The Trace Center's Photosensitive Epilepsy Analysis Tool (PEAT) assists Web developers in identifying content on their sites that might induce seizures in some people.
NOTE: Use of this tool is not necessary in many cases. Read in the next section about the type of content that may cause seizures.
Reducing Risk of Seizures
Photosensitive seizures can be provoked by certain types of flashing in Web or computer content, including mouseovers that cause large areas of the screen to flash. Hazardous, seizure-inducing content has been inadvertently broadcast on television in the past, causing mass seizures in children. As Web content becomes more dynamic and media-rich, it is important to prevent similar problems.
To minimize risk of visually induced seizures, Web designers and computer software developers should become familiar with the triggers of photosensitive disorder seizures. Content to consider includes bright and rapid flashes, especially red flash, and some spatial patterns. The Web Content Accessibility Guidelines 2.0 provides recommendations for using these forms of content safely. These guidelines include restrictions related to frequency, luminance, area and color of any flashing.
In general, Web or computer content will not provoke seizures if:
- Flash frequency is less than three flashes in any one second period or greater than 50 or 60 Hz
- The combined area of flashes occurring concurrently (but not necessarily contiguously) occupies more than one quarter of any 341 x 256 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 by 768 pixels
- The flash is less than 10% of full scale white brightness* and the darker image is below .80 of full scale white brightness
- Saturated red flash is avoided
* Brightness is calculated as 0.2126 x ((R / FS) ^ 2.2) + 0.7152 x ((G / FS) ^ 2.2) + 0.0722 x ((B / FS) ^ 2.2), where R, G, and B are the red, green, and blue RGB values of the color; FS is the maximum possible full scale RGB value for R, G, and B (255 for eight bit color channels); and the "^" character is the exponentiation operator. An "opposing change" is an increase followed by a decrease, or a decrease followed by an increase.
About This Tool
Photosensitive Epilepsy Analysis Tool (PEAT) is a free, downloadable tool, available from the Trace Center at the University of Wisconsin-Madison. PEAT allows Web content to be tested for compliance with accessibility guidelines. A video capturing what appears on the computer screen as it is used must be recorded at 24 fps or greater. With this screen capture as input, PEAT conducts luminance flash and red flash evaluations to determine risk of seizure-provoking content. The analysis uses algorithms developed specifically for web and computer applications by the Trace Center, Dr. Graham Harding, and Cambridge Research Systems working together, and is based on Dr. Harding’s extensive research on photosensitive seizure disorders.
Restrictions on Use
The Photosensitive Epilepsy Analysis Tool (PEAT) was developed to provide a free resource for Web designers and computer software developers. Use of PEAT to assess material commercially produced for television broadcast, film, home entertainment, or gaming industries is prohibited. For broadcast, film, home entertainment, and gaming applications, the Harding FPA software should be employed. Contact Cambridge Research Systems for more information. PEAT is copyrighted by the University of Wisconsin – Trace Center. The PSEe engine is copyrighted by Cambridge Research Systems Ltd. Use of this software is at the licensee’s own risk and liability.
Technical Requirements to Run PEAT Analysis and/or Viewing
- Pentium III 500Mhz or higher
- 1024 x 768 Screen resolution
- 24 bit screen color graphics card
- Windows 2000 or XP
- 256 MB RAM
- 10GB Hard drive
Video clips must be recorded at 24 fps or greater to be analyzed in PEAT.
IMPORTANT NOTE: PEAT currently requires that you capture the video of the screen separately. As a result it cannot be used easily by individuals who just want to check out a particular video clip or Web page. Trace is working on a version that will allow you to capture the screen for analysis.
PEAT is currently available as a beta 1.0.1.5 test release.
Free Download: Beta release of Photosensitive Epilepsy Analysis Tool (PEAT)
Note: This release is still a beta version. Future releases may produce somewhat different results as the threshold analysis routines are still being refined. If you indicate that you would like to receive notifications about PEAT updates when downloading this beta, you will be notified by email when an update is available.
Registration is required in order to download PEAT.
More Information
Funding for this work has been provided by the National Institute on Disability and Rehabilitation Research (NIDRR), U.S. Department of Education, under grants H133E030012 and H133E980008.