IEEE TRANSACTIONS ON IMAGE PROCESSING, VOL. 10, NO. 8, AUGUST 2001 1187
A Fast Super-Resolution Reconstruction Algorithm
for Pure Translational Motion and Common
Space-Invariant Blur
Michael Elad, Member, IEEE, and Yacov Hel-Or
Abstract—This paper addresses the problem of recovering a
super-resolved image from a set of warped blurred and decimated
versions thereof. Several algorithms have already been proposed
for the solution of this general problem. In this paper, we con-
centrate on a special case where the warps are pure translations,
the blur is space invariant and the same for all the images, and
the noise is white. We exploit previous results to develop a new
highly efficient super-resolution reconstruction algorithm for this
case, which separates the treatment into de-blurring and measure-
ments fusion. The fusion part is shown to be a very simple non-
iterative algorithm, preserving the optimality of the entire recon-
struction process, in the maximum-likelihood sense. Simulations
demonstrate the capabilities of the proposed algorithm.
Index Terms—Maximum-likelihood, reconstruction, super-reso-
lution, translation motion.
I. INTRODUCTION
T
HE super-resolution reconstructionproblemis well known
and extensively treated in the literature [1]–[13]. The main
idea is to recoverasingle high-resolution image from a set of low
qualityimagesofthesamephotographedobject.Inthisprocess,it
is conceptually possible to remove some of the aliasing and to in-
creasetheeffectiveresolutionofthesensoruptotheopticalcut-off
frequency.Recent work[10]–[13]relatesthisproblem torestora-
tion theory [14]. As such, the problem is shown to be an inverse
problem, where an unknown image is to be reconstructed, based
on measurements related to it through linear operators and addi-
tive noise. This linear relation is composed of geometric warp,
bluranddecimationoperations.In[13]asolution(usingthemax-
imum-likelihood (ML), maximum a-posteriori (MAP), and pro-
jectionontoconvexsets(POCS)methods)tothesuper-resolution
reconstruction problem is givenin a simple yet general algebraic
form. The proposed solution can deal with a general geometric
warp, space-varying blur, spatially uniform decimation with ra-
tional resolution ratio, and colored Gaussian additive noise. The
solution is based on the knowledge of the operators involved and
the noise characteristics.
This paper concentrates on a special super-resolution case. It
is assumed that the blur is space invariantand the same for all the
Manuscript received July 28, 1999; revised April 9, 2001. This work was
performed while the authors were with Hewlett-Packard Laboratories, Israel,
in 1998. The associate editor coordinating the review of this manuscript and
approving it for publication was Prof. Timothy J. Schulz.
M. Elad is with the Jigami Corporation, The Technion City 32000, Israel
(e-mail: elad@jigami.com).
Y. Hel-Or is with the Inter-Disciplinary Center, Herzelia, Israel (e-mail:
toky@idc.ac.il).
Publisher Item Identifier S 1057-7149(01)06037-7.
measured images; the geometric warps between the measured
images are pure translations; and the additive noise is white.
These assumptions are indeed very limiting, but in some cases
are quite practical. Such is the case in video sequences where the
photographed scene is static and the images are obtained with
slight translations. Another relevant application is increasing a
scanner resolution by scanning the same original document sev-
eral times with slight different initial points. Several papers al-
ready dealt with this special case [2], [4], [6], [7] and proposed
different reconstruction algorithms.
In this paper, we propose a new algorithm for the above spe-
cial super-resolution case. The algorithm is based on the general
solution proposed in [13]. Exploiting the properties of the op-
erations involved, the well-known fact that the de-blurring can
be separated from the fusion process is first established [2], [6].
The main contribution of this paper corresponds to the fusion
stage, where the measurements are merged into a higher reso-
lution image. It is shown that through a very simple nonitera-
tive algorithm, this fusion is achieved, while preserving the op-
timality in the Maximum-Likelihood sense. The new algorithm
is shown to be superior to the existing algorithms [2]–[13] in
terms of computational cost, and with high output quality.
II. G
ENERAL SUPER-RESOLUTION
In this section, we briefly describe the general super-reso-
lution model and solution. Detailed description of these topics
can be found in [13]. We denote the
measured images by
. These images are to be fused into a single improved
quality image, denoted as
. The images are represented lex-
icographically ordered column vectors. Each of these images
is related to the required super-resolution image through geo-
metric warp, blur, decimation, and additive noise
(1)
The matrix
stands for the geometric warp operation that ex-
ists between the images
and an interpolated version of the
image
(interpolation is required in order to treat the image
in the higher resolution grid). The matrix is the blur
matrix, representing the camera’s PSF. The matrix
stands
for the decimation operation, representing the reduction of the
number of observed pixels in the measured images. The vectors
represent Gaussian additive measurement noise with
zero mean and auto-correlation matrix
.
Ouraimistoestimate
basedontheknownimages ,
and the operations they went through. In order to do that we have
1057–7149/01$10.00 © 2001 IEEE