FRAMELET-BASED MULTIRESOLUTION IMAGE FUSION WITH AN IMPROVED 
INTENSITY-HUE-SATURATION TRANSFORM 
M. J. Choi *, D. H. Lee, H. S. Lim 
Satellite Information Research Institute, KARI, 45, Eoeun-dong, Yuseong-gu, Daejeon, 305-333, KOREA 
prime, dhlee - hslim@kari.re.kr 
WG VII/6 - Remote Sensing Data Fusion 
KEY WORDS: Satellite remote sensing, Pan-sharpening, Intensity-Hue-Saturation transform, Wavelets, Framelets, IKONOS 
imagery. 
ABSTRACT: 
The fusion of the panchromatic (PAN) image with multispectral (MS) images is a very useful tool for remote sensing applications 
that require both high-spatial and high-spectral resolution. A hybrid fusion method, which comprises of the standard intensity-hue- 
saturation (IHS) transform and a wavelet transform, was recently introduced in the literature. The hybrid fusion method was able to 
eliminate drawbacks of the IHS and wavelet-based methods, while keeping the advantages. In this paper, we introduce a new hybrid 
fusion method based on the fast IHS transform with a control parameter along with the framelet transform. The control parameter is 
used to minimize the radiance difference between the PAN image and the intensity image. In addition, the framelet transform, which 
is a natural generalization of orthonormal wavelets if redundancy is introduced into the wavelet system, is used to extract the 
detailed spatial information from the difference image of the PAN image and the intensity image. In order to verify the performance 
of the proposed method, an IKONOS PAN image with MS images were used. The proposed method produces more satisfactory 
results, both visually and quantitatively. 
1. INTRODUCTION 
Due to the technical limitation, most earth observe satellites, 
such as the SPOT, IKONOS, QuickBird, and KOMPSAT-2, 
provide a bundle of multispectral (MS) images at a lower 
spatial resolution and a panchromatic (PAN) image at a higher 
spatial resolution, instead of MS images at a high spatial 
resolution. Therefore, a pan-sharpening technique is very useful 
tool for remote sensing applications that require both high- 
spatial and high-spectral resolution (Zhang,2004). 
Many image fusion techniques and software tools have been 
developed for specific applications. Of the hundreds of varied 
image fusion techniques, the best known methods are the 
intensity-hue-saturation (IHS) transform, principal component 
analysis, arithmetic combinations, and wavelet-based fusion 
methods. However, most of the existing techniques which 
perform suitably well with medium-resolution images, cannot 
always satisfy the fusion of MS and PAN high resolution 
images. 
Recently, Gonzalez-Audicana et al. (2004) introduced a hybrid 
fusion method comprised of the standard IHS transform and an 
undecimated discrete wavelet transform (UDWT). The hybrid 
fusion method was able to eliminate drawbacks of the IHS and 
wavelet-based methods, while keeping the advantages. 
Nevertheless, it is not efficient enough to quickly merge 
massive volumes of data from high-resolution satellite images 
because of its high computational complexity. 
To reduce the computational cost, a fast IHS (FIHS) transform 
introduced by Tu et al. (2004) is employed on a new hybrid 
fusion method. Aside from its fast computing capability for 
fusing images, this method can extend traditional three-order 
transformations to an arbitrary order. In addition, we employed 
a framelet transform which is a natural generalization of 
orthonormal wavelets if redundancy is introduced into the 
wavelet system. It thereby avoids some of artifacts that arise 
when the decimated discrete wavelet transform is applied to the 
image fusion like the UDWT. Moreover, it can reduce the 
computational cost to a half of that of the UDWT. 
More importantly, the proposed hybrid method enables us to 
reduce the overall computational cost to a half one again 
through simplifying the original mathematical model. A 
detailed explanation will be given later in the body of this paper. 
On the other hand, one of disadvantages of IHS-based methods 
is that they destroy the spectral characteristics of the MS data 
(Choi,2006). Recent studies have shown that the large 
difference between the values of the PAN and intensity images 
appears to cause the large spectral distortion of fused MS 
images. Indeed, this difference (PAN-I) causes the altered 
saturation component in the RGB-IHS conversion model. 
Therefore, a FIHS transform with a control parameter is 
employed to minimize the radiance difference between the PAN 
image and the intensity image. 
In order to verify the performance of the proposed method, an 
IKONOS PAN image with MS images were used. Then the 
spatial and spectral quality of the resulting images were 
analyzed and compared to images obtained from other well- 
known methods. The following chapter will explain the theory 
of the framelet transform. Readers unfamiliar with the wavelet 
theory are advised to continue to the third chapter, which the 
Corresponding author.