Patent ID: 7471838

Claim:
An image-data processing apparatus for extracting a code repeatedly embedded in image data, the image-data processing apparatus comprising: a dividing unit that divides the image data into a plurality of blocks; a characteristic-amount extracting unit that extracts a characteristic amount of each of the blocks; and a decoding unit that extracts a code from a pair of the blocks based on a magnitude relation between a first characteristic amount extracted by the extracting unit from a first block and a second characteristic amount extracted by the extracting unit from a second block from among the pair of blocks, wherein the decoding unit includes a bit-information extracting unit that extracts a plurality of bit information corresponding to each bit of the extracted code, from each pair of the blocks based on the magnitude relation between the first characteristic amount and the second characteristic amount by comparing the first characteristic amount with the second characteristic amount, calculating a difference between the first characteristic amount and the second characteristic amount, and if the difference is smaller than an upper threshold and the first characteristic amount is smaller than the second characteristic amount then the bit-information extracting unit extracts a first candidate code as the bit information, if the difference is smaller than the upper threshold and the second characteristic amount is smaller than the first characteristic amount then the bit-information extracting unit extracts a second candidate code as the bit information, and if the difference is equal to or larger than the upper threshold then the bit-information extracting unit extracts a third candidate code as the bit information; and a bit-value determining unit that determines a bit value for each extracted code based on a majority decision processing from the extracted first, second and third candidate codes as the plurality of the extracted bit information.