1. A method comprising receiving, by a data encoder, image data to be encoded; accessing, via the data encoder, a reference data conversion function which determines a mapping between a set of reference digital code values and a set of reference levels based on contrast sensitivity of human vision; based on the receiving and the accessing, encoding, via the data encoder, the received image data into reference encoded image data; and outputting, via the data encoder, the reference encoded image data, wherein: color component values in the received image data are represented by the set of reference digital code values, the reference digital code values having a bit depth of 10 or 12 bits, the mapping is based at least in part on a functional model of: ( C 1 + C 2 ⁢ Y n 1 + c 3 ⁢ Y n ) m , and n, m, c 1 , c 2 , and c 3 are predetermined values.