Sub-pixel feature extraction and edge detection in 3-d measuring using structured lights

Improving sampling frequency and measurement accuracy is essential to 3-D measurements based on structured lights. In conventional applications, centerlines of light strips are extracted to represent 3D profiles of surfaces. Linear lasers are used as structured lights, and a concept of double featuring line extraction of laser beams is presented. In this way, two borders of a laser beam are extracted as two featuring lines, so sampling frequency is doubled. Sub-pixel detection method is introduced to improve measurement accuracy. Relationships of width of laser beams and obliquity of surfaces are studied, and based on Lambert reflection model, an algorithm of threshold modification for different obliquities is presented, which is tested by examinations.