An image acquisition method for raised characters based on laser vision technology

In this paper, based on laser three-dimensional (3D) vision technology, a fast gray-scale image acquisition method for no-color raised characters is presented. The image acquisition system is mainly composed of a CCD camera, a laser projector and a scanning galvanometer. The single-line laser stripe emitted by the laser projector is reflected to cross-sections of raised characters surface by the mirror rotated by a galvanometer. The CCD camera captures images of laser stripes distorted by heights of raised characters. Then, distortions of laser stripes are directly converted to gray values by the designed height-grayscale conversion function. The 3D vision model of the image acquisition system is established. System parameters are also determined. To get uniform image in the full field of view, distortions of laser stripes in various positions are analyzed and the distortion compensating method is proposed. To lessen the impact of surface reflection on image quality, and to extract the exact outline of the laser stripe, a laser stripe extracting method based on second-order gradient image is developed. Experiments on raised characters with different reflection properties and different structures show that the proposed method can get uniform and well-separated images of raised characters under various conditions. Experiments on image acquisition speed show that the time to scan a row of raised characters is 0.34 s. (c) 2012 Elsevier Ltd. All rights reserved.