Joint Optimization of Data Hiding and Video Compression

Jithendra K. Paruchuri & Sen-ching S. Cheung

Department of Electrical and Computer Engineering

Center for Visualization and Virtual Environments

University of Kentucky, Lexington, KY 40507

ISCAS - May 21, 2008

Overview

• Motivation and Problem• Data Hiding Framework• Rate-Distortion Optimized Data Hiding• Results• Conclusion & Future Work

www.vis.uky.edu | Dedicated to Research, Education and Industrial Outreach | 859.257.1257

• Smart video surveillance

• Biometric theft

• Mobile-media processing

• RFID tracking

Signal Privacy

Identity ObfuscationOriginal

Pixelation/Blurring

Black Box

Object Removal- Segmentation + Video In-painting[Venkatesh 06, 08]

Problem with Obfuscation

Police: Where were you 9am on Oct 1?

A: I was in my office.

Police: Do you have any proof?

A: ……

• Obfuscation destroys the authenticity• Original needed to legitimize the modification.• Accessed with proper authorization.

Privacy Data Preservation

• Separate Files or Meta-data• Cryptographic Scrambling [Boult05],

[Dufaux06]

• Data Hiding in DCT [Zhang05]

– Works with any obfuscation techniques– High capability and low distortion– Fragile embedding– Eight-fold increase in output bit-rate!

Data Hiding with Compression

Motion Compensation

DCTEntropyCoding

• DCT Domain• Frequency, contrast and luminance masking [Watson]

DCT PerceptualMask

ParityEmbedding

Last decodedframe

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Embedding & Perceptual Distortion

• To embed x in a quantized DCT coeff. c(i,j,k)

• Select coefficients to minimize distortion– Contrast masking

– Frequency masking

– Distortion

Causes of Bit-rate Explosion

• Disturbing the ‘favorable characteristics’ (zero blocks & long run-lengths) for entropy coding

• Data embedding inserts noise into motion compensation loop

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Proposed solution: Identify specific DCT coefficients for data hiding that minimizes both the output rate and distortion

Proposed solution: Identify specific DCT coefficients for data hiding that minimizes both the output rate and distortion

R-D optimized Data Hiding

Motion Compensation

DCTEntropyCoding

• DCT Domain• Frequency, contrast and luminance masking [Watson]

H.263 H.263

DCT PerceptualMask

ParityEmbedding

R-D Optimization

Positions of the “optimal’DCT coeff forembedding

Last decodedframe

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ParityEmbedding

Constrained Optimization

Let Rk(Mk) and Dk(Mk) be the rate and distortion after hiding Mk bits into the k-th DCT block. δ is a user-defined weight

Optimization Problem:

Calculations of Rk(Mk) and Dk(Mk)

• Two Issues:– Parity embedding depends on hidden data– Need to find optimal selection as well

• “Worst-case” embedding on previous frame

• Optimal selection– Dk(Mk) is additive (easy)– Rk(Mk) is not: Rk(N) and Rk(N+1) may use

very different coefficients

• Dynamic Programming

• Greedy Approximation– Pick next coefficient to minimize cost– Fast implementation

Dynamic Programming versus Greedy approach

EmbeddingK-th bit

EmbeddingK+1-st bit

i+1

i

i+2

i+1

i+2

i+3 i+3

Performance Comparison

• For CIF, Greedy needs 26 second/frame vs. DP needs 22 minutes/frame

Dual of the optimization• Lower bounded by unconstrained opt:

• Search λ to meet constraint – Start at 2nd order approximation of Ck(Mk)

• 3-5 seconds per one CIF frame

0 10 20 30 40 50 60 700

2

4

6

8

10

12

14

Nof of bits embedded

Dis

tort

ion

Distortion versus N for a DCT block in frame 1

Experiment 1: Hall Monitor

Hall Monitor (QP=10)

Weight δ

Rate In kbps

Perceptual Distortion

Rate Increase

Separate Files

119.5+81= 200.5 0 0%

0 328 21.65 63.8%

0.5 302 27 50.9%

1 287 102 43.4%

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Hall Monitor (QP=10)Original Distortion Optimized

Weight = 0.5 Rate Optimized

Surveillance Video

Surveillance (QP=10)

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Weight δ

Rate In kbps

Perceptual Distortion

Rate Increase

Separate Files

153.97+77.34 =231.31

0 0%

0 379.73 17.55 64.2%

0.5 359.76 21.58 55.5%

1 341.72 74.79 47.7%

Surveillance (QP=10)

Original

Distortion Optimized

Rate Optimized

Weight=0.5

Conclusions

• Privacy Data Preservation with Data Hiding• R-D Optimization Framework for Data Hiding• Current work

– Reversible Data Embedding: ICIP 2008– Privacy Data Management: ICIP 2008– Incorporate temporal dimension in perceptual and

rate model– Joint encryption and data hiding

www.vis.uky.edu | Dedicated to Research, Education and Industrial Outreach | 859.257.1257