An apparatus for embedding information in a signal includes a band dividing
device, a block divider, a quantization portion, a signal replacement
portion, a mean difference addition portion, a mean calculation portion,
and a band synthesis portion. The band dividing device divides the signal
into transform coefficients over a plurality of frequency bands. The block
divider divides one frequency band into a plurality of blocks in
accordance with a previously determined block size. The quantization
portion calculates for each block, a mean value M of the transform
coefficients in the block, and subjects the mean value M to linear
quantization, using a previously determined quantization step-size Q to
calculate a quantization value. The signal replacement portion replaces
the quantization value for each block, on the basis of the quantization
value and the value of the information to be embedded. The mean difference
addition portion subjects the replaced quantization value, for each block,
to inverse linear quantization using the quantization step-size Q to
calculate a mean value M', and adds a difference DM between the mean value
M' and the mean value M to all the transform coefficients in the block.
The mean calculation portion calculates a mean value LM of the transform
coefficients in the frequency band after the addition of the difference
DM. The band synthesis portion reconstructs a signal in which the
information has been embedded using the frequency band after the addition
of the difference DM and the other frequency bands.
