Image coding apparatus and method, and image decoding apparatus and method

Abstract

An image coding apparatus and method efficiently compresses a variety of images by a lossless or near-lossless coding, and an image decoding apparatus and method decodes code data encoded by the image coding apparatus and method. A windowing unit determines peripheral pixel values, which include a coding object pixel value and values of pixels located near the coding object pixel. An approximation unit uses plural approximation methods so as to output decoded pixel candidates, each of which approximates the coding object pixel value based on the values of the nearby pixels by using one of the plural approximation methods. The plural approximation methods can include an interpolation method and a quantization method. A minimum error selector calculates an error between the coding object pixel value and each of the decoded pixel candidates, and outputs a rank of the approximation method that produced the minimum error. A rank/runlength calculator counts the runlength of first ranks and outputs a coding symbol. The coding symbol can be the rank or the runlength. An encoder encodes the coding symbol so as to output code data.

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