Perceptual Watermarks for Perceptual Watermarks for Digital Image and VideoDigital Image and Video
ECE 738 paper ECE 738 paper
presentationpresentation
Pei QiPei QiECE at UW-MadisonECE at UW-Madison
[email protected]@cae.wisc.edu
What is ‘perceptual’ What is ‘perceptual’ watermarkwatermark
Prior knowledgePrior knowledge
Perceptual watermarkPerceptual watermark
Prior knowledgePrior knowledge
Additive watermarkAdditive watermark
Ideal watermarkIdeal watermark Three principlesThree principles
- Transparency or imperceptibility- Transparency or imperceptibility
- Robustness- Robustness
- Capacity- Capacity
Challenging problemChallenging problem
- Conflicts- Conflicts
- Tradeoff between transparency and - Tradeoff between transparency and
robustnessrobustness
Prior knowledgePrior knowledge
Human visual systemHuman visual system Three propertiesThree properties of the human visual system of the human visual system
1.1. Frequency sensitivityFrequency sensitivity
What’s freq. sensitivityWhat’s freq. sensitivity
Freq. sensitivity describes the human eye’s sensitivity to sine wave Freq. sensitivity describes the human eye’s sensitivity to sine wave gratings at various freq. Given that the minimum viewing distance is fixed, it’s gratings at various freq. Given that the minimum viewing distance is fixed, it’s possible to determine a static just noticeable difference threshold for each freq. possible to determine a static just noticeable difference threshold for each freq. band.band.
JND thresholdJND threshold
The JND threshold is such that changes in the frequency content in the The JND threshold is such that changes in the frequency content in the image in the particular frequency band below the threshold are not noticeableimage in the particular frequency band below the threshold are not noticeable
Prior knowledgePrior knowledge
Human visual systemHuman visual system Three propertiesThree properties of the human visual system of the human visual system
2.2. Luminance sensitivityLuminance sensitivity
What’s luminance sensitivityWhat’s luminance sensitivity
Luminance sensitivity measures the effects of the detectability threshold Luminance sensitivity measures the effects of the detectability threshold of noise on a constant background, which is a nonlinear function and depends of noise on a constant background, which is a nonlinear function and depends on local image characteristics.on local image characteristics.
3. Contrast masking3. Contrast masking
Contrast masking allows more dynamic control of the JND threshold Contrast masking allows more dynamic control of the JND threshold levels. Contrast masking refers to the detectability of one signal in the levels. Contrast masking refers to the detectability of one signal in the presence of another signal.presence of another signal.
Prior knowledgePrior knowledge
SummarySummary What is our goal to introduce human visual system in watermarking application?What is our goal to introduce human visual system in watermarking application?
1. 1. Determine if a watermark inserted into a image is invisible or not Determine if a watermark inserted into a image is invisible or not
2. We are always trying to insert the maximum strength and maximum length watermarks into an 2. We are always trying to insert the maximum strength and maximum length watermarks into an image, SINCE more watermarks are insertedimage, SINCE more watermarks are inserted
- more robust to attacks- more robust to attacks
- more likely to be detected- more likely to be detected
Make use of properties of human visual system to adjust the watermark so that it’s perfect for both Make use of properties of human visual system to adjust the watermark so that it’s perfect for both robustness and transparencyrobustness and transparency
JNDsJNDs
JNDs generated from different properties provide the quantized thresholds for embedding JNDs generated from different properties provide the quantized thresholds for embedding watermarks. watermarks.
- upper bounds on watermark strength levels- upper bounds on watermark strength levels
- upper bounds on watermark length (capacity)- upper bounds on watermark length (capacity)
Note: JND thresholds are NOT a fixed value, which depend on different images and approachesNote: JND thresholds are NOT a fixed value, which depend on different images and approaches
Perceptual watermark Perceptual watermark techniquestechniques
Image-Independent watermarkImage-Independent watermark
Image-dependent or Image-adaptive Image-dependent or Image-adaptive
watermarkwatermark
Image-Independent Image-Independent watermarkwatermark
A typical method (Cox approach)A typical method (Cox approach) Key pointsKey points
• Place watermark in perceptually significant components (low Place watermark in perceptually significant components (low frequency) (for robustness)frequency) (for robustness)
– Modify by a small amount below Just-noticeable-difference (JND)Modify by a small amount below Just-noticeable-difference (JND)
• Use long random vector as watermark to avoid artifactsUse long random vector as watermark to avoid artifacts
• Any difference if using other watermark instead (w-b images, logo)Any difference if using other watermark instead (w-b images, logo)(for imperceptibility & robustness)(for imperceptibility & robustness)
Embedding Embedding v’v’i i = v= vii + + v vi i wwii = v = vii (1+ (1+ w wii) )
• Perform DCT on entire image and embed watermark in DCT Perform DCT on entire image and embed watermark in DCT coefficientscoefficients
• Choose N=1000 largest AC coeff. and scale {vi} by a random factorChoose N=1000 largest AC coeff. and scale {vi} by a random factor DetectionDetection
Block diagram of Cox’s Block diagram of Cox’s schemescheme
2D DCT
sort v’=v (1+ w) IDCT & normalize
Original image
N largest coeff.
other coeff.
marked image
random vector generator
wmk
seed
ImplementationImplementation
Avoiding to change the corresponding location Avoiding to change the corresponding location of each coefficient in the image, when you sort the of each coefficient in the image, when you sort the vector projected from matrix of DCT coefficientsvector projected from matrix of DCT coefficients
Challenging problemChallenging problem
How to improve Cox approachHow to improve Cox approach• Global scaling factor is not suitable for all coefficientsGlobal scaling factor is not suitable for all coefficients
- Maybe beyond the threshold in some areas of image, especially - Maybe beyond the threshold in some areas of image, especially obvious in the smooth background areaobvious in the smooth background area
• More explicitly compute Just-noticeable-difference More explicitly compute Just-noticeable-difference
– JND ~ max amount each frequency coefficient can be JND ~ max amount each frequency coefficient can be modified imperceptiblymodified imperceptibly
– Use Use ii for each coefficients for each coefficients finely tune watermark strength finely tune watermark strength
• OverheadOverhead
- Cost of computation of thresholds for each coefficient- Cost of computation of thresholds for each coefficient
Image-dependent orImage-dependent orImage-adaptive Image-adaptive watermarkwatermark
Block-based DCT approachBlock-based DCT approach
Wavelet DWT approachWavelet DWT approach
Image-Adaptive Image-Adaptive watermarkwatermark
General Image-Adaptive watermark General Image-Adaptive watermark
schemescheme X*u,v : The watermarked image
Xu,v : The original image
Wu,v : The sequence of watermark values
Ju,v : The computed JND for each coefficient
Question:Question: Why Xu,v > Ju,v (from local image, considering properties of HVS)
otherwiseX
JifXwJXX
vu
vuvuvuvuvuvu
,
,,,,,*,
,
Block-based DCT approachBlock-based DCT approach
Nonoverlapping 8x8 blocksNonoverlapping 8x8 blocks DCT applied to each block independentlyDCT applied to each block independently XXu,v,bu,v,b: The DCT coefficients: The DCT coefficients
XX**u,v,bu,v,b: The watermarked DCT coefficients: The watermarked DCT coefficients
WWu,v,bu,v,b: The sequence of watermark values: The sequence of watermark values
ttCCu,v,bu,v,b: The computed JND calculated from the visual model: The computed JND calculated from the visual model
Key pointsKey points Block-by-block DCTBlock-by-block DCT
How to derive tHow to derive tCCu,v,bu,v,b
bvu
Cbvubvubvu
Cbvubvu
bvu X
tifXwtXX
,,
,,,,,,,,,,*,,
,
Block-based DCT approachBlock-based DCT approach
ttFFu,v u,v : a frequency threshold value, which is : a frequency threshold value, which is
an 8x8 matrix values for each DCT basis an 8x8 matrix values for each DCT basis functionfunction
ttLLu,v,bu,v,b : Luminance sensitivity estimated by : Luminance sensitivity estimated by
the formula.the formula.
XX0,0,b0,0,b: DC coeff. for block b: DC coeff. for block b
XX0,00,0: DC coeff. Corresponding to the : DC coeff. Corresponding to the
mean luminance of the displaymean luminance of the display
a: parameter controlling the degree of a: parameter controlling the degree of luminance sensitivity (empirical luminance sensitivity (empirical value=0.649)value=0.649)
ttCCu,v,b u,v,b :Contrast masking threshold, where w :Contrast masking threshold, where w
between 0 and 1, a empirical value for w between 0 and 1, a empirical value for w is 0.7is 0.7
abFvu
Lbvu
X
Xtt )(
0,0
,0,0,,,
])(,[ ,, 1,,,,,,,,
vuvu wLbvu
w
bvuL
bvuC
bvu tXtMaxt
Block diagram of IA-DCT Block diagram of IA-DCT approachapproach
CalculateJNDs
CalculateJNDs
WatermarkInsertion
WatermarkInsertionDCTDCT
Original image X(i,j) X(u,v)
Watermark sequence W(u,v)
Watermarked image X*(u,v)
J(u,v)
Wavelet DWT approachWavelet DWT approach
Key pointKey point Hierarchy DecompositionHierarchy Decomposition
The upper left corner: Lowest The upper left corner: Lowest
frequency band.frequency band.
l: resolution level 1, 2, 3, 4l: resolution level 1, 2, 3, 4
F: frequency orientation 1, 2, 3F: frequency orientation 1, 2, 3
Much simpler than DCT app.Much simpler than DCT app.
- Cost of computing JNDs- Cost of computing JNDs
Wavelet DWT approachWavelet DWT approach
XXu,v,l,fu,v,l,f : wavelet coefficient at position(u,v) in resolution level l and frequency : wavelet coefficient at position(u,v) in resolution level l and frequency
orientation forientation f
XX**u,v,l,fu,v,l,f : watermarked wavelet coefficient : watermarked wavelet coefficient
WWu,v,l,fu,v,l,f : watermark sequence : watermark sequence
ttFFl,fl,f : computed frequency weight at level l and frequency orientation f, which : computed frequency weight at level l and frequency orientation f, which
could be further refined by adding image-dependent components like DCT could be further refined by adding image-dependent components like DCT
approachapproach
flvu
Fflflvuflvu
Fflflvu
flvu X
tifXwtXX
,,,
,,,,,,,,,,,*,,,
,
DetectionDetection
Detection scheme for Block-based DCTDetection scheme for Block-based DCT 1. Based on classical detection theory as SS detection (Cox)1. Based on classical detection theory as SS detection (Cox)
- Original image is subtract from watermarked image and correlation between - Original image is subtract from watermarked image and correlation between
the signal difference and the watermark sequence is determinedthe signal difference and the watermark sequence is determined
- The correlation value is compared to a threshold to determine whether the - The correlation value is compared to a threshold to determine whether the
received image contains the watermark. received image contains the watermark.
Testing IA-DCT without original Testing IA-DCT without original imageimage
Key pointsKey points1.1. Assume original image has been Assume original image has been
JPEG compressedJPEG compressed
2.2. Feature vector {XFeature vector {Xff}, X}, XDD is greater is greater
than ½ of its corresponding than ½ of its corresponding
quantization table value Qquantization table value Q
3.3. W is only inserted in {XW is only inserted in {Xff}}
4.4. A correlation measure c is found A correlation measure c is found
between {Zbetween {Zff} and W} and W
5.5. A threshold test is performed on c to A threshold test is performed on c to
determine if the W under test is determine if the W under test is
present in Zpresent in Z
DetectionDetection
Detection for WaveletDetection for Wavelet
1. First, the correlation is performed 1. First, the correlation is performed
separately at each level separately at each level
2. Second, We calculate the average 2. Second, We calculate the average
for each resolution level l and freq. for each resolution level l and freq.
orientation forientation f
3. At last, we choose the maximum 3. At last, we choose the maximum
correlation value over all the possible correlation value over all the possible
levels as well as freq. locationslevels as well as freq. locations
ComparisonComparison
Image-Independent vs Image-AdaptiveImage-Independent vs Image-Adaptive
Image QualityImage Quality
All acceptable, but SS watermark is most visible in the smooth All acceptable, but SS watermark is most visible in the smooth
background area.background area.
Robustness to Compression and CroppingRobustness to Compression and Cropping
Winner: IA-WWinner: IA-W
Robustness to ScalingRobustness to Scaling
Winner: IA-W againWinner: IA-W again
Robustness to shiftRobustness to shift
Only IA-W survivesOnly IA-W survives
Video watermarksVideo watermarks
Unique requirements for watermarksUnique requirements for watermarks
Extension of the IA-DCT Technique to Extension of the IA-DCT Technique to
VideoVideo
Watermarking of MPEG-2Watermarking of MPEG-2
Scene-Adaptive Video WatermarkingScene-Adaptive Video Watermarking
Watermarking StandardsWatermarking Standards
Key points in paperKey points in paper
What’s the perceptual watermarkWhat’s the perceptual watermark
How does HVS work for watermark How does HVS work for watermark
applicationsapplications
Three typical watermarking techniquesThree typical watermarking techniques
PapersPapers
Perceptual Watermarks for Digital Image and Perceptual Watermarks for Digital Image and
videovideo RAYMOND B. WOLFGANGRAYMOND B. WOLFGANG
CHRISTINE I. PODILCHUK AND EDWARD J. DELPCHRISTINE I. PODILCHUK AND EDWARD J. DELP
Image-Adaptive Watermarking Using Visual Image-Adaptive Watermarking Using Visual
ModelsModels CHRISTINE I. PODILCHUK AND WENJUN ZENGCHRISTINE I. PODILCHUK AND WENJUN ZENG
Thank you for your Thank you for your attentionattention
PPT file and papers can be downloaded from PPT file and papers can be downloaded from
websitewebsite
http://www.cae.wisc.edu/~pqi/ece738/presentation/http://www.cae.wisc.edu/~pqi/ece738/presentation/
Contact info:Contact info:
Name: Qi, Pei Email: [email protected]: Qi, Pei Email: [email protected]
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