In this paper, we consider a dual-mode process for the electrophotographic laser printer--a low-frequency halftoning for smooth regions and a high-frequency halftoning for detail regions. These regions are described by an object map that is extracted from the page description language version of the document. This manner of switching screens depending on the local content provides a stable halftone without artifacts in smooth areas and preserves the detail rendering in detail or texture areas. However, when switching between halftones with two different frequencies, jaggies may occur along the boundaries between areas halftoned with low- and high-frequency screens. To reduce the jaggies, our screens obey a harmonic relationship. In addition, we implement a blending process based on a transition region. We propose a nonlinear blending process in which at each pixel, we choose the maximum of the two weighted halftones, where the weights vary according to the position in the transition region. Moreover, we describe an online tone-mapping for the boundary blending process, based on an offline calibration procedure that effectively assures the desired tone values within the transition region.

In this work, we discuss the use of depth information to correct the distortion due to the curved shape of the pages of an open book in captured images. This work is relevant to camera-based capture devices that can use a projector to cast structured light patterns to provide depth information. In order to improve the visual quality of captured documents, we use 3D shape reconstruction methods and geometric rectification to flatten the curvature of an open book. Shading correction is applied to the captured image, as well. Our models exploit specific prior assumptions about the nature of the printed material that is captured. The improvement in captured open book images obtained by using our method can be observed in the included experimental results.

3D shape reconstruction is one of the most important topics in computer vision due to its wide field of application. Among various technologies, structured light is considered to be one of the most reliable techniques. This paper addresses the problem of finding correspondences in a structured-light 3D shape reconstruction system. The work is based on the 3-symbol binary M-array encoded pattern proposed by Albitar. A new 6-symbol M-array pattern is designed with guaranteed minimum Hamming distance of three among all 3 × 3 windows. Improvements to the decoding algorithm are made, which allows successful identification of most symbols, and which corrects one possible error or missing symbol in each 3 × 3 window. Finally, refinements are made to the algorithm for finding correspondences, including back-projection of the captured structured light pattern to the projector plane to eliminate projective distortion.