According to the wavelet transform theory

several groups of multi-spectral images were decomposed 1~5 layers respectively by using Db9 wavelet function;and then under the principle of inverse wavelet transform

fused images were obtained.Finally

the image quality evaluation methods such as information entropy

standard deviation

mutual information

and image fusion quality assessment were used to evaluate the fused images under different decomposition layers.Experimental results show that one layer of wavelet decomposition owns the best results in image fusion.