Image analysis – Applications
Reexamination Certificate
1999-09-02
2003-05-13
Patel, Jayanti K. (Department: 2625)
Image analysis
Applications
C235S469000
Reexamination Certificate
active
06563935
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital watermark technique for digital data, particularly image data.
2. Description of Related Art
Recently, from the viewpoint of copyright protection for digital data such as image data, etc., much attention is being paid to a digital watermark technique. The digital watermark technique is defined as a technique of embedding specific information into digital data according to a predetermined rule so that the specific information cannot be extracted from the digital data without using at least the predetermined rule. According to this technique, for example, information on a purchaser of image data, etc. is beforehand embedded in the image data itself according to the predetermined rule in such a manner that the information is not visible, and when the image data are illegally copied, the embedded information is extracted according to the predetermined rule from the data thus illegally copied to specify a person (purchaser) who illegally copies the data.
FIG. 18
is a diagram showing the principle of information embedding/extracting processing into/from image data on the basis of a conventional digital watermark technique.
With respect to the information embedding processing, as shown in
FIG. 18
, when a bit b
i
(0≦i≦n) of bits b
1
to b
n
constituting information to be embedded is equal to 1, the bright of each of pixel data located at predetermined positions 1 to m of the image data is increased by U, and when the bit b
i
is equal to zero, the brightness of each pixel data is reduced by U. This processing is carried out on all the bits b
1
to bwhile the embedding position is shifted, thereby embedding the digital watermark information in the image data.
With respect to the processing of extracting the digital watermark information thus embedded, for the bit b
i
(0≦i≦n) of bits b
1
to b
n
constituting the information thus embedded, the brightness sum S of all the pixel data located at the predetermined positions 1 to m of the image data and the brightness sum R (Reference value) of all the pixel data located adjacently to the predetermined positions 1 to m are detected. If S−R≧T (here, T is varied in accordance with a demanded error rate, and it is set to satisfy T≧U×(the number m of pixel data in which b
i
is embedded)), it is judged that b
i
is equal to 1. If S−R≦−T, it is judged that b
i
is equal to zero. If −T <S−R<T, it is judged that no information is embedded in each of the pixel data located at the predetermined positions 1 to m. This processing is carried out on all the bits b
1
to b
n
to extract the digital watermark information in the image data.
The digital watermark technique is described in more detail in Kobayashi, et al.: Data Hiding Based on Neighbor Pixels Statistics,
In Proc. of IPSJ
56
th Annual Conference,
1V-03, (1998).
When a geometrical deformation such as scale-up/scale-down or rotation is applied to image data in which digital watermark information as described above is embedded, the embedding positions of the bit data constituting the digital watermark information (the positions on the X-Y coordinate used when the bit data are embedded) are also deformed. Therefore, the digital watermark information cannot be extracted. A technique to overcome the above problem is disclosed in U.S. Pat. No. 5,636,292.
According to this technique, as shown in
FIG. 19
, a calibrating digital watermark for estimating what geometrical deformation is applied to the image data, that is, what scale-up/scale-down or rotation processing is applied to the image data in addition to the digital watermark information such as copyright information or the like, is beforehand embedded in the image data concerned. When the digital watermark information is extracted, the calibrating digital watermark information is extracted from the image data, and the degree of the deformation is analyzed, thereby estimating the scale-up/scale-down degree or the rotational angle applied to the image data concerned. Subsequently, the image data concerned are returned to the original image data (the image data before the geometrical deformation is applied) by referring to the sale-up/scale-up rate or the rotational angle thus estimated. Thereafter, the pixel data located at a predetermined position and the adjacent pixel data are extracted, and the differential value (S−R) therebetween is compared with a predetermined threshold value to extract the digital watermark information.
SUMMARY OF THE INVENTION
However, in the conventional method using the calibrating digital watermark as described above, not only digital watermark information such as copyright information, etc. which are to be originally embedded, but also a calibrating digital watermark are embedded in image data, and thus this method has a problem that a great effect is imposed on the image quality.
Therefore, a first object of the present invention is to provide a digital watermark technique which can specify a digital watermark information embedding position from geometrically-deformed image data without using any calibrating digital watermark.
Further, in the above conventional method of judging the bit value of the digital watermark information, for a bit b
i
(0≦i≦n) of bits b
1
to b
n
constituting digital watermark information, the brightness sum S of all the pixel data located at the predetermined positions 1 to m of the image data and the brightness sum R (Reference value) of all the pixel data located adjacently to the predetermined positions 1 to m are detected. If S−R≧T, it is judged that b
i
=1. If S−R≦−T, it is judged that b
i
=zero. If −T<S−R<T, it is judged that no information is embedded in each of the pixel data located at the predetermined positions 1 to m.
Here, a predetermined value is usually used as the threshold value T. However, when the threshold value T is not optimized to the image data from which the digital watermark information is extracted, −T<S−R<T is established although the bit b
i
constituting the digital watermark information is embedded to predetermined positions 1 to m of the image data, and thus it may be judged that no information is embedded in the predetermined positions 1 to m. That is, the extraction sensitivity of the bits constituting the digital watermark information is lowered.
On the other hand, if the extraction sensitivity of the bits constituting the digital watermark information is increased by setting the threshold value T to a lower value in advance, for some image data from which the digital watermark information is extracted, the bit value judgment error of the bits constituting the digital watermark information extracted from the image data is increased, so that the bit value judgment precision is degraded. Therefore, the bit value of the digital watermark information extracted from the image data cannot be relied on.
Therefore, a second object of the present invention is to provide a digital watermark technique which can grasp whether the bit value of digital watermark information extracted can be relied on even when the extraction sensitivity of the bits constituting the digital watermark information is increased.
In order to attain the first object, according to a first aspect of the present invention, a method of extracting digital watermark information from image data which has the digital watermark information embedded therein by altering at least one pixel data located at a predetermined position on a specific coordinate and is geometrically deformed, comprises an embedding position check step of executing the processing of extracting at least one pixel data at a predetermined position on the specific coordinate from the image data and comparing the data value thus extracted with a reference value to judge whether the information is embedded in the pixel data while applying the geometrical deformation on the image dat
Anzai Kousuke
Echizen Isao
Kurosu Yutaka
Yoshiura Hiroshi
Antonelli Terry Stout & Kraus LLP
Azarian Seyed
Hitachi , Ltd.
Patel Jayanti K.
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