Digital Image Watermarking Er-Hsien Fu EE381K-15280 Student Presentation
Dec 24, 2015
Digital Image Watermarking
Er-Hsien Fu
EE381K-15280
Student Presentation
Overview• Introduction
• Background
Watermark Properties
Embedding
Detection
• The Project
Introduction
Embedding
Detection
• Conclusions
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
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]
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
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
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
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
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
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
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
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
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%
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
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
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
Questions