This paper presents a comprehensive overview of image fusion techniques using multiresolution decompositions. The primary aim is to frame multiresolution-based fusion methodologies within a common formalism and to develop a new region-based approach that combines aspects of both object and pixel-level fusion. The paper begins by introducing the concept of image fusion, its motivations, and the various challenges and requirements in designing a fusion scheme. It then reviews existing pixel-based fusion techniques, including weighted combination, color space fusion, optimization approaches, and biologically-inspired methods. The paper focuses on multiresolution decompositions, specifically pyramids and wavelets, and discusses their properties and applications. It also explores other multiresolution decomposition schemes such as wavelet packets, local bases, and multiwavelets. The authors propose a general framework for pixel-based multiresolution fusion and extend it to a region-based fusion strategy, demonstrating its effectiveness through experimental results. The paper concludes with a discussion on performance assessment and future research directions.This paper presents a comprehensive overview of image fusion techniques using multiresolution decompositions. The primary aim is to frame multiresolution-based fusion methodologies within a common formalism and to develop a new region-based approach that combines aspects of both object and pixel-level fusion. The paper begins by introducing the concept of image fusion, its motivations, and the various challenges and requirements in designing a fusion scheme. It then reviews existing pixel-based fusion techniques, including weighted combination, color space fusion, optimization approaches, and biologically-inspired methods. The paper focuses on multiresolution decompositions, specifically pyramids and wavelets, and discusses their properties and applications. It also explores other multiresolution decomposition schemes such as wavelet packets, local bases, and multiwavelets. The authors propose a general framework for pixel-based multiresolution fusion and extend it to a region-based fusion strategy, demonstrating its effectiveness through experimental results. The paper concludes with a discussion on performance assessment and future research directions.