1. A method for two-dimensional representation of an object using volume rendering, the method comprising: providing a representation of the object, in which values of a quantity characterizing the object are given at spatial points of the object; calculating, with a processor, with a volume rendering technique, a blended color value for representation as pixels on a screen; simulating, only once per blended color value, a single ray emanating from a single external surface of the object for calculating an effect of shadows or an effect of ambient occlusion; calculating, only once per blended color value, with the processor, a value for the effect of shadows as a function of the single ray; multiplying the blended color value by the value for the effect of shadows in order to obtain a blended color value that takes into account the effect of shadows; calculating an additional value for the effect of ambient occlusion; and multiplying the additional value by the product of the blended color value and the value for the effect of shadows; or multiplying the additional value by a factor that is a measure for light that exists in the ambient area, and adding the multiplied additional value to the product of the blended color value and the value for the effect of shadows; or multiplying the product of the additional value and the factor by the blended color value, and adding the multiplied product to the product of the blended color value and the value for the effect of shadows.