Towards an Evolution Strategy Approach in Binary Image
Registration for Solving Digital Signature Recognition Tasks
Catalina Cocianu and Alexandru Stan
Computer Science Department, Bucharest University of Economics, Bucharest, Romania
Keywords: Digital Signature based Security Systems, Evolution Strategies, Image Registration, Mutual Information.
Abstract: This paper focuses on the development of an image registration methodology for digital signature
recognition. We consider two perturbation models, namely the rigid transformation and a mixture of shear
and rigid deformation. The proposed methodology involves three stages. In the first stage, both the acquired
image and the stored one are binarized to reduce the computational effort. Then an evolution strategy (ES)
is applied to register the obtained binary images. The quality of each chromosome belonging to a certain
population is evaluated in terms of mutual information-based fitness function. In order to speed up the
computation of fitness values, we propose a computation strategy based on the binary representation of
images and the sparsity of the image matrices. Finally, we evaluate the registration capabilities of the
proposed methodology by means of quantitative measures as well as qualitative indicators. The
experimental results and some conclusions concerning the capabilities of various methods derived from the
proposed methodology are reported in the final section of the paper.
1 INTRODUCTION
Digital image registration is one of the most
important tasks in various systems which evaluate
images, including sensed image recognition, global
land monitoring in satellite images, aligning medical
images. The main aim of any registration technique
is to align images acquired at different times, using
different sensors and from different viewpoints. In
the following we adopt the assumption that the
variations in the analysed images are due to the
acquisition system and can be removed by applying
various geometric transformations (Goshtasby,
2012; Modersitzki, 2004).
The most studied perturbation models involves
spatial transformations of rigid, affine, projective,
and respectivelly global polynomial type. In our
work we consider two perturbation model, the rigid
one and the affine transformation. The rigid
transformation is described in terms of translation,
rotation, and scale changes. The affine
transformation is more general than the rigid one
and is expressed as a mixture of rigid, shear and
aspect ratio changes.
So far, various classes of registration techniques,
mainly depending on the perturbation model, have
been presented in the literature (Goshtasby, 2012;
Zhuang et al., 2016; Yang, Papa, 2017). One of the
most popular classes of registration techniques is the
optimization-based class that includes, besides direct
optimization methods, evolutionary-based
approaches (Zhang, Wu, 2012; Khader, Hamza,
2012; Mohamed, Hamza 2010; Singhai, Singhai,
2012). The evalutionary approaches of image
registration are developed based on certain similarity
measure corresponding to the fitness function. The
methods involve heuristic search through the
registration parameter values space to compute the
variant maximizing the fitness function.
Our research work focuses on the development
of an image registration methodology for digital
signature recognition. More preciselly, we address
the problem of a particular component of banking
security systems using the client’s signature. In
order to process payments, the system should
recognize the client signature prior to finalizing the
operation. The process mainly consists of the
following steps: scan the payment order, identify the
client’s signature and compare it with its
corresponding stored version. In most of the cases
the sensed signature is different from the stored one
from the geometrical point of view. We restrict the
problem to two perturbation models, namely the