Method of inserting/detecting digital watermark and apparatus for using thereof

• US 20040030899A1
• Filed: 08/19/2003
• Published: 02/12/2004
• Est. Priority Date: 04/21/2001
• Status: Active Grant

• Current Assignee: MarkAny, Inc.
• Original Assignee: MarkAny, Inc.
• Inventors: Lee, Jung-Soo, Lee, Han-Ho, Choi, Jong-Uk
• Granted Patent: US 7,386,729 B2
• Time in Patent Office: Days
• US Class Current: 713/176
• CPC Class Codes: G06T 1/0064 Geometric transfor invariant watermarking, e.g. affine transform invariant
• CPC Class Codes: G06T 1/0078 using multiple thresholds
• CPC Class Codes: H04N 1/32154 Transform domain methods H04N1/32309 takes precedence
• CPC Class Codes: H04N 1/3216 using Fourier transforms
• CPC Class Codes: H04N 1/32309 in colour image data
• CPC Class Codes: H04N 1/3232 Robust embedding or watermarking
• CPC Class Codes: H04N 19/467 characterised by the embedded information being invisible, e.g. watermarking
• CPC Class Codes: H04N 2201/3236 Details of authentication information generation
• CPC Class Codes: H04N 2201/327 which are undetectable to the naked eye, e.g. embedded codes

Abstract

For the purpose of designing watermark to be robust against image modification such as geometric modification (rotating, cutting, enlarging/shrinking, etc.), compression, and blurring, the watermark is embedded in frequency domain after formed as 2 dimensional shape, for example radial or concentric shape. In detecting watermark, it is possible to effectively detect the watermark, by using relation to a generated watermark in case where the peak is detected.

Claims

1. A digital watermark embedding method for embedding a digital watermark in an image signal, comprising steps of:

using a user key and an inherent key and generating respective pseudo-noise codes thereof;

adding the pseudo-noise code generated based on the user key and the pseudo-noise code generated based on the inherent key;

generating a digital watermark including a step of arranging in a two-dimensional form a watermark formed by the addition;

converting the image signal from a spatial domain to a frequency domain; and

adding a magnitude component of the image signal converted into the frequency domain and a watermark generated by the watermark generation step.

2. The method as claimed in claim 1, wherein the watermark arrangement step rotates the watermark of a stream format 360 degrees about a first value of a watermark of a predetermined length to be arranged in a radial format.

3. The method as claimed in claim 1, wherein the watermark arrangement step arranges the watermark of a stream format into plural concentric circles about a center portion of a block constructing the image signal.

4. The method as claimed in claim 3, wherein the watermark arranged in the concentric circles is arranged with enlargements/reductions by sampling a corresponding stream with reference to a predetermined radius.

5. The method as claimed in any one of claims 1 to 4, wherein the frequency domain conversion step includes steps of:

applying a two-dimensional Fourier transform to the image signal for the conversion from the spatial domain to the frequency domain;

separating a signal converted to the frequency domain into a magnitude component and a phase component; and

applying a Fourier transform shift to the separated magnitude component.

6. The method as claimed in claim 5, further comprising a step of converting from the frequency domain to the spatial domain the signal the watermark and the image signal are added, and the conversion step including steps of:

applying the Fourier transform shift to the watermark and the image signal;

applying an inverse two-dimensional Fourier transform to the shifted signal for a conversion from the frequency domain to the spatial domain; and

adjusting a value of the image signal to prevent an overflow of the converted image signal.

7. The method as claimed in claim 6, wherein the image signal is a 24-bit color signal, and, before adding the digital watermark and the image signal, a step of converting the image signal inputted in an RGB format into an YIQ format (Y:

Luminance, I;

In-Phase, and Q;

Quadrature) and a step of extracting only the Y component from the components of the converted YIQ format are further comprised, and the Y component is added to the digital watermark.

8. The method as claimed in claim 6, wherein the image signal is the 24-bit color signal, and the image signal inputted in the RGB format is added to the digital watermark by each of R, G, and B channels.

9. The method as claimed in claim 7, further comprising a step of storing an image signal the image signal and the digital watermark are added, and the storage step including steps of:

adding the IQ components and the added image signal;

converting the added signal into the RGB format; and

storing the converted signal in a storage medium as a record signal.

10. The method as claimed in claim 6, wherein the image signal adjustment step sets a value of the image signal to a boundary value of a range in case that the image signal has a value beyond the corresponding range.

11. A digital watermark detection method for detecting a digital watermark embedded in an image signal, comprising steps of:

strengthening a component of the digital watermark embedded in the image signal;

converting the digital watermark-strengthened image signal from a spatial domain to a frequency domain and extracting the digital watermark included in the image signal;

generating a digital watermark for comparison with the extracted digital watermark;

calculating correlation between the generated digital watermark and the digital watermark extracted from the image signal; and

detecting the watermark embedded in the image signal based on the correlation.

12. The method as claimed in claim 11, wherein the watermark generation step uses a user key and an inherent key, generates respective pseudo-noise codes, and forms a digital watermark.

13. The method as claimed in claim 12, wherein the image signal is a 24-bit color signal, before carrying out the step of strengthening the component of the digital watermark embedded in the image signal, further comprised are steps of:

converting the image signal inputted in an RGB format into a YIQ format; and

extracting only the Y component from the components of the converted YIQ format, and the step of strengthening the component of the digital watermark is to strengthen a component of the digital watermark embedded in the Y component.

14. The method as claimed in claim 12, wherein the image signal is the 24-bit color signal, a step of separating the image signal inputted in the RGB format into each of R, G and B channels is further comprised, and the step of strengthening the component of the digital watermark is to strengthen the components of the digital watermark embedded in signals separated channel by channel.

15. The method as claimed in claim 13, wherein the step of strengthening the component of the digital watermark includes a step of filtering a high frequency component of the image signal.

16. The method as claimed in claim 13, wherein the step of strengthening the component of the digital watermark includes a step of applying a masking in order to reduce an image component energy in the image signal and increase a watermark component energy.

17. The method as claimed in claim 15, wherein the high frequency filtering step is carried out through a high boost filter, a Laplacian filter, or a Difference of Gaussian (DoG) filter.

18. The method as claimed in claim 13, wherein the digital watermark extraction step comprises steps of:

converting the digital watermark-strengthened image signal from the spatial domain to the frequency domain;

extracting from the converted image signal in one dimension a region in which the digital watermark is embedded; and

adjusting a length of the extracted one-dimensional digital watermark to a predetermined length.

19. The method as claimed in claim 14, wherein the digital watermark extraction step comprises steps of:

converting the digital watermark-strengthened image signal from the spatial domain to the frequency domain;

extracting from the converted image signal in one dimension a region in which the digital watermark is embedded; and

adjusting a length of the extracted one-dimensional digital watermark to a predetermined length.

20. The method as claimed in claim 18 or claim 19, wherein correlation calculations are carried out with a Formula as below:

Corr=IFFT(FFT(W_EXT)×

conj(FFT(W_m)))

here, W_EXT denotes a digital watermark extracted from an image signal, and W_m respective watermarks generated by using a user key and an inherent key, IFFT an inverse fast Fourier transform, FFT a fast Fourier Transform, and conj a complex conjugate.

21. The method as claimed in claim 20, wherein the watermark detection step includes steps of:

calculating a peak position from the calculated correlation;

calculating a peak sharpness; and

determining whether the digital watermark is included in the image signal based on the peak position and the sharpness.

22. A digital watermark embedding apparatus for embedding a watermark in an image signal, comprising:

a first conversion means for converting the image signal from a spatial domain to a frequency domain;

a watermark generation means for generating a watermark;

a first addition means for adding the watermark to the frequency-converted image signal;

a second conversion means for converting from the frequency domain to the spatial domain the watermark-added image signal generated by the first addition means; and

an image record means for recording the watermark-embedded image signal converted into the spatial domain, the watermark generation means comprising;

a) a first pseudo-noise code generation means for generating a pseudo-noise code by using a user key;

b) a second pseudo-noise code generation means for generating a pseudo-noise code by using an inherent key;

c) a second addition means for adding pseudo-noise codes generated from the first pseudo-noise generation means and the second pseudo-noise generation means; and

d) a configuration means for configuring in a two-dimensional arrangement the watermark formed by the addition through the second addition means.

23. The apparatus as claimed in claim 22, wherein the watermark configuration means rotates the watermark of a stream format 360 degrees about a first value of a watermark of a predetermined length to be arranged in a radial format.

24. The apparatus as claimed in claim 22, wherein the watermark configuration means arranges the watermark of a stream format into plural concentric circles about a center portion of a block constructing the image signal.

25. The apparatus as claimed in claim 24, wherein the watermark configuration means enlarges and reduces the watermark arranged in the form of the concentric circles by sampling a corresponding stream with reference to a predetermined radius to be arranged in a form of plural concentric circles.

26. The apparatus as claimed in any one of claim 22 to claim 25, wherein the first addition means divides the image signal into a watermark size, and adds the divided image signal and the watermark channel by channel.

27. The apparatus as claimed in any one of claim 22 to claim 25, further comprising an image conversion means for converting a format of the image signal before adding the image signal and the watermark, the image conversion means including:

a first determination means for reading header information of the image signal and determining whether the image signal is a 24-bit color image;

a first conversion means for converting the image signal of RGB format into a YIQ format if the image signal is the 24-bit color image signal; and

an extraction means for extracting only a Y component from the image signal converted to the YIQ format, the image conversion means outputs the image signal to the first addition means without the conversion if the image signal is not the 24-bit color image.

28. The apparatus as claimed in claim 27, wherein the image record means comprises:

a first determination means for reading out the header information of the image signal and determine whether the image is a 24-bit color image;

an addition means for adding the watermark-embedded image signal of the Y component and the IQ components separated by the extraction means if the image signal is the 24-bit image signal; and

a second conversion means for converting the added signal of the YIQ format into the RGB format, the image record means storing the processed image signal in a record medium.

29. A digital watermark detection apparatus for detecting a watermark embedded in an image signal, comprising:

a pre-processing means for strengthening a component of a watermark embedded in the retrieved image signal;

an extraction means for converting the digital watermark-strengthened image signal from a spatial domain to a frequency domain and extracting the digital watermark embedded in the image signal;

a digital watermark generation means for generating respective digital watermarks based on a user key and an inherent key for a comparison with the extracted digital watermark;

a correlation calculation means for calculating a correlation between the generated digital watermark and the extracted digital watermark from the image signal; and

a watermark detection means for detecting a watermark embedded in the image signal according to the correlation.

30. The apparatus as claimed in claim 29, wherein the watermark generation means includes:

a) a first pseudo-noise code generation means for generating a pseudo-noise code based on the user key;

b) a second pseudo-noise code generation means for generating a pseudo-noise code based on the inherent key; and

c) a configuration means for arranging and configuring in a two-dimensional form a watermark comprising the pseudo-noise codes generated from the first pseudo-noise code generation means and the second pseudo-noise code generation means.

31. The apparatus as claimed in claim 30, wherein the image signal is the 24-bit color image, an image signal conversion means for converting a format of the image signal is further included before carried out by the pre-processor for strengthening a component of the digital watermark embedded in the image signal, and the image signal conversion means includes:

a conversion means for converting the image signal inputted in the RGB format into the YIQ format; and

an extraction means for extracting only the Y component of the components of the converted YIQ format.

32. The apparatus as claimed in claim 30, wherein the image signal is the 24-bit color signal, and the R, G, and B channels of the image signal inputted in the RGB format are inputted to the pre-processing means channel by channel.

33. The apparatus as claimed in any one of claim 29 to claim 32, wherein the pre-processing means filters a high frequency component of the image signal.

34. The apparatus as claimed in any one of claim 29 to claim 32, wherein the pre-processing means carries out a masking in order to reduce an image component energy and increase a watermark component energy in the image signal.

35. The apparatus as claimed in claim 33, wherein the high frequency filtering is carried out by a high boost filter, a Laplacian filter, or a Difference of Gaussian (DoG) filter.

36. The apparatus as claimed in claim 31, wherein the extraction means includes:

a means for converting from the spatial domain to the frequency domain the image signal the digital watermark component is strengthened;

a means for extracting in one dimension a region in which the digital watermark is embedded from the converted image signal; and

a means for adjusting a length of the extracted one-dimensional digital watermark to a predetermined length.

37. The apparatus as claimed in claim 32, wherein the extraction means comprises:

a means for converting from the spatial domain to the frequency domain the image signal the digital watermark component is strengthened;

a means for extracting in one dimension a region in which the digital watermark is embedded from the converted image signal; and

a means for adjusting a length of the extracted one-dimensional digital watermark to a predetermined length.

38. The apparatus as claimed in claim 36 or claim 37, wherein the correlation calculations are carried out based on a Formula as blow:

Corr=IFFT(FFT(W_EXT)×

conj(FFT(W_m)))

here, W_EXT denotes a watermark extracted from an image signal, and W_m respective watermarks generated by using a user key and an inherent key, IFFT an inverse fast Fourier transform, FFT a fast Fourier Transform, and conj a complex conjugate.

39. The apparatus as claimed in claim 38, wherein the watermark detection means includes:

a means for calculating a peak position and a peak sharpness from the correlation; and

a means for determining whether a watermark is included in the image signal based on the peak position and the sharpness.