Camera image quality testing device and testing method thereof

Abstract

The present application relates to the field of optical imaging test, especially to a camera image quality test device and a test method thereof, the method comprising: intersecting the optical axes of at least two collimating projection systems at a common test point, and presetting the regions of interest corresponding to each field of view; making the entrance pupil center of the camera to be tested coincide with the common test point; synchronously lighting up the light sources of all collimating projection systems and triggering the camera to be tested to take a shot, and obtaining an original image containing all field of view target images; directly extracting the edge region image according to the preset region of interest, and calculating the modulation transfer function. The present application simulates the real driving working condition by using the infinite conjugate optical path, realizes the multi-field of view synchronous test through the space intersection of multiple optical axes, and can obtain the meridian and sagittal direction MTF of all fields of view in a single imaging, without mechanical scanning and real-time image recognition, so that the test efficiency is high, the result consistency is good, and the present application is suitable for the batch detection of vehicle-mounted cameras.

Description

Technical Field

[0001] This invention belongs to the field of optical imaging testing technology, and particularly relates to a camera image quality testing device and its testing method. Background Technology

[0002] With the rapid development of intelligent driving technology, vehicle cameras, as core sensors for environmental perception, directly affect driving safety through their image quality. Modulation Transfer Function (MTF), a key indicator for evaluating the imaging resolution and contrast reproduction capabilities of optical systems, is widely used in image quality testing of vehicle cameras.

[0003] Currently, the MTF testing methods for automotive cameras can be mainly divided into the following categories: One type is the traditional MTF scanning test method, such as the invention patent published on June 15, 2016, with publication number CN105675266A, entitled "Apparatus and Method for Measuring the Modulation Transfer Function of an Optical Lens with an Infinite Conjugate Optical Path," which uses a moving detector to perform MTF scanning tests. This method requires sequential measurement of each field of view, resulting in a long testing time, which is difficult to meet the production line cycle requirements of mass production of automotive cameras.

[0004] Another type of test scheme uses finite conjugate close-range charts, such as the invention patent published on November 15, 2022, with publication number CN115345853A, entitled "Real-time Measurement Method, System, Device, and Storage Medium for Multiple Fields of View MTF of a Lens." This type of method evaluates camera performance through close-range target imaging. However, in actual use, vehicle-mounted cameras mainly focus on road scenes from several meters to infinity. Finite conjugate testing cannot accurately simulate their real working state, leading to a deviation between the test results and actual imaging performance.

[0005] Furthermore, some existing multi-field-of-view testing schemes rely on complex image recognition algorithms to automatically locate and segment targets within the field of view (such as the invention patent CN115345853A). The algorithm stability of such methods is easily affected by image quality and increases image processing time. Other schemes employ a multi-optical-axis intersection architecture (such as the invention patent application CN116888449A, published on October 13, 2023, entitled "Measuring Device and Method for Determining the Modulation Conversion Function of a Telephoto Optical System"), which primarily tests the transmission or emission characteristics of "observed" optical systems such as displays and waveguides. Their "light source-test device-external camera" optical path model differs fundamentally from that used for testing "imaging systems" such as vehicle-mounted cameras, and they are not optimized for rapid and stable testing in production line environments.

[0006] Some testing equipment (such as the utility model patent published on December 16, 2022, with publication number CN218066973U and titled "A Lens MTF Testing Equipment") integrates automated mechanical structures, but its core is still finite conjugate testing, and multi-field coverage relies on mechanically moving imaging units, which has mechanical error and timeliness issues.

[0007] In summary, existing technologies still have shortcomings in terms of testing efficiency, accuracy of environmental simulation, consistency of automation, and ease of operation. There is an urgent need for a method and device that can accurately simulate the real working optical path (infinite conjugate) of an automotive camera, simultaneously acquire multiple feature fields of view MTF at one time, and has a simple and stable process suitable for high-speed testing on production lines. Summary of the Invention

[0008] In view of this, the present invention aims to provide a camera image quality testing device and method that can simulate real driving observation conditions in an infinite conjugate manner, and simultaneously, quickly and accurately acquire MTF curves of multiple specified fields of view of the camera under test in a single imaging process, significantly improving production line testing efficiency and result consistency.

[0009] To achieve the above objectives, the technical solution created by this invention is implemented as follows: A camera image quality testing device, comprising: At least two collimating projection systems, each of which includes a lens barrel and a light source, a blade target, and a collimating objective lens installed sequentially inside the lens barrel; The support frame is used to mount each collimating projection system. The position and orientation of each collimating projection system are adjusted to ensure that the optical axes of each collimating projection system converge at the set common test point. Before testing, the standard lens camera is installed at a position where its entrance pupil center coincides with the common test point. The standard lens camera records the center coordinates and boundary range of the target image formed by each collimating projection system on the image sensor of the standard lens camera, which serves as the preset region of interest location information for subsequent testing. During testing, the standard lens camera is removed, and the camera under test is installed at a position where its entrance pupil center coincides with the common test point. The image acquisition and processing unit is connected to the image sensor of the camera under test. It is used to trigger the camera under test to take a picture once, acquire an original image containing the target images of all fields of view, and extract the edge region images of the meridional and sagittal directions corresponding to each field of view from the original image according to the preset region of interest location information. The modulation transfer function curves of each field of view in the meridional and sagittal directions are calculated by the edge method.

[0010] Furthermore, the blade target includes a circular transparent substrate, the surface of which is divided into four sectors. Two diagonal sectors are light-transmitting areas, and the other two diagonal sectors are neutral gray areas. The boundary between the light-transmitting areas and the neutral gray areas forms the blade edge for meridional and sagittal direction testing.

[0011] Furthermore, a metal film is deposited on the surface of the circular transparent substrate to form a neutral gray area.

[0012] Furthermore, the transmittance of the neutral gray area is 30%, the transmittance of the light-transmitting area is 100%, and the contrast ratio of the blade edge is 10:3.

[0013] Furthermore, the circular transparent substrate is a transparent glass substrate.

[0014] Furthermore, the light source is an LED surface light source with a color temperature of 5500K.

[0015] Furthermore, there are four collimation projection systems, corresponding to the front field of view, rear field of view, left field of view, and right field of view of the camera under test, respectively.

[0016] Furthermore, there are seven collimation projection systems, corresponding to the center field of view, front field of view, rear field of view, left field of view, right field of view, left front field of view, and right front field of view of the camera under test, respectively.

[0017] A camera image quality testing method, implemented using the aforementioned camera image quality testing device, includes: S1: Adjust the pose of each collimating projection system according to the field of view requirements of the camera under test, so that the optical axes of each collimating projection system converge at the set common test point. S2: Install the standard lens camera at a position where its entrance pupil center coincides with the common test point. Record the center coordinates and boundary range of the target image formed by each collimating projection system on the image sensor of the standard lens camera through the standard lens camera, as the preset region of interest location information for subsequent tests. S3: Remove the standard lens camera and install the camera under test at a position where its entrance pupil center coincides with the common test point; S4: Light up the light sources of each collimation projection system, trigger the camera under test to take a picture, and collect an original image containing all the target images in the field of view; S5: Extract the edge region images of each field of view in the meridional and sagittal directions from the original image based on the preset region of interest location information; S6: For the edge region images in the meridional and sagittal directions corresponding to each field of view, the modulation transfer function curves in the meridional and sagittal directions of each field of view are calculated using the edge method.

[0018] Compared with the prior art, the present invention can achieve the following beneficial effects: 1. Each collimated projection system of the present invention employs an infinitely conjugate collimated optical path, and the optical axes of each collimated projection system converge at a common test point. The entrance pupil center of the camera under test coincides with this common test point, thereby simulating the real working state of the camera under test observing a target at infinity. Compared with the finite conjugate near-range chart test method, the test results of the present invention can more realistically reflect the imaging performance of the camera in a road environment.

[0019] 2. This invention achieves multi-field synchronous testing through a static optical design that intersects multiple optical axes: the modulation transfer function curves of the meridional and sagittal directions of all target fields of view can be acquired simultaneously with a single shot, eliminating the need for mechanical scanning or time-division measurement, reducing the testing time from several minutes to seconds, and greatly improving measurement efficiency.

[0020] 3. The entire testing process involves no moving mechanical parts, eliminating the mechanical errors and uncertainties associated with traditional scanning methods or mechanically moving imaging units. By pre-calibrating and determining the region of interest (ROI) for each field of view, the target region is directly cropped from the original image during testing. This eliminates the need for complex real-time image recognition algorithms, avoiding algorithm instability issues caused by image quality fluctuations, resulting in stable and reliable test results. Test conditions for all fields of view (such as illumination color temperature, target contrast, and optical path alignment reference) are highly uniform, ensuring good comparability of test results between different fields of view and different cameras under test.

[0021] 4. This invention optimizes the design of the edge target (overall circular outline, zoned light transmission and gray areas, 10:3 contrast ratio), ensuring both the accuracy of modulation transfer function calculation based on the edge method and the recognizability and process feasibility during calibration. The strategy of pre-setting the region of interest simplifies the software processing flow, reduces system complexity, and makes the device easier to deploy, maintain, and automate in a production line environment.

[0022] 5. From camera installation, synchronous imaging, region of interest extraction, modulation transfer function calculation to result determination, the entire process can be executed fully automatically without manual intervention. Combined with automated conveyor lines and fixtures, it can be seamlessly integrated into existing automotive camera production line testing processes, enabling rapid, continuous, and high-volume image quality inspection. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of the camera image quality testing device described in an embodiment of the present invention; Figure 2A schematic diagram of the collimation projection system described in the embodiment of the present invention; Figure 3 A schematic diagram of the structure of the edge target described in the embodiment of the present invention; Figure 4 A schematic flowchart of the camera image quality testing method described in an embodiment of the present invention.

[0024] The attached reference numerals include: collimating projection system 1, lens barrel 11, light source 12, blade edge target 13, light-transmitting area 131, neutral gray area 132, collimating objective lens 14, support frame 2, mounting platform 3, and common test point 4. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0027] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0028] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "assembly," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] This invention provides a camera image quality testing device and method, innovatively employing a calibration-correction-calculation approach to test the camera's field of view. More specifically, the distortion parameters of the vehicle-mounted camera are first calibrated using a calibration image, and these distortion parameters are then used to correct the distortion of the subsequent test image used for field of view calculation. This fundamentally eliminates the influence of distortion factors on the measurement results, thereby achieving high-precision calculation of the true value of the field of view on distortion-free test images.

[0030] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0031] like Figure 1 As shown, the camera image quality testing device provided by the present invention includes a collimation projection system 1, a support frame 2, a mounting platform 3, a standard lens camera (not shown) and an image acquisition and processing unit (not shown).

[0032] The number of collimation projection systems 1 is at least two, and the specific number is determined according to the testing requirements of the camera under test (not shown in the figure). For example, when testing the front field of view, rear field of view, left field of view, and right field of view of the camera under test, the number of collimation projection systems 1 is four. Or, when testing the center field of view, front field of view, rear field of view, left field of view, right field of view, left front field of view, and right front field of view of the camera under test, the number of collimation projection systems 1 is seven.

[0033] like Figure 2 As shown, each collimating projection system 1 includes a lens barrel 11 and a light source 12, a blade target 13 and a collimating objective lens 14 installed sequentially inside the lens barrel 11. The light emitted by the light source 12 illuminates the blade target 13 and is collimated into parallel light by the collimating objective lens 14.

[0034] The collimation projection system 1 employs an infinitely conjugate collimated optical path to simulate the actual working state of the camera under test observing a target at infinity. Compared to the finite conjugate close-range chart test method, the test results of this invention can more realistically reflect the imaging performance of the camera in a road environment.

[0035] The light source 12 is an LED surface light source with a color temperature of 5500K to simulate sunlight illumination conditions. The focal length of the collimating objective lens 14 is selected according to the field of view and test distance requirements of the camera under test to ensure that the emitted parallel light can cover the corresponding field of view of the camera under test.

[0036] like Figure 3As shown, the cutting edge target 13 includes a circular transparent substrate, preferably a transparent glass substrate. The surface of the circular transparent substrate is divided into four sectors. Two diagonal sectors are left uncoated, maintaining the original shape of the glass substrate, forming a light-transmitting area 131 with 100% transmittance. The other two diagonal sectors are coated with a metal film, forming a neutral gray area 132 with 30% transmittance. A high-quality cutting edge with a contrast ratio of 10:3 is formed at the boundary between the light-transmitting area 131 and the neutral gray area 132. These cutting edges are used for MTF calculations in the meridional and sagittal directions, respectively.

[0037] The outer contour of the blade target 13 is circular, which facilitates preliminary positioning through image recognition during the calibration stage. The diagonal sector layout ensures that there are two mutually perpendicular blade directions in each target image at the same time.

[0038] This invention optimizes the design of the edge target (overall circular outline, zoned light transmission and gray areas, 10:3 contrast ratio), ensuring both the accuracy of modulation transfer function calculation based on the edge method and the recognizability and process feasibility during calibration. The strategy of pre-setting the region of interest simplifies the software processing flow, reduces system complexity, and makes the device easier to deploy, maintain, and automate in production line environments.

[0039] Back Figure 1 The number of support frames 2 is the same as the number of collimated projection systems 1, and each collimated projection system 1 is mounted on the mounting platform 3 via its corresponding support frame 2. The pose of each collimated projection system 1 is adjusted to ensure that the optical axes of each collimated projection system 1 converge at the set common test point 4.

[0040] The optical axes of each collimating projection system 1 intersect at a point in space, and this intersection point is the common test point 4. The position of the common test point 4 is set such that when the entrance pupil center of the camera under test coincides with the common test point 4, the target image formed by each collimating projection system 1 is located in a preset region of interest on the image sensor of the camera under test.

[0041] Before the test, the standard lens camera is installed at a position where its entrance pupil center coincides with the common test point. The center coordinates and boundary range of the target image formed by each collimating projection system 1 on the image sensor of the standard lens camera are recorded by the standard lens camera as the preset region of interest location information for subsequent tests. During the test, the standard lens camera is removed and the camera under test is installed at a position where its entrance pupil center coincides with the common test point.

[0042] The image acquisition and processing unit is connected to the image sensor of the camera under test. It is used to trigger the camera under test to take a picture once, acquire an original image containing the target images of all fields of view, and extract the edge region images of the meridional and sagittal directions corresponding to each field of view from the original image according to the preset region of interest location information. The modulation transfer function curves of each field of view in the meridional and sagittal directions are calculated by the edge method.

[0043] This invention achieves simultaneous testing of multiple fields of view through a static optical design that intersects multiple optical axes in space: the modulation transfer function curves of the meridional and sagittal directions of all target fields of view can be acquired simultaneously in a single shot, without the need for mechanical scanning or time-division measurement, reducing the testing time from several minutes to seconds, and greatly improving the measurement efficiency.

[0044] like Figure 4 As shown, the camera image quality testing method provided by the present invention is implemented using the above-mentioned camera image quality testing device and includes the following steps: S1: Adjust the pose of each collimating projection system according to the field of view requirements of the camera under test, so that the optical axes of each collimating projection system converge at the set common test point.

[0045] S2: Install the standard lens camera at a position where its entrance pupil center coincides with the common test point. Record the center coordinates and boundary range of the target image formed by each collimating projection system on the image sensor of the standard lens camera using the standard lens camera. This information will serve as the preset Region of Interest (ROI) location information for subsequent tests.

[0046] Based on the field-of-view requirements of the camera under test, the spatial pose of each collimating projection system was designed and adjusted. A standard lens camera calibrated with high-precision equipment was temporarily used to replace the camera under test and mounted on the fixture. During installation, it was ensured that the entrance pupil center of the standard lens camera precisely coincided with the common test point. Then, the light sources of each collimating projection system were turned on, and an image was captured through the standard lens camera. By analyzing the image, the position and orientation of each collimating projection system were finely adjusted to ensure that its target image was clear and all optical axes precisely converged at the common test point. After calibration, the center coordinates and boundary range of each target image on the image sensor of the standard lens camera were recorded as the preset region of interest location information for subsequent tests and stored in the database of the image acquisition and processing unit. This calibration process only needs to be performed once, and can be directly called upon for subsequent tests of the same model of camera.

[0047] S3: Remove the standard lens camera and install the camera under test at a position where its entrance pupil center coincides with the common test point.

[0048] Remove the standard lens camera and then install the camera under test on the fixture, aligning the entrance pupil of the camera under test with the common test point.

[0049] S4: Light up the light sources of each collimation projection system, trigger the camera under test to take a picture, and acquire an original image containing all target images in the field of view.

[0050] The operator selects the corresponding camera model on the control software, which automatically retrieves the preset region of interest location information. Clicking the "Start Test" button simultaneously illuminates the light sources of all collimated projection systems and triggers the camera under test to take a picture, acquiring a raw image that simultaneously contains the target images of the entire field of view.

[0051] S5: Extract the edge region images of each field of view in the meridional and sagittal directions from the original image based on the preset region of interest location information.

[0052] After the image acquisition and processing unit receives the original image, it directly crops the edge region image corresponding to each target image in the field of view from the original image based on the preset region of interest location information.

[0053] S6: For the edge region images in the meridional and sagittal directions corresponding to each field of view, the modulation transfer function curves in the meridional and sagittal directions of each field of view are calculated using the edge method.

[0054] For each edge region image, the meridional and sagittal edge directions are automatically identified. Following the edge method specified in ISO 12333, the Edge Spread Function (ESF) is first calculated. Then, the Line Spread Function (LSF) is obtained by differentiating the ESF. Finally, a Fourier transform is performed on the LSF to obtain the MTF curves for that field of view in the meridional and sagittal directions. The MTF curves for all fields of view can be displayed simultaneously on the screen, and the system can automatically determine whether they pass or fail, generating a test report.

[0055] Remove the tested camera, install the next camera to be tested, and repeat steps S2 to S6. Since there is no need to relocate the region of interest or perform mechanical scanning, the testing cycle for a single product mainly depends on the camera exposure and data processing time, and can usually be completed within a few seconds.

[0056] The entire testing process involves no moving mechanical parts, eliminating the mechanical errors and uncertainties associated with traditional scanning methods or mechanically moving imaging units. By pre-calibrating and determining the region of interest (ROI) for each field of view, the target region is directly cropped from the original image during testing. This eliminates the need for complex real-time image recognition algorithms, avoiding algorithm instability issues caused by image quality fluctuations, resulting in stable and reliable test results. Test conditions for all fields of view (such as illumination color temperature, target contrast, and optical path alignment reference) are highly uniform, ensuring good comparability of test results between different fields of view and different cameras under test.

[0057] From camera installation, synchronous imaging, region of interest extraction, modulation transfer function calculation to result determination, the entire process can be executed fully automatically without human intervention. Combined with automated conveyor lines and fixtures, it can be seamlessly integrated into existing automotive camera production line testing processes, enabling rapid, continuous, and high-volume image quality inspection.

[0058] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0059] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A camera image quality testing device, characterized in that, include: At least two collimating projection systems are provided. Each collimating projection system includes a lens barrel and a light source, a cutting edge target, and a collimating objective lens, which are sequentially installed inside the lens barrel. The cutting edge target includes a circular transparent substrate, the surface of which is divided into four sectors. Two diagonal sectors are light-transmitting areas, and the other two diagonal sectors are neutral gray areas. The boundary between the light-transmitting areas and the neutral gray areas forms the cutting edge for meridional and sagittal direction testing. The transmittance of the neutral gray area is 30%, the transmittance of the light-transmitting area is 100%, and the contrast ratio of the cutting edge is 10:

3. The support frame is used to mount each collimating projection system. The position and orientation of each collimating projection system are adjusted to ensure that the optical axes of each collimating projection system converge at the set common test point. Before testing, the standard lens camera is installed at a position where its entrance pupil center coincides with the common test point. The standard lens camera records the center coordinates and boundary range of the target image formed by each collimating projection system on the image sensor of the standard lens camera, which serves as the preset region of interest location information for subsequent testing. During testing, the standard lens camera is removed, and the camera under test is installed at a position where its entrance pupil center coincides with the common test point. The image acquisition and processing unit is connected to the image sensor of the camera under test. It is used to trigger the camera under test to take a picture once, acquire an original image containing the target images of all fields of view, and extract the edge region images of the meridional and sagittal directions corresponding to each field of view from the original image according to the preset region of interest location information. The modulation transfer function curves of each field of view in the meridional and sagittal directions are calculated by the edge method.

2. The camera image quality testing device according to claim 1, characterized in that, A metal film is deposited on the surface of a circular transparent substrate to form a neutral gray area.

3. The camera image quality testing device according to claim 1, characterized in that, The circular transparent substrate is a transparent glass substrate.

4. The camera image quality testing device according to claim 1, characterized in that, The light source is an LED surface light source with a color temperature of 5500K.

5. The camera image quality testing device according to claim 1, characterized in that, There are four collimation projection systems, corresponding to the front field of view, rear field of view, left field of view, and right field of view of the camera under test, respectively.

6. The camera image quality testing device according to claim 1, characterized in that, There are seven collimation projection systems, corresponding to the center field of view, front field of view, rear field of view, left field of view, right field of view, left front field of view, and right front field of view of the camera under test.

7. A method for testing the image quality of a camera, implemented using the camera image quality testing apparatus according to any one of claims 1 to 6, characterized in that, include: S1: Adjust the pose of each collimating projection system according to the field of view requirements of the camera under test, so that the optical axes of each collimating projection system converge at the set common test point. S2: Install the standard lens camera at a position where its entrance pupil center coincides with the common test point. Record the center coordinates and boundary range of the target image formed by each collimating projection system on the image sensor of the standard lens camera through the standard lens camera, as the preset region of interest location information for subsequent tests. S3: Remove the standard lens camera and install the camera under test at a position where its entrance pupil center coincides with the common test point; S4: Light up the light sources of each collimation projection system, trigger the camera under test to take a picture, and collect an original image containing all the target images in the field of view; S5: Extract the edge region images of each field of view in the meridional and sagittal directions from the original image based on the preset region of interest location information; S6: For the edge region images in the meridional and sagittal directions corresponding to each field of view, the modulation transfer function curves in the meridional and sagittal directions of each field of view are calculated using the edge method.

Images