Image analysis – Applications
Reexamination Certificate
1999-11-29
2004-06-29
Boudreau, Leo (Department: 2621)
Image analysis
Applications
C380S200000
Reexamination Certificate
active
06757405
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a digital watermark embedding device and a digital watermark detection device suited to protect a copyright and to control use of data on digital literary properties represented by images and the like by embedding into the data, information (to be referred to as ‘watermark information’ hereinafter), such as discrimination information on copyright owners and users of the data, information on the right of the copyright owners, conditions for using the data and confidential information necessary to use the data, in a state in which the watermark information is not easily perceived and then by detecting corresponding watermark information from data into which the watermark information is embedded at need.
In recent years, there is a growing interest in the copyright of digital literary properties such as an image (a static image, a dynamic image), voice data, music data, design data, CG (computer graphic) data and text data. As one of techniques for protecting the digital literary properties, there is known a digital watermark technique.
The digital watermark technique is mainly aimed to protect the copyright of the data and control use thereof by embedding, i.e., concealingly inputting into a digital literary property, watermark information (‘WM’ information) such as discrimination information on the copyright owner and users of the data, information on the right of the copyright owner, conditions for using the data and confidential information necessary to use the data, in a state in which the watermark information cannot be easily perceived.
For the purpose of this type, the digital watermark technique is required to satisfy, in particular, the following characteristics:
(1) Robustness Characteristics
Watermark information is difficult to remove from a literary property and to lose even by various data operations (filtering process, data compression/expansion, D/A conversion, A/D conversion and the like). If data is intentionally manipulated to remove the watermark information, data quality greatly deteriorates.
(2) Perceptual Invisibility Characteristics
The literary property into which watermark information is embedded is perceived similarly as the original literary property.
The digital watermark technique is also required to have embedding efficiency for efficiently embedding watermark information, detection efficiency for efficiently detecting watermark information and the like.
Now, as a typical method of embedding watermark information into, for example, image data by means of the digital watermark technique, there is known a method of converting image data into frequency domains and then embedding watermark information to a specific frequency component.
FIG. 1
is a block diagram showing the constitution of a conventional digital watermark embedding device
200
for embedding watermark information into the image data.
In the device
200
, orthogonal transform, such as DFT (discrete Fourier transform), DCT (discrete cosine transform), wavelet transform or Hadamard transform, is conducted to image data in pixel value domain which is a target for embedding of watermark information, by an orthogonal transform section
201
and frequency component value data forming image data in frequency domain is obtained.
Next, watermark (WM) information is embedded into a specific frequency component in the image data in frequency domain in the form of noise having a peak by a digital watermark embedding section
202
. The watermark information embedding is conducted in the digital watermark embedding section
202
as follows.
First, based on the frequency component data forming the image data in frequency domain, an embedding frequency component selection section
202
a
selects a frequency component suited for embedding of watermark information, e.g., a frequency component having a peak in case of embedding the above-stated watermark information as noise. The frequency component variation decision section
202
b
determines the variation of this frequency component value. The frequency component change section
202
c
changes the frequency component value forming the image data in frequency domain by a variation determined by the frequency component variation decision section
202
b
and thereby generates frequency component value data on the image into which the watermark information has been embedded.
Next, inverse transform of the orthogonal transform which has been conducted by the orthogonal transform section
201
, is conducted to the image data in frequency domain, into which watermark information has been embedded by the digital watermark embedding section
202
, by a reverse-orthogonal transform section
203
, to thereby obtain image data in pixel value domain into which watermark information has been embedded.
Thus, the watermark information embedded by the digital watermark device
200
shown in
FIG. 1
is embedded into the image data in pixel value domain in a state in which the watermark information is dispersed to the entire image and, therefore, robust against various operations. In addition, if the frequency component into which watermark information is embedded is the frequency component of an intermediate frequency or higher, the watermark information is not lost even by a low frequency pass filter which causes the loss of the LSB information of the image data.
With the constitution shown in
FIG. 1
, since it is necessary to perform orthogonal transformation twice by means of orthogonal transform, heavy load processing is required. Normally, therefore, an image is first divided into a plurality of blocks. For example, it is assumed that the number of pixels of a certain image in horizontal direction and vertical direction are W and H, respectively. The image is divided into a plurality of rectangular blocks each of which includes w and h pixels in horizontal and vertical directions, respectively. While a pixel positioned on upper-left end point in the image is set as an origin, the number of pixels is counted. If a pixel is in the x-th row and the y-th column, the position of the pixel is expressed as (x, y). If a certain pixel satisfies the following relationships: i×w≦x<(i+1)×w and h×h≦y<(j+i)×h, then it belongs to a block positioned in the i-th row in horizontal direction and the j-th column in vertical direction. All of or part of the blocks obtained by dividing the image are subjected to orthogonal transformation, respectively and watermark information is embedded into the blocks.
If orthogonal transform is used to embed watermark information, the quantity of embedding operation is the order of the square of a processed block size. As the block size is larger, the operation quantity considerably increases. Due to this, dedicated hardware is needed if watermark information is embedded into, for example, a dynamic image.
FIG. 2
is a block diagram showing the constitution of a conventional digital watermark detection device
210
for detecting corresponding watermark information from the image data into which watermark information has been embedded by the digital watermark embedding device
200
shown in FIG.
1
.
In the device
201
, image data in frequency domain is converted to frequency component value data forming image data in frequency domain by orthogonally transforming the image data in pixel value domain into which watermark information has been embedded by an orthogonal transform section
211
. Next, a digital watermark detection section
212
detects watermark information having a peak in a specific frequency component from the frequency component value data.
To embed watermark information into target data so that the watermark information is not likely to be lost by various operations, there is proposed a method for spreading and embedding watermark information into a wide range of data by the spread spectrum technique.
FIG. 3
is a block diagram showing the constitution of a conventional digital watermark embedding device
220
for embedding
Endo Naoki
Katoh Taku
Muratani Hirofumi
Boudreau Leo
Kabushiki Kaisha Toshiba
Lu Tom Y.
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