1. A two-dimensional coding method comprising: reconstructing a two-dimensional image recorded as a hologram by a hologram reconstructing apparatus, the two-dimensional image containing a plurality of reference pixels each having a brightness, wherein the different brightnesses of the plurality of reference pixels determines brightness levels, and data pixels representing data according to a set of codes associated with the brightness levels; and comparing a brightness of each data pixel of the reconstructed two-dimensional image with the different brightnesses of the plurality of reference pixels and coding each data pixel according to a code associated with a brightness level of the data pixel.