Pixel-based image fusion using wavelet transform for SPOT and ETM+ image

Image fusion means merging two or more images in such a way as to preserving the most desirable characteristics of each image. Because of standard image fusion methods are often successful at adding spatial detail into the multispectral imagery but distort the colour information in the fusion process. So, the paper presents an approach for multi-resolution image fusion of a high-resolution SPOT (Satellite Pour l´Observation de la Terre, SPOT) panchromatic image and a low-resolution Landsat 7 ETM+ multispectral image based on wavelet transform (WT) combined with filtering in the Fourier domain. Firstly, the images were decomposed to some wavelet coefficients by Mallat algorithm; Secondly, the wavelet transform methods add the wavelet coefficients of the SPOT PAN image to ETM+ image. Finally, the fused image is reconstructed by performing the inverse wavelet transform for obtaining multispectral images of higher spatial resolution. In order to evaluate the quality of the fused images, three quantitive indicators such as Gradients, RMSE, Correlation Coefficients were defined in the paper. In the mean time, the results from a number of wavelet-based image fusion schemes which are the intensity-hue-saturation (IHS) and high-pass filter method (HPF) are compared and these fusion methods were used to synthesize the Landsat ETM+ data and SPOT-5 PAN data were. The evaluation results showed that the WT fusion methods perform the fusion of SPOT PAN image and ETM+ image better than IHS and HPF, specially in preserving both spectral and spatial information. Experiment results showed that the proposed WT fusion algorithm works well in multi-resolution fusion and also preserve the original color or spectral characteristics of the input image data.