Implicit Active Contours Driven by Local Binary Fitting Energy
Chunming Li
1
, Chiu-Yen Kao
2
, John C. Gore
1
, and Zhaohua Ding
1
1
Institute of Imaging Science
2
Department of Mathematics
Vanderbilt University The Ohio State University
Nashville, TN 37232-2310, USA Columbus, OH 43210-1174, USA
{chunming.li,john.gore,zhaohua.ding}@vanderbilt.edu kao@math.ohio-state.edu
Abstract
Local image information is crucial for accurate segmen-
tation of images with intensity inhomogeneity. However, im-
age information in local region is not embedded in popular
region-based active contour models, such as the piecewise
constant models. In this paper, we propose a region-based
active contour model that is able to utilize image informa-
tion in local regions. The major contribution of this paper is
the introduction of a local binary fitting energy with a kernel
function, which enables the extraction of accurate local im-
age information. Therefore, our model can be used to seg-
ment images with intensity inhomogeneity, which overcomes
the limitation of piecewise constant models. Comparisons
with other major region-based models, such as the piece-
wise smooth model, show the advantages of our method in
terms of computational efficiency and accuracy. In addi-
tion, the proposed method has promising application to im-
age denoising.
1. Introduction
Active contour models have been one of the most suc-
cessful methods for image segmentation [1, 3–7, 12]. The
existing active contour models can be categorized into two
classes: edge-based models [1, 4–6] and region-based mod-
els [2,9,10]. These two types of models both have their pros
and cons, and the choice of them in applications depends on
different characteristics of images.
Edge-based models utilize image gradient to stop the
evolving contours on the object boundaries. Typical edge-
based active contour models have an edge-based stopping
term and a balloon force term to control the motion of the
contour. The edge-based stopping term serves to stop the
contour on the desired object boundary. The balloon force
term is introduced to shrink or expand the active contour
so that the initial contour can be placed far away from the
desired object boundary. However, appropriate choice of
balloon force is sometimes difficult. If the balloon force
is not large enough, the evolving contour may not able to
pass some narrow parts of the object. If the balloon force is
too large, the active contour is likely to pass through weak
object boundary.
Region-based active contour models have the following
advantages over edge-based models. First, region-based
models do not utilize the image gradient and therefore have
better performance for the image with weak object bound-
aries. Second, they are significantly less sensitive to the
location of initial contours. One of the most popular region-
based active contour models is Chan-Vese model [2]. This
model has been successful for images with two regions,
each having a distinct mean of pixel intensity. In [11], Vese
and Chan extended their earlier work in [2] by using a mul-
tiphase level set formulation, in which multiple regions can
be represented by multiple level set functions. These mod-
els are called piecewise constant (PC) models, since they
assume that an image consists of statistically homogeneous
regions. However, the regions of interest in images are often
not statistically homogeneous, and therefore the PC models
are not applicable to those types of images.
To handle more general scenario, Vese and Chan [11]
and Tsai et al. [10] proposed two similar region-based ac-
tive contour models, aiming at minimization of Mumford-
Shah functional [8]. In [11], Vese and Chan proposed a
piecewise smooth (PS) model, which overcomes the limita-
tion of their original work [2]. But these methods are com-
putationally inefficient. The technique proposed by Tsai et
al. [10] can address the segmentation of images with in-
tensity inhomogeneity. However, the computation in their
method is also expensive. As proposed in [10], one way to
reduce the computational cost is to use a contour near the
object boundaries as the initial contour. In their method,
such initial contour is obtained by a preliminary segmenta-
tion using other active contour models, such as Chan and
Vese’s PC model. However, for images with intensity inho-
mogeneity, PC model can result in a contour that is still far
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