A light field means a 4-D function which characterizes the flow of light rays from a target scene, and used for image-based rendering. This paper presents a novel theoretical framework which considers the aliasing problem in dealing with discrete light field data. We introduce a new scheme called the aliasing separation to isolate the additional aliasing component caused by subsampling, and give a new perspective for how to optimize the reconstruction filter to interpolate light field data without aliasing artifacts. This optimization is closely related with depth estimation. Both the focus measure for light field rendering and the multiple baseline stereo can be derived from our theoretical framework.