Techniques for Reversible

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6 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

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Expansion Embedding
Techniques for Reversible
Watermarking

Diljith M. Thodi and Jeffrey J. Rodríguez,

IEEE TRANSACTIONS ON IMAGE PROCESSING,

2007.

outline


Abstract


Difference Expansion


Alternative approaches


Difference Expansion Based Algorithms


Expansion Embedding


Experimental Results


Conclusions

1

Abstract


Tian’s

DE (difference embedding)


high embedding capacity


distortion , lack of capacity control



histogram shifting


overcome the drawback of
Tian’s

algorithm


prediction
-
error expansion


large embedding capacity



2


Difference Expansion



3



simple reversible integer transform






watermarked difference



:,:
2
1
,
2 2
x y
l h x y
h h
x l y l

 
  
 
 

   
   
   
   

Difference Expansion



4


expandable difference



changeable difference





Alternative Approaches



5


Histogram
-
Based Selection of Locations


avoid sending the location map


nonoverlapping

regions in the histogram of
expandable location


set threshold




0



Alternative Approaches



6


Histogram Shifting


expand inner region


the range [
-
2


-
2, 2

+1 ]


inner region overlap with outer region



Alternative Approaches



7


Alternative Approaches



8


Histogram Shifting


shift outer region


cancel all overlap between the two regions




no need to have a location map


reduce auxiliary information


less computational intensity



Alternative Approaches



9



Alternative Approaches



10


DE ( Difference Expansion)



LSB
-
embedding




return the worst
-
case values


Return the Worst
-
Case



11


histogram shifting






multiple expansion/shifting n times

Difference Expansion With Histogram Shifting
and
Overflow

Map (DE
-
HS
-
OM)



12


calculate auxiliary information



calculate
bitstream

embedded



embed the
bitstream


in changeable locations



Difference Expansion With Histogram Shifting
and Flag Bits (DE
-
HS
-
FB)



13


multiple expansion/shifting


order of modifiability


depend on selected threshold



encoder

Difference Expansion With Histogram Shifting
and Flag Bits (DE
-
HS
-
FB)



14


decoder






relationship between


and


Difference Expansion With Histogram Shifting
and Flag Bits (DE
-
HS
-
FB)



15


when


= 0




= 0 , 1


embed flag bit (
resolve ambiguity )


better efficiency ( most locations


> 1)



differs from DE
-
HS
-
OM


auxiliary information = header segment + flag bit


determine operating threshold recursively




Difference Expansion With Histogram Shifting
and Flag Bits (DE
-
HS
-
FB)



16


calculate the threshold


repeat until newly equal to previous

Difference Expansion With Histogram Shifting
and Flag Bits (DE
-
HS
-
FB)



17


decoding algorithm


identify changeable set


extract auxiliary information


retrieve the threshold, flag bits, size of payload


calculate

(i,j,

)


calculate

(i,j,


)


identify expandable set

Expansion Embedding



18


technique of embedding a bit


by expanding to create a vacant position


distortion depend on embedding magnitude



Difference expansion


expand the pixel difference


recursive or multiple embedding


Expansion Embedding



19


Predictor


predict the value of the pixel by its neighborhood


advantage


increases the number of feature


smaller magnitude


Prediction
-
Error Expansion


compute predictor


compute the PE ( prediction
-
error)


embed the information bit


Prediction Algorithm



20


one of edge
-
detection mechanism


context of a pixel



output of the predictor




Prediction
-
Error Expansion



21



1. compute the PE ( prediction error)

2. embed information bit



at the decoder

PE
-
Based Reversible Watermarking Algorithms



22



1. host image = predicted value + prediction errors

2. with watermark ( payload + auxiliary information )


Experimental Result


23


Experimental Result


24




Conclusion


Histogram
-
shifting technique


overcome the drawbacks of
Tian’s

algorithm


the lack of capacity control


undesirable distortion at low embedding
capacites



PE
-
based embedding technique


maximal embedding capacity : 1
bpp


good watermarked image quality

25