tailieunhanh - Advances in Theory and Applications of Stereo Vision Part 9

Tham khảo tài liệu 'advances in theory and applications of stereo vision part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 190 Advances in Theory and Applications of Stereo Vision Those two problems make it very difficult to detect or to recognize objects in water by observing their textures and colors. As to these two problems theories or methods for aerial environments can be expanded for underwater sensing. Several image processing techniques can be effective for removing adherent noises. Color information can be also restored by considering reflection absorption and scattering phenomena of light in theory Hulburt 1945 . Indeed we have already proposed underwater sensing methods for the view-disturbing noise problem Yamashita et al. 2006 and the light attenuation problem Yamashita et al. 2007 . The third problem is about the refraction effects of light. If cameras and objects are in the different condition where the refraction index differs from each other several problems occur and a precise measurement cannot be achieved. For example Fig. 1 c shows an image of a duck model when water is filled to the middle. In this case contour positions of the duck model above and below the water surface looks discontinuous and disconnected and its size and the shape look different between above and below the water surface. This problem occurs not only when a vision sensor is set outside the liquid but also when it is set inside because in the latter case we should usually place a protecting glass plate in front of viewing lens. As to the light refraction problem three-dimensional 3-D measurement methods in aquatic environments are also proposed Coles 1988 Tusting Davis 1992 Pessel et al. 2003 Li et al. 1997 Yamashita et al. 2010 . However techniques that do not consider the influence of the refraction effects Coles 1988 Tusting Davis 1992 Pessel et al. 2003 may have the problems of accuracy. Accurate 3-D measurement methods of objects in liquid with a laser range finder Yamashita et al. 2003 Yamashita et al. 2004 Kondo et al. 2004 Yamashita et al. 2005 and with a light projection method Kawai .