A MULTI-SCALE DENSELY DEEP LEARNING METHOD FOR PANSHARPENING
Zhikang Xiang
1
, Liang Xiao
1∗
, Pengfei Liu
2
, Yufei Zhang
1
1
School of Computer Science and Engineering,
Nanjing University of Science and Technology, Nanjing, China
2
School of Computer Science, Nanjing University of Posts and Telecommunications, Nanjing, China
xiaoliang@mail.njust.edu.cn
ABSTRACT
Pansharpening aims to produce a higher resolution multi-
spectral (HRMS) image by fusing the spectral information in
lower resolution multispectral (LRMS) image and the spatial
information in corresponding high resolution panchromatic
(PAN) image. In this work, we propose a multi-scale densely
deep learning based pansharpening method. Following an
end-to-end learning architecture, the proposed deep neural
network contains three modules: 1) a parallel multi-scale
convolutional layer is used to extract multiscale features of
PAN image; 2) a global identity branch structure is adopted to
preserve spectral structures; and 3) a dense learning block is
integrated to improve the spectral-spatial expressive power.
Compared with other state-of-the-art methods, experimen-
tal results obtained with our proposed method achieve high
pansharpening quality in visualization and quantification.
Index Terms— Pansharpening, Multiscale feature extrac-
tion, dense connection
1. INTRODUCTION
Since the remote sensing system is limited by optical diffrac-
tion, modulation transfer function, and signal-to-noise ratio, it
is difficult to obtain high resolution both in spatial and spec-
tral dimension. For this reason, pansharpening technique is
widely used to produce an HRMS image by fusing an LRMS
image and a corresponding PAN image.
In last decades, the researchers have developed various
pansharpening methods. Traditional pansharpening meth-
ods include component substitution (CS) and multiresolution
analysis (MRA) [1]. The former consists in transforming the
LRMS image in a suitable domain where one of the compo-
nents is replaced by the high-resolution PAN image, such as
This work has been supported by the National Natural Science Foun-
dation of China (Grant No. 61571230, 61871226, 61802202), the Na-
tional Major Research Plan of China (Grant No. 2016YFF0103604), the
Jiangsu Provincial Natural Science Foundation(Grant No. BK20161500,
BK20170905), the Jiangsu Provincial Key Developing Project(BE2018727),
the Postgraduate Research & Practice Innovation Program of Jiangsu
Province(KYCX18_0437). (corresponding author: Liang Xiao)
intensity-hue-saturation (IHS), principal component analy-
sis (PCA), and Gram-Schmidt (GS) [1]. These methods are
very popular owing to their easy implementation and fast
computation. The MRA based methods inject the resampled
LRMS band by spatial details obtained by multiresolution
decomposition of PAN image. The spatial details can be ex-
tracted according to approaches such as Laplacian pyramid
[3], wavelet transform [4] and nonseparable transform [1].
Compared with the CS methods, MRA based methods are
better in persevering spectral information, but worse in spa-
tial detail injecting. In summary, traditional methods usually
retain spatial information with the cost of spectral distortion.
Recently, convolutional neural network (CNN) has been
widely used in pansharpening. The advantage of CNN is the
fact that does not require manual priors, and it can learn the
mapping between input and output from the available LR and
HR remote sensing images. Existing CNN-based pansharp-
ening methods take the idea of single image super-resolution
as a reference, and can generally be divided into two groups.
The first group assumes that the relationship between LR/HR
MS image patches is same as LR/HR PAN image patches [5].
Actually, this assumption ignores the difference between PAN
image and each band of MS image, and makes no use of PAN
image in the reconstruction. The other one takes MS and
PAN images as input and trains an end-to-end network that
directly outputs the pan-sharpened image [6]. For example, a
deep pansharpening method by convolutional neural network
called PNN [7] adopts an architecture previously proposed for
image super-resolution and regards the problem as a simple
image regression with a black-box deep learning network.
In this paper, we proposed a multiscale deep neural net-
work shown in Fig. 1, which has the following features:
1.A parallel framework is used to extract the multiscale
features of PAN image together with high-pass information
of up-sampled LRMS image to reconstruct details of HRMS
image.
2.The network layers are densely connected to avoid the
vanishing-gradient problem during model training.
3.A global identity branch structure using up-sampled
LRMS image is adopted to preserve spectral structures.