ACCURACY OF VIDEOMETRY WITH CCD SENSORS

For accurate computer vision based on standard video signals, the term Videometry is introduced. Some geometrical, optical and electrical properties of CCD-cameras in conjunction with analog/digital-converters and frame buffers are investigated: lens distortion, sensor distortion, anisotropic modulation transfer function, space-variant impulse response due to discrete sensor elements and insufficient optical low-pass filtering, horizontal line jitter and scaling factor due to mismatch of sensor-shift- and A/D-conversion-clock, noise etc. Based on these results, a very simple camera model with a special radial lens distortion equation is proposed. This allows for a fast, fully linear calibration algorithm (15 msec calibration time for 36 coplanar calibration points) with good accuracy ( 1 30 of a frame buffer pixel residual error). It requires independent pre-calibration of the principal point and the horizontal scale factor. The latter is performed by Fourier analysis of the aliasing patterns produced by interference of camera- and A/D-converter clock. Only small improvements (3% average error, 30% maximum error) were obtained by subsequent nonlinear optimization (self-calibration with bundle adjustment) using the results from the linear approach as initial guess. © 1990.