EP1112636A1

EP1112636A1 - Watermarking of digital images using wavelet and discrete cosine transforms

Info

Publication number: EP1112636A1
Application number: EP99969197A
Authority: EP
Inventors: Jong Uk Choi; Jong Won Kim; Jung Suck Cho; Han Ho Lee
Original assignee: Markany Inc; Lee Sang Ki
Current assignee: Markany Inc; Lee Sang Ki
Priority date: 1998-09-10
Filing date: 1999-09-10
Publication date: 2001-07-04
Also published as: JP2003505895A; EP1112636A4; WO2000016516A1; CN1325577A; AU6031199A; KR20010079788A

Abstract

The present invention relates to a method for embedding a watermark into a black and white or color digital image [D(x)]. Basically the inventive method comprises the steps of transforming the digital image using a wavelet transform [WC(y)], transforming a watermark using discrete cosine transform (DCT), integrating the wavelet-transformed digital image with the DCT-transformed watermark [DW(x) + WC(y)] to insert the watermark into the image, and generating the watermarked image using inverse wavelet transform [D(x)']. For color images, RGB mode is converted into YIQ mode using a conversion matrix and the wavelet transform is applied to the Y-, I-, Q- values. This inventive digital watermarking of a color image is found to be highly robust against lossy compression and other image processing operations, compared to conventionally known methods which are known to be unsuitable for watermarking color images.

Description

WATERMARKING OFDIGITALIMAGESUSINGWAVELET AND DISCRETE COSINE

TRANSFORMS

This application is based on two Korean Patent applications, both filed

on September 10. 1998 at the Korean Intellectual Property Offices by the

same inventors, wherein one of the two applications is entitled, A

Watermarking Process of Digital Image Using Wavelet Transform and Discrete

Cosine Transform, with a Korean Patent Application Serial Number 37273

and the other of the two applications is entitled, A Digital Watermarking

Process of a Color Image Using Wavelet Transform and Discrete Cosine

Transform, with a Korean Patent Application Serial Number 37274

Technical Field

The present invention relates to a method of watermarking of digital images in

general, and in particular, to a method of embedding watermarks into digital images by

using wavelet transform (WT) and discrete cosine transform (DCT) so that the

impairment of the watermark during image processing operations, such as compression, filtering, cropping, re-scaling, resampling, rotation, and other manipulations is substantially avoided The present invention is applied to both black and white image and color image. Background of the Invention

The advent of information communication technology is rapidly changing the

form of data storage from an analog format to a high-quality digital format which is easily

adaptable to further processing. The importance of digital information is increasing,

especially in the area of computer graphics, digital library, cyber magazines and cyber

space communications. Among various digital informations, text and still-picture

information are widely traded in the virtual market through the Internet, which allow easy

and extensive distribution of the information throughout the world. Transmission of

audio and video information through the Internet is increasing at an exponential rate as

the media for audio and video transmission proliferates.

However, there are problems associated with the rapid distribution and

dissemination of the information. One of the problems are the proliferation of the

unauthorized copying and illegal distribution of copyrighted digital material. This

problem is compounded by the fact that the multimedia digital information of text, image,

video, and sound can be easily mass-duplicated in exact copies.

Infringement of intellectual property rights by copying and distributing digital

information in the virtual space is rapidly growing. Various protection measures are being

developed to protect the intellectual property rights of the owners from unauthorized

copying and distribution. Currently developed protection measures include encryption,

digital watermarking, and system security. The present invention is concerned with watermarking of digital images.

Watermarking (or digital signature) is a method developed to protect information by embedding additional information into the original information to be

protected. Watermarking may be classified into visible watermarking and invisible

watermarking. (See J.J.K. Ruanaidh, KM. Boland and O. Sinnen, 1996, "Watermarking

Digital Images for Copyright Protection", EVA).

Visible watermarking adds copyright notice and information to the original

information. It is illegal to remove the notice and illegal to copy without the author's

permission. But preservation of the copyright notice and prevention against illegal

copying is very difficult against infringement and illegal copying.. Invisible watermarking

designed to indicate ownership can prevent illegal erasure of the watermark by third

parties without impairing the original information,. But there is a problem of image

distortion in the information produced by the conventionally available watermarking

processes according to the known prior art.. Thus, there is a compelling need for an

improved watermarking method to overcome the foregoing and related problems.

Watermarking (or digital signature) is a method used to mark the proprietary

ownership by means of copyright notice, logo or trademark and identify unauthorized

copying and distribution of copyrighted material. The watermarking is accomplished by

inserting "marks" which is not visible to the naked eye on the information sought to be

protected. Extensive research has been underway in many industrialized countries

around the world to provide an improved watermarking method. This research effort

has been intensified for the following reasons. Enabled by the emerging digital technology

increasingly various media, such as newspapers, magazines, library, electronic museum, video-on-demand, audio-on-demand, MP3, web site, TV, digital radio, and certification of public documents, crdit checking transaction, transmittal of monetary and security information, has gone digital. The digital technology is bringing a form of revolution and

this is even further heightened by Internet, Internet TV, digital YN MP3 and so on.

The technologies developed to date for watermarking include the spatial method,

the frequency domain method, and the spread spectrum method. The spatial method has

the advantage that the watermark can be added easily, but has the disadvantage in that the

image or information being watermarked and the image itself is susceptible to distortion

as it is subjected to lossy compression and filtering. (See G.C. Langelaar, J.C.A. van der

Lubbe and J. Biemond, 1998, "Copy Protection for Multimedia Data based on Labeling

Techniques"; H. Berghel, and L. O'GorMan, 1998, "Digital Watermarking"; Aura T.,

"Practical invisibility in digital communication", 1998; O, Bryndonckx, J.-J. Quisquater

and B. Marcq, 1998, "Spatial Method for Copyright Labeling of Digital Images." )

The frequency domain method converts the digital data into the analog signals of

frequency components, and inserting a watermark using various transform techniqiues,

such as DCT, FFT or wavelet transforms. Although the watermark created by the

frequency domain method is difficult to erase because it is distributed over the entire data,

there is the problem of image distortion depending on the values of the coefficients. ( See

Peticolas, F.A.P., R.J. Anderson and M.G. Kuhn, 1998, "Attacks on copyright marking

systems"; Cox. I.J., J. Kilian, T. Legithton and T. Shamoon, 1996, "Secure Spread

Spectrum Watermarking for Images, Audio and Video", Proc. International Conference

on Image Processing. ICIP '96. Vol. III. Pp. 243-246; Wolfgang, R.B. and E.J.

Delp, 1996, "A Watermarking for Digital Images", proceedings of the 1996 International Conference on image processing, Lausanne, Switzerland, vol.3, pp. 219-222; M. Ejima,

A. Miyazaki, and T. Saito, 1998, "Digital Watermark based on the Dyadic Wavelet Transform and its Robustness on Image Compression", Proceedings of ITC-CSSSS '98,

Sokcho, Korea, pp. 125-128).

The spread spectrum method which has become popular in recent years.

Here the watermark is spread over the audio or the digital image during the DCT

(discrete cosine transform) process based on the spread spectrum method. During this

process, the spectrum is analyzed and n number of high coefficients; that is, the important

portions of the spectrum are modified. This method is similar, in part, to the frequency

domain method. This method also utilizes the CDMA technique, in part, by spreading

the watermark broadly. Tthis method avoids impairment of the watermark somewhat in

the transform processes, that is, in JPEG, copying, scanning, scaling

compression/expansion processes. But this method causes the watermark to suffer in

the data compression stage, that is, the watermark is considerably impaired in the data

compression stage

Objects of the Invention

It is an object of the present invention to overcome the aforementioned

shortcomings of the prior art watermarking methods and systems.

It is another object of the present invention to provide an improved

watermarking method and system which makes it very difficult to erase or remove the

watermarks.

It is yet another object of the present invention to provide a watermarking method which preserves and maintains the integrity of the watermark as it undergoes

the image processing, such as image compression or cropping, dithering, color re- quantization or scaling compression and expansion, and the like..

It is yet another object of the invention to provide a watermarking method and

system wherein the original image being watermarked remain intact as the invisible

watermark is inserted into the original image.

It is still another object of the present invention to provide a method of digital

watermarking which is robust against data, compression and filtering.

It is a further object of the present invention to provide improved watermarking

method and system in color images.

It is yet another object of the present invention is to provide a method of digital

watermarking that is not affected by compression processes, such as JPEG or MPEG.

Summary of the Invention

The foregoing and other objects of the present invention are achieved by the

present invention based on the use of a unique combination of two algorithms, namely, a

wavelet transform(WT) and a discrete cosine transform(DCT). In accordance with the

present invention, a watermark is embedded into a digital image by using wavelet

transform and discrete cosine transform. The present inventive method is found to be

effective against impairment of the watermark that would otherwise be caused by the

image processing operations, such as compression, filtering and cropping.

The present invention comprises the steps of transforming the digital image

using wavelet transform(WT), transforming a watermark using discrete cosine

transform(DCT), integrating the wavelet-transformed digital image with the DCT-

transformed watermark to insert the watermark into the image, and generating the watermarked image using inverse wavelet transform. ( See Figs. 3 and 4)

In accordance with the present invention, a wavelet transform and a discrete

cosine transform are applied to watermarking black and white images and color images.

Brief Description of the Drawings

Figure 1 is a flow diagram showing discrete wavelet transform (WT) and inverse

discrete wavelet transform (IWT).

Figure 2 is a diagram showing the distribution of coefficients.

Figure 3 is a flow diagram showing an embodiment of watermarking using

wavelet transform and Discrete Cosine Transform (DCT).

Figure 4 is a flow diagram showing another embodiment of watermarking using

WT and DCT.

Figure 5 is a diagram showing a digital watermarking process of a color image

using WT and DCT..

Figure 6 is a flow diagram showing yet another embodiment of digital

watermarking of a color image using WT and DCT.

Detailed Description of the Invention - Black and White Image -

According to the present invention, a watermarking method is provided which

includes the following steps of transforming an original digital image using wavelet transform, transforming a black and white watermark using discrete cosine transform,

integrating the wavelet-transformed digital image with the DCT-transformed watermark,

and generating a watermark-embedded image. A conventional method of making a watermark involves use a PRN (Pseudo

Random Number) as a watermark to reduce the image distortion. In contrast, the present

invention embeds a watermark of a general image, in facilitating the generation of a

"mark.". The general image includes symbols such as photos, 2-D drawings, logo,

trademark, emblems, seal-marks, and other graphic symbols.

The present invention is implemented in the hardware environment using an IBM

PC Pentium MMX 166 and a scanner and in the software environment involving the use

of Visual C++, readily available on the market. It is to be understood that the present

inventive method can be implemented by computers made by various different

manufacturers with the use of softwares written in any appropriate language. .

In general, when a watermark is transformed, the original mark cannot be

recognized in the transform plane. If a watermark of an impulse form is used, the

transformed watermark is distributed over the entire transform plane. Fourier transform

may be used, but the resulting complex coefficients in the transform plane are not easily

combined with the image values.

In order to solve these problems, the present invention uses discrete cosing

transform(DCT) to transform a watermark. While DCT has a similar characteristic as

Fourier transform, DCT has an advantage of having only real values rather than complex

numbers in the case of Fourier transform. The mathematical definition and theory of

discrete cosine transform (DCT) are described below.

1. Discrete Cosine Transform (DCT)

DCT, having a close relationship with high speed FFT, is used to encode signals or images. DCT is widely used in the standard JPEG compression. One-dimensional

DCT is defined as follows:

[Equation la]

t(k) = c(k)Ys(n)cos^{π{2n + l)k}, ώ 2N

where s denotes the original coefficients, t denotes Ν number of transformed value, and c

denotes the coefficients given as:

[Equation lb]

c(0) = /N, c(k) = j2fN forl≤k≤N-l

As for a square matrix, two-dimension DCT is defined as follows:

[Equation 2a]

„. ,. ! , , π(2m + \)i π(2n + \)j t(j,j) = c(ι,j) __j 2 s(m,ri)oo% cos π=0 m=₀ 27V 27V

where Ν, s, and t denote the same as defined in the one-dimensional case, and c(i, j ) is

assigned as follows:

[Equation 2b]

c(0, ]) = -)-, c(/,0) = , c(i,j) = ~ fori≠OJ≠O

N N N

DCT can be inverse-transformed and can be defined for one-dimension and

two-dimensions as follows:

[Equation 3a]

s(n) =

[Equation 3 b] _t s(m,n) =

2. Discrete Wavelet Transform (DWT)

In the present invention, a digital image is wavelet transformed (WT) before

being integrated with a watermark transformed by DCT. Particularly, discrete wavelet

transform is used, as illustrated in Fig. 2, which selects a set of wavelet coefficients with

respect to scaling and transposition. Preferably, a filter bank that facilitates fast wavelet

transform, as illustrated schematically in Fig, 1, is used. The mathematical definitions and

theory of wavelet transform are described below.

While Fourier transform uses the sine and cosine functions as a basis function,

wavelet transform (WT) uses wavelets as a basis function. There are two types of

wavelet transform: continuous wavelet transform and discrete wavelet transform.

Continuous wavelet transform is defined as follows:

(Equation 4]

W(s, τ) = f(t) ψ(s, t)dt ^•: s : Scaling, τ : translation

Scaling is related to frequency. Low scaling, i.e., compressed wavelet, extracts

the high frequency components while high scaling, i.e., expanded wavelet, extracts the

low frequency components.

Continuous wavelet transform cannot be realized in practice because there are infinite number of wavelet coefficients as a function of scaling and position translation.

Thus, a more effective algorithm results, if discrete wavelet transform selecting certain

number of subsets is used, as schematically illustrated in Fig, 2. However, since the discrete wavelet transform imposes a computational burden, it is preferable to use a filter

bank realizing high-speed wavelet transform, as illustrated in Fig. 1. This method

utilizes the classical 2-channel sub-band coding and the pyramid algorithm.

Now the present invention of watermarking a digital image in black and white

using wavelet transform (WT) and discrete cosine transform (DCT) will be described in

detail with reference to the drawings. Referring to Fig. 3, which is illustrative flow

diagram of an embodiment of the present, the watermarking method includes the

following steps:

1), transforming an original (target) image D(x) in black and white using wavelet

transform(WT);

2), transforming watermark data W(y) in black and white using discrete cosine

transform (DCT);

3), integrating the wavelet transformed image DW(x) with DCT-transformed

watermark WC(y);

4), generating D(x)' by transforming the integrated image DW(x)' using inverse

wavelet transform; and

5), generating a watermark-embedded image D(x)'.

A variation of the present inventive watermarking method is shown

schematically in a flow chart in Fig. 4. According to this variation, the watermarking

method includes the following steps of:

1), converting an original image D(x) in black and white;

2), transforming a watermark W(y) in black and white using DCT; 3), further transforming the DCT-transformed watermark WC(y) using m-level

discrete wavelet transform;

4), integrating the wavelet transformed image DW(x) with m-level wavelet-

transformed watermark WDC(y); and

5), generating a watermark-embedded image D(x)'.

When obtaining the image D(x)' integrated with a watermark W(y), a scaling

parameter α is used to adjust the spacing between the original image D(x) and the

watermark W(y). In accordance with the present invention, the following is used for

easy conversion.

[Equation 5]

D(x)' ,= D(x)_i + αW(y)_I

The software environment was provided by the C code using Visual C++. An

IBM PC of Pentium class was used to perform necessary calculations. This specific

environment is merely illustrative

Performance Test of the Present Inventive Watermarking Method.

Extensive tests were conducted to test the robustness of the watermarks

embedded in accordance with the present invention against the JPEG compression,

filtering resampling and cropping and other steps to which the method is subjected.

Examples and results of the tests are summarized below. The final results were judged to

assess the strength of the present watermarking method by analyzing the watermark

before the extraction (W) and after the extraction (W) using correlation analysis. The

correlation is defined as follows: [Equation 6]

C(Correlation)

Example 1 : Evaluation of watermark preservation after lossy compression of images

In general, images are compressed before being transmitted because

uncompressed files such as a BMP file could be huge in size. Image compressions may

be classified into lossy compressions and lossless compressions Lossy compressions

are widely used due to its high compression ratio despite minor degradation of the

original image. JPEG is a representative example of a lossy compression As

mentioned above, since watermarks should be preserved after image processing, a

watermarking method is commercially usable if no problem occurs after a lossy

compression

Accordingly, an experiment was conducted to test the preservation strength of

watermarks by changing the Q factor of JPEG to 50%, 30%, 20%, and 10% As a

result, the watermark after 20% JPEG compression was clearly identified The

watermark after 10% JPEG compression was somewhat blurred, but was still visually

identifiable

Example 2. Effect on watermarks after filtering of images

Since images typically go through filtering to eliminate the noise, an experiment was conducted to find out the effect on watermarks after a low-pass filter and a median

filter images The test confirmed that the watermarks could be successfully extracted

The correlation of watermarks extracted is shown in Table 1 Table 1.

The result shows that the watermarks were not affected by filtering through the

low-pass and median filter.

Example 3 : Effect on a watermark after resampling

An experiment was conducted to test a watermark generated according to the

algorithm of the present invention after resampling, where resampling extinct the entire

pixel values of an image. The correlation of an extracted watermark after losses of 3

bits, 4 bits, and 5 bits is shown in Table 2.

Table 2.

The test shows that the extracted watermark could be clearly recognized after

resampling.

Example 4: Effect on a watermark after cropping of an image block

An experiment was conducted to measure how much of a watermark remains at

the center of an image, the most essential part. An image block of 192x192 was

cropped from the whole image, and the correlation was shown in

Table 3.

The result confirms that successful extraction of a watermark is possible after

cropping of an image block.

Example 5: Evaluation of the digital watermarking algorithm

The watermark image used in evaluating the digital watermarking algorithm was

an image with a particular letter Since the image has the form of an impulse, it is

expected that the values after DCT transform be widely distributed. This is a similar

result found in spread spectrum techniques. Uniformly distributed watermarks can be

generated by inverse wavelet transform of the DCT-transformed watermark. The

successful nature of the present invention was demonstrated by an example according to

the present invention showing the correlation of 99.85%) between the watermark with the

original image and by another example showing the correlation of 88.04%.

In summary, as shown above, the present invention of digital watermarking, using

wavelet transform and DCT has a superior effect of preserving watermarks after lossy

compression or other image processing. Especially, extraction of a watermark was

possible after lossy compression of JPEG using the Q factor of 50%o, 30%, 20%, and 10%>.

Extraction of watermarks was possible after the images were subject to low-pass filtering

or median filtering. Extraction of watermarks was also possible after resampling and

cropping. In short, the watermarking method according to the present invention which

uses a combination of the two algorithms, WT and DCT, is found superior to the

conventional known method which uses DCT or wavelet transform (WT) alone in various aspects and especially in terms of preservation of the watermarks and the image being watermarked. in the watermarking processes.

Detailed Description of the Invention - Color Image Watermarking

The present digital watermarking invention was used in watermarking color

images. The use of the wavelet transform (WT) and discrete cosine transform (DCT) in

watermarking color image will now be described in detail with reference to the Figs. 5

and 6.

Referring to Fig. 5, the method includes the following steps of :

1), converting the color image data in the RGB mode (RGB(x)) to Y(x), I(x); and

Q(x) in the YIQ mode;

2), transforming the Y(x) using wavelet transform;

3), transforming watermark data W(y) in black and white using discrete cosine

transform (DCT);

4), integrating the wavelet transformed color image DW(x) with DCT-transformed

watermark WC(y);

5), generating Y(x)' by transforming the integrated image DW(x)' using inverse

wavelet transformation; and

6), generating a watermark-embedded image RGB(x)' by converting the image in

the YIQ mode to that in the RGB mode.

Referring to Fig. 6, which shows an alternative schematic flow chart of

watermarking a color image, the method includes the following steps of:

1), converting the color image data in the RGB mode, RGB(x), to Y(x), I(x) and Q(x) in the YIQ mode;

2), transforming the Y(x) using I-level wavelet transform;

3), transforming watermark data W(y) in black and white using DCT;

4), further transforming the DCT-transformed watermark using m-level discrete

wavelet transformation.

5), integrating the wavelet transformed color image DW(x) with m-level wavelet-

transformed watermark WDC(y);

6), transforming the integrated image DW(x)' using inverse wavelet transform to

provide Y(x)'; and

7), generating a watermark-embedded image RGB(x)' by converting the image in the YIQ mode to that in the RGB mode.

When obtaining the color image RGB(x)' integrated with a watermark W(y), a

scaling parameter α is used to adjust the spacing between the original image RGB(x) and

the watermark W(y). The present invention uses the following for easy conversion.

[Equation 7]

RGB(x)' ,= RGB(x), + αW(y),

For conversion from the RGB mode to YIQ mode, the conversion matrix and

inverse conversion matrix are disclosed in the following literature. ( See Janes F. Blinn

"NTSC: Nice Technology, Superior Color", IEEE Computer Graphic & Applications,

March 1993, pp. 17-23; James F. Blinn "The World of Digital Video", IEEE Computer

Graphics & Applications, September 1992, pp. 106-112).

As mentioned above, the software was provided in the C code using Visual C++. An IBM PC of Pentium class was used to perform necessary calculations.

Experiments were conducted to test the robustness of the watermarks embedded

in accordance with the present invention against the JPEG compression, filtering and

cropping. The final results were judged to compare the strength of the watermarks

using correlation analysis. The correlation is defined as follows:

[Equation 8]

W(i,j) C(Correlatιon) = _{(i )} , _{WU )}

In general, color images are compressed before being transmitted because

be classified into lossy compressions and lossless compressions. Lossy compressions

are widely used due to its high compression ratio despite minor degradation of an original

image. JPEG is a representative example of a lossy compression. As mentioned above,

since watermarks should be preserved after image processing, a watermarking method is

commercially usable only if no problem occurs after a lossy compression.

Example 6: Evaluation of watermark preservation after lossy compression of color

images:

An experiment was conducted to test the preservation strength of watermarks by changing the Q factor of JPEG to 50%, 40%, 30%, and 20% 10%, and 5%. As a result,

the watermarks after up to 5% JPEG compression were visually identifiable.. The

correlation of the watermarks extracted from the watermark-embedded image compressed by JPEG is shown in Table 4.

Table 4.

Since color images typically go through filtering to eliminate the noise, an

experiment was conducted to find out the effect on watermarks after a low-pass filter and

a high-pass filter filter color images. The test confirmed that the watermarks could be

successfully extracted. The correlation of a watermarks extracted is shown in Table 5.

Table 5.

The result shows that the watermarks were not affected by the filtering though

low-pass and high-pass filer. The correlation was somewhat low, but this would not

pose a serious problem in extracting and recognizing a watermark.

Example 7: Extraction of a watermark after a color image is converted from the RGB

mode to YIQ mode

There are many color image modes being used, such as the RGB mode, the

CMY mode, the YIQ mode, and the HIS mode. An experiment was conducted to

extract watermarks and measure correlation of those color images changed from the RGB

mode to the YIQ mode The test shows that the extracted watermarks could be clearly recognized despite low correlation values compared to the conventional RGB mode.

Example 8: Effect on a watermark after cropping of an image block

An experiment was conducted to measure how much of a watermark remains at

the center of a color image, the most essential part. An image block of 192x192 was

truncated from the whole image, and the correlation was shown in Table 6.

Table 6.

The result confirmed that successful extraction of a watermark is possible after cropping

of an image block.

Example 9: Evaluation of the digital watermarking algorithm with a letter

The watermark image used in evaluating of the digital watermarking algorithm

was an image with a particular letter. Since the image has the form of an impulse, it is

expected that the values after DCT transform be widely distributed. This lead to a

similar result as spread spectrum. Uniformly distributed watermarks can be generated

by inverse wavelet transform of the DCT-transformed watermark.

In conclusion, as shown above, the present invention of digital watermarking

using wavelet transform (WT) and DCT has a superior ability of preserving watermarks

after lossy compression or other image processing of a color image. Watermarks were

preserved even after the color image was converted from the RGB mode into the YIQ

mode. Especially, extraction of a watermark was possible after lossy compression of JPEG using the Q factor of 50%, 40%, 30%, 20%, and 5%. Extraction of watermarks

was possible after the images were subject to low-pass filtering, high-pass filter, or image

cropping. Therefore, the present invention was proved to be suitable for watermarking

color images, which was not possible using the conventional techniques, as far as the

present inventors are concerned..

While the invention has been described with reference to preferred embodiments,

it is not intended to be limited to those embodiments. It will be appreciated by those of

ordinary skill in the art that many modifications can be made to the structure and form of

the described embodiments without departing from the spirit and scope of the invention,

which is defined and limited only in the following claims.

Claims

What is claimed is:

1. A method of watermarking a digital image, comprising the steps of:

transforming the digital image using a wavelet transform(WT);

transforming a watermark using discrete cosine transform(DCT), and

integrating the DCT-transformed watermark with the wavelet-transformed

image to generate a watermark-embedded image.

2. The method of claim 1, comprising the step of inverse wavelet transforming the

wavelet transformed image.

3. The method of claim 1, wherein the DCT-transformed watermark is further

transformed using m-level wavelet transform before being integrated with the wavelet-

transformed image.

4. The method of claim 3, wherein said wavelet transform is performed using a

filter bank realizing high-speed wavelet -transform

5. The method of claim 1, wherein said wavelet transform is performed using a

filter bank realizing high-speed wavelet -transform.

6. The method of claim 1, wherein in obtaining the image integrated with a watermark, a scaling parameter, alpha, is used to adjust the spacing between

the original image and the watermark.

7. The method of claim 1, wherein the digital image and the watermark are black

and white.

8. A system for watermarking a digital image comprising:

means for providing a digital image and a watermark, and

a digital processing system for transforming the digital image using wavelet

transform(WT), transforming the watermark using discrete cosine transform

(DCT)- and integrating the DCT-transformed watermark with the wavelet -

transformed image to generate a watermark-embeded image.

9. A system of claim 8, wherein the system includes means for carrying out digital

watermarking a black and white image using the wavelet transform(WT) and the discrete

cosine transform (DCT), wherein the watermark is black and white.

10. A system of claim 9, comprising means for providing an m-level wavelet

transform (WT) before it is integrated wavelet transformed image.

11. A system of claim 9, wherein the system includes filter-banks for providing

high-speed wavelet-transform and for providing inverse wavelet transform.

12. A method of digital watermarking a color image comprising the steps of; discrete cosine transform (DCT) transforming a watermark,

wavelet transform (WT) a color image, and

integrating the DCT-transformed watermark with wavelet transform (WT) color

image.

13. A method of claim 12, comprising the steps of:

converting the color image in the RGB mode, RGB(x), into Y(x), I(x), and Q(x)

in the YIQ mode using a conversion matrix,

14. A method of claim 13, comprising the steps of:

transforming Y(x) of the converted image using wavelet transform;

transforming a watermark, W(y), using discrete cosine transform(DCT);

integrating the DCT-transformed watermark, WC (y), with the wavelet-

transformed color image, DW (x);

generating Y- values of the integrated image, Y (x)', using inverse wavelet

transform; and

generating a watermark-embedded image in the RGB mode, RGB(x)', by

inverse transformation of Y(x)', I(x)', and Q(x)\

15. The method of claim 12, wherein the DCT-transformed watermark WC(y)) is

further transformed using m-level wavelet transform before being integrated with

the wavelet-transformed color image DW(x).

16. The method of claim 12, wherein said wavelet transform is performed using

filter-banks realizing high-speed wavelet-transform.

17. The method of claim 12, wherein said wavelet transform is performed using

filter-banks realizing high-speed wavelet-transform.

18. A system of digital watermarking a color image comprising:

means for providing a color image and a black and white watermark; and

a digital data processing means for digital watermarking the color image with the

black and white watermark using wavelet transformation(WT) and discrete

cosine transform (DCT).

19. A system according to Claim 18, comprising :

means for converting the color image in the RGB mode, RGB(x), into Y(x), I(x),

and Q(x) in the YIQ mode using a conversion matrix,

means for transforming Y(x) of the converted image using wavelet transform;

means for transforming the watermark in black and white, W(y), using DCT;

means for integrating the DCT-transformed watermark, WC (y), with the

wavelet-transformed color image, DW (x);

means for generating Y-values of the integrated image, Y (x)', using inverse

wavelet transform; and

means for generating a watermark-embedded image in the RGB mode, RGB(x)',

by inverse transformation of Y(x)\ I(x)', and Q(x)'.

0. A system of digital watermarking a color image, comprising :

means for converting the color image in the RGB mode, RGB(x), into Y(x), I(x),

and Q(x) in the YIQ mode using a conversion matrix,

means for transforming Y(x) of the converted image using wavelet transform;

means for transforming a watermark, W(y), using DCT;

means for further transforming the DCT-transformed watermark WC(y)) using

m-level wavelet transform;

means for integrating the DCT-transformed watermark, WC (y), with the

wavelet-transformed color image, DW (x);

means for generating Y- values of the integrated image, Y (x)', using inverse

wavelet transform; and

means for generating a watermark-embedded image in the RGB mode, RGB(x)',

by inverse transformation of Y(x)\ I(x)\ and Q(x)'.