Reversible watermarking
Wu Dan
2008.2.20
Introduction
What?
Introduction
Why?
Military data
Medical data
How?
Data compression
Difference expansion
Histogram bin shifting
Reversible Data Embedding using aDifference Expansion
Jun Tian
IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS
FOR VIDEO TECHNOLOGY, VOL.13 NO.8
AUGUST 2003
How to measure a reversibledata embedding algorithm?
Payload capacity (bpp)
Visual quality (PSNR)
Complexity
A simple example of thedifference expansion
x=206, y=201; b=1.
l: the integer average
h: difference
DE: difference expansion
The new values:
Reversible data embedding
Reversible integer transform
The inverse transform:
To prevent the overflow and underflow :
Expandable and changeable differencevalues
Expandable:
(for both b=1,0)
Changeable:
(for both b=0,1)
By definition, we can find that:
If h is changeable, h’ is still changeable.
If h is expandable, h is changeable.
After the DE, the expanded differencevalue h’ is changeable.
if h=0 or -1, the conditions on expandableand changeable are equivalent.
Data embedding algorithm :
1.The original image is grouped into pairs ofpixels values. Then compute thedifference values h.
2.Create four disjoint sets of differencevalues: EZ, EN, CN, and NC
EZ: contains all expandable h=0 and
expandable h=-1.
EN: contains all expandable h EZ
CN: contains all changeable
NC: contains all non-changeable h.
3.Create a location map of selectedexpandable difference values.
4.Collect original LSBs of difference values inEN2 and CN. However for those h=1 orh=-2 in EN2 and CN, their LSBs will be notcollected.
5.The location map will be losslesslycompressed. The compressed bit stream isdenoted as L. Embed L, the original LSBsC, and a payload P.
6.Apply the inverse integer transform toobtain the embedded image.
Discussions:
Capacity:
Threshold:
The scanning order:
Non-changeable:
Scanning order :
Non-changeable:
decoding :
1.Calculate the difference values h.
2.Create two disjoint sets of differencevalues: CH and NC
changeable and non-changeable
3.Collect LSBs of all difference values in CH,and form a binary bit stream B.
4.Decode the location map from B, andrestore the original values of differencesas follows:
Experimental results:
Reversible data hiding
Zhicheng Ni, Yun-Qing,Nirwan Ansari, and Wei Su
IEEE TRANSACTIONS ON CIRCUITS ANDSYSTEMS FOR VIDEO TECHNOLOGY,
March 2006
Algorithm
Zero point and peak point
Embedding:
Generate the histogram H(x).
In the histogram, find the zero point H(a)and peak point H(b).
If H(b)>0,record the coordinate of thosepixels.
Assume a<b. Scan the image.
If x∈(a,b),x+1; leaving the value a+1empty.
If w=0, a=a; if w=1,a=a+1.
Pure payload:
C=H(a) - H(b)
Multiple pairs of Maximum andminimum points:
Extraction algorithm: ( Assume the zero point andpeak points are a ,b )
Scan the image in the same order as in theembedding procedure.
If the value is a+1,w=1; if the value is a, w=0.
Scan the image again, if the grayscale valuex∈(a,b], x-1.
If the overhead information found in theextracted data, set the pixel grayscale value asb.
Lower bound of the PSNR of a Markedimage
The total embedding time is just 100ms.
Experimental results
Discussion:
1) How to get the peak point andzero point for verifier?
2) How to use the a and a+1?
Reversible watermark using thedifference expansion of ageneralized integer transform
Adnan M.Alattar, Member, IEEE,
IEEE TRANSACTIONS ON IMAGE PROCESSING,
AUGUST 2004
Generalized differenceexpansion
Vector:
Reversible integer transform:
A difference expansion oriented datahiding scheme for restoring theoriginal host images
Chin-Chen Chang, Tzu-Chuen Lu
The Journal of systems and software,
May 2006
Very Fat Watermarking byReversible Contrast Mapping
Dinu Coltuc and Jean-Marc Chassery
IEE SIGNAL PROCESSING LETTERS,
APRIL 2007
Reversible contrast mapping:
Dc: the domain without the odd pixels pairs.
Embedding:
1 partition the entire image into pairs.
2 for each pair:
a) if (x,y) is even pixel pair, set the LSBx’ to 1, the LSB of y’ is the watermark.
b) if (x,y) ∈Dc, set the LSB of x to 0, andthe LSB of y is the watermark.
c) if (x,y) Dc, set the LSB of x to 0,
and save the ture value.
