A two-dimensional representation of an object using volume rendering, with a representation of the object being used in which values of a quantity characterizing the object are given at spatial points of the object, is provided. A blended color value for the representation as pixels on a screen is calculated using a volume rendering technique that does not use an illumination model or uses a local illumination model. At least one ray emanating from a surface of the object is simulated for the purpose of calculating the effect of shadows or the effect of ambient occlusion. A value for the effect of shadows or a value for the effect of ambient occlusion is calculated using the at least one ray. The blended color value and the calculated value are combined in order to obtain a blended color value that takes into account the effect of shadows or ambient occlusion.