Digital watermark-embedding apparatus and method, digital watermark-detecting apparatus and method, and recording medium

1. A digital watermark-embedding apparatus comprising:

an embedment signal-generating unit operable to generate an embedment signal in accordance with embedment information, the embedment signal being embedded as a digital watermark;

a block-dividing unit operable to divide a digital image signal into blocks that are formed by several pixels;

an orthogonal transform unit operable to practice orthogonal transformation of each of the blocks, thereby transforming the blocks into several frequency components;

a digital watermark-embedding unit operable to operate, under a predetermined rule, a value of at least one of the several frequency components in accordance with the embedment signal generated by said embedment signal-generating unit, in which the value is operated in such a manner that amounts of variations in image within the blocks follow a predetermined specific pattern in consideration of detection;

a first characteristic amount-extracting unit operable to extract a first characteristic amount in accordance with the several frequency components; and

a selecting unit operable to select a value of at least one of the several frequency components in accordance with the extracted first characteristic amount;

wherein the specific pattern has two different regions arranged in alternating sequence, one of the two different regions being where the amounts of variations in image serve as positive, and the other region being where the amounts of variations in image serve as negative; and

wherein the first characteristic amount is a combination of one or more frequency components selected from a total of specific frequency components corresponding to vertical edges in an image within the blocks, a total of specific frequency components corresponding to horizontal edges therein, and a total of specific frequency components corresponding to slanted edges therein.

2. A digital watermark-embedding apparatus as defined in claim 1 , wherein the embedment signal-generating unit transforms the embedment information into a binary bit string, and uses the binary bit string as the embedment signal.

3. A digital watermark-embedding apparatus as defined in claim 1 , wherein said embedment signal-generating unit selects a pseudo-random number sequence corresponding to the embedment information, with reference to a reference table having pseudo-random number sequences related to previously prepared embedment information, and uses the selected pseudo-random number sequence as the embedment signal.

4. A digital watermark-embedding apparatus as defined in claim 1 , wherein said first characteristic amount-extracting unit extracts the first characteristic amount in accordance with several frequency components in the blocks and several frequency components in neighboring blocks positioned adjacent to the former blocks.

5. A digital watermark-embedding apparatus as defined in claim 1 , wherein said selecting unit determines, in accordance with the first characteristic amount, which one of the vertical edges, the horizontal edges, and the slanted edges is dominant in the image within the blocks, and selects at least one of the several frequency components in accordance with results from the determination.

6. A digital watermark-embedding apparatus as defined in claim 1 , wherein said digital watermark-embedding unit operates the value in order to fluctuate the value.

7. A digital watermark-embedding apparatus as defined in claim 6 , further comprising:

a second characteristic-extracting unit operable to extract a second characteristic amount from the several frequency components,

wherein said digital watermark-embedding unit changes, in accordance with the extracted second characteristic amount, magnitude at which the value is fluctuated.

8. A digital watermark-embedding apparatus as defined in claim 7 , wherein the several frequency components include a direct current component value and a specific alternating current component value, and wherein the second characteristic amount is either one of the direct current component value and the specific alternating current component value or both.

9. A digital watermark-embedding apparatus as defined in claim 1 , wherein said orthogonal transform unit performs a discrete cosine transform.

10. A digital watermark-embedding apparatus as defined in claim 9 , wherein the specific pattern includes a pattern represented by a base image in the discrete cosine transform.

11. A digital watermark-embedding method comprising:

generating an embedment signal in accordance with embedment information, the embedment signal being embedded as a digital watermark;

dividing a digital image signal into blocks that are formed by several pixels;

practicing orthogonal transformation of each of the blocks, thereby transforming the blocks into several frequency components;

operating, under a predetermined rule, a value of at least one of the several frequency components in accordance with the embedment signal obtained by the generating the embedment signal, in which the value is operated in such a manner that amounts of variations in image within the blocks follow a predetermined specific pattern in consideration of detection; and

extracting a first characteristic amount in accordance with the several frequency components; and

selecting at least one of the several frequency components in accordance with the extracted first characteristic amount;

wherein the specific pattern has two different regions arranged in alternating sequence, one of the two different regions being where the amounts of variations in image serve as positive, and the other region being where the amounts of variations in image serve as negative; and

wherein the first characteristic amount is a combination of one or more frequency components selected from a total of specific frequency components corresponding to vertical edges in an image within the blocks, a total of specific frequency components corresponding to horizontal edges therein, and a total of specific frequency components corresponding to slanted edges therein.

12. A digital watermark-embedding method as defined in claim 11 , wherein said generating the embedment signal comprises transforming the embedment information into a binary bit string, and using the transformed binary bit string as the embedment signal.

13. A digital watermark-embedding method as defined in claim 11 , wherein said generating the embedment signal comprises selecting a pseudo-random number sequence corresponding to the embedment information, with reference to a reference table having pseudo-random number sequences related to previously prepared embedment information, and using the selected pseudo-random number sequence as the embedment signal.

14. A digital watermark-embedding method as defined in claim 11 , wherein said extracting the first characteristic amount comprises extracting the first characteristic amount in accordance with several frequency components in the blocks and several frequency components in neighboring blocks positioned adjacent to the former blocks.

15. A digital watermark-embedding method as defined in claim 11 , wherein said selecting at least one of the several frequency components comprises determining, in accordance with the extracted first characteristic amount, which one of the vertical edges, the horizontal edges, and the slanted edges is dominant in the image within the blocks, and selecting at least one of the several frequency components in accordance with results from the determination.

16. A digital watermark-embedding method as defined in claim 11 , wherein said operating the value under the predetermined rule is to fluctuate the value.

17. A digital watermark-embedding method as defined in claim 16 , further comprising:

extracting a second characteristic amount from the several frequency components,

wherein said operating the value under the predetermined rule comprises changing, in accordance with the extracted second characteristic amount, magnitude at which the value is fluctuated.

18. A digital watermark-embedding method as defined in claim 17 , wherein the several frequency components include a direct current component value and a specific alternating current component value, and wherein the second characteristic amount is either one of the direct current component value and the specific alternating current component value or both.

19. A digital watermark-embedding method as defined in claim 11 , wherein said practicing the orthogonal transformation comprises performing a discrete cosine transform.

20. A digital watermark-embedding method as defined in claim 19 , wherein the specific pattern includes a pattern represented by a base image in the discrete cosine transform.