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Digital Image Watermarking
Er-Hsien Fu
EE381K-15280
Student Presentation
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Overview• Introduction
• Background
Watermark Properties
Embedding
Detection
• The Project
Introduction
Embedding
Detection
• Conclusions
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Introduction
• Watermark--an invisible signature embedded inside an image to show authenticity or proof of ownership
• Discourage unauthorized copying and distribution of images over the internet
• Ensure a digital picture has not been altered• Software can be used to search for a specific
watermark
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BackgroundWatermark Properties
• Watermark should appear random, noise-like sequence
• Appear Undetectable
• Good Correlation Properties
High correlation with signals similar to watermark
Low correlation with other watermarks or random noise
• Common sequences
A) Normal distribution
B) m-sequences
W=[1 0 0 1 0 0 1 1 0 1 1 1 0 1 0 0 1 1 1 1 0 1 0 0 0]
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Project: Introduction
•Possible for watermark to be binary sequence•Error-correction coding techniques•Use convolutional codes•Decode by Viterbi algorithm •Compare with non-coding method•See if it improves watermark detection •More or less robust to attacks? Additive noise, JPEG Compression, Rescale, Unzign•Performance assessed by correlation coefficient
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Watermark Embedding
Watermark Original Image Watermarked image
•Watermark placed into information content of Original Image to create Watermarked Image •Image Content Spatial Domain (Least Significant Bit) FFT - Magnitude and Phase Wavelet Transforms DCT Coefficients
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Setup-Watermark Embedding
Image1000 Highest Coeff
ConvCode
DCT
Inter-leave
Water-mark
Water-markedImage
IDCT
•DC Component Excluded for 1000 Highest Coefficients•Interleaving prevents burst errors•Watermarked Image Similar to original image•Without coding, ignore Conv Code and Interleave block
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Original Image Watermarked Image, No Coding
Watermarked Image with Coding
•512x512 “Mandrill” Image•See Handout •Both watermarks imperceptible•Alterations to original image difficult to notice
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Watermark Detection
* =
Suspected Image ExtractedWatermark
Original Watermark
Correlation
•Watermark Extracted from Suspected Image•Compute correlation of Extracted and Original Watermark•Threshold correlation to determine watermark existence
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Watermark Detection
CorruptedImage
OriginalImage
Extracted Watermark
Owner’swatermark
CorrelationCoefficient
1000 HighestDCT Coeff
Deinterleave,Viterbi Decode
•For no coding, deinterleave and decode block ignored=E[W1*W2]/{ E[W12]E[W22]}•If W1=W2 then =1•if W1 and W2 are independent, then =0 if E[W1]=0•Corruptions are additive noise, JPEG CompressionImage scaling, and UnZign
W2
W1
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Convolutional Codes
Input=[...1011010101100000000]G0 = [1 1 1 1 0 1 0 1 1]G1 = [1 0 1 1 1 0 0 0 1]
C0
C1
•Output C0 = conv(G0,Input); Output C1=conv(G1,Input)•Convolutional code implemented using linear shift registers•Adds redundancy for error-correction•Encoding/Decoding well researched•Good coding performance, very popular
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Viterbi Decoding0123
State
…………
•Find most likely path through trellis
•Begin and end at all zero state
•Upper arrows => input=0, Lower arrow =>input=1
•Every possible input/output combination is compared with the received output
•Optimal Decoding Method
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With Coding:Additive Noise (0,900)
No Coding:Additive Noise(0,900)
•Zero mean additive noise, variance=100, 400, 900•Both methods had high correlation•Coding method performed slightly better•For variance = 900 (no coding) = 77%p (coding) = 84%
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4:1 JPEG Compression,No coding
4:1 JPEG CompressionWith Coding
•JPEG Compression: 1.4:1, 2.2:1, 4:1 ratio•Both methods resistant to JPEG compression•Coding method outperformed non-coding method•Perfect detection for coding method
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Watermark removal using Unzign Convert to grayscale and resize
•Unzign--watermark removal software•Image resized to 512x512 and convert to grayscale before detection•Moderate detection for without coding:(no coding) = 57%(coding) = 23%•Coding method sensitive to resizing
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Conclusions
•Convolutional coding more immune to additive noise andJPEG Compression•Coding method fragile w.r.t. rescaled images•Moderate detection levels for unzigned images•Further Suggestion:Try block DCTUse Wavelet TransformExploit Human Visual System
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Questions