While digital imaging systems have been widely used for many applications including consumer photography, microscopy, aerial photography, astronomical imaging, etc., their output images/videos often suffer from spatially varying blur caused by lens, transmission medium, post processing algorithms, and camera/object motion. Measuring the amount of blur globally and locally is an important issue. It can help us in removing the spatially varying blur, and enhancing the visual quality of the imaging system outputs. It can also provide useful information about the scene, such as saliency and depth map.