1. A method for determining depth in a light field image comprising (x,y,u,v) four-dimensional data for pixels, comprising: at a processor, obtaining a light field image; at the processor, identifying a subset of light field samples in the light field image for generating epipolar images; at the processor, re-sampling the light field image to generate at least one epipolar image from the identified subset of light field samples, wherein each epipolar image comprises at least one selected from the group consisting of: a two-dimensional (x,u) slice for a fixed value of y; and a two-dimensional (y,v) slice for a fixed value of x; at the processor, determining at least one gradient for at least a portion of at least one generated epipolar image; at the processor, determining a slope for the at least one gradient; at the processor, based on the determined slope, determining a depth for at least one element of the light field image; at an output device, generating output representing the determined depth; wherein identifying a subset of light field samples in the light field image comprises identifying samples corresponding to approximate centers of microlenses used in capturing the light field image; and wherein identifying samples corresponding to approximate centers of microlenses used in capturing the light field image comprises, for each of a plurality of microlenses: determining offset vectors indicating a distance between a desired coordinate of a sample and a center of a corresponding microlens; determining a location of the microlens center; and based on the determined offset vector, identifying a plurality of pixel locations to sample.