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Introduction to The Lifting Scheme
• Two approaches to make a wavelet transform:– Scaling function and wavelets (dilation
equation and wavelet equation) – Filter banks (low-pass filter and high-pass
filter)
• The two approaches produce same results, proved by Doubeches.
• Filter bank approach is preferable in signal processing literatures
Wavelet Transforms
|H0(w)|, |G0(w)|
/ 2/ 2Ideal low-pass filter
|H 1(w ) |, |G 1(w ) |
/ 2/ 2Ideal high- pass filter
Wavelet Transforms
2
2
2
2
+X(z) Y(z)
H0(z)
G1(z)
G0(z)
H1(z)
X1(z)
X0(z)X'0(z)
X'1(z) Y'1(z) Y1(z)
Y'0(z) Y0(z)
Practical Filter
Understanding The Lifting Scheme
signal
Splitting
)0(ks
)0(kd
)1(ks
)1(kd
signal
Merge
)1(kd
Predicting
)1(ks
Updating
)0(kd
Inverse Predicting
)0(ks
Inverse Updating
…
Transmitting
S (z )
D (z)
P (z ) U (z )
S '(z )
D '(z )
splitX (z )
-
Lifting Scheme in the Z-Transform Domain
Low band signal
High band signal
Update stage
Prediction stage
2
S '(z )
D '(z )
P (z )U (z )
S (z )
D (z )
-com-bine
X (z )
Lifting Scheme in the Z-Transform Domain
Inverse update stage
Inverse prediction stage
2
• A spatial domain construction of bi-orthogonal wavelets, consists of the following four basic operations:
• Split : sk(0)=x2i(0), dk(0)=x2i+1
(0)
• Predict : dk(r)= dk(r-1) – pj(r) sk+j(r-1)
• Update : sk(r)= sk(r-1) + uj(r) dk+j(r)
• Normalize : sk(R)=K0sk(R), dk(R)=K1dk(R)
Four Basic Stages
• Prediction and Update
d i-2(k- 1 )
p 0(k )... ...
......
d i-1(k- 1) d i
(k- 1) d i+ 1(k- 1) d i+ 2
(k- 1) d i+3(k - 1)
s i-2(k - 1 ) s i-1
(k- 1) s i(k- 1) s i+ 1
(k- 1) s i+ 2(k- 1) s i+3
(k- 1)
p 0(k )p 1
(k ) p 1(k )
d i-2(k) d i-1
(k) d i(k) d i+ 1
(k) d i+ 2(k) d i+3
(k)
u 0(k ) u 0
(k )u 1(k ) u 1
(k )
s i-2(k- 1 ) s i-1
(k - 1) s i(k - 1) s i+ 1
(k- 1) s i+ 2(k- 1) s i+3
(k- 1)
Two Main Stages
• A prediction rule : interpolation– Linear interpolation coefficients: [1,1]/2
• used in the 5/3 filter– Cubic interpolation coefficients: [-1,9,9,-1]/16
• used in the 13/7 CRF and the 13/7 SWE
xi- 1
xi+1
xi- 2
xi- 3
xi+2
xi+3xp
30- 1- 3 1
xi- 1
xi+1
xi- 2
xi- 3
xi+2
xi+3xp
30- 1- 3 1
Prediction Stage
• An update rule : preservation of average (moments) of the signal– The update coefficients in the 5/3 are [1,1]/4– The update coefficients in the 13/7 SWE are
[-1,9,9,-1]/32– The update coefficients in the 13/7 CRF are
[-1,5,5,-1]/16
Update Stage
• The 5/3 wavelet– The (2,2) lifting scheme
split
predic t
high pass
0p0p
0u 0u
2ix 1ix ix 1ix 2ix 3ix 4ix
1kd
ks
kd
0p 0p
low pass
update
Example
• We have p0 = 1/2 by linear interpolation and the detailed coefficient are given by
• In the update stage, we first assure that the average of the signal be preserved
• From an update of the form, we have
• From this, we get A=1/4 as the correct choice to maintain the average.
)(2
121 iiik xxxd
i
ik
k xs2
1
)( 1 kkik ddAxs
i
ii
ii k
kik
k xAxAdAxs 12)21(2
Example
• The coefficients of the corresponding high pass filter are {h1} = ½{-1,2,-1}
• The coefficients of the corresponding low pass filter are {h0} = ⅛{-1,2,6,2,-1}
• So, the (2,2) lifting scheme is equal to the 5/3 wavelet.
Example
• Complexity of the lifting version and the conventional version– The conventional 5/3 filter
• X_low = ( 4*x[0]+2*x[0]+2*(x[-1]+x[1])-(x[2]+x[-2]) )/8
• X_high = x[0]-(x[1]+x[-1])/2
• Number of operations per pixel = 9+3 = 12
– The (2,2) lifting• D[0] = x[0]- (x[1]+x[-1])/2
• S[0] = x[0] + (D[0]+D[1])/4
• Number of operations per pixel = 6
Example
• The lifting scheme is an alternative method of computing the wavelet coefficients
• Advantages of the lifting scheme:– Requires less computation and less memory. – Easily produces integer-to-integer wavelet
transforms for lossless compression. – Linear, nonlinear, and adaptive wavelet
transform is feasible, and the resulting transform is invertible and reversible.
Conclusions