Pan-sharpening of QuickBird multi-spectral images with spectral distortion minimisation

This work presents a viable solution to the problem of merging a multi-spectral image with an arbitrary number of spectral bands with a higher-resolution panchromatic observation. The proposed method relies on the generalized Laplacian pyramid, which is a multiscale oversampled structure in which spatial details are mapped on different scales. The goal is to selectively performs spatial-frequencies spectrum substitution from an image to another with the constraint of thoroughly retaining the spectral information of the coarser data. To this end, a vector injection model has been defined: at each pixel, the detail vector to be added is always parallel to the approximation. Furthermore, its components are scaled by factors measuring the ratio of local gains between the multi-spectral and panchromatic data. Such a model is calculated at a coarser resolution, where both types of data are available, and extended to the finer resolution by embedding the modulation transfer functions of the multi-spectral scanner into the multi-resolution analysis. In this way, the inter-band structure model can be extended to the higher resolution without the drawback of the poor enhancement occurring when the model assumes MTFs close to be ideal. Results are presented and discussed on very high resolution QuickBird data of an urban area