Harmonic distortion free distance estimation in ToF camera

A Time-of-Flight (ToF) camera uses a near infrared (NIR) to obtain the distance from the camera to an object. The distance is calculated from the amount of time shift between the emitted and reflected NIR. ToF cameras generally modulate NIR with a square wave rather than a sinusoidal wave due to its difficulty in hardware implementation. The previous method using simple trigonometric function estimates the time shift with the difference of electrons generated by the reflected square wave. Thus the estimated time shift includes a harmonic distortion caused by the nonlinearity of trigonometric function. In this paper, we propose a new linear estimation method to reduce the harmonic distortion. For quantitative evaluation, the proposed method is compared to the previous method using our prototype ToF depth camera. Experimental results show that the distance obtained by the proposed method is more accurate than that by the previous method.