Harris corner detection in checkerboard images for camera calibration often suffer from uneven illumination. The key to camera calibration lies in that how to robustly detect corners from the degraded images. To this end, an image processing method is proposed to deal with non-uniform illumination problems. Experiments show that the stabilities of Harris corner detection under uneven illumination are improved obviously.
Camera calibration is a key step in three-dimensional (3-D) reconstruction; however, the calibration accuracy and stability often suffer from complicated illumination in real applications. The camera calibration method using the checkerboard pattern is improved for high-precision calibration under complicated illumination. First, an improved Harris corner detector based on color constancy, as well as a subpixel optimization method based on prior knowledge of the checkerboard, are proposed to overcome the influence of bad lighting. Second, a checkerboard pattern with a central circle point is designed for better reference point location for uneven illumination. The checkerboard identification by Delaunay triangulation is also improved for the situation of discontinuity caused by over-saturation. Finally, the camera parameter optimization process is improved to reduce the calibration error produced by complicated illumination. Experimental results show that the improvements achieve more accurate and stable calibration results in complicated lighting conditions compared with traditional methods.
The phase-shifting algorithm is widely used for noncontact three-dimensional (3-D) reconstruction, traditionally leveraging gray values to recover phase angles. It is difficult to reconstruct the shape of an object with a specular or dark surface. We propose an algorithm for accurate phase recovery based on high dynamic range imaging. Unlike most existing methods that use gray values to calculate the phase angle, the proposed method uses E values, which are the recovered irradiance from low dynamic range images, to calculate the phase angle. Experiments show that the proposed method improves phase recovery accuracy and achieves good results for the 3-D reconstruction of specular or dark objects.
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