Improvement of an LCD-Based Calibration Site for Reliable Focus-Dependent Camera Calibration

Abstract

This paper proposes an improved calibration site design for reliable focus-dependent camera calibration in close-range photogrammetry. The proposed calibration site displays an adjustable checkerboard on a large liquid crystal display television (LCD TV), such that the same number of checker cells appear at the same position at any focusing distance. By adjusting the roll and pitch of the LCD TV bracket, various convergent angles were implemented in order to successfully conduct self-calibration. To obtain a greater depth of field and to facilitate reproducibility, the images were acquired using a small aperture from a camera that was firmly mounted on a distance-adjustable rail. The interior orientation parameters of the camera were estimated, and the estimation errors were assessed. The results revealed a flat error level for each focusing distance; thus, consistent reliability was achieved regardless of the focusing distance. Using the estimated parameters, a 3D measurement test was conducted, and the proposed method yielded 2% smaller root mean square error. The proposed method can be implemented easily and performs reliable and accurate focusdependent calibration.

Fast drawing method of circular patterns based on Gaussian circles for camera calibration

“…Recently, the method of projecting a pattern on a liquid crystal display (LCD) has been introduced instead of pattern printing due to its ease of preparation. 24,25 However, the LCD dots are large; thus, there is no escape from the quantization error of pattern printing. In particular, since differences in luminance values are essential for detecting the center of gravity, the shading of the circle boundary differs depending on how the circle is drawn, and these differences affect the accuracy of pattern coordinate detection.…”