Metric aspects of zoom vision

This investigation was aimed at studying the calibration of array camera systems equipped with 12.5-75mm variable focal length lenses. Specific objectives included: identifying distortion parameters that effect 3-D positioning accuracy; developing a procedure for modeling the changes in distortion parameters that occur as the focal length of a zoom lens changes; verifying the repeatability and stability of zoom lens calibration results; and conducting tests, using real data, that demonstrates the effectiveness of calibrated zoom lens systems. Ten datasets were obtained using six different camera-lens configurations. Each dataset consisted of 16 images collected at varying focal settings ranging between 12.5 and 75mm. Both interline-transfer and frame-transfer device CCD cameras were used. The results showed that the focal length (f) and 6 additional parameters of interior orientation could be used to effectively model the interior geometry of a variable focal length CCD vision system. These included two location parameters to define the principal point (x$\sb{\rm p}$, y$\sb{\rm p}$), a parameter for affine scaling (K), one parameter of symmetric radial lens distortion (L$\sb1$), and two parameters of lens decentering distortion (P$\sb1$ and P$\sb2$). With the exception of affine scaling, these parameters were effected by changes in the focal length and were modeled as functions of f using first and second degree polynomials. It was also found that although P$\sb1$ and P$\sb2$ were intended to model decentering distortions, their role in the calibration model appeared largely to be to compensate for displacement that was caused by misalignment of the optical axis with the image plane. Calibration parameter models were shown to be repeatable over periods in excess of seven days. The root-mean-square (RMS) residual error of image points for calibrated systems was consistently less than 0.4 pixels throughout the range of zoom. Test results showed that improvement in 3-D positioning accuracy on the order of 200-300% could be achieved through the use of the zooming capability.U of I OnlyETDs are only available to UIUC Users without author permissio