Pulse or digital communications – Spread spectrum
Reexamination Certificate
1998-07-09
2001-05-29
Tse, Young T. (Department: 2734)
Pulse or digital communications
Spread spectrum
C380S001000, C382S248000
Reexamination Certificate
active
06240121
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a watermark data insertion method for inserting watermark data into a digitalized signal representing images, sounds, and/or the like to indicate their copyrights, and a watermark data detection method for detecting inserted watermark data.
2. Description of the Related Art
Techniques for inserting watermark data into a digitalized signal representing images, sounds, and/or the like to indicate their copyrights having been vigorously studied and developed. Such watermark data is required to have minimum interference with the images and/or sounds of interest, be hardly visible (in the case of image data) and hardly audible (in the case of sound data), and yet be easily detected by a person knowing the detection method while preventing unauthorized removal of the watermark data by third parties. By using such watermark data, for example, infringement of a copyright (by illegal copying of images and/or sounds) by unauthorized third parties can be established or prevented.
One conventional method for inserting watermark data into an original signal representing images, sounds, and/or the like utilizes a spread spectrum technology. In principle, this method involves: multiplying the original signal representing images, sounds, and/or the like by random numbers to obtain a uniform spectrum; adding watermark data to the multiplied signal; and again multiplying the resultant signal with the same random numbers to restore the original signal. At the time of restoring the original signal, the added watermark data is also multiplied by the random numbers. As a result, the watermark data has a uniformly spread spectrum, i.e. becomes white noise, in the restored original signal.
FIG. 7
is a block diagram illustrating the structure of a conventional watermark data insertion apparatus utilizing a spread spectrum technology. As shown in
FIG. 7
, an original signal al (into which watermark data x
i
is to be inserted) is input to a multiplier
52
, where it is multiplied by predetermined pseudo random numbers to become a
i
×c
i
. Since the pseudo random numbers c
i
are a random sequence of +1 and −1, the frequency spectrum of a
i
×c
i
becomes uniform.
Next, the watermark data x
i
is input to an adder
53
to be added to a DC component of the above multiplication product a
i
×c
i
. Although not shown, the adder
53
includes a cascade connection of a Fourier transformer, an adder, and an inverse Fourier transformer for extracting a DC component of an input signal.
The signal a
i
×c
i
+x
i
(i.e., the randomized original signal plus the watermark data) is input to a multiplier
54
, where it is again multiplied by the same pseudo random numbers to give a
i
×c
i
2
+x
i
×c
i
. Since the pseudo random numbers are +1 or −1, c
i
2
equals 1. Therefore, a signal having a value of a
i
+x
i
×c
i
(=a
i
×c
i
2
+X
i
×c
i
) is obtained, i.e., a signal with embedded watermark data.
FIG. 8
is a block diagram illustrating the structure of a conventional watermark data detection apparatus utilizing a spread spectrum technology for detecting embedded watermark data. As shown in
FIG. 8
, a signal with embedded watermark data a
i
+x
i
×c
i
is input to a multiplier
62
, where it is multiplied by predetermined pseudo random numbers to become a
i
×c
i
+x
i
×c
i
2
=a
i
×c
i
+x
i
. Since the pseudo random numbers ci are a uniform random sequence of +1 and −1, the DC component of a
i
×c
i
becomes zero, so that only the watermark data x
i
is extracted by an extractor
63
. The extractor
63
includes a Fourier transformer for extracting a DC component of an input signal.
The above-described technique is reported in “Watermark data signature method for images utilizing PN series”, Electronic Information Communication Society, “Encryption and Information Security Symposium” proceedings, SCIS '97-26B, 1997.
However, the above-described conventional technique has a disadvantage in that the watermark data may become noticeable where the original signal has a small amplitude because the watermark data is inserted into the original signal in a uniform manner, i.e., regardless of the characteristics of the original signal. There is also a disadvantage in that, if the amplitude of the watermark data is decreased in order to prevent the watermark data from becoming noticeable, the watermark data may be masked by the original signal and therefore difficult to detect. Furthermore, unauthorized third parties can make the watermark data impossible to detect by intentionally adding noise or the like to the original signal.
SUMMARY OF THE INVENTION
A watermark data insertion method for inserting watermark data into an input original signal according to the present invention includes: a frequency transform step for applying a frequency transform to the original signal to form an intermediate signal; a watermark data insertion step for inserting the watermark data into a first set of frequency components of the intermediate signal; and a frequency inverse transform step for applying an inverse frequency transform to the intermediate signal, the watermark data having been inserted into the intermediate signal, thereby obtaining a signal containing the watermark data embedded therein, wherein the watermark data insertion step includes: determining, based on pseudo random numbers, the first set of frequency components of the intermediate signal into which the watermark data is inserted; and using a second set of frequency components of the intermediate signal as a reference signal, the watermark data not being inserted into the second set of frequency components.
In one embodiment of the invention, the frequency transform applied in the frequency transform step is a wavelet transform, and the inverse frequency transform applied in the frequency inverse transform step is an inverse wavelet transform.
In another embodiment of the invention, the watermark data insertion step includes: a weighting step for increasing or decreasing a signal amplitude of the watermark data in accordance with an amplitude of the first set of frequency components of the intermediate signal into which the watermark data is inserted.
In still another embodiment of the invention, the watermark data insertion step includes determining the first set of frequency components of the intermediate signal into which the watermark data is inserted by using pseudo random numbers having frequency-dependent weights.
In still another embodiment of the invention, the watermark data insertion step includes: a weighting step for increasing or decreasing a signal amplitude of the watermark data in accordance with a frequency of the first set of frequency components of the intermediate signal into which the watermark data is inserted.
In still another embodiment of the invention, the watermark data insertion step includes converting binary data representing the watermark data into predetermined positive and negative values, and thereafter inserting the converted binary data into the first set of frequency components of the intermediate signal.
Alternatively, the watermark data insertion method for inserting watermark data into an input original signal according to the present invention includes: determining a position at which the watermark data is to be inserted in accordance with pseudo random numbers which have been subjected to an inverse transform; subjecting the watermark data to an inverse transform; increasing or decreasing a signal amplitude of the inverse-transformed watermark data in accordance with an amplitude of the original signal; and inserting the inverse-transformed watermark data with the increased or decreased signal amplitude into the original signal.
A watermark data detection method for detecting watermark data within a signal containing embedded watermark data according to the present invention in
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
Tse Young T.
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