information than (e) and (f). 
pp.1245-1257 
215 
Then we evaluate the performance of the fusion method using 
some image quality indexes. The indexes we selected are 
average value, standard difference, entropy, average grads and 
correlated coefficient. Average value can show the distribution 
of the image grayscale in the roughness. Standard difference 
and entropy can measure the information abundance in the 
image. Average grads shows exiguous contrast, varied texture 
characteristic and definition of the image. Correlated 
coefficient is calculated between fused image and SPOT5 
multi-spectral image, which shows how much spectral 
information have been conserved. The statistics is shown in tab 
1. 
Average values in table 1 show that the mean gray level of 
fused image is very close to the SPOT5 image. Standard 
difference, entropy and average grads in table 1 show that the 
information insufficiency of SAR image has decreased the 
information insufficiency of fused images, but the fused images 
with DT-CWT have conserved more information than DWT at 
corresponding level. Correlated coefficients in table 1 show 
that spectral characteristics of the fused images with DT-CWT 
are closer to the multi-spectral SPOT5 image than DWT at 
corresponding level. 
In a word, not only at information enhancement but also at 
spectral information conservation, fusion based on DT-CWT is 
superior to DWT. 
5. CONCLUSIONS 
In this paper, the dual-tree complex wavelet transform has been 
used to fuse SAR and optical images. According to the 
characteristic of SAR image, it is first denoised by Gamma 
MAP and Lee-Sigma filter. And then the low and high 
frequency parts of decomposed SAR and optical images have 
been fused by maximum gray value rule and maximum energy 
value rule respectively. Finally images fused by DT-CWT and 
DWT at different level have been compared in experiments. 
Observation results and statistics of quality indexes have shown 
that the fusion algorithm based on DT-CWT was better than 
DWT. 
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Images 
Average Value 
Standard 
Difference 
Entropy 
Average Grads 
Correlated 
Coefficients 
SAR 
53.340197 
26.879212 
5.037007 
8.630476 
— 
SPOT5 multi-spectral 
94.890384 
27.411184 
11.468343 
12.181283 
— 
Fused by 1-level DWT 
97.061614 
29.517138 
11.524848 
11.650854 
0.836114 
Fused by 2-level DWT 
96.100397 
27.015098 
11.397434 
9.548232 
0.843378 
Fused by 3-level DWT 
95.309379 
25.254701 
11.284076 
8.770403 
0.833622 
Fused by 1-level DT-CWT 
97.127747 
29.676878 
11.560681 
12.729831 
0.873973 
Fused by 2-level DT-CWT 
96.097643 
27.800316 
11.476087 
11.813529 
0.914931 
Fused by 3-level DT-CWT 
95.367769 
26.061456 
11.375349 
11.354203 
0.908619 
Table 1. Statistics of quality indexes of the images in figure 4 and 5