abstract = "Figure-ground segmentation is a process of separating
regions of interest from unimportant backgrounds. It is
essential to various applications in computer vision
and image processing, e.g. object tracking and image
editing, as they are only interested in certain regions
of an image and use figure-ground segmentation as a
pre-processing step. Traditional figure-ground
segmentation methods often require heavy human workload
(e.g. ground truth labelling), and/or rely heavily on
human guidance (e.g. locating an initial model),
accordingly cannot easily adapt to diverse image
domains. Evolutionary computation (EC) is a family of
algorithms for global optimisation, which are inspired
by biological evolution. As an EC technique, genetic
programming (GP) can evolve algorithms automatically
for complex problems without predefining solution
models. Compared with other EC techniques, GP is more
flexible as it can use complex and variable length
representations (e.g. trees) of candidate solutions. It
is hypothesised that this flexibility of GP makes it
possible to evolve better solutions than those designed
by experts. However, there have been limited attempts
at applying GP to figure ground segmentation. In this
thesis, GP is enabled to successfully address
figure-ground segmentation through evolving well
performing segmentors and generating effective
features. The objectives are to investigate various
image features as inputs of GP, develop multiobjective
approaches, develop feature selection/construction
methods, and conduct further evaluations of the
proposed GP methods. The following new methods have
been developed. Effective terminal sets of GP are
investigated for figureground segmentation, covering
three general types of image features, i.e.
colour/brightness, texture and shape features. Results
show that texture features are more effective than
intensities and shape features as they are
discriminative for different materials that foreground
and background regions normally belong to (e.g. metal
or wood). Two new multi-objective GP methods are
proposed to evolve figure-ground segmentors, aiming at
producing solutions balanced between the segmentation
performance and solution complexity. Compared with a
reference method that does not consider complexity and
a parsimony pressure based method (a popular bloat
control technique), the proposed methods can
significantly reduce the solution size while achieving
similar segmentation performance based on the
Mann-Whitney U-Test at the significance level 5percent.
GP is introduced for the first time to conduct feature
selection for figure-ground segmentation tasks, aiming
to maximise the segmentation performance and minimise
the number of selected features. The proposed methods
produce feature subsets that lead to solutions
achieving better segmentation performance with lower
features than those of two benchmark methods (i.e.
sequential forward selection and sequential backward
selection) and the original full feature set. This is
due to GP's high search ability and higher likelihood
of finding the global optima.
GP is introduced for the first time to construct high
level features from primitive image features, which
aims to improve the image segmentation performance,
especially on complex images. By considering
linear/nonlinear interactions of the original features,
the proposed methods construct fewer features that
achieve better segmentation performance than the
original full feature set. This investigation has shown
that GP is suited for figure-ground image segmentation
for the following reasons. Firstly, the proposed
methods can evolve segmenters with useful class
characteristic patterns to segment various types of
objects. Secondly, the segmentors evolved from one type
of foreground object can generalise well on similar
objects. Thirdly, both the selected and constructed
features of the proposed GP methods are more effective
than original features, with the selected/constructed
features being better for subsequent tasks. Finally,
compared with other segmentation techniques, the major
strengths of GP are that it does not require
pre-defined problem models, and can be easily adapted
to diverse image domains without major parameter tuning
or human intervention.",