Image Fusion can be defined as a process of combining information from multiple input images in such way that final fused image having good quality information then individual image. Combining various modalities of medical images increases robustness and improve accuracy in medical research and diagnosis of diseases. A significant task for retrieving complementary information from different modalities of medical images such as MRI, CT, PET and SPECT can be achieved by multimodal medical image

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... sion. Different characteristics of low and high frequency sub bands are taken into account and fusion rules are applied. Medical imaging field demands images with high resolution and higher information contents for necessary disease diagnosis and visualization. This paper reviews different methods of image fusion i.e., PCA (principal Component Analysis), DCT (Discrete Cosine Transform), SWT (Stationary Wavelet Transform) and DWT (Discrete Wavelet Transform) and further comparative analysis is done.