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Why Shape Coding? Asymptotic Analysis of the Entropy Rate for Digital Images
Gangtao Xin1,2, Pingyi Fan1,2, Khaled B Letaief3
1Department of Electronic Engineering, Tsinghua University, Beijing 100084, China.
Abstract:
This paper focuses on the ultimate limit theory of image compression. It proves that for an image source, there exists a coding method with shapes that can achieve the entropy rate under a certain condition where the shape-pixel ratio in the encoder/decoder is O(1/logt). Based on the new finding, an image coding framework with shapes is proposed and proved to be asymptotically optimal for stationary and ergodic processes. Moreover, the condition O(1/logt) of shape-pixel ratio in the encoder/decoder has been confirmed in the image database MNIST, which illustrates the soft compression with shape coding is a near-optimal scheme for lossless compression of images.
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