  The light field camera is useful for computer graphics and vision
applications. Calibration is an essential step for these applications. After
calibration, we can rectify the captured image by using the calibrated camera
parameters. However, the large camera array calibration method, which assumes
that all cameras are on the same plane, ignores the orientation and intrinsic
parameters. The multi-camera calibration technique usually assumes that the
working volume and viewpoints are fixed. In this paper, we describe a
calibration algorithm suitable for a mobile camera array based light field
acquisition system. The algorithm performs in Zhang's style by moving a
checkerboard, and computes the initial parameters in closed form. Global
optimization is then applied to refine all the parameters simultaneously. Our
implementation is rather flexible in that users can assign the number of
viewpoints and refinement of intrinsic parameters is optional. Experiments on
both simulated data and real data acquired by a commercial product show that
our method yields good results. Digital refocusing application shows the
calibrated light field can well focus to the target object we desired.
