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U.S. Food and Drug Administration

Toolkit for Evaluation of Head Mounted Display Image Quality

Catalog of Regulatory Science Tools to Help Assess New Medical Devices

 

This regulatory science tool presents a method for creating immersive 3D scenes using a web browser.

 

Technical Description

The WebXR tool [1, 2] allows for the creation of immersive 3D scenes using a web browser. Using the WebXR API [3], typically a standard component of web browsers, users can instantaneously deploy Extended Reality applications to any compatible device. WebXR allows for an instant deployment of any 3D scene and scripts and does not need to cater to a specific 3D engine or headset hardware. Since most (if not all) modern head mounted displays (HMD) can use WebXR within their respective web browsers, website content can be directly accessed through the relevant URL.

A set of predefined patterns is provided, including solid colors, grilles, and checkerboards, each of which is linked to corresponding measurements for which they are useful (e.g., luminance, contrast). These patterns allow for the measurements and assessment of display features such as the ones recommended by the International Committee for Display Metrology (ICDM) [4].

Intended Purpose

This tool presents a set of virtual test objects, scenes and tools for measurements and assessments of HMD image quality.

The developed tools are the following:

  • Chromatic aberration test script allows for the measurement of the color differences due to the lenses. [4]
  • Scene generator: allows for the creation of a scene containing simple primitives (circle, triangle, plane, etc.) and other patterns (grille, checkerboard, calibrating textures, etc.). This tool allows for the export of pre-made scenes to be shared. A set of default scenes is provided to be used for standard measurements [1, 5].
  • Compatibility tool: allows for the test of headset and controller compatibility with WebXR as well as quick validation of sensors and buttons.

With a compatible headset and web browser, the URL can be opened, and a specific scene or tool can be chosen. Then, WebXR can activate an immersive mode.

Current compatible headsets are:

  • Meta/Oculus Go, Quest, Quest Pro, Quest 2
  • HP Reverb
  • Microsoft Hololens and Hololens 2

Testing

Every HMD can be subject to chromatic aberration. The component lenses can lead to different wavelengths (colors) following a different trajectory, thus causing a discrepancy of color position, especially towards the display periphery.  A tool has been developed to measure the angular chromatic aberration for HMDs. Pictures were taken from the screen and compared with previous publications using the same experimental setup [4], the WebXR tool was able to replicate the same visualizations.

The scene generator allows for the display of arbitrary patterns that the user can create or upload [1]. These patterns are shown on the display in native 3D immersive mode within the WebXR environment. This tool was used to render test patterns for the assessment of spatial contrast variation on virtual reality headsets [6].

The compatibility tool was developed to test and validate the headset sensors, controllers, and buttons and their compatibility with the WebXR environment in general. The tool was tested on a range of headsets, and currently compatible headsets are those based on Windows Mixed Reality and standalone Android-based headsets. An updated list can be found on the GitHub repository [7].

Limitations

These tools rely on a web browser running natively on the HMD. Browsers and WebXR are continuously updating, and this could cause some features unavailable. Moreover, older headsets can become outdated due to the rapid development of WebXR that is constantly adding and modifying features.

Additionally, although modern web browsers follow the established standards for web development, they are only interpreting the code and there is a possibility that the visual result has small variations. These variations will, however, be constant within a headset model or even a family of headsets.

Only HMDs with web browser capabilities are compatible with these tools. We developed a tool that shows the compatibility of the headset as well as the sensors and controller support for WebXR. A list of compatible browsers and updated documentation for WebXR can be found in [3].

In case of unknown errors or need of additional assistance, the GitHub repository [7] provides an issue forum in which questions can be posted. We will monitor this site to address bugs and respond to raised issues.

Supporting Documentation

  1. B. Collins, R. Beams, M. Lago “Open-Source Pattern Creation Tool for Medical Extended Reality Image Quality Assessment” Journal of Open Source Software, 9(93), 6021 (2024). https://doi.org/10.21105/joss.06021
  2. Toolkit for Evaluation of Head Mounted Display Image Quality
  3. WebXR documentation
  4. R. Beams, A. S. Kim, A. Badano “Transverse chromatic aberrations in virtual reality head-mounted displays” Optics Express 27, 24877-24884 (2019). https://doi.org/10.1364/OE.27.024877
  5. https://www.sid.org/Standards/ICDM
  6. C. Zhao, R. Beams, A. Badano “Radially variant contrast measurement in virtual reality headsets using circular concentric ring patterns” J Soc Inf Display. 2023; 31(5): 387 – 397. https://doi.org/10.1002/jsid.1208
  7. DIDSR/WebXR-tools (github.com)

The GitHub repository [7] is organized in the following folders:

  • Compatibility: This directory includes the code for the compatibility test and instructions for use.
  • Custom: This directory includes the code for the custom scene creator as well as instructions for use and documentation.
  • TCA: This directory contains the code for the transverse chromatic aberration testing too as well as instructions for use and documentation.

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