It is shown that an infinitesimally small surface element of a Lambertian scene exists as a plane of constant value in a 4D light field, where the orientation of the plane is determined by the depth of the element in the scene. By applying 2D gradient operators to appropriate subsets of the light field, the orientations of these constant-valued planes, and thus the depths of the corresponding elements of the scene, may be estimated. The redundancy associated with using three color channels, and having two depth estimates based on orthogonal 2D gradient estimates, is resolved using a weighted sum based on the confidence of each estimate.