Adaptive exposure control method and system for digital image correlation measurement

Abstract

The application discloses a kind of digital image correlation measurement adaptive exposure control method and system, belong to optical measurement and image processing technical field, this method includes: S1, with current exposure time acquisition high temperature test piece surface laser speckle image;S2, the average gray G_avg of region of interest in laser speckle image is calculated;S3, if the deviation between G_avg and target average gray value does not exceed gray deviation threshold, then execute S4;Otherwise, adjust exposure time and return S1, until the deviation between G_avg and target average gray value does not exceed gray deviation threshold when executing S4;S4, within the scope of exposure time, gradually increase exposure time according to exposure incremental step, until certain stop condition is satisfied, and exposure time when meeting stop condition is used as final exposure time.The application solves the problem that laser speckle DIC image is overexposed and DIC measurement is interrupted under high temperature environment.

Description

Technical Field

[0001] This invention relates to the field of optical measurement and image processing technology, and in particular to an adaptive exposure control method and system for digital image correlation measurement. Background Technology

[0002] Digital Image Correlation (DIC) is a non-contact, full-field deformation measurement technique based on image feature matching. It obtains the full-field displacement and strain fields by tracking the displacement of the speckle pattern on the surface of the specimen. It has outstanding advantages such as non-contact, full-field, and high resolution, and has been widely used in fields such as material mechanical property characterization, structural damage detection, and high-temperature deformation measurement.

[0003] In high-temperature mechanical testing, laser speckle induction (DIC) has been used for high-temperature strain measurement. This technique utilizes a solid-state single-mode laser to irradiate the specimen surface, forming a coherent speckle pattern. A narrowband filter, linear polarizer, and neutral density attenuator are then used in conjunction with the camera lens to suppress interference from the specimen's self-heating radiation on the imaging. However, under high-temperature conditions, the intensity of thermal radiation from the specimen increases significantly with temperature. Even after filtering and attenuation, the thermal radiation entering the camera target surface can still lead to overall overexposure of the image under fixed exposure conditions, obscuring the speckle pattern, and causing failure in DIC cross-correlation calculations.

[0004] Currently, existing speckle image quality evaluation metrics mainly include global average gray level, image entropy, mean intensity gradient (MIG), and speckle image mean-variance analysis. Among these, the mean intensity gradient (MIG) calculates the intensity gradient of the image in both the x and y directions and is a commonly used DIC image quality metric; image entropy has a large computational burden; the mean-variance analysis method has high complexity; and global average gray level only reflects brightness and cannot directly reflect speckle quality.

[0005] Existing automatic exposure control schemes typically adjust exposure time based on feedback from the average gray level of the entire frame or ROI, the brightness histogram, or image entropy. Other high dynamic range (HDR) multi-frame fusion methods extend the imaging dynamic range by fusing images with different exposures. While these methods can improve exposure in ordinary scenes or extend the imaging dynamic range, they do not optimize for the statistical characteristics of laser speckle images and struggle to distinguish the difference between the average brightness of the image and the speckle texture quality required for DIC. In high-temperature DIC, two images with similar average gray levels may still have different speckle discernibility; therefore, relying solely on average gray level to control exposure is insufficient to guarantee stable DIC calculations.

[0006] In summary, the existing technologies have the following shortcomings: First, the existing speckle quality evaluation indicators have not been optimized for the statistical isotropic characteristics of laser speckle, resulting in computational redundancy; second, existing automatic exposure control schemes mostly use a single brightness index, making it difficult to balance response speed and speckle quality; and third, there is a lack of lightweight closed-loop exposure control schemes suitable for continuous heating experiments of high-temperature laser speckle DIC. Summary of the Invention

[0007] This invention provides an adaptive exposure control method and system for digital image correlation measurement to solve the technical problems of overexposure of fixed exposure images, obscuring of speckle patterns, and failure of DIC measurement caused by enhanced thermal radiation under high temperature conditions.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: On one hand, the present invention provides an adaptive exposure control method for digital image correlation measurement, comprising: S1, control the industrial camera to acquire laser speckle images of the surface of the high-temperature specimen using the current exposure time; S2, calculate the average gray level of the region of interest in the laser speckle image; S3, if the deviation between the average gray level of the currently calculated region of interest and the preset target average gray level does not exceed the preset gray level deviation threshold, then execute S4; otherwise, adjust the exposure time and return to S1 until the deviation between the average gray level of the region of interest in the laser speckle image acquired at the current exposure time and the preset target average gray level does not exceed the preset gray level deviation threshold, then execute S4. S4. Within the preset exposure time limit, gradually increase the exposure time according to the preset exposure increment step until the preset stopping condition is met, and use the exposure time when the stopping condition is met as the final exposure time.

[0009] Furthermore, when acquiring laser speckle images, the imaging lens aperture of the industrial camera is fixed, and a narrowband filter with a center wavelength matching the laser wavelength is installed at the front end of the industrial camera lens.

[0010] Furthermore, the region of interest corresponds to the speckle region of the specimen and excludes the background thermal radiation region outside the specimen region.

[0011] Furthermore, the deviation between the average gray level of the region of interest and the preset target average gray level is represented by the absolute value of the difference between the average gray level of the region of interest and the preset target average gray level.

[0012] Furthermore, within the preset exposure time limit, the exposure time is gradually increased according to the preset exposure increment step until the preset stopping condition is met, and the exposure time at which the stopping condition is met is taken as the final exposure time, including: Within the preset exposure time limit, the exposure time is gradually increased according to the preset exposure increment step. After each increase in exposure time, the industrial camera is controlled to acquire laser speckle images of the surface of the high-temperature specimen using the adjusted exposure time, and the one-sided average intensity gradient of the acquired laser speckle images is calculated. When the difference between the average intensity gradient of one side of two adjacent laser speckle images is less than the preset speckle quality difference threshold, or when the actual number of exposure increments reaches the preset maximum number of exposure increments, adaptive exposure adjustment is completed, and the exposure time obtained at this time is used as the final exposure time.

[0013] Furthermore, the one-sided average intensity gradient is calculated by averaging the absolute value of the image intensity gradient in one spatial direction only for the region of interest in the laser speckle image to obtain the one-sided average intensity gradient of the image.

[0014] Furthermore, after obtaining the final exposure time, the method further includes: The industrial camera is controlled to acquire laser speckle images of the surface of the high-temperature specimen using the current final exposure time. Digital image correlation and cross-correlation calculations are performed between the current laser speckle images and the reference image to output the full-field displacement field and strain field.

[0015] On the other hand, the present invention also provides an adaptive exposure control system for digital image correlation measurement, the adaptive exposure control system for digital image correlation measurement comprising: The image acquisition module is used to control the industrial camera to acquire laser speckle images of the surface of the high-temperature specimen with the current exposure time, and to transmit the currently acquired laser speckle images to the exposure time coarse adjustment module. The exposure time coarse adjustment module is used for: After receiving the laser speckle image, calculate the average gray level of the region of interest in the laser speckle image; If the deviation between the average gray level of the currently calculated region of interest and the preset target average gray level does not exceed the preset gray level deviation threshold, the exposure time fine-tuning module is activated; otherwise, the exposure time is adjusted and the image acquisition module is activated until the deviation between the average gray level of the region of interest in the laser speckle image acquired at the current exposure time and the preset target average gray level does not exceed the preset gray level deviation threshold, at which point the exposure time fine-tuning module is activated. The exposure time fine-tuning module is used for: Within the preset exposure time limit, the exposure time is gradually increased according to the preset exposure increment step until the preset stopping condition is met, and the exposure time at which the stopping condition is met is taken as the final exposure time.

[0016] In another aspect, the present invention also provides an electronic device comprising a processor and a memory; wherein the memory stores at least one instruction, which is loaded and executed by the processor to implement the above-described method.

[0017] In another aspect, the present invention also provides a computer-readable storage medium storing at least one instruction, which is loaded and executed by a processor to implement the above method.

[0018] The beneficial effects of the technical solution provided by this invention include at least the following: 1. The UMIG index proposed in this invention is designed for the statistical isotropic characteristics of laser speckle. It only calculates the image intensity gradient in one spatial direction. By utilizing the statistical isotropic characteristics of laser speckle, redundant gradient calculations are reduced. Compared with the traditional MIG, the UMIG index of this invention can reduce the amount of computation while maintaining comparable evaluation accuracy. It can directly reflect the speckle image quality required for DIC calculation.

[0019] 2. This invention adopts a two-step control strategy that combines ROI average grayscale coarse adjustment with UMIG quality difference incremental fine adjustment. The coarse adjustment quickly brings the image brightness into the usable range, and the fine adjustment further determines the exposure time based on the speckle quality change, thus taking into account both response speed and DIC speckle quality.

[0020] 3. The real-time closed-loop control of the present invention enables the acquired speckle images to be directly used for DIC calculation, and is suitable for high-temperature laser speckle DIC measurement during continuous heating process.

[0021] 4. Experimental verification shows that under the experimental conditions of heating C / C braided composite materials from 1100℃ to 1600℃, when using this method, UMIG is still 3.42 at 1600℃, and effective strain results can still be obtained for DIC. Under fixed exposure conditions, UMIG drops to 0 at 1500℃, and effective DIC results cannot be obtained after 1400℃. This method will increase the upper limit of the effective measurement temperature by at least 200℃ under the experimental conditions.

[0022] In summary, this invention solves the problems of overexposure of laser speckle DIC images and DIC measurement interruption under high temperature conditions by establishing a real-time closed-loop adaptive exposure control method and system with UMIG as the speckle quality evaluation index and ROI average gray level coarse adjustment and UMIG incremental fine adjustment as the core. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the overall hardware of the laser speckle image acquisition system; Figure 2 This is a schematic diagram illustrating the implementation principle of the adaptive exposure control method for digital image correlation measurement provided in this embodiment of the invention; Figure 3 This is a schematic diagram illustrating the specific implementation process of the adaptive exposure control method for digital image correlation measurement provided in this embodiment of the invention; Figure 4 This is a comparative experimental result diagram of the adaptive exposure scheme and the fixed exposure scheme of the present invention; Figure 5 This is a system block diagram of the electronic device provided in the embodiments of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0026] First, it should be noted that in the embodiments of the present invention, the words "exemplarily," "for example," etc., are used to indicate that they are examples, illustrations, or descriptions. Any embodiment or design scheme described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or design schemes. Specifically, the use of the term "exemplarily" is intended to present the concept in a concrete manner. Furthermore, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either one or the other.

[0027] First Embodiment

[0028] This embodiment provides an adaptive exposure control method for digital image correlation measurement, applicable to non-contact measurement scenarios of full-field deformation in laser speckle digital image correlation during continuous high-temperature heating where thermal radiation gradually increases. It is used to adjust the exposure time of the laser speckle image acquisition system; the acquisition system is as follows: Figure 1As shown, the system includes: a laser, a spatial filter beam expander assembly, a vacuum / inert atmosphere high-temperature furnace with a quartz window for accommodating the specimen, a narrowband filter, an industrial camera, and an industrial control computer. Specifically, this embodiment uses a solid-state laser with a wavelength of 532 nm and an output power of 1200 mW, and a spatial filter beam expander assembly as the laser illumination unit; a CCD camera and lens supporting external real-time exposure time control as the image acquisition unit; a narrowband filter with a center wavelength of 532 nm (the center wavelength of the narrowband filter matches the laser wavelength), a linear polarizer, and a neutral density attenuator as the thermal radiation suppression unit; and a vacuum / inert atmosphere high-temperature furnace with a heating rate of 0.8 °C / s, a temperature accuracy of 0.1 °C, and a maximum temperature of 2500 °C, using radiative heating, as the high-temperature heating device, to apply a high-temperature environment to the specimen and provide an observation window for the image acquisition unit to perform optical observation; the surface of the C / C composite specimen forms a laser speckle pattern that can be used for DIC calculation under 532 nm laser irradiation. The adaptive exposure and DIC processing program runs on the industrial control computer and is used to perform ROI average gray coarse adjustment, UMIG calculation, incremental exposure fine adjustment and DIC calculation, forming a closed-loop control loop with the image acquisition unit.

[0029] like Figure 2 As shown, this method designs a one-sided average intensity gradient (UMIG) index for the isotropic characteristics of laser speckle, and combines it with a two-step exposure control algorithm that coarsely adjusts the average gray level of the ROI and finely adjusts the UMIG quality difference incrementally. This allows for real-time adjustment of the exposure time of the industrial camera, maintaining the speckle image quality of the ROI region to meet the requirements of DIC calculation, and ensuring that DIC calculation is continuous and uninterrupted during high-temperature measurement.

[0030] The technical problems solved by this method include the following: 1. Design a computationally efficient image quality evaluation index UMIG that targets the isotropic characteristics of laser speckle; calculate the mean intensity gradient in only one spatial direction of the ROI region, and reduce redundant calculations by utilizing the statistical isotropic characteristics of laser speckle, which has higher computational efficiency than traditional MIG. 2. Design a two-step adaptive exposure control algorithm that combines rapid coarse adjustment based on ROI average gray level with incremental fine adjustment based on UMIG quality difference; the coarse adjustment quickly brings the image brightness into the usable range, and the fine adjustment determines the exposure adjustment stopping condition based on the UMIG quality difference between adjacent images.

[0031] 3. It is integrated into a complete hardware-software integrated real-time closed-loop control system. The acquired speckle images can be directly used for DIC calculation with minimal impact on DIC measurement.

[0032] To address the aforementioned issues, the implementation flow of the method in this embodiment is as follows: Figure 3 As shown, the main steps include: Step 1, System Initialization: Configure the laser, beam expander group, narrowband filter, industrial camera, computer, and heating device; fix the imaging lens aperture, and set the initial exposure time, region of interest (ROI) coordinates, target average gray value G_target, gray value deviation threshold ΔG_th, allowable exposure time range [t_min, t_max], exposure increment step size, speckle quality difference threshold ΔQ_th, and maximum exposure increment count N_max; Among them, fixed imaging lens aperture refers to keeping the aperture value unchanged during the measurement process and achieving adaptive exposure only by adjusting the exposure time of the industrial camera, so as to avoid the aperture change from altering the speckle field distribution on the surface of the specimen.

[0033] The exposure increment step size, speckle quality difference threshold, and maximum exposure increment number can be preset according to the industrial camera's exposure response, heating rate, and measurement frequency.

[0034] Step 2, speckle image acquisition: The industrial camera is controlled to acquire laser speckle images of the surface of the high-temperature specimen using the current exposure time t_old. The laser speckle is formed by a single longitudinal mode laser irradiating the surface of the specimen. A narrowband filter with a center wavelength matching the laser wavelength is installed at the front end of the camera lens. Step 3: Calculate the average gray level G_avg of the region of interest (ROI), where the ROI corresponds to the speckle area of ​​the specimen and excludes the background thermal radiation area outside the specimen area. Step 4, coarse adjustment: If |G_avg - G_target| is greater than the grayscale deviation threshold ΔG_th, then adjust the exposure time according to the difference between G_avg and G_target to make the average grayscale of the ROI close to the target average grayscale value, and return to step 2 to re-acquire; if the deviation does not exceed the grayscale deviation threshold ΔG_th, then proceed to step 5. The coarse adjustment uses the average gray level of the ROI as feedback to bring the average gray level of the ROI into the preset usable brightness range, providing initial exposure time for subsequent fine adjustment based on UMIG.

[0035] Step 5: Calculate the one-sided average intensity gradient UMIG. The absolute value of the image intensity gradient in one spatial direction of the ROI region is averaged only to obtain the current speckle image quality evaluation value. The unilateral average intensity gradient UMIG is implemented using forward differencing or central differencing, and only the intensity gradient of the ROI region in one of the x or y directions is calculated. The ROI is the projection area of ​​the speckle gauge length segment on the specimen surface in the image, and the furnace wall, fixtures, or background areas outside the ROI are not included in the average grayscale and UMIG calculations.

[0036] Step 6, fine-tuning: Starting from the exposure time after coarse adjustment, increase the exposure time within the allowable range according to the preset exposure increment step, and re-acquire the speckle image and calculate UMIG after each increment; when the UMIG quality difference between two adjacent acquired images is less than the speckle quality difference threshold ΔQ_th, or when the number of exposure increments reaches the maximum number of exposure increments N_max, the adaptive exposure adjustment is completed, and the exposure time that meets the stopping condition is taken as the current measured exposure time; Step 7, DIC calculation: Perform digital image correlation and cross-correlation calculations between the speckle image acquired at the current measurement exposure time and the reference image, and output the full-field displacement field and strain field. Step 8: Loop, proceed to the next measurement moment and return to step 2, repeat until the measurement ends.

[0037] Specifically, in this embodiment, the specimen was heated from 1100℃ to 1600℃, with an image acquisition interval of 1℃. In the fixed exposure experiment, the camera exposure time remained constant during the heating process; in the automatic exposure experiment, the two-step adaptive exposure process of this invention was executed at each temperature acquisition moment. Experimental results show that under fixed exposure conditions, when the specimen temperature reaches 1500℃, the speckle field is completely submerged by background radiation, UMIG is 0, and DIC calculation cannot continue after 1400℃; under automatic exposure conditions, measurable speckle contrast can still be obtained at 1600℃, UMIG is 3.42, and effective strain results can still be obtained by DIC.

[0038] The experimental results comparing the adaptive exposure scheme and the fixed exposure scheme of this invention are as follows: Figure 4 As shown, Figure 4 The results of UMIG comparison between the fixed exposure scheme and the adaptive exposure scheme of the present invention during the temperature rise process from 1100℃ to 1600℃ are presented. In the C / C braided composite material experiment from 1100℃ to 1600℃, the UMIG of the fixed exposure scheme decreased from 30.35 at 1100℃ to 3.36 at 1400℃, and reached 0 at 1500℃ and 1600℃; the UMIG of the adaptive exposure scheme of the present invention remained at 3.42 at 1600℃, and effective strain results of DIC could still be obtained. It can be seen that under the experimental conditions, the present invention increases the upper limit of the effective DIC measurement temperature from 1400℃ under the fixed exposure condition to 1600℃, an increase of at least 200℃.

[0039] UMIG computational efficiency test: On speckle images of different resolutions, UMIG only calculates the image intensity gradient in one spatial direction, saving an average of about 28% of the computation time compared to traditional MIG, making it suitable for repeated calculations in adaptive exposure feedback loops.

[0040] In summary, this embodiment provides an adaptive exposure control method for digital image correlation measurement, employing an aperture-first two-step adaptive exposure control strategy: first, coarse adjustment is performed using the average grayscale of the ROI region of the specimen as feedback to bring the image brightness into a usable range; then, fine adjustment is performed using the one-sided average intensity gradient (UMIG) as the speckle quality evaluation index, following a preset exposure increment step size, and the stopping condition is set by the UMIG quality difference threshold between adjacent images or the maximum number of exposure increments. UMIG only calculates the image intensity gradient in one spatial direction, utilizing the statistical isotropic characteristics of laser speckle to reduce redundant calculations, resulting in higher computational efficiency compared to traditional average intensity gradient (MIG). In the C / C braided composite material heating experiment from 1100℃ to 1600℃, this method can maintain usable speckle quality; fixed exposure DIC cannot continue after 1400℃, and UMIG is 0 at 1500℃, while this method can still obtain effective DIC results at 1600℃.

[0041] Second Embodiment

[0042] This embodiment provides an adaptive exposure control system for digital image correlation measurement, including: The image acquisition module is used to control the industrial camera to acquire laser speckle images of the surface of the high-temperature specimen with the current exposure time, and to transmit the currently acquired laser speckle images to the exposure time coarse adjustment module. The exposure time coarse adjustment module is used for: After receiving the laser speckle image, calculate the average gray level of the region of interest in the laser speckle image; If the deviation between the average gray level of the currently calculated region of interest and the preset target average gray level does not exceed the preset gray level deviation threshold, the exposure time fine-tuning module is activated; otherwise, the exposure time is adjusted and the image acquisition module is activated until the deviation between the average gray level of the region of interest in the laser speckle image acquired at the current exposure time and the preset target average gray level does not exceed the preset gray level deviation threshold, at which point the exposure time fine-tuning module is activated. The exposure time fine-tuning module is used for: Within the preset exposure time limit, the exposure time is gradually increased according to the preset exposure increment step until the preset stopping condition is met, and the exposure time at which the stopping condition is met is taken as the final exposure time.

[0043] It should be noted that the adaptive exposure control system for digital image correlation measurement in this embodiment corresponds to the adaptive exposure control method for digital image correlation measurement in the first embodiment described above; the functions implemented by each functional module in the adaptive exposure control system for digital image correlation measurement in this embodiment correspond one-to-one with the process steps in the adaptive exposure control method for digital image correlation measurement in the first embodiment described above; therefore, they will not be described again here.

[0044] Third Embodiment

[0045] This embodiment provides an electronic device, such as... Figure 5 As shown, the electronic device includes a processor and a memory; wherein the processor and the memory can be connected via a communication bus; the memory stores at least one instruction, which is loaded and executed by the processor to implement the method of the first embodiment described above. Furthermore, the electronic device may also include a transceiver, the processor and the transceiver can be connected via a communication bus, and the transceiver is used to communicate with other devices.

[0046] Below, in conjunction with Figure 5 A detailed introduction to each component of this electronic device is provided below: The processor is the control center of the electronic device. The electronic device may include multiple processors, each of which can be a single-core processor (single-CPU) or a multi-core processor (multi-CPU). The term "processor" can refer to a single processor or a collective term for multiple processing elements. For example, a processor can be one or more central processing units (CPUs), other general-purpose processors, application-specific integrated circuits (ASICs), or one or more integrated circuits configured to implement embodiments of the present invention, such as one or more digital signal processors (DSPs), one or more field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor. The processor can perform various functions of the electronic device by running or executing software programs stored in memory and by calling data stored in memory.

[0047] In a specific implementation, as one example, the processor may include one or more CPUs, for example... Figure 5 CPU0 and CPU1 shown are, of course, merely illustrative examples.

[0048] The memory is used to store the software program that executes the solution of the present invention, and the processor controls its execution. For specific implementation methods, please refer to the above method embodiments, which will not be repeated here.

[0049] Optionally, the memory may be a read-only memory (ROM) or other type of static storage device capable of storing static information and instructions, random access memory (RAM) or other type of dynamic storage device capable of storing information and instructions, or electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM) or other optical disc storage, optical disc storage (including compressed optical discs, laser discs, optical discs, digital universal optical discs, Blu-ray discs, etc.), magnetic disk storage media or other magnetic storage devices, or any other medium capable of carrying or storing desired program code in the form of instructions or data structures and accessible by a computer, but not limited thereto. The memory may be integrated with the processor or exist independently, and may be accessed through the interface circuit of the electronic device ( Figure 5 (Not shown in the image) is coupled to the processor; however, this embodiment of the invention does not impose specific limitations on this.

[0050] The transceiver may include a receiver and a transmitter. Figure 5 (Not shown separately). The receiver is used to implement the receiving function, and the transmitter is used to implement the transmitting function. The transceiver can be integrated with the processor or exist independently, and can be connected through the interface circuit of the electronic device (…). Figure 5 (Not shown in the image) is coupled to the processor, and this embodiment of the invention does not specifically limit this.

[0051] In addition, it should be noted that, Figure 5 The structure of the electronic device shown is not intended to limit the device. Actual devices may include more or fewer components than shown, or combine certain components, or have different component arrangements. Furthermore, the technical effects achieved by this electronic device when performing the method of the first embodiment described above can be referenced to the technical effects described in the first embodiment; therefore, they will not be repeated here.

[0052] Fourth embodiment

[0053] This embodiment provides a computer-readable storage medium storing at least one instruction, which is loaded and executed by a processor to implement the method of the first embodiment described above. The computer-readable storage medium may be a ROM, random access memory, CD-ROM, magnetic tape, floppy disk, or optical data storage device, etc. The instruction stored therein can be loaded and executed by a processor in a terminal.

[0054] Furthermore, it should be noted that the present invention can be provided as a method, apparatus, or computer program product. Therefore, embodiments of the present invention can take the form of a completely or partially hardware embodiment, a completely or partially software embodiment, or an embodiment combining software and hardware aspects. Moreover, when implemented in software, embodiments of the present invention can take the form of a computer program product implemented on one or more computer-usable storage media containing computer-usable program code. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer program are loaded or executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any usable medium accessible to a computer or a data storage device such as a server or data center containing one or more sets of usable media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium. A semiconductor medium can be a solid-state drive (SSD).

[0055] Embodiments of the present invention are described with reference to flowchart illustrations and / or block diagrams of methods, terminal devices (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, embedded processor, or other programmable data processing terminal device to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing terminal device, generate instructions for implementing the flowchart illustrations. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0056] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing terminal device to operate in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1The functions specified in one or more boxes. These computer program instructions may also be loaded onto a computer or other programmable data processing terminal equipment to cause a series of operational steps to be performed on the computer or other programmable terminal equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable terminal equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0057] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. The terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element. Furthermore, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, and B alone, where A and B can be singular or plural. Additionally, the character " / " in this text generally indicates an "or" relationship between the preceding and following objects, but it can also indicate an "AND / OR" relationship. Please refer to the context for specific interpretations. "At least one" refers to one or more items, while "more than" refers to two or more items. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, at least one of a, b, or c can be represented as: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0058] Furthermore, it is understood that in various embodiments of the present invention, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0059] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0060] In the several embodiments provided by this invention, it should be understood that the disclosed devices, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative. For instance, the division of functional modules / units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another device, or some features may be ignored or not executed. Furthermore, the shown or discussed mutual couplings or direct couplings or communication connections may be through some interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms. Units described as separate components may or may not be physically separate, and components shown as units may or may not be physical units, i.e., they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs. Additionally, the functional units in the various embodiments of this invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0061] If the method is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0062] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention. It should be pointed out that although preferred embodiments of the present invention have been described, those skilled in the art, once they understand the basic inventive concept of the present invention, can make several improvements and modifications without departing from the principles described herein. These improvements and modifications should also be considered within the scope of protection of the present invention. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present invention.

Claims

1. An adaptive exposure control method for digital image correlation measurement, characterized in that, include: S1, control the industrial camera to acquire laser speckle images of the surface of the high-temperature specimen using the current exposure time; S2, calculate the average gray level of the region of interest in the laser speckle image; S3, if the deviation between the average gray level of the currently calculated region of interest and the preset target average gray level does not exceed the preset gray level deviation threshold, then execute S4; Otherwise, adjust the exposure time and return to S1 until the deviation between the average gray value of the region of interest in the laser speckle image acquired at the current exposure time and the preset target average gray value does not exceed the preset gray value deviation threshold, then execute S4. S4. Within the preset exposure time limit, gradually increase the exposure time according to the preset exposure increment step until the preset stopping condition is met, and use the exposure time when the stopping condition is met as the final exposure time.

2. The adaptive exposure control method for digital image correlation measurement as described in claim 1, characterized in that, When acquiring laser speckle images, the imaging lens aperture of the industrial camera is fixed, and a narrowband filter with a center wavelength matching the laser wavelength is installed at the front end of the industrial camera lens.

3. The adaptive exposure control method for digital image correlation measurement as described in claim 1, characterized in that, The region of interest corresponds to the speckle area of ​​the specimen, excluding the background thermal radiation area outside the specimen area.

4. The adaptive exposure control method for digital image correlation measurement as described in claim 1, characterized in that, The deviation between the average gray level of the region of interest and the preset target average gray level is expressed as the absolute value of the difference between the average gray level of the region of interest and the preset target average gray level.

5. The adaptive exposure control method for digital image correlation measurement as described in claim 1, characterized in that, Within the preset exposure time limit, the exposure time is gradually increased according to the preset exposure increment step until the preset stopping condition is met. The exposure time at which the stopping condition is met is taken as the final exposure time, including: Within the preset exposure time limit, the exposure time is gradually increased according to the preset exposure increment step. After each increase in exposure time, the industrial camera is controlled to acquire laser speckle images of the surface of the high-temperature specimen using the adjusted exposure time, and the one-sided average intensity gradient of the acquired laser speckle images is calculated. When the difference between the average intensity gradient of one side of two adjacent laser speckle images is less than the preset speckle quality difference threshold, or when the actual number of exposure increments reaches the preset maximum number of exposure increments, adaptive exposure adjustment is completed, and the exposure time obtained at this time is used as the final exposure time.

6. The adaptive exposure control method for digital image correlation measurement as described in claim 1, characterized in that, The method for calculating the one-sided average intensity gradient is as follows: the absolute value of the image intensity gradient in one spatial direction of the region of interest in the laser speckle image is averaged to obtain the one-sided average intensity gradient of the image.

7. The adaptive exposure control method for digital image correlation measurement as described in claim 1, characterized in that, After obtaining the final exposure time, the method further includes: The industrial camera is controlled to acquire laser speckle images of the surface of the high-temperature specimen using the current final exposure time. Digital image correlation and cross-correlation calculations are performed between the current laser speckle images and the reference image to output the full-field displacement field and strain field.

8. An adaptive exposure control system for digital image correlation measurement, characterized in that, include: The image acquisition module is used to control the industrial camera to acquire laser speckle images of the surface of the high-temperature specimen with the current exposure time, and to transmit the currently acquired laser speckle images to the exposure time coarse adjustment module. The exposure time coarse adjustment module is used for: After receiving the laser speckle image, calculate the average gray level of the region of interest in the laser speckle image; If the deviation between the average gray level of the currently calculated region of interest and the preset target average gray level does not exceed the preset gray level deviation threshold, then the exposure time fine-tuning module will be activated. Otherwise, adjust the exposure time and start the image acquisition module until the deviation between the average gray value of the region of interest in the laser speckle image acquired at the current exposure time and the preset target average gray value does not exceed the preset gray value deviation threshold, then start the exposure time fine adjustment module. The exposure time fine-tuning module is used for: Within the preset exposure time limit, the exposure time is gradually increased according to the preset exposure increment step until the preset stopping condition is met, and the exposure time at which the stopping condition is met is taken as the final exposure time.

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