user, so that the electronic device 100 can interact with the user.

Taking the example of an OLED screen as the screen 120 as shown in fig. 2, the under-screen fingerprint acquisition device 200 may utilize a display unit of the OLED screen located in the acquisition area 102 as an excitation light source for fingerprint acquisition, a finger is pressed in the acquisition area 102, and the display unit of the screen 120 is utilized to emit bright light at a selected position to illuminate the finger, and as different reflected lights are generated by ridges and valleys of the fingerprint, the reflected lights penetrate the screen 120 downwards into the under-screen fingerprint acquisition device 200 as shown by dotted lines, the under-screen fingerprint acquisition device 200 converts the light signals into corresponding electrical signals, and then obtains a fingerprint image based on the electrical signals, and the acquired fingerprint image can be further verified, thereby realizing the function of optical fingerprint acquisition/detection.

In one possible embodiment, the off-screen fingerprint acquisition device 200 is disposed in the entire area under the screen 120, allowing the acquisition area 102 to extend to the entire display area 101 of the screen 120, thereby enabling full-screen optical fingerprint acquisition/fingerprint detection.

The off-screen fingerprint sensing device 200 may also employ an internal or external light source to provide an excitation light source for fingerprint sensing/detection, such that the off-screen fingerprint sensing device 200 may be used with non-self-luminous screens (e.g., liquid crystal screens or other passive light emitting screens). At this time, the fingerprint acquisition device 200 under the screen further includes an acquisition light source, which is applied to the liquid crystal screen in the example provided by the embodiment, and the liquid crystal screen includes a backlight module and a liquid crystal panel, and the acquisition light source is, for example, disposed below the backlight module or in an edge area below the transparent cover plate 110. The fingerprint acquisition device 200 under the screen is also arranged below the backlight module, so that the reflected light of the finger can pass through the liquid crystal screen to enter the fingerprint acquisition device 200 under the screen, and the backlight module can be subjected to hole opening and other designs. Wherein the collection light source is selected, for example, from an infrared light source or other non-visible light source having a selected wavelength.

It should be understood that in a practical application scenario, the electronic device 100 further includes a transparent cover plate 110, where the transparent cover plate 110 is selected from a glass cover plate or a sapphire glass cover plate, for example. The transparent cover plate 110 is disposed on the screen 120 and covers the screen 120, or covers a surface of the electronic device 100 where the screen 120 is located, so as to protect the screen 120. Thus, in embodiments of the present application, a finger pressing on the screen 120 can also be interpreted as a finger pressing on the transparent cover plate 110.

Specifically, referring to fig. 3, fig. 3 shows a partial enlarged view of area a in fig. 2, the electronic device 100 further includes a stand 130 and a base 140, and the stand 130 is disposed above the base 140 and provides support to the screen 120 so that a receiving space is formed between the screen 120 and the base 140. The off-screen fingerprint sensing device 200 is positioned in the receiving space below the screen 120 above the base 140. The off-screen fingerprint sensing device 200 is illustratively positioned above the base 140.

The off-screen fingerprint acquisition device 200 includes at least a light detection assembly including an image sensor 230 and a reading circuit and other ancillary circuits electrically connected to the image sensor 230. By way of example, the image sensor 230 may be coupled to a processor (not shown) of an electronic device, where the processor may be represented as electronic components that interpret computer instructions and process data in computer software, and the processor may be implemented by one or more Application Specific Integrated Circuits (ASICs), digital Signal Processors (DSPs), digital Signal Processing Devices (DSPDs), programmable Logic Devices (PLDs), field Programmable Gate Arrays (FPGAs), controllers, microcontrollers, microprocessors, or other electronic components.

In the embodiment of the present application, the image sensor 230 may be selected from a CCD (Charge-coupled Device) sensor, a CMOS (complementary metal Oxide Semiconductor) sensor, or the like, and the embodiment of the present application does not limit the type of the image sensor 230.

The optical components are disposed above the image sensor 230 and may include other optical elements such as filter layers, light guide layers, and the like. The filter layer is configured, for example, to filter out ambient light, and the light guide layer is configured, for example, to guide reflected light reflected from the finger surface to the image sensor 230.

In the present embodiment, the light guiding layer is selected from the lens assembly 210, the lens assembly 210 includes a lens case 211 and a lens group 212 disposed in the lens case 211, and the lens group 212 includes a plurality of lens units, for example. The reflected light reflected from the finger surface is collimated or converged by the lens group 212 to reach the image sensor 230, so that the image sensor 230 can collect the fingerprint image.

Further, the under-screen fingerprint acquisition device 200 further includes a camera box 240, the camera box 240 is disposed on the base 140, the image sensor 230 is disposed in the base 140, and a portion of the upper surface of the camera box 240 opposite to the image sensor 230 includes a through hole, where the lifting rail 220 and the lens assembly 210 are disposed. The darkroom box 240 is made of opaque material, for example, so that reflected light on the surface of the finger can reach the image sensor 230 through the lens assembly 210, and meanwhile, other light sources can be prevented from reaching the image sensor 230 to influence the performance of optical fingerprint collection/fingerprint detection.

However, during imaging, lens groups 212 having the same equivalent focal length have different magnifications according to the equivalent distance and/or the equivalent distance of lens groups 212, and the sizes of the resulting images are different. The module height H and air gap a will directly affect the quality of the fingerprint image and the recognition performance of the electronic device. Where the air space a represents the distance between the upper surface of the lens case 211 and the lower surface of the screen 120, and the module height H represents the distance between the upper surface of the lens case 211 and the lower surface of the image sensor 230.

Accordingly, the under-screen fingerprint acquisition device 200 according to the embodiment of the present application further includes a lifting rail 220, where the lifting rail 220 is connected to the lens assembly 210, so that the lens assembly 210 can move along the z-axis direction, and the module height H and the air space a can be changed. In view of this, the present application also provides a method for adjusting an on-screen fingerprint acquisition device, as shown in fig. 4, fig. 4 shows an adjusting method for an on-screen fingerprint acquisition device according to an embodiment of the present application, including:

and step S10, calculating to obtain theoretical optimal parameters according to an equivalent optical model of the under-screen fingerprint acquisition device.

Referring to fig. 5, fig. 5 shows an equivalent optical model of the under-screen fingerprint sensing device of the present application, in fig. 5, a represents an air space, H represents a module height, P represents an equivalent object distance of the lens assembly 210, Q represents an equivalent distance of the lens assembly 210, F represents an equivalent focal length of the lens assembly 210, d0 represents a thickness of the screen 120, d1 represents a distance from the object main surface 2121 to an upper surface of the lens box 211, d2 represents a thickness of the lens group 212, and d3 represents a thickness of the image sensor 230.

As can be seen from fig. 5, the equivalent distance p=a+d0+d1, the equivalent distance q=h-d 1-d2-d3, according to the imaging formulaAvailable->In the case where the thickness d0 of the screen 120, the distance d1 from the main object surface 2121 to the upper surface of the lens box 211, the thickness d2 of the lens group 212, the thickness d3 of the image sensor 230, and the equivalent focal length F of the lens assembly 210 are all constant values, it is known that the module height H is a function of the air space a, and h=f (a), and taking a=a0, the theoretical optimal parameters, that is, the theoretical optimal module height H0 and the theoretical optimal air space a0, can be obtained by calculating h0=f (a 0).

In one possible embodiment, the theoretical optimal air spacing a0 is selected from 1mm.

Step S20, traversing the theoretical parameters according to the selected step length to obtain a plurality of intermediate parameters, and adjusting an on-screen fingerprint acquisition device by using the intermediate parameters to acquire a plurality of test images by using the stripe card.

Taking Δh as a first selected step length, traversing around the theoretical optimal module height H0 to obtain a plurality of intermediate module heights, taking Δa as a second selected step length, traversing around the theoretical optimal air space a0 to obtain a plurality of intermediate air spaces, and illustratively, obtaining a parameter traversing table as shown below, wherein the air space A and the module height H in the parameter traversing table respectively comprise five parameters, and combining to form twenty-five groups of intermediate parameters.

The height of the lens assembly 210 is changed by adjusting the elevating rail 220 according to the intermediate parameters, and a plurality of test images are acquired by the fringe card. In this embodiment, as shown in fig. 6, the stripe card includes parallel black and white stripes for reflecting the light source to image, and in order to reduce interference during the acquisition, the stripe card rotates at an angle, for example, an angle of 45 ° or 135 ° with respect to the horizontal line.

In step S30, the pixel Per inch (DPI, dots Per Inches) and the modulation transfer function (MTF, modulation Transfer Function) of each test image are calculated, and the acquisition quality thereof is evaluated to obtain the actual optimal parameters.

According to the test image collected in step S20, a corresponding gray scale/pixel graph can be obtained, as shown in fig. 7, the abscissa in fig. 7 represents the distance in units of pixels, the coordinate represents the gray scale for the pair, and the number of pixels per inch and the modulation transfer function corresponding to different intermediate parameters can be calculated by bringing the data in fig. 7. Wherein the number of pixels per inch can represent the resolution of the test image and the transfer modulation function can represent the blur level of the image.

Specifically, the stripe width of the stripe card is selected from 0.4mm, and the peak value of ten peaks of the cross section is selected in the test image, for example, from 14 to 167, at which time the number of Pixels Per inch= (167-14)/10/(0.4/25.4) =971, where 1 inch=25.4 mm, since the number of Pixels Per Inch (PPI, pixels Per Inch) is in inches, one conversion with millimeters is required. And the like, calculating the pixel number per inch of all the test images, and filling the pixel number per inch into a parameter traversal table to obtain the following table. In practical applications, the number of pixels per inch is required to be within a selected range [ D1, D2], that is, D1 is less than or equal to DPI is less than or equal to D2, and as can be seen from the following table, the module height H is selected from H0-2, H0- Δh, H0, and the air space A is selected from nine combinations of a0-2, a0- Δa, and a0.

The transmission modulation function of the test image can be obtained from the gray scale/pixel correspondence curve shown in fig. 7 by calculating the transmission modulation function of all the test images and filling the transmission modulation function into the parameter traversal table to obtain the following table. In practical applications, the transmission modulation function is required to be greater than the selected threshold M, i.e. MTF is greater than or equal to M, and as can be seen from the following table, the module height H is selected from H0, h0Δh, h0+2×Δh, and the air space a is selected from nine combinations of a0, a0+Δa, a0+2×Δa, which satisfy the condition.

In summary, the intermediate parameter, in which the number of pixels per inch is within the selected range [ D1, D2] and the transmission modulation function is greater than the selected threshold M, is selected as the actual optimal parameter. The height of the lens assembly 210 is adjusted according to the actual optimal parameters, so that the quality of the fingerprint image acquired by the on-screen fingerprint acquisition device 200 can be effectively improved.

In this embodiment, the actual optimum parameter is h0, a0, the same as the theoretical optimum parameter,

it should be understood that the actual optimum parameters may also be different from the theoretical optimum parameters. Illustratively, D1 is selected from 600, D2 is selected from 700, and M is selected from 0.8.

In summary, the under-screen fingerprint acquisition device provided by the application includes the lifting rail 220 connected with the lens assembly 210, the lifting rail 220 can drive the lens assembly 210 to move along the direction perpendicular to the screen 120, so as to adjust the distance between the lens assembly 210 and the screen 120 and between the lens assembly and the image sensor 230.

Optionally, the application also traverses around the theoretical optimal air space a0 and the theoretical optimal module height h0 according to the selected step length to obtain a plurality of intermediate parameters, applies the plurality of intermediate parameters to the under-screen fingerprint acquisition device, evaluates the acquisition quality according to the test image obtained by the acquisition stripe card, takes the intermediate parameters corresponding to the test image with DPI falling in the selected range and MTF larger than the selected threshold value as the actual optimal parameters, and further improves the quality of the acquired fingerprint image.

It should be noted that the words "during", "when" and "when … …" as used herein in relation to circuit operation are not strict terms indicating an action that occurs immediately upon the start of a start-up action, but rather there may be some small but reasonable delay or delays between it and the reaction action (reaction) initiated by the start-up action, such as various transmission delays and the like, as will be appreciated by those of ordinary skill in the art. The word "about" or "substantially" is used herein to mean that an element value (element) has a parameter that is expected to be close to the stated value or position. However, as is well known in the art, there is always a slight deviation such that the value or position is difficult to strictly assume the stated value. It has been well established in the art that deviations of at least ten percent (10%) (at least twenty percent (20%)) for semiconductor doping concentrations are reasonable deviations from the exact ideal targets described. When used in connection with a signal state, the actual voltage value or logic state of the signal (e.g., "1" or "0") depends on whether positive or negative logic is used.

Embodiments in accordance with the present application, as described above, are not intended to be exhaustive or to limit the application to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the application and the practical application, to thereby enable others skilled in the art to best utilize the application and various modifications as are suited to the particular use contemplated. The scope of the application should be determined by the appended claims and their equivalents.

Claims (12)

1. An adjusting method of an off-screen fingerprint acquisition device, which is arranged in an electronic device with a screen, comprises an image sensor and a lens assembly formed by a lens box and a lens group,

the adjusting method comprises the following steps:

calculating to obtain theoretical optimal parameters according to an equivalent optical model of the under-screen fingerprint acquisition device;

traversing the vicinity of the theoretical optimal parameters according to the selected step length to obtain a plurality of intermediate parameters, adjusting the under-screen fingerprint acquisition device by using the intermediate parameters, and acquiring a stripe card to obtain a plurality of test images;

calculating the pixel number per inch of the test image and a modulation transfer function to evaluate the acquisition quality of each test image, wherein the intermediate parameter corresponding to the test image with the acquisition quality within a selected range is the actual optimal parameter.

2. The method of claim 1, wherein the parameters include module height and air spacing,

the height of the module is equal to the distance between the lens box and the surface of the image sensor opposite to the lens box;

the air space is equal to a distance between the opposite surfaces of the lens case and the screen.

3. The adjustment method according to claim 2, wherein the calculating theoretical optimal parameters according to the equivalent optical model of the on-screen fingerprint acquisition device comprises:

calculating to obtain an equivalent object distance according to the air space, the equivalent distance of the screen and a first distance, wherein the first distance is equal to the distance between the object side main surface of the lens group and the upper surface of the lens box;

the equivalent distance is reached according to the height of the module, the first distance, the second distance and the third distance, wherein the second distance is equal to the thickness of the lens group, and the third distance is equal to the thickness of the image sensor;

and according to the equivalent object distance, the equivalent distance and the equivalent focal length of the lens group, combining an imaging formula to obtain the mapping relation between the air distance and the module height so as to calculate and obtain the theoretical optimal parameter.

4. The adjustment method according to claim 3, wherein the calculating the equivalent distance according to the air space, the equivalent distance of the screen, and the first distance includes:

and calculating the sum of the air space, the equivalent distance of the screen and the first distance to obtain the equivalent distance.

5. The adjustment method according to claim 3, wherein the waiting for equivalent distances according to the module height, the first distance, the second distance, and the third distance includes:

subtracting the first distance, the second distance and the third distance from the module height to obtain the equivalent distance.

6. The adjustment method of claim 1, the traversing around the theoretical optimal parameter according to a selected step size to obtain a plurality of intermediate parameters comprising:

traversing the theoretical optimal module height by a first selected step length to obtain a plurality of middle module heights;

traversing the vicinity of the theoretical optimal air spacing with a second selected step size to obtain a plurality of intermediate air spacing;

and combining the heights of the plurality of intermediate modules with the plurality of intermediate air spaces in pairs to obtain the plurality of intermediate parameters.

7. The adjustment method of claim 1, the calculating the number of pixels per inch of the test image comprising:

obtaining a corresponding gray scale/pixel curve graph according to the test image;

and calculating according to the pixel distances among the plurality of peaks to obtain the average pixel distance among the peaks.

8. The adjustment method according to claim 7, wherein the intermediate parameter corresponding to the test image with the acquisition quality within the selected range is an actual best parameter, comprising:

and selecting the intermediate parameter of which the pixel number per inch is in a selected range and the transmission modulation function is larger than a selected threshold value, namely the actual optimal parameter.

9. An under-screen fingerprint acquisition device disposed within an electronic device having a screen, comprising:

an image sensor, and a lens assembly composed of a lens box and a lens group, the lens assembly guiding the off-screen fingerprint reflection light to the image sensor to collect fingerprint images; and

the lifting track is connected with the lens assembly and can enable the lens assembly to move along the direction perpendicular to the screen so as to change the distance between the lens assembly and the screen and between the lens assembly and the sensor.

10. The off-screen fingerprint acquisition device of claim 9, further comprising:

the camera box is arranged in the camera box, and the part of the camera box opposite to the image sensor comprises a through hole;

the lifting rail is connected with the darkroom box at the through hole.

11. The off-screen fingerprint acquisition device of claim 9, the lens group comprising at least two lenses;

the lens close to the screen is an object principal surface, and the lens close to the image sensor is a phase principal surface.

12. An electronic device comprising a base and a bracket disposed on the base, the bracket configured to support the screen; the method comprises the steps of,

the off-screen fingerprint acquisition device of any one of claims 9-11, the darkroom box being disposed over the base, the image sensor being disposed over a surface of the darkroom box proximate the base.