FlashBan
New: the Grain demo

FlashBan

A live 3D shape, dithered in two close tones. It doesn't move on its own.

Inside FlashBan

What it is

FlashBan is a free Chrome extension for people with photosensitive epilepsy. It finds flashing video, GIFs, canvas and animation and tones it down to reduce exposure.

Soften first. Cover only if it won't calm down. Dim what it can't check. No account and no server: the only record is a site's domain, on your computer, for 30 days.

Not a medical device. It reduces exposure to flashing content; it can't guarantee protection.

How it decides

How it decides

  1. 01Sample every frameVideo frames, canvas pixels, animated images and CSS animations are read as they're drawn, never on a slow timer a strobe could slip between.
  2. 02Measure brightness and redRelative luminance per WCAG, plus a separate check for saturated red. Near-black noise counts as having no colour.
  3. 03Count in a one-second windowBy the clock, not by frames. Flashing area is added up across elements, so one big flash split into tiles still counts.
  4. 04DecideOver the limit (WCAG by default; Strict and Relaxed in the popup) means act. Can't read it at all means fail closed.
  5. 05Soften, cover or dimFlashing media stays playing but is dimmed and in greyscale. CSS animation is slowed; a cover or lockdown protects content when needed. Unreadable media stays dimmed.

Tested

Threat model →

Attack pages it beats ▪ node harness/run.mjs

Tested build: the judging tag final (129e645), headless runs on our Windows laptop, plugged in. 29 of 29 pages matched every run; all 16 attack pages were protected and all 8 benign/control pages allowed. Full results. These results describe that build and test set; later builds need their own checks.

  • 1.3 sA page deletes FlashBan's cover every frame: locked down in 1.24–1.25 s.Overlay killer ▪ T6
  • DimRed-only flashes with almost no brightness change: dimmed and in greyscale.Red only ▪ T3
  • DimA 12.5 Hz strobe timed between samples: dimmed and in greyscale.Aliasing ▪ T1
  • DimFlashing after 10 calm seconds: dimmed after it starts.Late start ▪ T8
  • Dim40 strobes plus busy work: protected by dimming.CPU flood ▪ T5
  • DimA strobe on a canvas it can't read: dimmed and labelled.Tainted canvas ▪ T4
  • 16 tilesOne big flash split into small tiles: still blocked.Split area ▪ T2
  • 0 of 8Benign/static pages flagged across three runs (24 allow verdicts).False positives in this test set

From the changelog

Merged pull requests from the hackathon build, newest first. Every fix to a false alarm gets an everyday test page, so the harness keeps it fixed.

Near-black isn't red

Compression noise in dark scenes was being read as red flashing. Near-black now has no hue, so letterbox bars stop tripping the red-flash rule. (#94)

Sharper soften

The brightness clamp runs on the GPU at full resolution, only inside the flashing area. Everything outside it stays sharp and in colour. (#84)

YouTube, measured

YouTube video can now be read and measured instead of only dimmed, and ambient glows are faded rather than covered. (#77)
Older changes

Every presented frame

Sampling every presented frame closed a gap where a 30 Hz strobe at 60 fps could slip between samples. (#65)

One bypass bar

A single "Show original on this site" bar replaces per-video buttons. Pages can't press it for you: only real clicks count. (#64)

Get FlashBan

Download for Chrome Install steps + checksum