engleski

Underwater Camera Calibration

A common laboratory setup for underwater imaging places a camera in the air to capture the image of an object placed in a water-filled tank and observed through a flat glass interface. In such a setup light is refracted twice, at air-glass and glass-water interfaces, and this refraction of light is physical phenomenon which makes the underwater camera calibration difficult. Such an underwater camera may be calibrated using a standard planar calibration object. First, a standard in-air calibration is performed to recover the projection matrix and the distortion parameters of the in-air camera. Next, the calibration board is submerged in thewater-filled tank, is imaged, and coordinates of calibration points on the board are extracted. The core part of the underwater camera calibration then proceeds in the following steps: First, the eight point algorithm is used to estimate the essential matrix. Second, pose parameters of the glass interface w.r.t. the camera (rotation and axis) are estimated. Third, the layer thicknesses are estimated for air and glass. Finally, a numerical optimization of all recovered parameters may be performed to refine them. The described calibration procedure is implemented in MATLAB and is used to recover the imaging parameters of the laboratory setup for underwater imaging. The obtained parameters are used to visualize imaging geometry showing that the calibration results match the expected values.

camera calibration ; underwater imaging ; light refraction

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