Electronic watermark generating apparatus, method, and program for generating electronic watermark

An electronic watermark generating method in an electronic watermark generating apparatus, the method comprising:

• embedding to-be-embedded information as an electronic watermark in a quantized block of an irreversible compression image produced by carrying out quantization on a block-by-block basis after an RGB image has been subjected to color conversion to be divided in a plurality of blocks;
• restoring an RGB image by carrying out de-quantization with respect to a block in which the to-be-embedded information has been embedded;
• color-converting the restored RGB image and dividing the color-converted RGB image into a plurality of blocks, and then, carrying out quantization on a block-by-block basis, thereby extracting to-be-embedded information from the quantized blocks;
• checking whether or not to-be-embedded information has been correctly extracted;
• when it is not checked that the to-be-embedded information has been correctly extracted, embedding the to-be-embedded information as an electronic watermark again in the quantized blocks;
• and
• setting an upper limit value of the repetition count of extracting to-be-embedded information by the extracting step and checking whether or not the to-be-embedded information has been correctly extracted by the checking step.

An electronic watermark generating program stored in a computer readable medium, said program causing a computer to execute:

• an embedding function of embedding to-be-embedded information as an electronic watermark in a quantized block of an irreversible compression image produced by carrying out quantization on a block-by-block basis after an RGB image has been subjected to color conversion to be divided in a plurality of blocks;
• a restoring function of restoring an RGB image by carrying out de-quantization with respect to a block in which the to-be-embedded information has been embedded;
• an extracting function of color-converting the restored RGB image and dividing the color-converted RGB image into a plurality of blocks, and then, carrying out quantization on a block-by-block basis, thereby extracting to-be-embedded information from the quantized blocks;
• a re-embedding function for, when it is not checked that the to-be-embedded information has been correctly extracted by a checking function of checking whether or not the to-be-embedded information has been correctly extracted, embedding the to-be-embedded information as an electronic watermark again in the quantized blocks;
• and
• an upper limit value setting function for setting an upper limit value of the repetition count of extracting to-be-embedded information by the extracting function and checking whether or not the to-be-embedded information has been correctly extracted by the checking function.