视频特技外文翻译.doc

Video Special Effects Peng Huang 2.1.2 Object-space NPAR Meier was the first one who produced painterly animations from object-space scenes[53].He triangulated surfaces in object-space and distributed strokes over each triangle in proportion to its area. Since his initial work, many object-space NPAR systems have been presented. Hall’s Q-maps[29](A Q-map is a 3D texture which adapts to the intensity of light to give the object in the image a 3D look, for example, more marks are made where an object is darker) may be applied to create coherent pen-and-ink shaded animations.A system capable of rendering object-space eometries in a sketchy style was outlined by Curtis[15], and operates by tracing the paths of particles traveling stochastically around contours of a depth image generated from a 3D object. See Figure 2.3 for some examples.In addition, most modern graphical modeling packages(3D Studio MAX!,Maya,XSI Soft-Image) support plug-ins which offer the option of rendering object-space scenes to give a flat shaded, cartoon-like appearance. 2.1.3 Image-space NPAR Most NPAR systems in image-space are still based on static painterly rendering techniques,brushing strokes frame by frame and trying to avoid unappealing swimming which distractsthe audience from the content of the animation. Liwinowicz extends his static method and makes use of optical flow to estimate a motion vector field to translate the strokes painted on the first frame to successive frames[47]. A similar method is employed by Kovacs and Sziranyi[42]. A simpler solution is proposed by Hertzmann[33], who differences consecutive frames of video, re-painting only those areas which have changed above some global(userdefined) threshold. Hays and Essa’s approach[32] builds on and improves these techniques by using edges to guide painterly refinement. See Figure 2.4 for some examples. In their current work, they are looking into studying region-based methods to extend beyond pixels to cell-based renderings, wh