Patent ID: 7613345

Claim:
An image coding apparatus for encoding multi-valued image data, comprising: a block dividing unit configured to divide multi-valued image data into a plurality of blocks having pixel values; a determination unit configured to determine, by block, whether an occurrence distribution of the pixel values, existing in a block from the plurality of blocks, along an axis of a possible pixel value range, is discrete; a conversion unit, responsive to the determination unit determining that the occurrence distribution of the pixel values is discrete, to convert the pixel values in the block into index values by allocating continuous index values to each distinct pixel value existing in the block so that the number of types of index values coincides with the number of pixel types represented by the number of distinct pixel values; a predictive coding unit configured to: perform predictive coding on the pixel values in the block if said determination unit determines that the occurrence distribution of pixel values in the block is not discrete, and perform the predictive coding on the index values converted by said conversion unit, as if the index values are pixel values, if said determination unit determines that the occurrence distribution of pixel values in the block is discrete, wherein the units are formed by at least one computer processor.