prediction supports. In general, a larger template region can in-
crease the matching accuracy. Therefore, the template region with
thickness being set to
T
1
is used in the searching process, shown in
Fig. 3(b). In this paper, the
T
1
equals to the size of the current
coding block. The next subsection gives the details of the process
to derive the prediction supports.
2.2. Derive the prediction supports
Suppose the region S consists of current coding block CB and its
neighbor template NT, as shown in Fig. 2(b). Let each coding block
be comprised of
×nn
pixels. Hence, region S is of size
=Nn4
2
pixels. The principle of acquiring the prediction supports (K-NN
patches) of the coding block is to first search for K-nearest ap-
proximates of the NT in horizontal and vertical search windows
under Euclidean distance and then obtain the K-NN patches of CB
according to the K-nearest approximates of NT.
Let the N sample values be stacked in a column vector
, which
is compacted in a vector
of 3 n
2
known pixels and a vector
of
n
2
unknown pixels. Let C denote a so-called dictionary represented
by a matrix of dimension
×NM
, which means all the possible
patches that have the same geometric shape as region S in given
horizontal and vertical searching windows. M here means the total
number of the possible patches in the searching windows. Con-
sequently, the dictionary matrix can also be assumed to be formed
by two submatrices
0
of size
×n
2
and
P
of size
×n
2
,
respectively, corresponding to the spatial location of NT and CB.
The details of acquiring the prediction supports are as follows.
1) Derive vector
and submatrix
0
. Record the indexes of each
atom
m0
(i.e., stacked in the mth column of
0
) in submatrix
0
.
2) Compute Euclidean distance
D
m
between
and each atom
m0
,
based on the following equation:
=‖ − ‖
()
D Bc
1
mm002
2
3) Derive K-NN set
of NT. Here,
is composed by the top K
atoms of submatrix
0
, which minimize
D
m
. Record the indexes
of these selected atoms in
0
.
4) Generate the prediction supports
P
of the current coding block
CB, composed by the K atoms of submatrix
P
according to the
recorded indexes of the selected atoms in
0
.
2.3. Filtrate the prediction supports
The 3D holoscopic image is composed of numerous EIs, which
is quite different from the natural 2D images. The texture homo-
geneous areas hardly prevail in 3D holoscopic image. Since Eu-
clidean distance is not a reasonable matching criterion for edges
and texture regions [22], it is essential to design a filtration
method to ensure that the selected prediction supports are all
approximate to current coding block. In this paper, a filtration
method is put forward, in which NCC [23] is selected as the
Fig. 2. Holoscopic image captured by microlens array: (a) full image; (b) enlargement of the holoscopic image showing the EIs.
Reconstruction blocks
Reconstruction blocks
Fig. 3. Searching windows: (a) a full causal searching window W; (b) specifi ed searching windows in horizontal and vertical directions.
D. Liu et al. / Signal Processing: Image Communication 47 (2016) 438–451440