We present Back-Mirror, a low-cost camera-based approach for widening the interaction space on the back surface of a smartphone by using mirror reflection. Back-Mirror consists of two main parts: a smartphone accessory with a mirror that can reflect the back surface to the rear-facing camera of the phone, and a computer-vision algorithm for gesture recognition based on the visual pattern on the back surface. Our approach captures the finger position on the back surface, and tracks finger movement with higher resolution than the previous methods. We further designed a set of intuitive gestures that can be recognized by Back-Mirror, including swiping up, down, left and right, tapping left, middle, right, and holding gestures. Furthermore, we created applications of Back-of-device, such as game, media player, photo gallery, and unlock mechanism, allowing users to experience the use of Back-Mirror gestures in the real-life scenarios.

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Co-authors: Pui Chung Wong, Hongbo Fu