A Study on Postprocessing of Video Signals for Image Display

• Main Authors: Liu, Tsann-Shyong, 劉燦雄
• Other Authors: Chang, Long-Wen
• Format: Others
• Language: en_US
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/15503652692476643354

博士 === 國立清華大學 === 資訊科學學系 === 84 === The techniques for a receiver to produce good quality video signals and to show the image on the image display are proposed. To produce good quality video signals in the receiver, an adaptive postprocessing algorithm to enhance the quality of a noisy video sequence is proposed. The algorithm employs motion compensated frame averaging to improve picture quality in the temporal domain. A classification algorithm divides subblocks of pixels in the averaged frame into some classes. Spatial algorithm applys different filters to the pixels belonging to different class for preserving the details. Since the edge is very important for human perception, the multi-level median filter is applied to the edge pixels to remove the noise and preserve the edge information. To display the image on the display with limited color palette, a fast unbalanced greedy tree growing is proposed. The algorithm is based on the construction of a binary tree. The tree is designed one node at a time by splitting the node with the largest error reduction. For reducing the false contouring caused by abrupt color changes across region boundaries, a pixel mapping algorithmis proposed. The algorithm extracts the boundary of each color region by morphological erosion filter, and then applys the error diffusion to the boundary to alleviate the false contouring. Halftoning is a technique for rendering the continuous-tone image on the bilevel display. A new algorithm for halftoning based on discrete cosine transform is proposed. The algorithm replaces continuous-tone image subblock with a bilevel pattern which minimize the distortion between the continuous-tone image subblock and bilevel pattern in the frequency domain. From the experimental results, it is clear that the proposed algorithm can produce high quality of halftoned images.