Characterization of output color reproduction devices has the purpose of ensuring accurate color reproduction. In the characterization process, two transforms are required: from device dependent colorant space to device independent color space, and in reverse direction. This paper identifies the sources of discrepancies between forward and reverse characterization models and investigates possibilities of their improvement. It is shown that lookup tables such as those used in ICC profiles inherently introduce errors near process boundaries. Partial improvements are possible by populating tables with proper values in critical regions.