Image and Video Watermarking - Institut Teknologi Bandunginformatika.stei.itb.ac.id/~rinaldi.munir/Kriptografi/buchner.pdf · – Steganography • ... in host signal: –Image ...

Image and VideoWatermarking

Herbert BuchnerUniversity of Erlangen-Nuremberg

16.12.1998

Telecommunications Seminar WS 1998

“Data Hiding, Digital Watermarking and Secure Communications”

2H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Outline

1. Introduction: Watermarking of Visual Data2. Some Approaches for Image Data

• Spread spectrum concept• Image adaptive schemes• Robustness to geometric distortions

3. Watermarking of Video Data• Uncompressed video• Compressed video

4. Conclusions

3H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

1.Watermarking of Images and Video

• Data embedding / datahiding

– Watermarking

– Steganography

• ... in host signal:

– Image

– Video

– Audio

– Formatted text

– ...

4H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

General Requirements

• Invisibility for the human visual system (HVS)

• Robustness to intentional and unintentionalattacks:– Lossy compression schemes (JPEG, MPEG,...)– Linear and nonlinear filtering– Geometric distortions (scaling, cropping, rotation...)– Collusion– ...

• Security

5H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Building a Watermark I

consists of two parts:

INSERTIONSTRATEGY

Where in the host signalshall we place theinformation?

WATERMARKSTRUCTURE

How shall we place theadditional information intothe signal?

in order to comply with the requirements

6H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Building a Watermark II

➨ Basic principle of all approaches for dataembedding: exploitation of the limitations of the HVS:

• Minimum intensity or contrast sensitivity

spatialfreq.• ‘Masking’ phenomena:

- spatial masking

- temporal masking

- freq. masking

☞ Note: framework has no general optimum solution !

spatialfreq.

contrastmin.

7H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

2. Some Approaches for Image Data

LSB-type methods - one of the simplest concepts for dataembedding in noise-free environments.

➪ LSBs of the image are replaced by other data bits.

• Embedded data invisible (LSBs=least perceptible bits!)

original bit plane 8 bit plane 5 bit plane 4 bit plane 1

• INSECURE: it is known where the information bits are

• NOT ROBUST: since changes of LSBs invisible !

8H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Spread Spectrum Concept I

Spread spectrum approach in the spatial domain (1D watermark)

+

scalarfactor

Embedding:

image (line-scanned)

spreading

PN seq.(secret key)

PN seq.(secret key)

Retrieval:

Σ sign

recoveredinformationbits (+1/-1)

informationbits

Water-markedimage

1

-1

1

-1

inform. bits spread seq.

➾crcr cr cr cr

Matched filter:

Original image notnecessary forwatermark retrieval.

Greater robustness: How to imperceptibly insert a watermark intoperceptually significant portions of the image?

9H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Spread Spectrum Concept II

Extension: 2D watermark in the spatial domain (by Kutter)

+

scalarfactor α

image

set of orthogonal, non-overlapping 2D sequences Φi(secret key)

informationbits bi

Water-markedimage

Σ

w x y x y b x yii

N

i( , ) ( , ) ( , )==∑α

1

Φwatermark

10H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Spread Spectrum Concept III

Watermarking in frequency domain increases robustness

• Robustness to cropping: watermark spread over whole spatial extent

• Lossy compression (JPEG) usually eliminates non-salient spectral comp.

• Shrinking leads to loss in HF components only

DCT IDCT+

scalar factor (->HVS/ robustness)

image watermarkedimage

watermark (chosen according to normal distribution)

Watermark embedded in largest magnitude DCT coefficients(>1000 coeff. recommended) ➩ frequency spreading !

Approach by Cox et al .:

11H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Spread Spectrum Concept IV

DCT +

Extraction of the watermark (Cox et al.)

DCT

(possibly)watermarkedimage

similiar?

Original image

extractedwatermark X

originalwatermark X0

y/n

• Very reliable (robust to JPEG encoding, dithering, clipping withJPEG encoding, averaging of separately watermarked images, and combination of printing, photocopying, subsequent rescanningand rescaling)

• Major drawback: watermarked and original images necessary!

Properties of the method:

-

12H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Image Adaptive Schemes I

Simple example in spatial domain: image adaptiveseparation in histogram (by Langelaar et al .):

• Select (secret key 1 ) one 8x8 block B of the image

• Create a low quality copy of the block (preventive simulation of JPEG image to increase the robustness!):

• Create a binary 8x8 pseudo-random pattern (secret key 2 ) PN:

DCT IDCTQoriginal8x8 blockB

low quality8x8 blockb

“stencil”

Can make explicit use of characteristics of the image and/or HVS.

13H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Image Adaptive Schemes II

Watermarking procedure for each bit:

Calc. mean Io (I1) of luminance values in B, where PN is 0 (1)

Difference of means: ∆:=I1-I0Similar procedure for low quality image b: δ:=i1-i0

bit toembed

∆<0ANDδ<0 ?

∆>TANDδ>T ?

B←B-PN B←B+PN

‘0’ ‘1’

no no

Process next 8x8 block

yesyes

PN

BI1I0

10

BB I1I0I0

I1

14H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Robustness to Geometric Distortions

Two different types of approaches possible:

• Watermarking in a transformation invariant domain (e.g.magnitude of Fourier transform is shift invariant)

• Embedding some additional hidden grid to determineand invert the distortion before watermark retrieval

Method by Kutter: multiple embedding at shifted locations

Method allows watermark recovery after translation, cropping, scaling,rotation, shearing, change of aspect ratio

watermarked image autocorrelation funct. extracted peaks

15H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

3. Watermarking of Video Data

Main differences to imagewatermarking:

• Much higher volume of data(bandwidth)

• Real-time embedding

Possible requirements (in addition to those of still image watermarking):

• Constant bit-rate (with/without watermark)

• Low complexity

• Compressed domain processing

• Interoperability

illegalcopy

....

DigitalLibrary

mark 1

mark 2

mark 3

Fingerprinting:

16H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Watermarking of Uncompressed Video

• If real-time embedding is not required: uncompressedvideo can be watermarked frame by frame using theconventional methods for still images

• One watermark bit can be distributed over several video frames to increase robustness

17H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Hybrid Coding Schemes I

(MPEG, H.261, H.263)Basic principles:

• Block-based transform coding (DCT)

• Motion compensated prediction

DCTzig-zagscan

Q

Intra-coded frames (‘I-frames’)

8x8 block offrame

run-levelcoding

entropycoding

Inter-coded frames (‘P-frames’, ‘B-frames’)Residual prediction error signal frames are used

➩ ‘Group of pictures’: I B B P B B P B B I B . . .pred. / interpol.

prediction

bitstream

DCT coeff.threshold

18H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Hybrid Coding Schemes II

DCT+Video in

Simplified Block Diagram of a Generic Hybrid Coding Scheme:

Q

Codingcontrol

VLC

intraframedecoder

+Motion compen-sated predictor

motion vectors

intraframeDCT coder

bit streamout

Intra

inter

-

19H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Watermarking of Compressed Video I

Method for additive spread spectrum watermarkíng in hybridcoding schemes by Hartung and Girod : Adding video dataand watermark for each 8x8 block in the DCT domain:

EC-1 Q-1 ECQ

DCT

compare no.of bits andselect lowest

DCT

+

watermark signal drift compensation signal

non-zeroDCTcoeffs. of8x8 block

markedDCT coeff.

• AC coefficients:

• DC coefficients of I-blocks are always watermarked (fixed length code - comparison of code length not necessary)

20H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

Watermarking of Compressed Video II

• Scheme works with all additive watermark signals

• Visible artifacts avoided by addition of a drift compensation signal (motion-compensated hybrid coding works recursively!)

• Complexity comparable to MPEG decoding

• Method exploits masking characteristics indirectly, since onlynon-zero DCT coefficients are watermarked

• The watermark can be retrieved from the decoded sequence

21H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

4. Conclusions

• Watermarking is data embedding with several strict requirements

• Watermarks must be invisible:

All approaches for watermarking of visual data implicitly or explicitly exploit the limitations of the human visual system

• Watermarks should be placed in perceptibly significant portions of the image/video to ensure robustness

• Most additive methods based on spread spectrum concept

• Applications for video watermarking usually require more sophisticated approaches if real time embedding is desired (embedding in the compressed domain)

22H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

References

• B. Girod, “Image Communication”, Lecture, Univ. of Erlangen-Nuremberg

• H. Niemann, “Mustererkennung”, Lecture, Univ. of Erlangen-Nuremberg

• M.D. Swanson, M. Kobayashi, A.H.Tewfik, “Multimedia Data-Embeddingand Watermarking Technologies”, Proc. IEEE, vol. 86, no. 6, June 1998

• I.J. Cox, J. Kilian, T. Leighton, T. Shamoon, “Secure Spread Spectrum Watermarking for Multimedia”, IEEE Trans. Image Processing, vol. 6, no.12, Dec. 1997

• F. Hartung, B. Girod, “Watermarking of uncompressed and compressedvideo”, Signal Processing, vol. 66, 1998

• F. Hartung, U. Horn, “Codierung digitaler Videosignale nach dem MPEG-Standard”, me, vol. 9, 1995 (in German)

23H. Buchner, Image and Video Watermarking, LNT I Seminar, WS 1998

References

• F. Hartung, B. Girod, “Digital watermarking of MPEG-2 coded video in thebitstream domain”, Proc. ICASSP97, Apr. 1997

• E. Koch, J. Zhao, “Towards Robust and Hidden Image Copyright Labeling”, Proc. Of 1995 IEEE Workshop on Nonlinear Signal and ImageProcessing, June 1995 (available at: http://poseidon.csd.auth.gr/workshop/papers/p_19_1.html)

• G. C. Langelaar, J. C. A. van der Lubbe, J. Biemond, “Copy Protection forMultimedia Data based on Labeling Techniques” (available at: http:// www-it.et.tudelft.nl/html/research/smash/public/benlx96/benelux_cr.html)

• M. Kutter, F. Jordan, F. Bossen, “Digital Signature of Color Images usingAmplitude Modulation”, Proc. SPIE-E197, 1997, pp. 518-526

• M. Kutter, “Watermarking resisting to translation, rotation and scaling”, Proc. of SPIE, Nov. 1998