Estimating sensor orientation in cameras

For most imaging cameras, it is desirable that the sensor plane be perpendicular to the optical axis. Such an orientation ensures that the imaging configuration is perspective and planar scene objects perpendicular to the optical axis can be focussed in their entirety. In this paper, we present an image processing method to estimate and subsequently correct the sensor tilt with precision. We propose to measure the tilt by measuring the variation of defocus in an image of a planar calibration chart placed perpendicular to the optical axis. We show that the proposed defocusing based method is inherently more accurate than geometry based techniques which estimate tilt by measuring the deviation in the geometry of a scene pattern. We analyze the sensitivity of the tilt estimates to errors in the experimental setup and show that the proposed technique is quite robust to errors even as large as 1 degree in the orientation of the calibration chart.