Electrical computers and digital processing systems: support – Multiple computer communication using cryptography – Particular communication authentication technique
Reexamination Certificate
1998-09-01
2002-01-22
Peeso, Thomas R. (Department: 2132)
Electrical computers and digital processing systems: support
Multiple computer communication using cryptography
Particular communication authentication technique
C713S178000, C713S179000
Reexamination Certificate
active
06341350
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device and method for processing image data, a transmitting medium, and a recording medium. More particularly, the present invention relates to a device and method for processing image data, a transmitting medium, and a recording medium, in which a watermark is blocked, thereby the watermark can be certainly appended to coded image data and can be detected.
2. Description of the Related Art
There is existing a technology of appending some accompanying information associated with the image data into a particular image data (of a static image or a time-varying image sequence) and detecting the accompanying information when reproducing. A representative example thereof is appendage of information regarding the copyright.
In the case where there is a possibility that unspecified users can use particular image data, it is necessary to append information regarding the copyright of the image into the image data in order that a copyright holder of the image asserts his copyright. By appending copyright information in advance, it becomes possible to take measures such as disabling display of the image data when copyright information indicative of inhibiting display of the image data is detected during processing in an image reproducing apparatus or a data reproducing method.
The aforementioned appendage and detection of copyright information is currently much used for preventing the unauthorized copying of videotapes and the like. Recently, there are many video-rental shops lending videotapes. If many of users make an unauthorized duplication of the videotape lent from a video-rental shop at a low price and enjoy the duplicated recordings, economical damages of the copyright holders of the videotape and the video rental shops are significant.
Since image data is recorded on videotape in an analogue fashion, the quality of the copied image is more or less degraded. Accordingly, if such copying is repeated a plurality of times, maintaining the same image quality as the first copy is very difficult.
On the other hand, in a reproducing apparatus and the like which records and reproduces image data in a digital fashion, economical damages produced by the unauthorized copying becomes more serious. This is because that the image quality is not degraded fundamentally by copying in a device or the like that manipulates image data in a digital fashion. Therefore, prevention of the unauthorized duplication in a device or the like that employs digital fashion processing is much more important compared with an apparatus or the like performing the analogue fashion processing.
Mainly, there are two methods for appending accompanying information associated with image data into the image data.
In accordance with the first method, the accompanying information is appended to an auxiliary part of the image data. In videotape, for example, the auxiliary information of the image data is recorded at the top (auxiliary part) of the picture that is substantially invisible when viewed. It is possible to append the accompanying information by using a part of this area.
In accordance with the second method, the accompanying information is appended to a main part (substantially visible part) of the image data. This is done by appending a particular pattern (watermark pattern) to the whole or a part of the image to an invisible extent. An example thereof is spread spectrum communication in which information is appended or detected using a key pattern generated through the use of random numbers, a maximum length sequence, etc.
Hereinafter, a description will be made of one example of appendage of the accompanying information to a main part of image data or detection thereof when a watermark pattern is used.
FIG. 26
to
FIG. 29
show one embodiment thereof.
Here, it is assumed that a watermark pattern corresponding to 4n×4n pixels as shown in
FIG. 26
is used. Each pixel of the watermark pattern takes on a plus or minus symbol. It is desirable that the pixels take on either one of these two symbols at random, and the shape and size of the area may be optional.
For appending a watermark, an area having the same size as the watermark pattern area is selected from the image to be subjected to the appendage. The selected area is superimposed over the watermark pattern and compared therewith. Value “a” is added to each of pixels corresponding to the plus symbol, and value “b” is subtracted from each of pixels corresponding to the minus symbol. Both values “a” and “b” may be optional, but each of the values should be constant through the watermark pattern.
In the example shown in
FIG. 27
to
FIG. 29
, it is assumed that a=1 and b=1. When values of the pixels to be subjected to the appendage are all
100
as shown in
FIG. 27
, pixel values of
101
and
99
are generated by an embedding operation corresponding to the watermark.
For detecting a watermark, an area having the same size as the watermark pattern is area having the same size as the watermark pattern area is selected from the image that is to be subjected to the appendage. The value obtained by adding all the pixel values in this area is used as an evaluation value. For adding all the pixel values, the selected area is superimposed over and compared with the watermark pattern. Then each of the pixels corresponding to the plus symbol is subjected to addition and each of the pixels corresponding to the minus symbol is subjected to subtraction. In the example shown in
FIG. 28
, the pixels having a pixel value of
101
are subjected to addition while the pixels having a pixel value of
99
are subjected to subtraction, and all the results thereof are added. At this time, unless the same watermark pattern as that of used for appending the watermark is used, the watermark can not be detected properly. According to the aforementioned detection operation, the evaluation value when the watermark is appended becomes (4n)
2
(that is equal to the number of the pixels contained in the area) as shown in
FIG. 28
, and the evaluation value when the watermark is not appended becomes 0 as shown in FIG.
29
.
When the area of the watermark pattern is large enough and the watermark pattern is arranged in a sufficiently random fashion, the evaluation value when no watermark is appended always becomes about 0. Therefore, when the evaluation value exceeds a particular threshold value, it is determined that any watermark is appended. According to the procedure mentioned above, it becomes possible to append binary data (1 bit) indicating whether or not the watermark is appended. When much more information is desired to be appended, the entire image is divided into k areas and each of the areas is subjected to proper processing such as performing the foregoing operations, thereby 2
k
(k bit) piece of information can be appended.
For example, a watermark pattern generated through M-sequences may be used. The M-sequence (maximum length sequence) is a number sequence consisting of binary symbols of 0 or 1. The statistical distribution of 0's and 1's are homogeneous. A correlation code at zero point is 1, and the others are inversely proportional to a code length. It is of course that the watermark pattern may be used through the use of other method than that of using the M-sequence.
When recording and reproducing image data in a digital fashion, the image data is generally compressed since the information volume thereof becomes considerably abundant as it is. High-efficiency coding methods such as JPEG (Joint Photographic Experts Group) (color still-picture coding method), MPEG (Moving Picture experts Group) (color moving-picture coding method) and the like are standardized internationally as the image data compressing methods and put to practical use. Next, a description will be made of a configuration example of appending and detecting the accompanying information, taking the case of compressing image data in accordance with this high-efficiency coding.
FIG. 30
Miyahara Nobuyoshi
Yagasaki Yoichi
Frommer William S.
Frommer & Lawrence & Haug LLP
Peeso Thomas R.
Simon Darren M.
Sony Corporation
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