Device for determining the optical characteristics of a camera

Abstract

The technology of the present disclosure relates to determining the optical characteristics of a camera. The device includes a housing that receives a test fixture for holding the camera. The housing includes a first part and a second part, thereby creating a chamber around the camera. The first part is attached to the test fixture and defines a first hole located on one side of the first part. The first hole guides gas out of the chamber. The second part defines a second hole that is located on a first side of the second part to guide gas into the chamber. An orifice is located on a second side of the second part and is positioned opposite the test fixture to define a field of view that includes the camera target. The orifice receives the lens barrel of the camera and enables the determination of the optical characteristics.

Description

Background Art

[0001] Cameras, especially wide-angle cameras for advanced driver assistance systems (ADAS), may be tested in extreme temperature and humidity environments. These extreme environments may not be suitable for precision test instruments used to determine the optical characteristics of cameras, such as instruments for determining the modulation transfer function (MTF). Challenges are associated with testing cameras, especially when testing at focal lengths compatible with an environmental test chamber that may not be large enough to position a test target at the distances required by the test protocol. An environmental test chamber with a transparent window between the camera and the test target may introduce optical aberrations because the image may be affected by the optical properties of the window material. Summary of the Invention

[0002] This document describes one or more aspects of a device for determining the optical characteristics of a camera. In one example, a device includes a housing configured to receive a test fixture that holds a camera for determining the optical characteristics of the camera. The housing includes a first portion and a second portion removably attached to the first portion, creating a chamber in which the camera is disposed. The first portion is configured to attach to the test fixture and defines a first orifice on one side of the first portion. The first orifice is configured to direct gas out of the chamber. The inlet flow direction of the gas into the chamber is perpendicular to the outlet flow direction of the gas out of the chamber. The second portion defines a second orifice on a first side of the second portion to direct gas into the chamber. An aperture on a second side of the second portion is positioned opposite the test fixture to define a field of view that includes the camera target. The aperture is configured to receive the lens barrel of the camera, enabling the determination of the optical characteristics.

[0003] In another example, a method includes: using a processor to adjust a rotation angle of a test fixture about an optical axis of a camera held by the test fixture. The test fixture and the camera are disposed within a housing. The housing includes a first portion and a second portion removably attached to the first portion to create a chamber. The first portion is configured to be attached to the test fixture and defines a first aperture on one side of the first portion. The first aperture is configured to direct gas out of the chamber. The second portion defines a second aperture located on a first side of the second portion to direct gas into the chamber. The second portion also defines an orifice located on a second side of the second portion. The orifice is positioned opposite the test fixture to define a field of view including a camera target. The orifice is configured to receive a lens barrel of the camera, enabling determination of optical characteristics of the camera. The method further includes receiving image data from the camera, the image data representing a captured image of the camera target within the camera's field of view. The method further includes: when the temperature of the camera is at a camera temperature set point, adjusting the position of the camera target within the camera's field of view and determining the optical characteristics of the camera based on the camera target.

[0004] The present invention content is provided to introduce aspects of an apparatus for determining optical characteristics of a camera, which is further described in the following detailed description and the accompanying drawings. For ease of description, the present disclosure focuses on vehicle-based or automotive systems, such as those integrated on a vehicle traveling on a road. However, the techniques and systems described herein are not limited to vehicle or automotive scenarios and are also applicable to other environments where a camera can be used to detect objects. The present invention content is not intended to identify essential features of the claimed subject matter nor to be used for determining the scope of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Details of one or more aspects of an apparatus for determining optical characteristics of a camera are described in this document with reference to the following drawings. The same numbers are used throughout the drawings to refer to like features and components:

[0006] Figure 1 An example apparatus configured to determine optical characteristics of a camera attached to a test bench is shown;

[0007] Figure 2A Example graphs of an edge spread function, a line spread function, and a modulation transfer function are shown;

[0008] Figure 2B An example image of a slant-edge target for developing the example graphs is shown.

[0009] Figure 3 An example is shown configured to determine with Figure 1An example device for separating the camera's optical characteristics from the test bench, where a part of the device is shown as a transparent layer;

[0010] Figure 4 An example device is shown that has a solid lid and is configured to determine Figure 3 the optical characteristics of a camera;

[0011] Figure 5 is a cross-sectional view of the lid of an example device configured to determine Figure 3 the optical characteristics of a camera, showing the orifice;

[0012] Figure 6 is an exploded view of an example device configured to determine Figure 3 the optical characteristics of a camera separated from the test bench;

[0013] Figures 7A - 7C An example of the air flow inside an example device configured to determine Figure 3 the optical characteristics of a camera is shown;

[0014] Figure 8 is an example system that includes an example device configured to determine Figure 3 the optical characteristics of a camera;

[0015] Figure 9 is a flowchart showing an example process flow for determining the optical characteristics of a camera; and

[0016] Figure 10 An example method for determining the optical characteristics of a camera is shown. DETAILED DESCRIPTION

[0017] OVERVIEW

[0018] The technology of the present disclosure relates to a device for determining the optical characteristics of a camera. The modulation transfer function (MTF) is a measurement of the image quality characteristics of a camera and is an industrially accepted metric for characterizing advanced driver assistance system (ADAS) cameras for automotive applications. Typical methods for testing the MTF characteristics of camera images include sampling the image data from several different positions or locations across the camera's field of view.

[0019] ADAS cameras are expected to operate within a temperature range of -40°C to 85°C, and performance is verified through laboratory testing using instruments that may not be rated for operation within the specified temperature range. MTF testing can be accomplished within the specified temperature range by enclosing the camera in an environmental chamber mounted on a test bench specifically designed for MTF testing. The environmental chamber maintains the camera at a predetermined temperature set point while performing MTF measurements at various points within the camera's field of view. The environmental chamber receives conditioned air through an inlet port and circulates it around the camera, transferring heat into and out of the camera to achieve the camera's temperature set point. The conditioned air then exits the environmental chamber and enters the test cell. The environmental chamber has an orifice that exposes the camera's lens to the test bench, allowing the camera to focus on a movable target for MTF testing across the camera's entire field of view.

[0020] This disclosure introduces an apparatus for determining the optical properties of a camera. It also describes an environmental chamber for determining MTF measurements at all positions within a camera's field of view. A method for determining MTF using the environmental chamber is also disclosed. MTF measurements can be determined for any camera field position and automatically indexed to improve testing efficiency while maintaining the camera at a desired temperature set point.

[0021] Example device

[0022] Figure 1 An example apparatus 100 is shown for determining optical properties of a camera 102. One such property is MTF, which is a measure of the image quality of the camera 102, which will be explained in more detail below. In an example implementation, the apparatus 100 is an environmental chamber placed on a test bench 104 that is designed to determine the MTF of the camera 102. In the example disclosed herein, the test bench is a ProCam Test R&D test bench manufactured by TRIOPTICS GmbH of Wedel, Germany. It will be understood that the apparatus 100 may be applied to other test benches for measuring optical properties of a camera. The camera 102 (see Figure 3 ) can be located within an environmental chamber with a field of view through aperture 106 to a collimator 108 on a test stand 104 housing a back-lit target 110. The collimator simulates target distances from about one meter (1 m) to infinity that the camera 102 may experience in the field, and the target 110 is a cross-type reticle (see Figure 2B ), the crosshair is generated with collimated light to form a test image for camera 102 to capture for analysis by the test equipment. The reticle image can be optically focused by the test equipment to simulate the desired physical distance of the test image relative to camera 102.

[0023] The environmental chamber can maintain the temperature of the environment to which the camera 102 is exposed and receive conditioned air from the air conditioning unit via a conduit 111 attached to the device 100. The conduit 111 can be insulated to reduce heat transfer between the conduit and the environment, thereby reducing the overshoot temperature setting and undershoot temperature setting of the air conditioning unit. Cameras for automotive applications are required to operate within a temperature range of -40 degrees Celsius (°C) to 85 °C (and in some applications, up to 125 °C). The camera 102 can be any camera 102 suitable for use in automotive applications such as ADAS applications and / or occupant detection applications. The camera 102 includes optics, which can include one or more fixed-focus lenses. The camera 102 includes an image sensor, which is composed of a two-dimensional pixel array organized into rows and columns that define the resolution of the camera 102. The pixels can be composed of charge-coupled devices (CCDs) and / or complementary metal-oxide-semiconductors (CMOSs) that convert light into electrical energy based on the intensity of the light incident on the pixels.

[0024] Example modulation transfer function (MTF)

[0025] Typically, the MTF varies inversely with both the spatial frequency of the image feature and the focusing distance from the optical axis 116 or boresight of the camera 102. Typically, a larger MTF is considered a desirable feature of the camera 102. The MTF of the camera 102 is a measure of the camera 102's ability to transfer contrast from an object to an image at a specific resolution and enables the resolution and contrast to be combined into a single metric. For example, as the line spacing between two parallel lines or line pairs on a test target decreases (i.e., the spatial frequency increases), it becomes more difficult for the camera lens to effectively transfer contrast variations to the image sensor of the camera 102. In another example, for a test target imaged at two positions within the field of view 120 (FOV 120) with a given spacing between the line pairs, the camera has more difficulty resolving the line pairs of the target imaged at a distance from the optical axis. As a result, the MTF decreases, or the area under the curve of the MTF graph decreases.

[0026] The MTF is the modulus or absolute value of the optical transfer function (OTF), and the MTF can be determined in various ways depending on the type of target 110 used. The target type can include a bevel target 110 and a point source or pinhole target 110. The MTF can be determined based on the type of target 110 and the camera application. In an example, the MTF is the two-dimensional Fourier transform of the line spread function (LSF) of the imaging system extracted from the edge spread function (ESF) of the bevel target 110 (see Figure 2A part c).

[0027] Figure 2A Shows example curves of an edge spread function, a line spread function, a modulation transfer function, and Figure 2B shows an example image of a bevel target for developing the example curves. The bevel target 110, as shown in Figure 2B is shown as an image of the bevel target captured by the camera 102 and can be used to measure the MTF and is defined by the requirements of the International Organization for Standardization (ISO) 12233 for the spatial resolution measurement of the camera. The LSF (see Figure 2A part b) is the normalized spatial signal distribution in the linearized output of the imaging system, which is generated by imaging a theoretically infinitely thin line. The ESF (see Figure 2A part a) is the normalized spatial signal distribution in the linearized output of the imaging system, which is generated by imaging a theoretically infinitely sharp edge. The LSF is determined by taking the first derivative of the ESF.

[0028] Figure 2A Parts a - c show example curves of the progression from the ESF to the MTF. One aspect of the determination of the MTF measurement is that the edge of the bevel target 110 being imaged by the camera 102 is oriented off - axis from the horizontal and vertical axes of the FOV 120 of the camera 102. That is, the edge of the target 110 is not aligned or overlapped with the horizontal reference axis and the vertical reference axis of the FOV 120 such that the boundary from bright to dark does not align with the rows and columns (e.g., pixel axes) of the pixels of the image sensor of the camera 102. This off - axis alignment can be achieved by rotating the target 110 within a range of about 5 degrees to about 20 degrees relative to the horizontal axis of the FOV 120 and within a range of about 5 degrees to about 20 degrees relative to the vertical axis of the FOV 120 (hereinafter referred to as the desired off - axis measurement range). Since the MTF measurement uses two focal planes: the sagittal plane (horizontal plane) and the tangential plane (vertical plane) orthogonal or perpendicular to the sagittal plane, this rotation range is required. When the edge of the target 110 is less than about 5 degrees relative to the reference axes of the FOV120 to sample the sagittal plane and / or sample the tangential plane, the Fourier transform calculation becomes infinite and the MTF measurement cannot be performed. On the other hand, when the edge of the target is greater than about 20 degrees relative to the horizontal reference axis and the vertical reference axis, the MTF calculation may combine the horizontal plane with the vertical plane and confound the MTF measurement.

[0029] Housing

[0030] Figure 3is a perspective view showing the device 100 separated from the test bench 104. For purposes of illustration, a portion of the device 100 is shown as a transparent layer to expose the camera 102. The device 100 includes a housing 112 configured to receive a test fixture 114 that holds the camera 102 for determining the MTF. The test fixture 114 can be mounted to the test bench 104 and can rotate about a rotation axis through a rotation angle 118 of at least 90 degrees and up to 180 degrees. The optical axis 116 of the camera 102 defines the line of rotational symmetry of the camera 102 and can be aligned with the rotation axis of the test fixture 114 during the installation of the camera 102. Aligning the optical axis 116 with the rotation axis enables the MTF to be measured at all points in the FOV 120 of the camera 102 by rotating the camera 102 to a specific angle and moving the collimator 108 to position the target 110 at a desired point or angle in the FOV120. The illustrations used herein show the optical axis 116 aligned with the rotation axis, and it should be understood that the line depicting the optical axis 116 also depicts the rotation axis of the test fixture 114.

[0031] When determining the MTF, the housing 112 can rotate through an angle of at least 90 degrees together with the test fixture 114 and the camera 102. In some examples, the test fixture 114, the camera 102, and the housing 112 rotate through a rotation angle 118 of 180 degrees to test the MTF over approximately half of the FOV 120. In addition to the test fixture 114 rotating about the optical axis 116 of the camera 102, the objective arm on the test bench 104 that holds the collimator 108 can rotate or swing about an axis perpendicular to the optical axis 116. The combination of the rotation of the test fixture 114 and the swinging objective arm enables the entire FOV120 of the camera 102 to be mapped for MTF measurement.

[0032] Return reference Figure 3 , the housing 112 includes a first portion 122 (hereinafter referred to as the base 122) and a second portion 124 (hereinafter referred to as the cover 124) removably attached to the base 122. The base 122 is configured to be attached to the test fixture 114 such that the relative movement between the base 122 and the test fixture 114 is minimized, enabling the base 122 to rotate with the test fixture 114. This attachment can be made via threaded fasteners inserted into holes in the bottom plate of the base that engage corresponding threaded holes in the test fixture 114. The cover 124 creates a chamber in which the camera 102 is placed. For purposes of showing the test fixture 114 and the camera 102, the cover 124 is at Figure 31. The cover 124 can be attached to the base 122 via fasteners that allow for quick attachment and detachment. The removability of the cover 124 enables access to the chamber and facilitates mounting the camera 102 to the test fixture 114 or adjusting the position of the camera 102 after the base 122 has been mounted on the test table 104.

[0033] The base 122 may define a first hole 126 or port through a side of the base 122. The first hole 126 may be Figure 3 In the example shown, the first hole 126 is on the right side of the base 122. In other examples, the first hole 126 is on the left side of the base 122. The first hole 126 is located near the bottom plate of the base and can direct the flow of gas out of the chamber, as will be described in more detail below.

[0034] A second hole 128 is defined by the cover 124 and is positioned through a first side 130 of the cover 124 (hereinafter referred to as the front 130 of the cover 124) to direct gas flow into the chamber. The second hole 128 is positioned proximate to a second side 132 (hereinafter referred to as the top 132 of the cover 124) such that the second hole 128 and the first hole 126 are positioned at different heights relative to the test fixture 114.

[0035] For clarity, the axis of rotation aligned with the optical axis 116 defines a plane 134 that is parallel to the inlet flow direction. The second aperture 128 and the first aperture 126 are positioned on the same side of the plane 134 and are aligned with the plane 134. Figure 3 1 is shown on the right side of the housing 112. This arrangement of the second hole 128 and the first hole 126 causes the inlet flow direction of gas into the chamber to be perpendicular to the outlet flow direction of gas out of the chamber, which enables a circulating gas flow around the camera 102, as will be explained in more detail below.

[0036] The area of the first hole 126 is equal to the area of the second hole 128 to minimize the pressure drop across the chamber that may occur due to a restriction in the outlet or due to header loss at the inlet. The area of the holes can be any area, and in the example shown in Figures 2-3, the area of each hole is approximately 5.2 square centimeters (5.2 cm 2 The area of the hole can also be adjusted based on the flow rate of the gas through the chamber to maintain a desired back pressure in the chamber, as the back pressure can affect the flow dynamics of the gas within the chamber.

[0037] Figure 4 is with Figure 3 Same perspective view, where the cover 124 is shown as opaque. Fitting 136 is attached to the cover 124 and can direct the flow of gas through the second hole 128 into the chamber. Fitting 136 is configured to receive conduit 111 (see Figure 1) This conduit delivers gas to device 100, which in the examples disclosed herein is air. Before the air enters the conduit, an air conditioning unit can condition the air by heating or cooling it to a desired temperature. The air temperature can be based on test requirements and the air can also be humidified.

[0038] The angle of fitting 136 can be approximately 90 degrees relative to the front portion 130 of cover 124, and fitting 136 is oriented such that the inlet end 138 of fitting 136 faces the bottom plate of the test unit. This orientation facilitates reducing the accumulation of condensate within fitting 136 (which could occur with different orientations); the condensate will drop onto the bottom plate of the test unit within the conduit. This orientation also facilitates reducing the torque applied to housing 112 by the weight of conduit 111, which could limit the ability of test stand 104 to rotate housing 112 to the angles required for testing MTF.

[0039] Fitting 136 includes a lip 140 configured to hold the conduit such that the conduit can rotate freely about fitting 136 as housing 112 rotates about the axis of rotation of test fixture 114. The rotation of the conduit relative to fitting 136 reduces the torque on fitting 136, which could limit the ability of test stand 104 to rotate housing 112 to the angles required for testing MTF. The conduit can be held on fitting 136 via a conduit clamp or other holding device placed over lip 140; for example, corrugations in the conduit can engage around lip 140 to prevent separation of the conduit from fitting 136.

[0040] Orifice

[0041] Figure 5 is a cross-section of cover 124 that passes through the center of orifice 106. Orifice 106 is located in the top 132 of cover 124 and is positioned opposite test fixture 114 to define FOV 120 that includes camera target 110 in collimator 108. Test stand 104 can move or rotate collimator 108 through an arc such that target 110 can be placed at different points or angles within FOV 120. The size, shape, and arrangement of orifice 106 are designed to receive barrel 142 of camera 102, enabling determination of MTF, and in Figure 5 the example shown, FOV 120 is in the range of approximately 50 degrees to approximately 120 degrees.

[0042] The orifice 106 is further defined by a conical portion 144 attached to the cover 124 that projects or extends into the chamber towards the test fixture 114 and the camera 102. The conical portion 144 may be integrally formed with the cover 124 or may be attached as a separate component of the cover 124. The conical portion 144 defines an annulus 146 or open ring between the barrel 142 and the leading edge of the conical portion, thereby providing a clearance between the barrel 142 and the conical portion 144. In Figure 5 the example shown, the annulus 146 ranges from about one millimeter (1.0 mm) to about 15 mm and may vary based on the diameter of the barrel 142. Minimizing the annulus 146 helps to maintain the temperature within the chamber and reduce air flow from the chamber through the annulus 146, and air flow from the chamber through the annulus 146 may create optical aberrations during MTF measurements. Optimizing the size of the annulus 146 to achieve a relatively low air flow rate through the annulus 146 can help reduce fogging of the camera lens that may be caused by humidity in the surrounding room air.

[0043] The size of the orifice 106 and the distance X from the camera lens 148 to the top 132 of the cover 124 can be determined based on the angle of the FOV 120. For example, the diameter of the orifice 106 in the top 132 of the cover 124 (as Figure 5 shown by parameter Y in ) can be determined by the equation Y = 2 * X * tan(B), where X is the distance from the top 132 of the cover 124 to the vertex or highest point of the camera lens, and B is the half-angle of the FOV 120. Knowing the FOV 120 of the camera 102 being tested, the user can fabricate or select a cover 124 with an appropriate diameter Y for the annulus 146 such that the cover 124 does not obscure the FOV 120 during measurement of the MTF. In scenarios where the diameter Y and the FOV 120 are predetermined, the distance X can be solved for by rearranging the equation. For example, given Y = 45 mm and B = 50 degrees, X = 18.8 mm. In this example, the vertex of the camera lens 148 cannot exceed a depth of 18.8 mm below the top 132 of the cover 124 to maintain a clear or unobscured FOV 120.

[0044] Insulation

[0045] Figure 6 is an exploded view of the device 100, showing the camera 102 mounted to the test fixture 114. When the camera 102 is held at the test temperature set point, a cap 150 or plug can be used to seal the orifice 106 to inhibit heat loss, and subsequently the cap 150 or plug is removed to measure the MTF. The cap 150 may include a skirt that inserts into the orifice 106 or may have a flat surface that seals the top 132 of the cover 124. As Figure 6As shown, the skirt portion can have a clearance fit with the vertical sides of the orifice 106, and the cap can include opposing inclined portions that engage corresponding opposing mounting lugs formed in the top 132 of the cover 124. The cap 150 can rotate about the optical axis 116 to engage the inclined portions with the mounting lugs to seal the orifice 106.

[0046] The base 122 and the cover 124 can include an insulating layer 152 attached to the inner or outer surface, and in Figure 6 the example shown, the insulating layer 152 lines the inner surfaces (not shown) of both the base 122 and the cover 124. In this example, the insulating layer has a thickness of approximately 6 mm and has an R-value or the ability of the insulating material to resist heat flow, ranging from R = 4 to R = 5. As the R-value increases, the insulating ability of the material also increases.

[0047] The base 122 and the cover 124 can be formed from a polymer material, for example, acrylonitrile butadiene styrene (ABS), nylon, or a polyetherimide sold under the name manufactured by SABIC in Riyadh, Saudi Arabia. The material can be selected based on the temperature range determined by the test requirements. The base 122 and the cover 124 can be manufactured via additive manufacturing or 3D printing injection molding, and in Figure 6 the example shown, the base 122 and the cover 124 are 3D printed from ABS, resulting in the fitting 135, the orifice 106, and the mounting lugs integrally formed with the cover 124.

[0048] Airflow

[0049] The walls of the housing 112 are configured to circulate the flow of air around the camera 102 before leaving the chamber, and at least two sides or walls of the base 122 are arranged at a 45-degree angle relative to the inlet flow direction, as Figure 6 shown. The placement of the walls with a 45-degree angle also provides a clearance between the device 100 and the test bench 104, enabling the housing 112 to rotate without interference from the test bench 104.

[0050] Figures 7A - 7C Flow modeling is shown for three different positions of the first hole 126 in the cover 124. Figure 7A The flow dynamics are shown in the case where the first hole 126 is at the center of the front portion 130 of the cover 124. This placement allows the airflow to directly impinge on the camera 102 before leaving the chamber at the second hole 128 on the lower right side of the device 100. This placement of the first hole 126 results in an unstable flow pattern within the chamber and may also create aberrations in the MTF measurement.

[0051] Figure 7BShows the flow dynamics when the first hole 126 is located to the left of the front portion 130 of the cover 124. This placement guides the airflow to pass around the back of the camera 102 before leaving the chamber. Compared with Figure 7A the central placement shown in

[0052] Figure 7C This placement improves the flow efficiency and the heat transfer from the air to the camera 102. The efficiency of the heat transfer can be determined based on the time to reach the temperature set point, where a higher efficiency results in a shorter time to reach the set point. Figures 1 - 3 Shows the flow dynamics when the first hole 126 is located to the right of the front portion 130 of the cover 124 (as Figure 7A shown). This placement guides the airflow to circulate around the back of the camera 102 and then around the front of the camera 102 before leaving the chamber. Compared with the placements in Figure 7B This placement results in improved air circulation and improved heat transfer from the air to the camera 102.

[0053] Example test system

[0054] Figure 8A test system 800 for determining MTF is shown, where the device 100 further includes a processor 154 or a controller that communicates with the test fixture 114 and the camera 102. The processor 154 can be attached to the housing 112 or can be located remotely from the housing 112. The processor 154 can be implemented as a microprocessor or other control circuitry, such as analog control circuitry and / or digital control circuitry. The control circuitry can include one or more application specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs) programmed to perform the techniques, or can include one or more general hardware processors programmed to perform the techniques according to program instructions in firmware, memory, other storage, or a combination thereof. The processor 154 can also combine custom hardwired logic, ASICs, or FPGAs with custom programming to implement the techniques. The processor 154 can include a memory or storage medium (not shown), including non-volatile memory, such as electrically erasable programmable read only memory (EEPROM) for storing one or more routines, thresholds, and captured data. The EEPROM stores data and allows individual bytes to be erased and reprogrammed by applying a programming signal. Other examples of non-volatile memory that the processor 154 can include are flash memory, read only memory (ROM), programmable read only memory (PROM), and erasable programmable read only memory (EPROM). The processor 154 can include volatile memory, such as dynamic random access memory (DRAM), or static random access memory (SRAM). One or more routines can be executed by the processor to perform the steps for determining the MTF based on signals received by the processor 154 from the camera 102 and the test fixture 114, as described herein.

[0055] The processor 154 can adjust the rotation angle 118 of the test fixture 114 about the optical axis 116 of the camera 102 to position the camera 102 for measuring the MTF at all points in the FOV 120. The processor 154 can send a signal to a motor or a rotary actuator in the test bench 104 that controls the rotation of the test fixture 114 that holds the camera 102. The processor 154 can also send a signal to the test bench 104 to position the target 110 in a plane perpendicular to the line of sight of the camera 102 at any position within the FOV 120 by swinging the objective arm that holds the collimator 108, as Figure 5As shown. For example, the target 110 can be positioned by the test bench 104 by oscillating the objective lens arm such that the target 110 is perpendicular to any line of sight. Positioning the target 110 perpendicular to the line of sight reduces errors in MTF measurement because the target 110 can be sampled most accurately by measuring it perpendicular to the field angle radius or line of sight. The test bench 104 is configured to position the center of the target 110 at the same radial distance from the camera 102 at all positions within the FOV 120 by moving the target 110 along an arc from one position to the next, where the radius of the arc remains constant.

[0056] The processor 154 can receive image data representing a captured image of the camera target 110 in the FOV 120 of the camera 102 and adjust the position of the target 110 within the FOV 120. When the temperature of the camera is at the camera temperature set point, the processor 154 can determine the MTF of the camera 102 based on the camera target 110 at the adjusted position within the FOV 120. The camera temperature can be determined by one or more thermocouples attached to the camera 102, and the thermocouples can be shielded to avoid air flow impinging on the thermocouples. The thermocouples can be located in the space between the camera 102 and the test fixture 114, where the air flow is minimized. Additional thermocouples can be placed in the chamber as a reference for determining the air temperature entering the device 100.

[0057] After mounting the camera 102 on the test fixture 114 and at all points within the FOV 120, the processor 154 can determine the MTF at room temperature. The processor can then determine the MTF after the camera 102 reaches the set point temperature of 85 °C and soaks or holds at the set point temperature for a period of at least ten minutes to ensure camera temperature stability. The cap 150 can be mounted on the cover 124 to retain heat within the housing 112 when adjusting the temperature of the camera, and then the cap 150 can be removed for MTF measurement. Removing the cap 150 can result in a relatively small temperature drop, e.g., in the range of 1 °C to 2 °C, and is achieved by the insulating properties of the housing 112 and the geometry of the aperture 106 that minimizes the flow out of the aperture 106. The ramp rate from room temperature to the set point temperature of 85 °C can occur in the range of 15 minutes to 20 minutes and is achieved by the insulating properties of the housing 112. The air conditioning unit can be set to a temperature higher than the camera temperature set point, e.g., 15 °C to 20 °C higher than the set point temperature, to overcome heat losses in the system 800.

[0058] When the camera has reached the camera temperature set point of -40°C and after the camera 102 has been soaked at that set point temperature for at least ten minutes, the processor 154 can then determine the MTF at all points in the FOV 120. The ramp rate of the set point temperature from 85°C to -40°C can be in the range of 30 minutes to 40 minutes, and the air conditioning unit can be set to a temperature lower than the camera temperature set point, for example, 15°C to 20°C lower than the set point temperature, to overcome the thermal gain in the system 800.

[0059] The air conditioning unit can be manually controlled to achieve the desired camera set point temperature, or the air conditioning unit can be controlled by the processor 154. The air flow rate delivered by the air conditioning unit can be in the range of approximately 10 meters per second (10 m / s) and can vary based on the test requirements and the desired temperature ramp rate.

[0060] Example processing flow

[0061] Figure 9 is an example of the overall process flow 900 that starts at 902 with attaching the test fixture 114 to the test bench 104 and ends at 930 with repeating the MTF measurement on other cameras 102. In this example, at 902, the test fixture 114 is attached to the test bench 104. At 904, the camera 102 and the thermocouple are attached to the test fixture 114. The harness connects the camera 102 and the thermocouple to the processor 154. At 906, the base of the housing 112 is placed above the test fixture 114 and the camera 102 and attached to the test fixture 114 using fasteners.

[0062] At 908, the test bench 104 and the camera 102 are powered on, and the camera viewing software for measuring the MTF is started. At 910, the software for operating the test bench is started, and the test settings for the MTF test are initialized.

[0063] At 912, the optical axis 116 of the camera 102 is aligned with the rotation axis of the test bench 104, and at 914, the performance of the camera 102 is measured to verify the functionality of the camera 102 and the system 800 before closing the housing 112.

[0064] At 916, the camera 102 is powered off, and at 918, the cover 124 is attached to the base of the housing 112 and the air duct is installed on the fitting 136.

[0065] At 920, the air conditioning unit is powered on and set to a first temperature set point. At 922, the camera thermocouple temperature is monitored, and when the thermocouple has reached the temperature set point, at 924, the camera 102 is soaked at the temperature set point for 10 minutes.

[0066] At 926, the camera 102 is powered on, and MTF measurements are made at all points in the FOV 120, as determined by the test specification. The camera can be rotated about the optical axis 116 through 90 degrees to 180 degrees, and the target 110 can be moved across the entire FOV 120 to capture all images at the designated test points.

[0067] Once the MTF measurements are complete, at 928, the air conditioning unit is set to room temperature, and once the temperature of the camera 102 has reached room temperature, at 930, the cover 124 and the camera 102 are removed, and the test is repeated with another camera 102.

[0068] Example method

[0069] Figure 10 An example method 900 performed by the system 800 is shown. For example, the processor 154 configures the system 800 to perform operations 902 through 908 by executing instructions associated with the processor 154. The operations (or steps) 902 through 908 are performed, but not necessarily limited to the order or combination in which the operations are shown herein. Additionally, any one of the one or more operations can be repeated, combined, or reorganized to provide other operations.

[0070] Step 1002 includes "adjusting the rotation angle". This can include using the processor 154 to adjust the rotation angle 118 of the test fixture 114 about the optical axis 116 of the camera 102 held by the test fixture 114, as described above. The camera 102 is placed within an insulating housing 112 that includes a cover 124 removably attached to a base 122. The base 122 is attached to the test fixture 114 such that the housing 112 can be rotated with the test fixture 114 through a rotation angle 118 of at least 90 degrees and up to 180 degrees, as described above. The processor 154 adjusts the rotation angle 118 such that the MTF of the camera 102 can be measured at all points within the FOV of the camera, as described above.

[0071] The housing 112 includes a first aperture 126 that directs conditioned air out of the housing 112 and a second aperture 128 that directs conditioned air into the housing 112. The inlet air flow direction is perpendicular to the outlet air flow direction, and the apertures are arranged such that air circulates around the camera 102 before leaving the housing 112, as described above. The cover 124 includes an aperture 106 that is positioned opposite the test fixture 114 and the camera 102, and defines a FOV 120 that includes a target 110 for determining the MTF of the camera 102. The aperture 106 is sized to receive the barrel 142 of the camera 102, and the geometry of the aperture 106 reduces the flow of air leaving the housing 112 around the barrel 142 during testing, as described above.

[0072] Step 1004 includes "receiving image data". This can include receiving, by the processor 154, image data representing a captured image of the camera target 110 in the FOV 120 of the camera 102, as described above. The camera 102 can capture an image of the target 110 at different magnifications of a collimator representing target distances from 1 meter to infinity, as described above. The images can be stored in the memory of the processor 154 for determining the MTF. The target 110 can be a hypotenuse target 110 or a pinhole target 110, and the hypotenuse target 110 or the pinhole target 110 is back-lit to enhance the sharpness of the image captured by the camera 102.

[0073] Step 1006 includes "adjusting target position". This can include adjusting, by the processor 154, the position of the camera target 110 in the FOV 120 of the camera 102. The processor 154 can send a signal to the test bench 104 to move the collimator 108 such that the target 110 is held and moved through an arc to different points in the FOV 120. When the target 110 is moved along the arc from one position to the next while maintaining a constant arc radius, the test bench 104 positions the center of the target 110 at the same radial distance from the camera 102 at all positions in the FOV 120, as described above. The position of the target 110 can be adjusted in any increment (e.g., in 1-degree increments across the extent of the FOV 120).

[0074] Step 1008 includes "determining optical characteristics". This can include: when the temperature of camera 102 is at the camera temperature set point, determining the optical characteristics or MTF of the camera based on camera target 110. The MTF can be determined over a temperature range of -40°C to 85°C (and up to 125°C in some applications). The temperature of camera 102 is held or soaked at each temperature set point for at least ten minutes prior to measuring the MTF to ensure a stable camera temperature. The time to ramp the camera temperature set point from room temperature to -40°C or from room temperature to 85°C is approximately fifteen minutes to approximately twenty minutes, and the time to adjust the camera temperature set point from -40°C to 85°C or from 85°C to -40°C is approximately thirty minutes to approximately forty minutes. Processor 154 determines the MTF using known software based on the type of target 110 held in collimator 108.

[0075] Example

[0076] In the following sections, examples are provided.

[0077] Example 1. An apparatus, comprising: a housing configured to receive a test fixture that holds a camera for determining optical characteristics of the camera, the housing including: a first portion and a second portion, the second portion removably attached to the first portion to create a chamber in which the camera is disposed, the first portion configured to attach to the test fixture and defining a first aperture on one side of the first portion, the first aperture configured to direct gas out of the chamber, an inlet flow direction of gas into the chamber being perpendicular to an outlet flow direction of gas leaving the chamber, the second portion defining: a second aperture on a first side of the second portion to direct gas into the chamber; and an orifice on a second side of the second portion, the orifice: positioned opposite the test fixture to define a field of view including a camera target; and configured to receive a lens barrel of the camera such that optical characteristics can be determined.

[0078] Example 2. The apparatus of the previous example, wherein a fitting is attached to the second portion and configured to direct gas flow through the second aperture, and wherein an angle of the fitting is approximately 90 degrees relative to the first side.

[0079] Example 3. The apparatus of any of the previous examples, wherein the fitting includes a lip configured to rotatably hold a conduit configured to deliver gas to the fitting.

[0080] Example 4. The apparatus of any of the previous examples, wherein an area of the first aperture is equal to an area of the second aperture.

[0081] Example 5. The device of any one of the previous examples, wherein at least two sides of the first part are arranged at an angle of 45 degrees relative to the inlet flow direction.

[0082] Example 6. The device of any one of the previous examples, wherein the wall of the housing is configured to circulate the flow of the gas around the camera before leaving the chamber.

[0083] Example 7. The device of any one of the previous examples, wherein the optical axis of the camera defines the axis of rotation of the test fixture, and wherein the housing is configured to rotate with the test fixture through an angle of at least ninety degrees.

[0084] Example 8. The device of any one of the previous examples, wherein the axis of rotation defines a plane parallel to the inlet flow direction, and wherein the second hole and the first hole are located on the same side of the plane.

[0085] Example 9. The device of any one of the previous examples, wherein the second hole and the first hole are positioned at different heights relative to the test fixture.

[0086] Example 10. The device of any one of the previous examples, wherein the first part and the second part include an insulating layer attached to one or more of the inner surface and the outer surface.

[0087] Example 11. The device of any one of the previous examples, wherein the field of view is in the range of approximately fifty degrees to approximately 120 degrees.

[0088] Example 12. The device of any one of the previous examples, wherein the orifice is further defined by a tapered portion attached to the second part, the tapered portion projecting into the chamber towards the test fixture, and the tapered portion defining an annulus between the barrel and the leading edge of the tapered portion.

[0089] Example 13. The device of any one of the previous examples, wherein the annulus is in the range of from approximately one millimeter to approximately fifteen millimeters.

[0090] Example 14. The device of any one of the previous examples, wherein the optical characteristic of the camera is the modulation transfer function (MTF).

[0091] Example 15. The device of any one of the previous examples, wherein the device further includes a processor, the processor communicating with the test fixture and the camera, the processor being configured to: adjust the rotation angle of the test fixture about the optical axis of the camera; receive image data from the camera, the image data representing a captured image of a camera target in the field of view of the camera; adjust the position of the camera target in the field of view of the camera; and determine the optical characteristic of the camera based on the camera target when the temperature of the camera is at a camera temperature set point.

[0092] Example 16. The apparatus of any of the previous examples, wherein the processor is further configured to: determine the optical characteristics when the camera temperature set point is in the range of -40 degrees Celsius to 85 degrees Celsius.

[0093] Example 17. A method, the method comprising: adjusting, using a processor, a rotational angle of a test fixture about an optical axis of a camera held by the test fixture, the test fixture being disposed within a housing that includes a first portion and a second portion, the second portion being removably attached to the first portion to create a chamber; the first portion being configured to attach to the test fixture and define a first aperture on one side of the first portion, the first aperture being configured to direct gas out of the chamber, the second portion defining: a second aperture on a first side of the second portion to direct gas into the chamber; and an aperture located on a second side of the second portion, the aperture: being positioned opposite the test fixture to define a field of view that includes a camera target; and being configured to receive a lens barrel of the camera so as to enable determination of optical characteristics of the camera; receiving image data from the camera, the image data representing a captured image of the camera target in the field of view of the camera; adjusting a position of the camera target in the field of view of the camera; and determining the optical characteristics of the camera based on the camera target when the temperature of the camera is at a camera temperature set point.

[0094] Example 18. The method of the previous example, further comprising: determining the optical characteristics using the processor when the camera temperature set point is in the range of -40 degrees Celsius to 85 degrees Celsius.

[0095] Example 19. The method of any of the previous examples, further comprising: adjusting the camera temperature set point from room temperature to -40 degrees Celsius, or from room temperature to 85 degrees Celsius, over a time period of from about fifteen minutes to about twenty minutes.

[0096] Example 20. The method of any of the previous examples, further comprising: maintaining the temperature of the camera at the camera temperature set point for a period of at least ten minutes.

[0097] Conclusion

[0098] Although various embodiments of the present disclosure have been described in the foregoing description and illustrated in the accompanying drawings, it should be understood that the present disclosure is not limited thereto, but may be practiced in various ways within the scope of the following claims. From the foregoing description, it will be apparent that various changes may be made without departing from the scope of the present disclosure as defined by the appended claims.

[0099] Unless the context clearly dictates otherwise, the use of "or" and grammatically related terms means unrestricted non-exclusive alternatives. As used herein, the phrase "at least one" in reference to a list of items means any combination of those items, including a single member. As an example, "at least one of a, b, or c" is intended to cover: a, b, c, a - b, a - c, b - c, and a - b - c, as well as any combination having multiple of the same element (e.g., a - a, a - a - a, a - a - b, a - a - c, a - b - b, a - c - c, b - b, b - b - b, b - b - c, c - c, and c - c - c, or any other ordering of a, b, and c).

Claims

1. A device for determining the optical characteristics of a camera, comprising: a housing configured to receive a test fixture that holds the camera for determining the optical characteristics of the camera, the housing comprising: a first part and a second part, the second part removably attached to the first part to create a chamber in which the camera is disposed, the first part configured to be attached to the test fixture and defining a first hole on one side of the first part, the first hole configured to direct gas out of the chamber, an inlet flow direction of the gas into the chamber being perpendicular to an outlet flow direction of the gas leaving the chamber, the second part defining: a second hole located on a first side of the second part to direct the gas into the chamber; and an aperture located on a second side of the second part, the aperture: defined by a tapered portion attached to the second part, the tapered portion protruding and extending into the chamber; positioned opposite the test fixture to define a field of view including a camera target; and configured to receive the lens barrel of the camera, enabling the optical characteristics to be determined across the entire field of view of the camera.

2. The device for determining the optical characteristics of a camera according to claim 1, characterized in that, An accessory is attached to the second part and configured to direct the gas flow through the second hole, and wherein the angle of the accessory is 90 degrees relative to the first side.

3. The device for determining the optical characteristics of a camera according to claim 2, characterized in that, The accessory includes a lip configured to rotatably hold a conduit configured to deliver the gas to the accessory.

4. The apparatus for determining the optical characteristics of a camera according to claim 1, characterized in that, The area of the first hole is equal to the area of the second hole.

5. The device for determining the optical characteristics of a camera according to claim 1, characterized in that, At least two sides of the first part are arranged at a 45-degree angle relative to the inlet flow direction.

6. The apparatus for determining the optical characteristics of a camera according to claim 1, wherein, The walls of the housing are configured to circulate the gas flow around the camera before the gas exits the chamber.

7. The apparatus for determining the optical characteristics of a camera according to claim 1, wherein, The optical axis of the camera defines the axis of rotation of the test fixture, and wherein the housing is configured to rotate with the test fixture through an angle of at least ninety degrees.

8. The apparatus for determining the optical characteristics of a camera according to claim 7, characterized in that, The axis of rotation defines a plane parallel to the inlet flow direction, and wherein the second hole and the first hole are located on the same side of the plane.

9. The apparatus for determining an optical characteristic of a camera according to claim 8, wherein, The second hole and the first hole are positioned at different heights relative to the test fixture.

10. The apparatus for determining the optical characteristics of a camera according to claim 1, characterized in that, The first part and the second part include an insulating layer attached to one or more of the inner and outer surfaces.

11. The apparatus for determining the optical characteristics of a camera according to claim 1, characterized in that, The field of view is in the range of 50 degrees to 120 degrees.

12. The apparatus for determining the optical characteristics of a camera according to claim 1, characterized in that, The tapered portion protrudes into the chamber towards the test fixture, and the tapered portion defines an annulus between the lens barrel and the leading edge of the tapered portion.

13. The device for determining the optical characteristics of a camera according to claim 12, characterized in that, The annulus is in the range from one millimeter to fifteen millimeters.

14. The device for determining the optical characteristics of a camera according to claim 1, characterized in that, The optical characteristic of the camera is the modulation transfer function (MTF).

15. The apparatus for determining the optical characteristics of a camera according to claim 1, characterized in that, The device further includes a processor in communication with the test fixture and the camera, the processor configured to: adjust the rotation angle of the test fixture about the optical axis of the camera; Receiving image data from the camera, the image data representing a captured image of a camera target in the field of view of the camera; Adjusting the position of the camera target in the field of view of the camera; And When the temperature of the camera is at a camera temperature set point, determining the optical characteristics of the camera based on the camera target.

16. The apparatus for determining the optical characteristics of a camera according to claim 15, wherein, The processor is further configured to: determine the optical characteristics when the camera temperature set point is in the range from -40 degrees Celsius to 85 degrees Celsius.

17. A method for determining the optical characteristics of a camera, the method comprising: Using a processor to adjust the rotation angle of a test fixture about the optical axis of the camera, the camera being held by the test fixture disposed within a housing, The housing includes a first part and a second part, the second part being removably attached to the first part to create a chamber; The first part is configured to be attached to the test fixture and defines a first hole located on one side of the first part, The first hole is configured to direct gas out of the chamber, The second part defines: A second hole located on a first side of the second part to direct the gas into the chamber; And An orifice located on a second side of the second part, the orifice: Is defined by a tapered portion attached to the second part, the tapered portion protruding and extending into the chamber; Is positioned opposite the test fixture to define a field of view including the camera target; And Is configured to receive the lens barrel of the camera, thereby enabling determination of the optical characteristics of the camera across the entire field of view of the camera; Receiving image data from the camera, the image data representing a captured image of a camera target in the field of view of the camera; Adjusting the position of the camera target in the field of view of the camera; And When the temperature of the camera is at a camera temperature set point, determining the optical characteristics of the camera based on the camera target.

18. The method for determining the optical characteristics of a camera according to claim 17, characterized in that, [[ID=?]]Further comprising: When the camera temperature set point is in the range from -40 degrees Celsius to 85 degrees Celsius, using the processor to determine the optical characteristics.

19. The method for determining the optical characteristics of a camera according to claim 18, characterized in that, Further comprising: Adjusting the camera temperature set point from room temperature to -40 degrees Celsius, or from room temperature to 85 degrees Celsius, within a time period of fifteen minutes to twenty minutes.

20. The method for determining the optical characteristics of a camera according to claim 19, characterized in that, Further comprising: Maintaining the temperature of the camera at the camera temperature set point for a period of at least ten minutes.

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