Plenoptic camera measurement and calibration of head-mounted displays

Abstract

A method for measuring performance of a head-mounted display module, the method comprising: arranging the head-mounted display module relative to a plenoptic camera assembly such that an exit pupil of the head-mounted display module coincides with a pupil of the plenoptic camera assembly; emitting light from the head-mounted display module while the head-mounted display module is arranged relative to the plenoptic camera assembly; filtering the light at the exit pupil of the head-mounted display module; acquiring, with the plenoptic camera assembly, one or more light field images projected from the head-mounted display module using the filtered light; and determining information related to performance of the head-mounted display module based on the acquired light field images.

Description

[0001] Priority Statement

[0002] This application claims priority to U.S. Patent Application Serial No. 63 / 048,331, filed July 6, 2020, pursuant to 35 USC §119(e), the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the measurement and calibration of head-mounted displays, and more specifically, to the use of an all-optical camera to calibrate eyepieces used in head-mounted displays. Background Technology

[0004] Wearable head-mounted display systems include one or more eyepieces through which users view the outside world. Eyepieces are typically made of a transparent, highly refractive material, allowing information to be projected to the user while simultaneously transmitting a view of the external world. In many cases, the eyepieces in a head-mounted display undergo a calibration process to normalize the light field displayed to the user of the wearable display system, thereby ensuring a consistent image across head-mounted display systems.

[0005] In some cases, the calibration process involves evaluating multiple white-field images projected through the eyepiece over a wide dynamic range. These images can be acquired using a camera and various neutral density filters. A similar process can be used to evaluate red, green, and blue color balance, as well as several relief distances and positions from the eyepiece, to simulate multiple user pupil positions and interpupillary distances. Based on these images, the calibration process may include adjusting the head-mounted display to match the image field to an external standard. Typically, these steps should be performed for each head-mounted display system, resulting in a time-consuming and costly process. Summary of the Invention

[0006] This disclosure describes methods and systems for calibrating head-mounted displays using an all-light camera. An all-light camera (also called a light field camera) captures information related to the light field emanating from a scene. The light field refers to the intensity of light emanating from the scene and also the direction in which light rays travel in space. In contrast, conventional cameras only capture intensity information related to the scene.

[0007] In the system disclosed herein, the optical system for the all-optical camera is characterized by a pupil that is physically accessible, with spatially discrete filters arranged across the pupil, enabling multiplexed measurements of different optical properties (e.g., brightness, polarization, spectral content) across the pupil. For example, the all-optical camera assembly in a measurement and calibration system may include an entrance pupil outside the lens of the camera assembly, providing sufficient physical space for one or more filter arrays. The system may include a stage that positions a head-mounted display to be tested, wherein the exit pupil of the display is located at the same position as the entrance pupil of the all-optical camera.

[0008] In some embodiments, the measurement and calibration system may include an optical component that provides a view from multiple pupil positions in a single image, thereby allowing calibration of multiple user pupil positions in a single capture, thus saving measurement and calibration time.

[0009] The various aspects of this invention are summarized below.

[0010] Typically, in a first aspect, the present invention relates to a method for measuring the performance of a head-mounted display module, the method comprising: arranging the head-mounted display module relative to an all-optical camera assembly such that the exit pupil of the head-mounted display module coincides with the pupil of the all-optical camera assembly; emitting light from the head-mounted display module while arranging the head-mounted display module relative to the all-optical camera assembly; filtering the light at the exit pupil of the head-mounted display module; acquiring one or more light field images projected from the head-mounted display module using the all-optical camera assembly; and determining information related to the performance of the head-mounted display module based on the acquired light field images.

[0011] Embodiments of a method for displaying images using a wearable display system may include one or more of the following features: The light can be filtered by a plurality of spatially discrete filters located at the pupil of the all-light camera assembly. The spatially discrete filters may include color filters. The color filters may include X, Y, Z color matching function color filters. The spatially discrete filters may include polarization filters. The spatially discrete filters may include neutral density filters.

[0012] The light can be filtered by a first set of spatial discrete filters and a second set of spatial discrete filters that overlap with the first set of spatial discrete filters. The first set of spatial discrete filters and the second set of spatial discrete filters filter different characteristics of the light. The characteristics of the light can be selected from a group consisting of color, polarization, and intensity.

[0013] Acquiring the one or more light field images may include: using a microlens array to re-image the real image from the head-mounted display module onto a multi-element sensor.

[0014] The microlens array can sample a portion of the exit pupil of the lens of the all-optical camera assembly to provide different angle views of the real image from the head-mounted display module.

[0015] The all-optical lens assembly can define an optical path from the pupil to the sensor. The all-optical lens assembly can include a camera lens assembly in the optical path that defines the pupil of the all-optical camera assembly and defines an image plane. The all-optical camera assembly can also include a focusing element array in the optical path between the image plane and the sensor array.

[0016] The information relating to the performance of the head-mounted display module may include information relating to at least one of the performance parameters selected from the group consisting of: emissivity, brightness, color, geometric distortion, virtual image distance, and field curvature.

[0017] The information relating to the performance of the head-mounted display module may include: calculating two-dimensional images at multiple different depths on a three-dimensional volume of interest within the head-mounted display module.

[0018] Determining the information may further include: determining information relating to one or more characteristics of each of the two-dimensional images.

[0019] The method may further include: combining emitted light from multiple different locations of the exit pupil of the head-mounted display module to form multiple overlapping images at the sensor of the all-light camera assembly, each of the multiple overlapping images corresponding to a different user view of the head-mounted display module.

[0020] In a second aspect, the present invention relates to a method for calibrating a head-mounted display, comprising: measuring the performance of the head-mounted display using a method for measuring the performance of a head-mounted display module; and adjusting the operation of the head-mounted display based on the measured performance.

[0021] In a third aspect, the present invention relates to a system comprising: an all-optical camera assembly including a camera lens defining an image plane, a camera sensor, and a microlens array arranged to image light at the image plane onto the camera sensor; a stage for receiving a head-mounted display and positioning the head-mounted display relative to the all-optical camera assembly such that the exit pupil of the head-mounted display module coincides with the pupil of the all-optical camera assembly; one or more filter arrays located at the pupil of the all-optical camera assembly, each of the one or more filter arrays including a plurality of spatially discrete filters extending across the aperture of the camera lens; and a system controller communicating with the all-optical camera assembly and programmed to acquire one or more light field images projected from the head-mounted display module during operation of the system, and to determine information related to the performance of the head-mounted display module based on the acquired light field images.

[0022] Embodiments of the system may include one or more of the following features. One of the filter arrays may include a spatially discrete color filter. The spatially discrete color filter may include X, Y, and Z tri-color filters.

[0023] One of the filter arrays may include a spatially discrete polarization filter.

[0024] One of the filter arrays may include spatially discrete neutral density filters.

[0025] The one or more filter arrays may include a first spatial discrete color filter array and a second spatial discrete filter array overlapping the first group, wherein the first spatial discrete filter array and the second spatial discrete filter array filter different properties of the light. The properties of the light may be selected from a group consisting of color, polarization, and intensity.

[0026] The system further includes an optical component disposed at the pupil of the all-light camera assembly, configured to combine light emitted from multiple different positions of the exit pupil of the head-mounted display module to form multiple overlapping images at a sensor of the all-light camera assembly, each of the multiple overlapping images corresponding to a different user view of the head-mounted display module.

[0027] The optical components may include: one or more polarized beam splitters arranged at different positions in the exit pupil of the head-mounted display module, and a beam combiner arranged in the pupil of the all-light camera assembly, the beam combiner being configured to receive light from each of the polarized beam splitters and guide the light from each polarized beam splitter to the camera lens along a common path.

[0028] Other features and advantages will become apparent from the description, drawings and claims. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of an example measurement and calibration system for a wearable head-mounted display.

[0030] Figure 2A Is Figure 1 A plan view of the example color filter array used in the system shown.

[0031] Figure 2B Is Figure 1 A plan view of the sample neutral density filter array used in the system shown.

[0032] Figure 2C Is Figure 1 A plan view of an example polarization filter array used in the system shown.

[0033] Figure 3 This is a schematic diagram of an example optical assembly that extends the entrance pupil of an all-light camera to include multiple user pupil positions.

[0034] Figure 4 This is a schematic diagram illustrating an example of a wearable head-mounted display system.

[0035] In the diagram, the same symbols represent the same elements. Detailed Implementation

[0036] refer to Figure 1 An example measurement and calibration system 100 for a wearable head-mounted display 150 (e.g., an eyepiece) includes an all-optical camera assembly 101, a filter module 120, and a stage 130 for supporting the display 150 and positioning it relative to the all-optical camera assembly 101. Specifically, the display 150 is arranged such that the exit pupil of the display 150 coincides with the entrance pupil 103 of the all-optical camera assembly 101. A system controller 110 (e.g., a computer controller) communicating with the all-optical camera assembly 101 and the display 150 is programmed to control the operation of the camera assembly 101 and the display 150 to acquire and analyze images from the display in order to calibrate the display.

[0037] Typically, the entrance pupil 103 is located in a position accessible to other optical components that are not part of the imaging optics of system 100. For example, as Figure 1 As shown, the entrance pupil 103 is located outside the all-light camera assembly 101 and in the space between the camera assembly and the display 150.

[0038] Filter module 120 is located at the entrance pupil 103. Filter module 120 includes three spatially discrete filters 120a, 120b, and 120c, each located at the same position relative to axis 102. The filters are spatially discrete because they occupy a non-overlapping area of ​​the entrance pupil 103. Support 121 positions the filter array 120 appropriately along axis 102.

[0039] The all-light camera assembly 101 includes a sensor 106, a microlens array 105, and a camera lens 104, which are arranged sequentially along the axis 102 of the camera assembly. The sensor 106, the microlens array 105, and the camera lens 104 are housed in a common housing with mounting elements to maintain the relative position of each component and protect each component from environmental influences.

[0040] Stage 130 supports display 150, thereby oriented display 150 toward all-light camera assembly 101, such that light 160 from the image projected from display 150 is received by camera assembly along axis 102. Camera lens 104 images display 150 onto image plane 108. Each microlens in microlens array 105 relays the image from display to sensor; however, each image at sensor 106 captures information related to the direction of light in addition to intensity. Note that typically the number of pixels in sensor is much greater than the number of lenses in microlens array 105, allowing each microlens to form an image at a different region of sensor. Sensor 106 is typically a solid-state image sensor device comprising a conventional pixel array. For example, sensor 106 may be a charge-coupled device (CCD) or an active pixel sensor (CMOS). The final image read from sensor 106 corresponds to a micro-image array, each micro-image corresponding to a slightly different angular viewpoint of the imaged object (in this case, display 150).

[0041] Although camera lens 104 is depicted as a single lens element, it is typically a compound lens comprising two or more lens elements that collectively image the display onto image plane 108. Generally, camera lens 104 may include spherical, aspherical, conical, or deformable lens elements, or any combination thereof, to provide sufficiently low aberration imaging suitable for system 100.

[0042] During operation, the all-light camera assembly 101 captures light field images projected from the display 150 of the head-mounted display module for processing by the system controller 110. The system controller 110 may be implemented using digital electronic circuitry, or as computer software, firmware, or hardware, or a combination thereof. For example, in some cases, the system controller 110 may be at least partially implemented as one or more computer programs (e.g., one or more modules of computer program instructions encoded on a computer storage medium for execution by or control of the operation of a data processing apparatus). The computer storage medium may be or may be included in a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination thereof. The term "processing apparatus" encompasses all types of devices, apparatuses, and machines for processing data, including, for example, programmable processors, computers, systems-on-a-chip, or a combination thereof. The apparatus may include special-purpose logic circuitry, such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit). In addition to hardware, the device may also include code that creates an execution environment for the computer program in question, such as code that constitutes processor firmware, protocol stack, database management system, operating system, cross-platform runtime environment, virtual machine, or a combination of one or more of these. The device and execution environment can implement a variety of different computing model infrastructures, such as web services, distributed computing, and grid computing infrastructures.

[0043] Typically, various types of filter arrays can be used as filter module 120. For example, in some embodiments, filters 120a, 120b, and 120c are neutral density filters, each with different attenuations. For example, filters 120a, 120b, and 120c can attenuate light from display 150 by different amounts. Therefore, in a single capture, sensor 106 can acquire image volume from display 150 over a large dynamic range, rather than having to capture different intensity levels with different volume captures.

[0044] Although Figure 1 The illustrated filter module 120 includes three different filter arrays, but other filter array arrangements are also possible. Furthermore, in some embodiments, multiple filter arrays may be arranged sequentially along axis 102. For example, see reference... Figure 2A and 2BThe color filter array 220 and the neutral density filter array 222 are designed to be arranged sequentially along an axis, enabling the measurement and calibration system to acquire an image of the light field, which includes information on different spectral profiles from the display, as well as information on each spectral profile over a wide dynamic range. In this example, the filter array 220 is a color filter array with three different color filters 220a, 220b, and 220c. For example, filter 220a could be a filter for the CIE 1931 color matching function X, filter 220b could be a filter for the CIE 1931 color matching function Y, and filter 220c could be a filter for the CIE 1931 color matching function Z. Other spectral filter arrays are also possible. The filter array is shown in a plan view and is arranged in system 100 such that axis 102 is perpendicular to the page plane.

[0045] The filter array 222 consists of three neutral density filters (e.g., 50% or more attenuation, 80% or more attenuation, 90% or more attenuation) 222a, 222d, and 222e, and three clear windows 222b, 222c, and 222f (i.e., providing little or no light attenuation). The dimensions and shapes of the filter arrays 220 and 222 are determined such that when positioned within the filter module of system 100, color filter 220a overlaps with neutral density filter 222a and clear window 222b. Similarly, color filter 220b overlaps with neutral density filter 222d and clear window 222c, and color filter 220c overlaps with neutral density filter 222e and clear window 222f.

[0046] Therefore, when arranged together in system 100, filter arrays 220 and 222 provide light field capture, wherein a portion of the incident pupil samples light of three different spectral components within a large dynamic range provided by the neutral density filter.

[0047] Figure 2C Another example of a filter array that can be used in system 100 is shown. Filter array 224 includes four filters 224a, 224b, 224c, and 224d, each composed of a linear polarizer with a different through-axis orientation. Alternatively, in some embodiments, the four polarization filters may include two linear polarizers with orthogonal axes and two circular polarizers with respect to orthogonal circular polarization states. The light field image obtained using the polarization filter array can be used to evaluate the characteristics of different components of the display under test, such as birefringence.

[0048] Other filter array arrangements are also possible. For example, a polarization filter array may include 24 filters arranged such that four polarization filters overlap with each filter in filter array 222. With this arrangement, a single light field image can contain color and polarization information over a large dynamic range.

[0049] As a replacement or supplement to the filter module, other components can be positioned within the entrance pupil of the all-light camera assembly 101 to provide additional functionality to the system 100. For example, in some embodiments, a multiplexing assembly can be used to capture the light field across multiple user pupil positions in a single light field capture. Figure 3 An example of such a component is shown, depicting an optical assembly 300 positioned at the outer entrance pupil 103 of an all-optical camera assembly 101 to extend the pupil plane and capture a large portion of the exit pupil 320 of the display under test. The optical assembly 300 includes two polarized beam splitters (PBS) 304a and 304b fixed to opposite sides of an orthogonal prism 302. Two high-retardation films 306a and 306b are positioned between the two polarized beam splitters 304a and 304b and the display under test, respectively. Optionally, a linear polarizer 308 is located between the orthogonal prism 302 and the camera assembly 101.

[0050] Typically, the exit pupil 320 of a head-mounted display can be significantly larger than the user's pupil, thereby accommodating multiple different user pupil positions corresponding to the user's eye movements. Figure 3 The illustrated component 300 expands the entrance pupil of the all-optical camera component 101 to extend in conjunction with three different user pupil positions. Specifically, arrows 310a, 310b, and 310c represent light from three different pupils of the display. Light 310a is passed through a retardation film 306a before the PBS 304a directs the component of light 310a with a first polarization state to the orthogonal prism 302. Similarly, light 310c is passed through a retardation film 306b before the PBS 304b directs the component of light 310c with a second polarization state to the orthogonal prism 302. Retardation films 306a and 306b may have the effect of randomizing the polarization of light from the display under test. The first and second polarization states may be the same. Light 310b may be a combination of the first and second polarization states, or it may be orthogonal.

[0051] Orthogonal prism 302 combines light from PBSs 304a and 304b with light 310b, thereby directing the light toward the all-optical camera assembly 101. The surface of orthogonal prism 302 can be 50% reflective (e.g., 50% transmissive), or it can be tuned to produce similar transmissivity through the three optical paths. Note that the reflective surfaces of the PBS and the orthogonal prism are planar surfaces, thus preserving the directional characteristics of the light rays representing the light field at exit pupil 320. Therefore, the light entering the camera assembly consists of light from three different pupils, and the light field image captured from this light includes information from each of these pupils. Therefore, the performance of the sum of the three pupil positions can be evaluated based on a single light field image.

[0052] Component 300 is generally positioned in the optical path between the display and the all-optical camera assembly via a mounting device (e.g., an optomechanical bracket) that allows precise positioning of the component at the entrance pupil 103. In some embodiments, one or more actuators can be used to automatically close various optical components at the entrance pupil 103. One example is a filter wheel that can rotate different filter arrays in and out of the optical path. These components can also be replaced manually.

[0053] Typically, system 100 may include additional components in combination with the components described above. For example, in some embodiments, the system may include a focusless optical relay system between the stage and the all-light camera assembly. Such a relay system can provide additional space in the optical path without significantly affecting the imaging characteristics of the optics. Alternatively or additionally, one or more folding mirrors may be used to fold the optical path of the system, for example, to provide a more compact form factor for the system.

[0054] Typically, system 100 can be used to characterize various performance parameters associated with a display. These performance parameters may include, but are not limited to, emissivity, brightness, color, geometric distortion, virtual image distance, and field curvature. Conventional light field analysis techniques can be used to characterize the display's performance.

[0055] In some implementations, super-resolution techniques are used to enhance the accuracy of pixel location. For example, geometric correction may require very accurate pixel location measurements and can benefit from the use of super-resolution techniques.

[0056] Display calibration can be performed by comparing the uniformity of one or more performance parameters across the display's exit pupil and / or by comparing the performance parameters to a standard. Display operation can be adjusted based on measurements and additional measurements performed to evaluate the adjustment. The measurement and adjustment sequence can be repeated until the performance parameters are within a pre-set threshold.

[0057] System 100 can be used to measure performance parameters and calibrate displays suitable for augmented reality head-mounted display systems. Figure 4 An example of such a system is illustrated in the figure, which shows an example head-mounted display system 60, including a display (or eyepiece) 70 and various mechanical and electronic modules and systems supporting the functionality of the display 70. The display 70 is housed within a frame 80, which can be worn by a display system user 20 and configured to position the display 70 in front of the user 20's eyes. In some embodiments, the display 70 can be considered as eyeglasses. A camera 81 for viewing the world (e.g., the user's environment and having a similar field of view) is mounted in the frame 80. In some embodiments, a speaker 90 is coupled to the frame 80 and positioned near the user 20's ear canal. The display system may also include one or more microphones 112 for detecting sound. The microphones 112 may allow the user to provide input or commands to the system 60 (e.g., voice menu commands, natural language questions, etc.) and / or may allow audio communication with other people (e.g., users of other similar display systems). The microphones 112 may also collect audio data from the user's surrounding environment (e.g., sounds from the user and / or the environment). In some embodiments, the display system may further include a peripheral sensor 122a, which may be detached from the frame 80 and attached to the body of the user 20 (e.g., head, torso, limbs, etc.). In some embodiments, the peripheral sensor 122a may acquire data characterizing the physiological state of the user 20.

[0058] Display 70 is operatively coupled to local data processing and module 140 via communication link 132 (e.g., via wired lead or wireless connection). Local data processing and module 140 can be mounted in various configurations, such as being fixedly attached to frame 80, fixedly attached to a helmet or hat worn by a user, embedded in headphones, or detachably attached to user 20 (e.g., in a backpack configuration or a belt-coupled configuration). Similarly, sensor 122a can be operatively coupled to local processing and data module 140 via communication link 122b (e.g., via wired lead or wireless connection). Local processing and data module 140 may include a hardware processor and digital memory such as non-volatile memory (e.g., flash memory or hard disk drive), both of which can be used for auxiliary processing, caching, and storing data. The data may include: 1) data captured from sensors (which may be operatively coupled to frame 80 or otherwise operatively attached to user 20), such as image capture devices (e.g., cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, gyroscopes, and / or other sensors disclosed herein; and / or 2) data acquired and / or processed using remote processing module 152 and / or remote data storage 162 (which includes data related to virtual content), which may be transmitted to display 70 after such processing or retrieval. Local processing and data module 140 may be operatively coupled to remote processing module 152 and remote data storage 162 via communication links 170, 180, such as via wired or wireless communication links, such that these remote modules 152, 162 are operatively coupled to each other and can be used as resources of local processing and data module 140. In some embodiments, the local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a radio device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be attached to the frame 80 or may be a separate device that communicates with the local processing and data module 140 via a wired or wireless communication path.

[0059] Remote processing module 152 may include one or more processors to analyze and process data such as image and audio information. In some embodiments, remote data storage 162 may be a digital data storage facility that is available via an internet or other network configuration in a “cloud” resource configuration. In some embodiments, remote data storage 162 may include one or more remote servers that provide information (e.g., information for generating augmented reality content) to local processing and data module 140 and / or remote processing module 152. In other embodiments, all data is stored and all computations are performed in the local processing and data module, thereby allowing for completely autonomous use from the remote module.

[0060] Other embodiments are described in the following claims.

Claims

1. A system for measuring the performance of a head-mounted display module, comprising: An all-light camera assembly includes a camera lens defining an image plane, a camera sensor, and a microlens array arranged to image light at the image plane onto the camera sensor; A stage for receiving the head-mounted display module and positioning the head-mounted display module relative to the all-optical camera assembly such that the exit pupil of the head-mounted display module coincides with the entrance pupil of the all-optical camera assembly, the entrance pupil of the all-optical camera assembly being located outside the camera lens of the all-optical camera assembly. One or more filter arrays located at the entrance pupil of the all-light camera assembly, each of the one or more filter arrays comprising a plurality of spatially discrete filters extending across the aperture of the camera lens; as well as A system controller, which communicates with the all-light camera assembly, is programmed to acquire one or more light field images projected from the head-mounted display module during operation of the system, and to determine information related to the performance of the head-mounted display module based on the acquired light field images.

2. The system according to claim 1, wherein, One of the filter arrays in the filter array includes a spatially discrete color filter.

3. The system according to claim 2, wherein, The spatial discrete color filter includes X, Y, and Z color filters.

4. The system according to any one of claims 1-3, wherein, One of the filter arrays in the filter array includes a spatially discrete polarization filter.

5. The system according to any one of claims 1-3, wherein, One of the filter arrays in the filter array includes a spatially discrete neutral density filter.

6. The system according to any one of claims 1-3, wherein, The one or more filter arrays include a first spatial discrete filter array and a second spatial discrete filter array that overlaps with the first spatial discrete filter array, wherein the first spatial discrete filter array and the second spatial discrete filter array filter different properties of the light.

7. The system according to claim 6, wherein, The properties of the light are selected from a group consisting of color, polarization, and intensity.

8. The system according to any one of claims 1-3, further comprising: An optical component arranged at the entrance pupil of the all-light camera assembly is configured to combine light emitted from multiple different positions of the exit pupil of the head-mounted display module to form multiple overlapping images at the sensor of the all-light camera assembly, each of the multiple overlapping images corresponding to a different user view of the head-mounted display module.

9. The system according to claim 8, wherein, The optical components include: one or more polarizing beam splitters arranged at different positions in the exit pupil of the head-mounted display module, and a beam combiner arranged in the entrance pupil of the all-optical camera assembly, the beam combiner being configured to receive light from each of the polarizing beam splitters and guide the light from each polarizing beam splitter to the camera lens along a common path.

10. A method for measuring the performance of a head-mounted display module, the method comprising: The head-mounted display module is arranged relative to the all-light camera assembly such that the exit pupil of the head-mounted display module coincides with the entrance pupil of the all-light camera assembly, and the entrance pupil of the all-light camera assembly is located outside the camera lens of the all-light camera assembly. While arranging the head-mounted display module relative to the all-light camera assembly, light is emitted from the head-mounted display module; The light at the exit pupil of the head-mounted display module is filtered; The all-light camera assembly is used to acquire one or more light field images projected from the head-mounted display module using filtered light; as well as Information related to the performance of the head-mounted display module is determined based on the acquired light field image.

11. The method according to claim 10, wherein, The light is filtered by a plurality of spatially discrete filters located at the entrance pupil of the all-light camera assembly.

12. The method according to claim 11, wherein, The spatial discrete filter includes a color filter.

13. The method according to claim 12, wherein, The color filters include X, Y, and Z color matching function color filters.

14. The method according to claim 11, wherein, The spatial discrete filter includes a polarization filter.

15. The method according to claim 11, wherein, The spatial discrete filter includes a neutral density filter.

16. The method according to any one of claims 10-15, wherein, The light is filtered by a first set of spatial discrete filters and a second set of spatial discrete filters that overlap with the first set of spatial discrete filters, and the first set of spatial discrete filters and the second set of spatial discrete filters filter different characteristics of the light.

17. The method according to claim 16, wherein, The properties of the light are selected from a group consisting of color, polarization, and intensity.

18. The method according to any one of claims 10-15, wherein, Acquiring the one or more light field images includes: re-imaging the real image from the head-mounted display module onto a multi-element sensor using a microlens array.

19. The method according to claim 18, wherein, The microlens array samples a portion of the exit pupil of the lens of the all-optical camera assembly to provide different angle views of the real image from the head-mounted display module.

20. The method according to any one of claims 10-15, wherein, The all-optical camera assembly defines an optical path from the entrance pupil to the sensor array. The all-optical camera assembly includes a camera lens assembly in the optical path that defines the entrance pupil of the all-optical camera assembly and defines an image plane. The all-optical camera assembly also includes a focusing element array in the optical path between the image plane and the sensor array.

21. The method according to any one of claims 10-15, wherein, The information relating to the performance of the head-mounted display module includes information relating to at least one of the performance parameters selected from the group consisting of: emissivity, brightness, color, geometric distortion, virtual image distance, and field curvature.

22. The method according to any one of claims 10-15, wherein, The information relating to the performance of the head-mounted display module includes: calculating two-dimensional images at multiple different depths on a three-dimensional volume of interest within the head-mounted display module.

23. The method according to claim 22, wherein, Determining the information further includes determining information relating to one or more characteristics of each of the two-dimensional images.

24. The method according to any one of claims 10-15, further comprising: The emitted light from multiple different locations of the exit pupil of the head-mounted display module is combined to form multiple overlapping images at the sensor of the all-light camera assembly, each of the multiple overlapping images corresponding to a different user view of the head-mounted display module.

25. A method for calibrating a head-mounted display, comprising: The performance of the head-mounted display was measured using the method according to any one of claims 10-24; as well as The operation of the head-mounted display is adjusted based on the measured performance.

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