  The detection of face-screen distance on smartphone (i.e., the distance
between the user face and the smartphone screen) is of paramount importance for
many mobile applications, including dynamic adjustment of screen on-off, screen
resolution, screen luminance, font size, with the purposes of power saving,
protection of human eyesight, etc. Existing detection techniques for
face-screen distance depend on external or internal hardware, e.g., an
accessory plug-in sensor (e.g., infrared or ultrasonic sensors) to measure the
face-screen distance, a built-in proximity sensor that usually outputs a
coarse-grained, two-valued, proximity index (for the purpose of powering on/off
the screen), etc. In this paper, we present a fine-grained detection method,
called "Look Into My Eyes (LIME)", that utilizes the front camera and inertial
accelerometer of the smartphone to estimate the facescreen distance.
Specifically, LIME captures the photo of the user's face only when the
accelerometer detects certain motion patterns of mobile phones, and then
estimates the face-screen distance by looking at the distance between the
user's eyes. Besides, LIME is able to take care of the user experience when
multiple users are facing the phone screen. The experimental results show that
LIME can achieve a mean squared error smaller than 2.4 cm in all of
experimented scenarios, and it incurs a small cost on battery life when
integrated into an SMS application for enabling dynamic font size by detecting
the face-screen distance.
