Summary: | 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.
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