Feature Extraction Based on Morphological Attribute Profiles for
Classification of Hyperspectral Image
Zhen Ye, Yuchan Yan, Lin Bai, Meng Hui
School of Electronics and Control Engineering, Chang'an University, Xi’an, China,
yezhen525@126.com
ABSTRACT
Traditional hyperspectral image classification typically uses raw spectral signatures without considering the spatial
characteristics. In this paper, we proposed a novel method for hyperspectral image classification based on morpho-
logical attribute profiles. We employed independent component analysis for dimensionality reduction and designed an
extended multiple attribute profiles (EMAP) to extract spatial features in ICA-induced subspaces. For accurate clas-
sification, we proposed a Bayesian maximum a posteriori formulation that couples EMAPs-based feature extraction for
the class-conditional probability with an MRF-based prior. Experimental results show that the proposed method
substantially outperforms traditional and state-of-the-art methods tending to result in smoother classification maps
with fewer erroneous outliers.
Keywords: Hyperspectral image, classification, morphological attribute profiles (AP), Markov random field (MRF).
1. INTRODUCTION
Due to the high spectral resolution, hyperspectral imagery (HSI) has been widely used to provide finer classification in
various fields, such as agriculture, military and mineralogy. In traditional systems, classification of HSI has focused on
the pixelwise application of classifiers operating on spectral information exclusively. However, there has been in-
creasing interest in recent years in HSI classification that exploits spatial information. There are usually two types of
approaches for spatial information extraction. The first one considers spatial and contextual dependence within a
predefined neighborhood system [1], such as a Bayesian maximum a posteriori formulation coupled with a Markov
random field (MRF) (e.g. [2, 3]). Specifically, for an n-sample dataset
, we wish to find the image of
class labels,
. By Bayes’ rule, the posterior density of the class labels is
( ) ( | )
( | )
()
pp
p
p
=
y X y
yX
X
is a constant and can be disregarded, while
is the prior probability of the
classes, and
is the class-condition probability of
. Applying a Bayesian maximum a posteriori formu-
lation to (1), we arrive at the estimated class image being
1, ,
ˆ
arg max log ( ) log ( )
n
yk
pp
=+y X y y
K
In the typical application of (2) to spatial-spectral HSI classification,
is considered as a spatial class prior
and is usually provided by an MRF which promotes the assigning of neighboring pixels to the same class. Naturally,
then, the class-conditional probability,
, is designed to exploit spectral information, typically in the form of
a pixelwise probability estimate driven by the spectral signature of the pixel being classified. To this end, support
vector machine (SVM) [4] is commonly used to provide
for (2). In each of these formulations, however,
this class-conditional probability is devoid of spatial information and is, instead, derived exclusively from spectral
signatures. While the partitioning of (2) into a spectral-only term and a spatial-only term makes some sense concep-
tually, it is not necessarily optimal. Indeed, the MRF may override otherwise correct results from the spectrally-driven
class-conditional probability if the latter provides only relatively weak support (i.e.,
is maximum for the
correct class labeling but not by a wide margin over other labelings).
To address the shortcomings of the first type of approaches, an adaptive and given neighborhood system can be
considered for classification, such as morphological profiles (MP)-based approaches [1, 5-8]. M. Pesaresi and J. A.
Benediktsson used morphological transformations to build MP [5]. Specifically, bright and dark spatial structures of
image were isolated by morphological opening and closing, respectively. Recent years, the strategy has been extended
to HSI analysis by principal component analysis (PCA) to reduce the dimensionality of HSI, which is named extended
morphological profiles (EMP) [6, 7]. Since the structuring element (SE) of MP cannot characterize in formation