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`
0
TV: A New Method for Image Restoration in the Presence of
Impulse Noise
Ganzhao Yuan
1
and Bernard Ghanem
2
1
South China University of Technology (SCUT), P.R. China
2
King Abdullah University of Science and Technology (KAUST), Saudi Arabia
yuanganzhao@gmail.com, bernard.ghanem@kaust.edu.sa
Abstract
Total Variation (TV) is an effective and popular
prior model in the field of regularization-based im-
age processing. This paper focuses on TV for image
restoration in the presence of impulse noise. This
type of noise frequently arises in data acquisition and
transmission due to many reasons, e.g. a faulty sen-
sor or analog-to-digital converter errors. Removing
this noise is an important task in image restora-
tion. State-of-the-art methods such as Adaptive Out-
lier Pursuit(AOP) [
42
], which is based on TV with
`
02
-norm data fidelity, only give sub-optimal perfor-
mance. In this paper, we propose a new method,
called
`
0
T V
-PADMM, which solves the TV-based
restoration problem with
`
0
-norm data fidelity. To
effectively deal with the resulting non-convex non-
smooth optimization problem, we first reformulate it
as an equivalent MPEC (Mathematical Program with
Equilibrium Constraints), and then solve it using a
proximal Alternating Direction Method of Multipli-
ers (PADMM). Our
`
0
T V
-PADMM method finds a
desirable solution to the original
`
0
-norm optimiza-
tion problem and is proven to be convergent under
mild conditions. We apply
`
0
T V
-PADMM to the
problems of image denoising and deblurring in the
presence of impulse noise. Our extensive experi-
ments demonstrate that
`
0
T V
-PADMM outperforms
state-of-the-art image restoration methods.
1. Introduction
Image restoration is an inverse problem, which
aims at estimating the original clean image
u
from a
blurry and/or noisy observation
b
. Mathematically,
this problem is formulated as:
b = (Ku ε
m
) + ε
a
, (1)
where
K
is a linear operator,
ε
m
and
ε
a
are the noise
vectors, and
denotes an elementwise product. Let
1
and
0
be column vectors of all entries equal to one
and zero, respectively. When
ε
m
=
1
and
ε
a
6
=
0
(or
ε
m
6
=
0
and
ε
a
=
0
), Eq (1) corresponds to the addi-
tive (or multiplicative) noise model. For convenience,
we adopt the vector representation for images, where
a 2D
M × N
image is column-wise stacked into a
vector
u ∈ R
M×N
. So, for completeness, we have
1, 0, b, u, ε
a
, ε
m
∈ R
n
, and K ∈ R
n×n
.
In general image restoration problems,
K
rep-
resents a certain linear operator, e.g. convolution,
wavelet transform, etc., and recovering
u
from
b
is
known as image deconvolution or image deblurring.
When
K
is the identity operator, estimating
u
from
b
is referred to as image denoising [
35
]. The prob-
lem of estimating
u
from
b
is called a linear inverse
problem which, for most scenarios of practical in-
terest, is ill-posed due to the singularity and/or the
ill-conditioning of
K
. Therefore, in order to stabilize
the recovery of
u
, it is necessary to incorporate prior-
enforcing regularization on the solution. Therefore,
image restoration can be modelled globally as the
following optimization problem:
min
u
`(Ku, b) + λ Ω(∇
x
u, ∇
y
u) (2)
where
`
(
Ku, b
) measures the data fidelity between
Ku
and the observation
b
and
∇
x
∈ R
n×n
and
∇
y
∈ R
n×n
are two suitable linear transformation
matrices such that
∇
x
u ∈ R
n
and
∇
y
u ∈ R
n
com-
pute the discrete gradients of the image
u
along
the
x
-axis and
y
-axis, respectively
1
, Ω(
∇
x
u, ∇
y
u
)
is the regularizer on
∇
x
u
and
∇
y
u
, and
λ
is a
1
In practice, one does not need to compute and store
the matrices
∇
x
and
∇
y
explicitly. Since the adjoint of the
gradient operator
∇
is the negative divergence operator
−div
,
i.e.,
hr, ∇
x
ui
=
h−div
x
r, ui, hs, ∇
y
ui
=
h−div
y
s, ui
for any
1