Ambient light sensors spotted on tablets and laptops could be used to capture gestures

According to news from this site on January 19, due to privacy considerations, many users will physically block the selfie cameras on laptops and tablets, and some manufacturers even provide special physical switches.

However, researchers recently discovered that the ability to capture hand position and gestures can also be achieved using ambient light sensors on most mobile devices and laptops.

Researchers from the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) recently published a paper "Imaging Privacy Threats From an Ambient Light Sensor", pointing out this potential security vulnerability.

#The ambient light sensor, unlike the selfie camera, has no option to turn it off, and the app call does not require user permission. Yang Liu, co-author of the paper, said:

People are aware of the selfie cameras on laptops and tablets, and sometimes use physical blockers to block them. .

But with the ambient light sensor, people don’t even know the app is using the data, and the sensor is always on.

The main function of the ambient light sensor is to provide ambient light data to the operating system for automatically adjusting screen brightness. However, developers can access and call it through the API, such as turning on the eye protection mode through the API.

Ambient light sensors can be thought of as single-pixel sensors without a lens, measuring brightness at about five "frames" per second. In order to overcome this shortcoming, the researchers sacrificed temporal resolution for spatial resolution through the Helmholtz reciprocity principle, so that the image can be reconstructed.

Note from this site: Helmholtz's reciprocity principle means that if the paths of light are opposite, then the reflection, refraction and absorption experienced by the light along the path are the same.

The researchers conducted the demonstration using a new, unmodified Samsung Galaxy View2 tablet (17-inch display). They placed the tablet in front of a mannequin's head, using cardboard and actual human hands to simulate gestures.

#The algorithm uses reverse path tracing from the sensor to the light source (i.e. the display). Therefore, researchers must illuminate specific parts of the screen to obtain a readable image.

This dual photography method produces low-resolution images (32x32) that are clear enough to display gestures such as two-finger scrolling or three-finger pinching. Due to the extremely low resolution, this technology can only be used on larger displays such as tablets and laptops.

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