1. A method for automatically differentiating types of kidney stones by way of computed tomography, the method comprising: recording two computed tomography pictures of an object area including kidney stones, in the context of a different spectral distribution of the X-radiation; reconstructing, from raw data of the two computed tomography pictures, two image data records of the object area that include X-ray attenuation values of voxels of the object area in the context of the respective spectral distribution of the X-radiation; calculating from the two image data records, for each voxel of at least one interesting slice of the object area whose mean value from the two assigned X-ray attenuation values of the two image data records lies above a threshold value that is characteristic of kidney stones, a ratio r that is yielded in the following way in the context of the respective spectral distribution of the X-radiation at least one of from the two X-ray attenuation values of the voxel and from two averaged X-ray attenuation values that are obtained by averaging the X-ray attenuation values of voxels inside a prescribed volume around the voxel in the respective image data record, and prescribed X-ray attenuation values o 1 , o 2 of pure urine: r = x 1 - o 1 x 2 - o 2 x 1 , x 2 being at least one of the X-ray attenuation values and averaged X-ray attenuation values in the context of the respective spectral distribution of the X-radiation, the respective voxel being assigned to one or at least two types of kidney stones as a function of the magnitude of r.