What happens to Animoji when you cover the TrueDepth camera?

This all started with this tweet:

Frederick Riedel used stickers to cover the:

  • Infrared camera
  • Flood Illuminator
  • Dot Projector

on his iPhone X. But Animoji still worked without them. Portrait mode stopped working. Face ID stopped working too. So the stickers were doing their job.

Why do Animoji still work?

The answer is in this post from Rene Ritchie:

Some confusion has cropped up about whether or not Animoji really requires iPhone X-specific hardware. It does, but it’s easy to see how some people have come to think otherwise. After all, you can cover the IR system and it keeps working but, if you cover the RGB camera, it stops.

The reason for the misconception comes from the implementation: The IR system only (currently) fires periodically to create and update the depth mask. The RGB camera has to capture persistently to track movements and match expressions. In other words, cover the IR system and the depth mask will simply stop updating and likely, over time, degrade. Cover the RGB, and the tracking and matching stops dead.