Electrical computers and digital processing systems: support – Multiple computer communication using cryptography – Particular communication authentication technique
Reexamination Certificate
1999-04-08
2004-11-23
Barrón, Gilberto (Department: 2132)
Electrical computers and digital processing systems: support
Multiple computer communication using cryptography
Particular communication authentication technique
C380S038000, C380S054000
Reexamination Certificate
active
06823455
ABSTRACT:
BACKGROUND
1. Field
The present invention relates to the field of digital watermarking.
2. General Background
Each day, consumers receive information from content providers in a variety of forms such as movies or television programming. When transmitted in a standard analog format, the information is somewhat protected due to its inherent analog nature. For example, a recorded movie normally has poorer image quality than the original analog version.
Over the last few years, there has been a growing demand for digital content. In general, “digital content” is data that is perceived during display or playback (e.g., a still image, video, text, audio, programs, etc.). Unlike analog, digital content can be easily copied or manipulated without affecting its perceived quality. This “quality” may be measured through visual clarity during display, audible clarity during audio playback, accuracy of characters in text or code as well as other factors. Since digital content can be easily manipulated, content providers have been hesitant in providing premier digital content due to the absence of any mechanism to protect the content against illegal copying and/or distribution.
Recently, digital watermarking has emerged as a technique to protect against unauthorized copying and distribution of digital content. More specifically, “digital watermarking” comprises an act of inserting information (referred to as a “watermark”) into content either in a spatial domain or in a compressed domain. The insertion of a watermark may be performed in an unobtrusive way so that the quality of the content is not reduced. For example, an invisible watermark is inserted into content in the spatial domain by adding or subtracting small numbers from pixel values. When watermarks are inserted into content in the compressed domain, however, values are added or subtracted from transform coefficients.
Digital watermarking further comprises the act of detecting and subsequently extracting a watermark from content, even if the content is altered with significant degradation. Conventional detection methods use a spread spectrum approach as set forth in equation (2). As denoted, “B
j
” is a signal with values of −1 or 1, where “j” refers to a particular signal bit, “S
i
” as a spread sequence of signal bit B
j
where “i” refers to a number (N) of pixels or blocks of pixels used to encode bit B
j
. “A
i
” is an amplitude factor, and R
i
is a pseudo-random number modulation sequence with a series of values being “−1” or “1”. The addition of watermark (W
i
) changes the intensity of an image from its normal intensity (I
i
) to its watermarked intensity (I
i
) as set forth in equation (1):
I
i
+W
i
=I
i
=S
i
A
i
R
i
(1)
Thus, as set forth in equation (2), B
j
can be detected by multiplying the watermarked pixels I
i
by R
i
.
B
j
=
sign
(
∑
i
=
1
N
I
i
′
R
i
)
=
sign
(
∑
i
=
1
N
I
i
R
i
+
∑
i
=
1
N
S
i
A
i
R
i
2
)
(
2
)
Thus, the value of the first term
∑
i
=
1
N
I
i
R
i
should approach zero when “N” (the number of encoded pixels) is large so that the sign of B
j
is equal to the sign of the second term
∑
i
=
1
N
S
i
A
i
R
i
2
.
Since, in practice,
∑
i
=
1
N
I
i
R
i
is not truly zero, B
j
is calculated as follows:
B
j
=
sign
(
∑
i
=
1
N
I
i
′
R
i
-
mean
(
I
i
′
)
×
∑
i
=
1
N
R
i
)
(
3
)
These conventional watermarking functions have the desired features of efficient detection, no requirement of original material for detection and little impact on compressibility. However, they do not address invisibility, high detection reliability and robustness. For example, a watermark can be kept invisible by determining an appropriate amplitude factor value. As set forth on pages 92-99 of a 1997 reference by Ingemar J. Cox and Matt L. Miller entitled “A Review of Watermarks and the Importance of Perceptual Modeling,” SPIE vol. 3016, one technique for determining the amplitude factor value is based on properties of the image such as its contrast and brightness. However, this technique does not account for watermarks that are invisible in still images but produce artifacts in video.
The conventional watermarking functions have an inherent weakness in that detection reliability is limited where the term
∑
i
=
1
N
I
i
R
i
dominates the term
∑
i
=
1
N
S
i
A
i
R
i
2
.
Normally, each individual I
i
R
i
product is about a factor of 100 larger than each S
i
A
i
R
i
2
product. Thus, if N is not sufficiently large so that the I
i
R
i
product approaches zero, a substantial percentage of the sign detection for B
j
will be incorrect. While proposals have been made to increase N to improve detection reliability, this would drastically increase the number of frames required for reliable detection.
It is now appreciated that conventional watermarking techniques do not fully address invisibility and security considerations. For example, a watermark invisible in a still image may produce visible artifacts in a video sequence when the sign of the watermark changes between adjacent frames. Also, watermarks produced from the same key may be detected when inserted into successive frames of the video sequence by averaging images found in successive frames.
Hence, it would be desirable to develop digital watermarking mechanisms supporting improved detection reliability through frame differences or image-dependent watermark generation.
SUMMARY OF THE INVENTION
Briefly, one embodiment of the invention relates to a method for improving detection of a watermark. The method comprises generating a pseudo-random sequence of numbers based on data associated with the data set, producing a watermark based on the pseudo-random number sequence, and embedding the watermark into the data set.
REFERENCES:
patent: 5768426 (1998-06-01), Rhoads
patent: 5905800 (1999-05-01), Moskowitz et al.
patent: 5949885 (1999-09-01), Leighton
patent: 5960081 (1999-09-01), Vynne et al.
patent: 6272634 (2001-08-01), Tewfik et al.
Holliman Matthew J.
Macy William W.
Yeung Minerva Ming-Yee
Barrón Gilberto
Blakely , Sokoloff, Taylor & Zafman LLP
Intel Corporation
Lanier Benjamin E.
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