COL 10(1), 013001(2012) CHINESE OPTICS LETTERS January 10, 2012
Rapid matching algorithm for hyperspectral image based on
norm sifting
Hao Li (李李李 皞皞皞)
1,2
, Yong Ma (马马马 泳泳泳)
1,2∗
, Kun Liang (梁梁梁 琨琨琨)
1,2
, and Yin Yu (余余余 寅寅寅)
1,2
1
Department of Electronics and Information Engineering, Huazhong University of
Science and Technology, Wuhan 430074, China
2
Wuhan National Laboratory for Optoelectronics, Wuhan 430074, China
∗
Corresp onding author: mayong@hust.edu.cn
Received February 28, 2011; accepted June 14, 2011; posted online August 24, 2011
We propose a rapid spectral matching method by lowering number of comparisons, pro cessing time can be
saved. Firstly, 1-norm is chosen as length measure of spectrum, and with this criterion, a 1-norm database
is built. Secondly, a subspace is constructed from the whole reference library by retaining the references
with the most similar 1-norm values. Finally, matching operations are performed in the subspace to obtain
the match result. Simulations of geological mapping with ASTER spectral library show that the proposed
metho d can significantly reduce processing time and enhance accuracy compared with traditional and
dimension reduction methods.
OCIS codes: 300.6340, 280.4991.
doi: 10.3788/COL201210.013001.
Hyperspectral images provide both spatial and spectral
information with fine resolution. Analysis of hyperspec-
tral data has been applied to environment monitoring, ge-
ological mapping, target recognition, etc.
[1−3]
. Lately the
study of hyperspectral image processing has been mainly
focused on anomaly detection, mixture analysis and clas-
sification methods according to specific applications
[4]
.
On the other hand, as a pre-processing step of these
methods, techniques of band selection, feature extrac-
tion, and dimension reduction are also topics of inter-
est. They deal with the problem of high dimensionality
of hyperspectral data
[5]
, which is of great importance in
applications like military target detection where the pro-
cessing speed really matters
[6]
. Spectral matching pro-
grams also benefit from these methods, compared to tra-
ditional spectral matching measures like Euclidean dis-
tance (ED) and spectral angle measure (SAM)
[7,8]
, after
dimensional reduction, redundant spectral information is
removed, therefore the calculation complexity is reduced.
In recent years, numerous dimension reduction meth-
ods have been proposed
[9−12]
to avoid redundancy be-
tween bands. For spectral matching tasks, a feasible di-
mension reduction method is band selection
[13−17]
. Guo
et al. proposed a band selection method based on mu-
tual information (MI)
[16]
. The method estimates MI val-
ues using priori knowledge of a reference dataset, and by
eliminating bands with low MI values, which result in the
reduction of the computational cost of spectral matching.
Another method, proposed by Li et al. is called adaptive
band selection algorithm (ABS)
[17]
, which retains bands
with the largest possible amount of information and the
least correlation among them. Similarly, the method is
capable of reducing the computational cost of matching
algorithms.
These methods are designed to reduce the dimensions
of every single spectrum by eliminating redundant bands,
in this way the calculation time required for each compar-
ison between spectra will be reduced. However, a great
number of comparisons are still needed during spectral
matching procedure, which is especially true when the
spectral library contains a large quantity of reference
spectra. Therefore the total processing time for spec-
tral matching is still problematic for certain applications.
Band selection methods overlooked this factor, so it is
necessary to develop a method to reduce matching time
by avoiding unwanted comparisons.
In this letter, a new sp ectral matching algorithm based
on norm information of spectrum is prop osed, by lower-
ing the numb er of comparisons, processing time can be
saved. Reference spectra in spectral library are viewed
as n-dimensional vectors, which are sparsely distributed
in an n-dimensional space. The 1-norm values of these
vectors are calculated and used as an index for sifting.
When a pixel is analyzed, reference spectra with similar
1-norm values are retained and subsequently compared
with the pixel. In this method, spectral matching is pro-
cessed inside a significantly smaller subspace rather than
in the entire n-dimensional space. As fewer comparisons
are needed, time consumption is considerably decreased.
In geographical mapping applications, sp ectral match-
ing algorithm performs a pixel-by-pixel analysis for an
image containing N pixels with n bands. Each pixel is
compared with M reference spectrums in the library to
determine the most similar material. The time needed
for these operations can be expressed as follows:
T
1
= M × (T
d
+ T
c
) × N, (1)
where T
d
refers to the reading and writing time of a ref-
erence spectrum record and T
c
stands for time spent on
comparison operations.
A sp ectrum with n bands can be viewed as a vector
x
n
= {x
1
, x
2
, · · · , x
n
} in n-dimensional space. The dis-
tance between target spectrum x
n
and a reference spec-
trum y
n
can be calculated using spectral similarity mea-
sures. Two of the most popular similarity measures are
ED and SAM
[7]
. They are expressed as
1671-7694/2012/013001(4) 013001-1
c
° 2012 Chinese Optics Letters