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Adaptive data hiding based on VQ compressed image
Authors: Wei-Chang Du and Wei-Jun Hsu
Source: IEE Proceedings-Vision, Image and Signal Processing, Vol. 150, No. 4, August 2003, pp
Speaker: Chi-Nan Lin
Date: 2004/04/21

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Outline
Introduction
Image coding using VQ
Data hiding on VQ
Experimental results
Conclusions

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Introduction (1)
Two fundamental requirements on data hiding in an image:
The distortion of cover image should be minimized.
The hiding capacity should be large enough.
Usually the above two requirements are a trade off of each other.
Earlier study:
On spatial domain.
ex. to hide data in the LSB bit.

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Introduction (2)
Recent study:
To hide data in compressed images.
-->in palette-based images (ex.,GIF image).
-->in frequency-domain images (ex.,JPEG image)
-->in VQ compressed images.

5. Image coding using VQ(1)
EarthTour Presentations
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Image coding using VQ(1)
VQ Encoder

6. Image coding using VQ(2)
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Image coding using VQ(2)
VQ Decoder

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Data hiding on VQ (1)
Pre-processing:
Secret data should be compressed to save space.
Secret data need to be encrypted for security (use DES, RSA etc.).
Fixed embedding method:
Data to hide (embed) in the LSB of indices on VQ compressed format.
Codebook was divided into two sub-codebooks.

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Data hiding on VQ (2)
MGLE (mean grey-level embedding) or PNNE (pairwise nearest-neighbour embedding) was used to divide the codebook (into two sub-codebooks).
(MGLE)
(PNNE)

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Data hiding on VQ (3)
Fixed embedding method:
(the secret data)
codeword Yi and Yi+1 are very similar to each other.
secret bit stream help decide which sub-codebook to use.

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Data hiding on VQ (4)
Fixed embedding method:
Two main drawbacks:
Fixed capacity --> each image block can hide only one bit.
Large distortion --> especially when MGLE was used.
(MGLE)
(PNNE)

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Data hiding on VQ (5)
Adaptive embedding method:
(MGLE)
(PNNE)
Adaptive clustering embedding
(ACE)

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Data hiding on VQ (6)
Adaptive embedding method: Y1 Y2 Y3 Y4 Y5 Y6 Y7 Y8 G0 Y1 Y2 G1 Y3 G2 Y4 Y5 Y6 G3 Y7 Y8
Grouping
(ACE)
unsigned integer value of
bit stream, stop grouping

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Data hiding on VQ (7)
Adaptive embedding method: G0 Y1 Y2 G1 Y3 G2 Y4 Y5 Y6 G3 Y7 Y8
Image encoded by VQ
Bit stream: (1101)2=13 Y7 Y5 Y2
Y4(00)
Y5(01)
Y6(10)
Y1(0)
Y2(1)
Y7(0)
Y8(1) G2 : ︷ Y4 Y5 Y6 ︸ G0 : ︷ Y1 Y2 ︸ G3 : ︷ Y7 Y8 ︸
After embedding Y8 Y6 Y2
Codebook

14. Experimental Results (1)
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Experimental Results (1)
Original image VQ
PSNR:31.24
MGLE
PNNE
ACE
Results for various embedding methods (capacity = 16 Kbit)

15. Experimental Results (2)
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Experimental Results (2)

16. Conclusions Based on VQ compressed images.
ACE (Adaptive Clustering Embedding) has higher hiding capacity and better image quality than traditional methods.
It is possible for ACE to be applied to other media in which VQ is applicable.