DCT Domain Watermarking

UNDER THE GUIDANCE OF DR K.GIRIBABU

HEAD OF THE DEPARTMENT ECE

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

,0

)0,0(*)0,0(*

),(*),(),(

,1),(

• Effects of the JPEG quantization table are also considered

EMBEDDING BLOCK DIAGRAM

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EXTRACTION BLOCK DIAGRAM

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