Image compression apparatus and computer-readable recording medium recorded with image compression program
A pattern data storage stores a plurality of different pattern data having the same data size as bit planes. An image compressing/decoding unit calculates code amounts of the respective encoded bit planes and successively adds the code amounts of the respective bit planes in decreasing order from that of the bit plane of the most significant bit to such an extent that the sum does not exceed a limited code amount. Then, the image compressing/decoding unit selects the bit planes with highest degrees of coincidence by comparing the bit planes other those whose code amounts were added to such an extent that the sum does not exceed the limited code amount and the respective pattern data stored in the pattern data storage and replaces the bit planes by the selected pattern data.
1. An image compression apparatus, comprising:
a conversion unit configured to convert the color system of an input image data into the one composed of luminance components and color difference components;
a division unit configured to divide the converted image data into a plurality of tiles;
a wavelet transform unit configured to perform wavelet transform on each divided tile;
a quantization unit configured to quantize each wavelet-transformed tile;
a coding unit configured to code the quantized tiles by developing them into bit planes;
a storage unit configured to store a plurality of different pattern data having the same data size as the bit planes;
a determination unit configured to determine the bit planes having a small influence on image quality after decoding out of the developed bit planes;
a selection unit configured to select the pattern data with a highest degree of coincidence with each determined bit plane by comparing the bit plane determined to have a small influence on image quality by the determination unit and the respective pattern data stored in the storage unit; and
a replacement unit configured to replace each bit plane determined to have a small influence on image quality by the determination unit by the pattern data selected as the one with the highest degree of coincidence with the determined bit plane by the section unit.
2. An image compression apparatus according to claim 1 , wherein the determination unit includes:
a calculator configured to calculate code amounts of the respective encoded bit planes, and
an adder configured to successively add the code amounts of the respective bit planes in decreasing order from that of the bit plane of the most significant bit to such an extent that the sum does not exceed a limited code amount calculated based on a data amount of a compressed data obtained when the input image data is compressed at a set compression rate, and the determination unit determines the bit planes other than those whose code amounts were added by the adder to such an extent that the sum does not exceed the limited code amount as bit planes with small degrees of influence on the image quality.
3. An image compression apparatus according to claim 1 , wherein the determination unit includes:
a calculator configured to calculate a degree of influence of each encoded bit plane on image quality, and
an adder configured to successively add the code amounts of the respective bit planes in order of decreasing degree of influence on the image quality to such an extent that the sum does not exceed a limited code amount calculated based on a data amount of a compressed data obtained when the input image data is compressed at a set compression rate, and the determination unit determines the bit planes other than those whose code amounts were added by the adder to such an extent that the sum does not exceed the limited code amount as bit planes with small degrees of influence on the image quality.
4. An image compression apparatus according to claim 1 , wherein:
the storage unit stores identification information with small code amounts unique to the respective pattern data in correspondence with the respective pattern data, and
the image compression apparatus further comprises an output unit configured to indicate the pattern data caused to replace the bit planes by the replacement unit by the identification information stored in correspondence with the pattern data in the storage unit and outputting the pattern data together with the other encoded bit planes as a compressed data.
5. A non-transitory computer-readable recording medium storing an image compression program for causing a computer to function as:
a conversion unit configured to convert the color system of an input image data into the one composed of luminance components and color difference components;
a division unit configured to divide the converted image data into a plurality of tiles;
a wavelet transform configured to perform wavelet transform on each divided tile;
a quantization unit configured to quantize each wavelet-transformed tile;
a coding unit configured to code the quantized tiles by developing them into bit planes;
a storage unit configured to store a plurality of different pattern data having the same data size as the bit planes;
a determination unit configured to determine the bit planes having a small influence on image quality after decoding out of the developed bit planes;
a selection unit configured to select the pattern data with a highest degree of coincidence with each determined bit plane by comparing the bit plane determined to have a small influence on image quality by the determination unit and respective pattern data stored in a storage unit for storing a plurality of different pattern data having the same data size as the bit planes; and
a replacement unit configured to replace each bit plane determined to have a small influence on image quality by the determination unit by the pattern data selected as the one with the highest degree of coincidence with the determined bit plane by the section unit.