| 摘要 |
An image compression apparatus transforms original image data partitioned into first blocks, each of which is composed of a plurality of pixels, to reduced-image data composed of a smaller number of pixels than that of the original image data. Further, the apparatus generates expanded-image data from the reduced-image data by fluency transform. Based on the expanded-image data and the original image data, differential value data is obtained, and the differential value is transformed to differential DCT coefficient data by DCT processing. Based on the differential DCT coefficient data, a code-length corresponding to a bit-length necessary for a Huffman coding is calculated. The fluency transform has a plurality of modes, each mode being selected in order, the code-length being calculated for all of the modes. Then, a mode which makes the code-length minimum is determined as the optimum mode. The differential DCT coefficient data is Huffman encoded, so that Huffman-encoded bit data is generated. Then, in an image expansion apparatus, the original image data is restored on using the optimum mode, reduced-image data and the Huffman-encoded bit data.
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