The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
(g) normal wavelet transform fused image (h) the novel method fused image 
Figure. 2 SAR image, multispectral image, and the result images of different fusion methods 
4.1 Subjective Qualitative Analysis and Comparison 
As for visual effect, the normal wavelet transform and the novel 
method have the advantages of preserving spectral information 
over the other methods. Brovey is the simplest, but the fusion 
effect is the worst. Triangle IHS, PCA and Gram-Schmidt keep 
too much information of SAR image, but lose most of spectral 
information. Besides, the spectral information distributes 
unevenly, resulting the distortion of the image hue. In so far as 
the normal wavelet transform and the novel method, the former 
is not as good as the latter in preserving information of the SAR 
image, and also with hue distortion from the original 
multispectral image; while the novel method not only preserves 
spectral information better, but also auto-adaptively keeps the 
texture feature of the SAR image, so that the fused image is 
smooth and natural in visual. Furthermore, the novel method 
has the advantage of preserving information of SAR image. For 
instance, the representative object circled by the red rectangle 
in 
In statistics, mean ju and standard deviation o are 
defined: 
¿=—( 6 ) 
n m 
~ 2 
(J 
(7) 
Figure 1(a) is the special information in the SAR image, which 
preserved fully in the novel method, while relatively poor for 
PCA or normal wavelet transform method. Comprehensively, 
concerning visual effect, the novel method is relatively the best 
fusion method. 
4.2 Objective Quantitative Analysis and Comparison 
Certain objective quantitative analyzing indexes are utilized to 
compare the fusion effects and information preservation 
abilities of different fusion methods adopted in this paper. We 
employed mean, standard deviation, entropy, correlation 
coefficient, average gradient and spectral distortion to reflect 
image luminance, spatial detail information preservation, and 
spectral information preservation (Luclen, 1997). 
1. Mean and Standard Deviation (S. D.): 
where, n is the sample size, x. is the value of the z'th 
sample. 
Here, mean is the average gray value of all the pixels in 
the image, and for the human visual system, it is the 
average luminance. So if the mean is moderate, the visual 
effect is fine. Standard deviation represents the discrete 
degree of the pixel value relative to the mean. The larger 
the deviation is, the more dispersedly the gray grades 
distribute, and if the probability of each gray grade equals, 
the information capacity is the maximum. 
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