dct domain watermarking
DESCRIPTION
DCT Watermaring, Image processingTRANSCRIPT
A GENERIC IMAGE WATERMARKING SYSTEM
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Requirements Invisibility Robustness No ambiguity
Watermark
EmbeddingDistortions•Image processing•Compression•…...
ExtractionWatermark
Comparison
ADVANTAGES OF THIS SCHEME Advantages:
Semantically meaningful watermark pattern Good perceptual invisibility Acceptable robustness Various user-selected options Reasonable complexity/execution time
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SYSTEM OVERVIEW
Watermarks are randomly permuted to spread their spatial relationship, and then embedded in the DCT domain of the host image, with consideration of invisibility/robustness
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BLOCK DIAGRAMS OF THE ORIGINAL ALGORITHM
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Original Image
FDCT
Embedding(Polarity Reversing)
IDCT
Watermark Image
Pseudo-random Permutation
Block-based Mapping
Watermarked Image
BLOCK DIAGRAMS OF THE ORIGINAL ALGORITHM
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Original Image
FDCT
Suspected Image
FDCT
Extract the Permutated Data (XOR)
Reverse Block-based Permutation
Reverse Pseudo-random Permutation
Extracted Watermark
BLOCK DCT/IDCT
Advantages Fast Suitable for robustness against JPEG
compression Disadvantages
Block effect Effect of picture cropping
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SEMANTIC MEANINGFUL WATERMARKS
Watermarks can be verified with naked eyes by understanding the semantics of the extracted watermark patterns
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The seal of CML (in Chinese characters)
PSEUDO-RANDOM PERMUTATION
A n-bit Linear Feedback Shift Register (LFSR) is used to generate the maximal length (2n-1) sequence
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+
The 14-bit Shift Register thatpermutes 1-16384
Original Watermark
Permuted Watermark
BLOCK-BASED MAPPING
Watermark blocks with more signal pixels are embedded into image blocks with higher variances to achieve better perceptual invisibility.
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EMBEDDING(1/2)
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Choices of embedding positions within each block: Low-frequency
Bad invisibility High-frequency
Bad robustness=> Middle-frequency
Fix positions in each block
0 1 5 6 14 15 27 282 4 7 13 16 26 29 423 8 12 17 25 30 41 439 11 18 24 31 40 44 5310 19 23 32 39 45 52 5420 22 33 38 46 51 55 6021 34 37 47 50 56 59 6135 36 48 49 57 58 62 63
Embedding 4 watermark pixels
EMBEDDING(2/2) Polarity: the inequality relations between the scaled
DC value and the selected AC coefficients
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otherwise
QQrScaleFacto
DCjiQ
jiQjiAC
ifjiP
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)0,0(*)0,0(*
),(*),(),(
,1),(
• Effects of the JPEG quantization table are also considered