How China built facial recognition for people wearing masks
Hanwang says its technology has reached 95% accuracy in identifying mask wearers.
YUAN YANG, FT.COM - 3/18/2020

Hanwang, the facial-recognition company that has placed 2 million of its cameras
at entrance gates across the world, started preparing for the coronavirus in early January.

Huang Lei, the company’s chief technical officer, said that even before
the new virus was widely known about, he had begun to get requests from hospitals
at the centre of the outbreak in Hubei province to update its software
to recognise nurses wearing masks.

“We wouldn’t wait until something explodes to act.
If three or five clients ask for the same thing...we’ll see that as important,”
said Mr Huang, adding that its cameras previously only recognised
people in masks half the time, compared with 99.5 percent accuracy for a full face image.

Since then, demand has soared, from police stations, railway stations
and all the office towers that use Hanwang’s cameras to screen employees,
and Mr Huang reassigned teams of people to work on the challenge.

The company now says its masked facial recognition program
has reached 95 percent accuracy in lab tests, and even claims
that it is more accurate in real life, where its cameras take
multiple photos of a person if the first attempt to identify them fails.

“The problem of masked facial recognition is not new, but belongs
to the family of facial recognition with occlusion,” Mr Huang said,
adding that his company had first encountered similar issues with
people with beards in Turkey and Pakistan, as well as with
northern Chinese customers wearing winter clothing that covered their ears and face.

Counter-intuitively, training facial recognition algorithms
to recognize masked faces involves throwing data away.
A team at the University of Bradford published a study last year
showing they could train a facial recognition program to accurately recognize
half-faces by deleting parts of the photos they used to train the software.
...(less than fiddy)