Apparatus for and method of embedding and extracting digital information and medium having program for carrying out the method recorded thereon

A digital information embedding method of embedding inherent digital information in a digital image signal, comprising the steps of:

• dividing said digital image signal into transform coefficients over a plurality of frequency bands using either a discrete wavelet transform or sub-band division;
• dividing the lowest frequency band out of said plurality of frequency bands obtained by the division into a plurality of blocks in accordance with a previously determined block size;
• calculating, for each of said blocks, a mean value M of the transform coefficients in the block, and subjecting the mean value M to linear quantization using a previously determined quantization step-size Q, wherein Q is an integer of not less than one, to calculate a quantization value;
• replacing, for each of said blocks, and on the basis of said quantization value and the value of said digital information to be embedded which correspond to the block, the quantization value;
• subjecting for each of said blocks said replaced quantization value to inverse linear quantization using said quantization step-size Q to calculate a mean value M′, and adding a difference DM, wherein DM=M′−M, between the mean value M′ and said mean value M to all the transform coefficients in the block;
• calculating a mean value LM of the transform coefficients in the lowest frequency band after the addition of said difference DM;
• and
• reconstructing a digital image signal in which said digital information has been embedded using the lowest frequency band after the addition of said difference DM and the other frequency bands.

A recording medium having a program executed in a computer recorded thereon, the program realizing on said computer an operational environment comprising the steps of:

• dividing a digital image signal into a plurality of frequency bands to obtain transform coefficients using either a discrete wavelet transform or sub-band division;
• dividing the lowest frequency band out of said plurality of frequency bands obtained by the division into a plurality of blocks in accordance with a previously determined block size;
• calculating for each of said blocks a mean value M of the transform coefficients in the block, and subjecting the mean value M to linear quantization using a previously determined quantization step-size Q, wherein Q is an integer of not less than one, to calculate a quantization value;
• replacing, for each of said blocks, and on the basis of said quantization value and the value of said digital information to be embedded which correspond to the block, the quantization value;
• subjecting, for each of said blocks, said replaced quantization value to inverse linear quantization using said quantization step-size Q to calculate a mean value M′, and adding a difference DM, wherein DM=M′−M between the mean value M′ and said mean value M to all the transform coefficients in the block;
• calculating a mean value LM of the transform coefficients in the lowest frequency band after the addition of said difference DM;
• and
• reconstructing a digital image signal in which said digital information has been embedded using the lowest frequency band after the addition of said difference DM and the other frequency bands.

A digital information embedding apparatus for embedding inherent digital information in a digital image signal, said apparatus comprising:

• a band dividing device operable to divide the digital image signal into transform coefficients over a plurality of frequency bands using either discrete wavelet transform or sub-band division;
• a block divider operable to divide the lowest frequency band out of the plurality of frequency bands into a plurality of blocks in accordance with a previously determined block size;
• a quantization portion operable to calculate for each of the blocks, a mean value M of the transform coefficients in the block, and subjecting the mean value M to linear quantization, using a previously determined quantization step-size Q, wherein Q is an integer of not less than one, to calculate a quantization value;
• a signal replacement portion operable to replace the quantization value for each of the blocks, on the basis of the quantization value and the value of said digital information to be embedded, which correspond to the block;
• a mean difference addition portion operable to subject the replaced quantization value, for each of the blocks, to inverse linear quantization using the quantization step-size Q to calculate a mean value M′, and to add a difference DM, wherein DM=M′−M, between the mean value M′ and the mean value M to all the transform coefficients in the block;
• a mean calculation portion operable to calculate a mean value LM of the transform coefficients in the lowest frequency band after the addition of the difference DM;
• and
• a band synthesis portion for reconstructing a digital image signal in which the digital information has been embedded using the lowest frequency band after the addition of the difference DM and the other frequency bands.

A digital information embedding method of embedding inherent digital information in a digital image signal, said method comprising:

• dividing the digital image signal into transform coefficients over a plurality of frequency bands using either discrete wavelet transform or sub-band division;
• dividing the lowest frequency band out of said plurality of frequency bands into a plurality of blocks in accordance with a previously determined block size;
• calculating for each of the blocks a mean value M of the transform coefficients in the block, and subjecting the mean value M to linear quantization, using a previously determined quantization step-size Q, wherein Q is an integer of not less than one, to calculate a quantization value;
• replacing the quantization value for each of the blocks, on the basis of said quantization value and the value of the digital information to be embedded which correspond to the block;
• subjecting the replaced quantization value for each of the blocks to inverse linear quantization using said quantization step-size Q to calculate a mean value M′, and adding a difference DM, wherein DM=M′−M, between the mean value M′ and the mean value M to all the transform coefficients in the block;
• calculating a mean value LM of the transform coefficients in the lowest frequency band after the addition of the difference DM;
• and
• reconstructing a digital image signal in which the digital information has been embedded using the lowest frequency band after the addition of the difference DM and the other frequency bands.

A computer program embodied on a computer readable medium for use with a computer for embedding inherent digital information in a digital image signal, said computer program comprising:

• computer readable program code for dividing a digital image signal into a plurality of frequency bands to obtain transform coefficients using either discrete wavelet transform or sub-band division;
• computer readable program code for dividing the lowest frequency band out of the plurality of frequency bands into a plurality of blocks in accordance with a previously determined block size;
• computer readable program code for calculating for each of the blocks a mean value M of the transform coefficients in the block, and subjecting the mean value M to linear quantization, using a previously determined quantization step-size Q, wherein Q is an integer of not less than one, to calculate a quantization value;
• computer readable program code for replacing the quantization value for each of the blocks, on the basis of the quantization value and the value of said digital information to be embedded, which correspond to the block;
• computer readable program code for subjecting the replaced quantization value, for each of the blocks, to inverse linear quantization using the quantization step-size Q to calculate a mean value M′, and adding a difference DM, wherein DM=M′−M, between the mean value M′ and the mean value M to all the transform coefficients in the block;
• computer readable program code for calculating a mean value LM of the transform coefficients in the lowest frequency band after the addition of the difference DM;
• and
• computer readable program code for reconstructing a digital image signal in which the digital information has been embedded using the lowest frequency band after the addition of the difference DM and the other frequency bands.

A digital information embedding apparatus for embedding inherent digital information in a digital image signal, said apparatus comprising:

• a band dividing device operable to divide the digital image signal into transform coefficients over a plurality of frequency bands;
• a block divider operable to divide one frequency band out of the plurality of frequency bands into a plurality of blocks in accordance with a previously determined block size;
• a quantization portion operable to calculate for each of the blocks, a mean value M of the transform coefficients in the block, and subjecting the mean value M to linear quantization, using a previously determined quantization step-size Q, wherein Q is an integer of not less than one, to calculate a quantization value,
• a signal replacement portion operable to replace the quantization value for each of the blocks, on the basis of the quantization value and the value of said digital information to be embedded, which correspond to the block;
• a mean difference addition portion operable to subject the replaced quantization value, for each of the blocks, to inverse linear quantization using the quantization step-size Q to calculate a mean value M′, and to add a difference DM, wherein DM=M′−M, between the mean value M′ and the mean value M to all the transform coefficients in the block;
• a mean calculation portion operable to calculate a mean value LM of the transform coefficients in the frequency band after the addition of the difference DM;
• and
• a band synthesis portion for reconstructing a digital image signal in which the digital information has been embedded using the frequency band after the addition of the difference DM and the other frequency bands.

A digital information embedding method of embedding inherent digital information in a digital image signal, said method comprising:

• dividing the digital image signal into transform coefficients over a plurality of frequency bands;
• dividing a frequency band out of said plurality of frequency bands into a plurality of blocks in accordance with a previously determined block size;
• calculating for each of the blocks a mean value M of the transform coefficients in the block, and subjecting the mean value M to linear quantization, using a previously determined quantization step-size Q, wherein Q is an integer of not less than one, to calculate a quantization value;
• replacing the quantization value for each of the blocks, on the basis of said quantization value and the value of the digital information to be embedded, which correspond to the block;
• subjecting the replaced quantization value for each of the blocks to inverse linear quantization using said quantization step-size Q to calculate a mean value M′, and adding a difference DM, wherein DM=M′−M, between the mean value M′ and the mean value M to all the transform coefficients in the block;
• calculating a mean value LM of the transform coefficients in the frequency band after the addition of the difference DM;
• and
• reconstructing a digital image signal in which the digital information has been embedded using the frequency band after the addition of the difference DM and the other frequency bands.

A computer program embodied on a computer readable medium for use with a computer for embedding inherent digital information in a digital image signal, said computer program comprising:

• computer readable program code for dividing a digital image signal into a plurality of frequency bands to obtain transform coefficients;
• computer readable program code for dividing a frequency band out of the plurality of frequency bands into a plurality of blocks in accordance with a previously determined block size;
• computer readable program code for calculating for each of the blocks a mean value M of the transform coefficients in the block, and subjecting the mean value M to linear quantization, using a previously determined quantization step-size Q, wherein Q is an integer of not less than one, to calculate a quantization value;
• computer readable program code for replacing the quantization value for each of the blocks, on the basis of the quantization value and the value of said digital information to be embedded, which correspond to the block;
• computer readable program code for subjecting the replaced quantization value, for each of the blocks, to inverse linear quantization using the quantization step-size Q to calculate a mean value M′, and adding a difference DM, wherein DM=M′−M, between the mean value M′ and the mean value M to all the transform coefficients in the block;
• computer readable program code for calculating a mean value LM of the transform coefficients in the frequency band after the addition of the difference DM;
• and
• computer readable program code for reconstructing a digital image signal in which the digital information has been embedded using the frequency band after the addition of the difference DM and the other frequency bands.