US 6,661,924 B1Granted

Method and apparatus for compressing and expanding image data

AssigneePENTAX Corporation

InventorNobuaki Abe

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Abstract

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.

Claims17

Dependent claims

A compression apparatus for compressing image data comprising:

a reduced-image generating processor that 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 said original image data;
a fluency transform processor that applies a fluency transform to said reduced-image data so as to generate expanded-image data partitioned into second blocks corresponding to said first blocks, said fluency transform having a plurality of modes;
a differential value calculating processor that obtains differential value data indicating a difference between said original image data and said expanded-image data;
an orthogonal transform processor that obtains orthogonal transform coefficient data by applying an orthogonal transform to said differential value data;
a mode setting processor that selects one mode from said plurality of modes, said orthogonal transform coefficient data being generated in accordance with said selected mode;
a code-length calculating processor that calculates a code-length corresponding to a bit length of Entropy-encoded bit data obtained by an Entropy coding to said orthogonal transform coefficient data, said code-length calculating processor calculating said code-length in each of said plurality of modes;
an optimum mode determining processor that determines an optimum mode, by which said code-length becomes minimum, from said plurality of modes;
and
an optimum Entropy coding processor that obtains said Entropy-encoded bit data by applying said Entropy coding to said orthogonal transform coefficient data in accordance with said optimum mode.

6 more elements

A compression method for compressing image data comprising:

transforming 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 said original image data;
applying a fluency transform to said reduced-image data so as to generate expanded-image data partitioned into second blocks corresponding to said first blocks, said fluency transform having a plurality of modes;
obtaining differential value data indicating a difference between said original image data and said expanded-image data;
obtaining orthogonal transform coefficient data by applying an orthogonal transform to said differential value data;
selecting one mode from said plurality of modes, said orthogonal transform coefficient data being generated in accordance with said selected mode;
calculating a code-length corresponding to a bit length of Entropy-encoded bit data obtained by an Entropy coding to said orthogonal transform coefficient data, said code-length being calculated in each of said plurality of modes;
determining an optimum mode, by which said code-length becomes minimum, among said plurality of modes;
and
obtaining said Entropy-encoded bit data by applying said Entropy coding based on said optimum mode to said orthogonal transform coefficient data.

6 more elements

A memory medium that stores a program for compressing image data, said program comprising:

transforming 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 said original image data;
applying a fluency transform to said reduced-image data so as to generate expanded-image data partitioned into second blocks corresponding to said first blocks, said fluency transform having a plurality of modes;
obtaining differential value data indicating a difference between said original image data and said expanded-image data;
obtaining orthogonal transform coefficient data by applying an orthogonal transform to said differential value data;
selecting one mode from said plurality of modes, said orthogonal transform coefficient data being generated in accordance with said selected mode;
calculating a code-length corresponding to a bit length of an Entropy-encoded bit data obtained by an Entropy coding to said orthogonal transform coefficient data, said code-length being calculated in each of said plurality of modes;
determining an optimum mode, by which said code-length becomes minimum, among said plurality of modes;
and
obtaining said Entropy-encoded bit data by applying said Entropy coding, based on said optimum mode, to said orthogonal transform coefficient data.

6 more elements

Dependencies are inferred from the claim text.