SUPERVISED LINEAR MANIFOLD LEARNING FEATURE EXTRACTION FOR
HYPERSPECTRAL IMAGE CLASSIFICATION
Jinhuan Wen, Weidong Yan, Wei Lin
School of Science, Northwestern Polytechnical University, Xi’an, Shaanxi, 710072, P.R. China
ABSTRACT
A supervised neighborhood preserving embedding (SNPE)
linear manifold learning feature extraction method for
hyperspectral image classification is presented in this paper.
A point’s k nearest neighbors is found by using new
distance which is proposed according to prior class-label
information. The new distance makes intra-class more
tightly and inter-class more separately. SNPE overcomes the
single manifold assumption of NPE. Data sets lay on (or
near) multiple manifolds can be processed. Experimental
results on AVIRIS hyperspectral data set demonstrate the
effectiveness of our method.
Index Terms—feature extraction, dimensionality
reduction, neighborhood preserving embedding, manifold
learning, hyperspectral image classification
1. INTRODUCTION
Comparable to multispectral image data, hyperspectral
image has high spectral dimension, vast data and altitudinal
interband redundancy which present a challenge to
traditional data processing techniques. In many cases, it is
unnecessary to process all the spectral bands of a
hyperspectral image, since most materials have specific
characteristics only at certain bands, which makes the
remaining spectral bands somewhat redundant. Jimenez [1]
pointed out that the hyperspectral data is centralized in low-
dimensional space because of the high-dimensional space of
hyperspectral image is relatively empty. Therefore, reducing
the dimensionality of hyperspectral data without loosing
important information about objects of interest is a very
important issue for the remote sensing community. The
dimension reduction of hyperspectral image is mainly
divided into two categories, feature extraction and feature
selection. Feature extraction transforms the original data
from high dimension into low dimension with the most of the
desired information content preserved. A number of methods
have been developed to mitigate the effects of dimensionality
on information extraction from hyperspectral data, such as
principal component analysis (PCA) [2] and segmented
principal components transform (SPCT) [3]. Because of not
taking the class information of the input data into account,
PCA may probably discard much useful information and
weaken the recognition accuracy, especially when the
number of sample points is very large [4].
Recently, nonlinear manifold learning dimension
reduction techniques, such as locally linear embedding
(LLE) [5], Isomap [6] and laplacian eigenmaps (LE) [7]
have been successfully applied to hyperspectral data [8]-
[17]. These methods are appropriate for representation of
nonlinear data, but only defined on the training data.
Another major drawback is that these methods are much
more intensive in computation and memory consumption,
which result incapability to process image larger than 70×70
[8-11]. Because it remains a difficult issue to map a new test
sample to the low dimensional space, the above manifold
learning algorithms cannot be easily extended for
classification problems. To address this problem, locally
preserving projection (LPP) [18] and neighborhood
preserving embedding (NPE) [19] are
proposed to be
directly applicable for dealing with new test data.
When the class information is available, NPE becomes
supervised NPE (in order to distinguish with our proposed
algorithm, we denote it as S-NPE). In S-NPE, the Euclidean
distance is used to compute a data point’s k nearest
neighbors. The main assumption behind S-NPE is that data
set is sampled from a single manifold. But in real world,
data set is always sampled from multiple manifolds. To
address this problem, a supervised neighborhood preserving
embedding (SNPE) linear manifold learning feature
extraction method for hyperspectral image classification is
presented in this paper. According to prior class-label
information, a new distance which makes intra-class more
tightly and inter-class more separately is proposed. The
intrinsic structure of original data in low-dimensional space
can be better described by using the new distance to
compute a data point’s k nearest neighbors. Data sets lay on
(or near) multiple manifolds can be processed.
The rest of the paper is organized as follows. In section
2, we briefly review the NPE algorithm. Section 3
introduces our SNPE algorithm, followed with new distance.
Experimental results on AVIRIS hyperspectral data set are
presented in Section 4. Section 5 ends the paper by
presenting some conclusions.
2. NEIGHBORHOOD PRESERVING EMBEDDING