Measurement and Analysis of Depth Resolution Using Active Stereo Cameras

We propose a novel method to measure and analyze depth resolution in near range. Depth resolution is the smallest depth difference that can be detected by a depth camera, which is an important parameter but is hard to be measured accurately. Intuitively, a stair-shaped target is preferred to measure depth resolution but has many limitations. To overcome the difficulties, we use a flat target and move a depth camera at specified steps to form a stair-shaped depth map. Then, the depth map is compressed to one-dimensional profile by an average cross-section method. The 68-95-99.7 rule is applied for identifying the depth resolution. In order to obtain accurate data, a computer-controlled positioning platform is used to move or rotate a depth camera and a target in high precision. Three types of targets are made and tested, including a stair-shaped metal plate, a flat acrylic board, and a tensioned electric screen. A procedure is provided for aligning the optical plane of depth camera to the target before measuring. The Intel RealSense D400 series depth cameras are adopted for verification. Their theoretical depth resolution is derived and compared to the measured depth resolution. The effect of image resolution (x, y) on the depth resolution (z) is also analyzed. The experimental results offer useful information for researchers to design a depth camera and verify its depth resolution.