1. An apparatus for coding a bit stream representing a three-dimensional video comprising a sequence of views, wherein a depth map is associated to each view, the depth map comprises depth information of each view with respect to a position to a camera capturing each view, the apparatus comprising: a partitioner configured to partition the depth map into coding units; a determiner configured to a. determine a type of model function for each coding unit based on the depth information of the coding unit, b. determine a DC type when the depth information of the coding unit indicates a constant depth, c. determine a gradient type when the depth information of the coding unit indicates a gradual depth change, and d. determine an edge type when the depth information of the coding unit indicates two segments of different but constant depths; a reducer configured to reduce the coding unit to a single residual value for each segment generated by the model function; and a signaler configured to signal the model function and the single residual value into the bitstream.