CrossbowCam: a handheld adjustable multi-camera system

This paper presents a novel multi-functional, low-cost handheld multi-camera system (one dimensional camera array) - “CrossbowCam”. The CrossbowCam is suitable for multi-viewpoint image acquisition, smooth switching, alignment and seamless stitching applications. The proposed system differs from the traditional fixed image acquisition systems which are large-sized, high-priced, single functional, and can only captured images at specific locations. With the proposed system, the users can push one single button to change the configuration of the camera array rapidly to divergence (convex arc), parallel (linear), or convergence (concave arc). The three camera configurations can each be suitable for applications such as panorama image stitching, autostereoscopic 3D display, bullet-time (time-freeze) visual effect, 3D scene reconstruction, etc. To rapidly acquire the relationship among cameras after configuration change, we propose a two-stage calibration method to compensate the mechanical misalignment. The first stage adopts the traditional checkerboard calibration method to get the intrinsic parameters (focal length, principal point) and the lens distortion for each camera. The second stage requires no auxiliary tool but utilizes a large number of common feature points from multiple viewpoint images to acquire the extrinsic parameters (translation and rotation matrix) and to compensate the vertical misalignment and the horizontal uneven angle distribution due to the mechanical structure. The proposed system can then insert virtual viewpoint images between actual viewpoint images to allow the viewpoint switching more smoothly. The proposed system has eight cameras with maximum viewing angle of 90° in divergence mode, 38 mm spacing in parallel mode, and imaging radius of 10 m ∼ 0.5 m in convergence mode. We believe that the proposed system can potentially change the consumer habits and becomes the new type of home-use handheld camcorder system in the future.