The acquisition of both sets of images should be carried out under controlled lighting of the scene in order to easily extract with subpixel accuracy the reference points of each pattern. However, if these sets of images were acquired under uncontrolled lighting, detection methods of interest points, such as the Harris corner detector,40 could be used to increase the detection accuracy.
Table 1 shows the accuracy of the camera-calibration procedure of a prototype of the flatness inspection system proposed in this paper. The accuracy evaluation of the camera calibration is based on analyzing the discrepancy between the real position of the reference points of the pattern in the scene with respect to the 3-D position estimated from its 2-D projection. For each 2-D reference point extracted from the image, the calibrated model is used to project back, or reproject, the point over the laser plane of the scene, measuring the distance between the 3-D reference point and its reprojection.