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

A band division portion 11 receives an image signal 71, and divides the image signal 71 into 10 frequency bands by discrete wavelet transform, to calculate transform coefficients. A block division portion 12 divides an LL3 signal obtained by the division into a plurality of blocks previously determined. A quantization portion 13 finds for each of the blocks a mean value M of the transform coefficients, and subjects M to linear quantization using a quantization step-size Q previously determined, to calculate a quantization value q. A signal replacement portion 14 replaces q with q' on the basis of the value of digital information to be embedded. A mean difference addition portion 15 subjects q' to inverse linear quantization using Q, to find a mean value M', calculates a difference DM between M' and M, and adds the difference to the transform coefficients in the block. A mean calculation portion 16 calculates a mean value LM of the transform coefficients after the addition. A band synthesis portion 17 synthesizes the LL3 signal which has been subjected to the embedding processing and a signal in the other frequency band, to reconstruct an image signal 72. Further, the band division portion 11 receives a digitized image signal 71, and divides the image signal 71 into 10 frequency bands by discrete wavelet transform, to calculate transform coefficients. A map information generation portion 52 generates, with respect to one of the 10 frequency bands, map information indicating whether or not the absolute amplitude values of all the transform coefficients in the same space representation region in the same direction of division as the frequency band are not more than a set value R. A signal replacement portion 53 refers to the value of each of the transform coefficients in the map information, and replaces, when the value of the transform coefficient is not more than the set value R, the value with another value in accordance with the digital information to be embedded. A band synthesis portion 17 synthesizes signals in the 10 frequency bands each including the replaced transform coefficients, to reconstruct an image signal 75.