1. A processor-implemented graphics rendering method, the method comprising: determining, via the processor, in accordance with a variance of an x-component and a y-component of a normal vector of a highest resolution level MIP-map, reflectance parameters for all resolution levels of a MIP-map excluding the highest resolution level MIP-map, wherein for each resolution level of the MIP-map, excluding the highest resolution level MIP-map, the reflectance parameters are determined by calculating an error between using a current resolution level MIP-map and a higher resolution level MIP-map.