1. A method for visualizing a tomographic volume data record of an object volume, comprising: assigning a scalar to each voxel of the volume data record which represents at least one of a measured variable and a variable derived therefrom, at a location of the voxel in the object volume; determining a gradient magnitude for each voxel of the volume data record; providing an at least two-dimensional transfer function which assigns a color value and an opacity value to each combination of gradient magnitude and scalar so that at least the opacity value and the color value are modulated by the gradient magnitude in order to improve the display; applying the at least two-dimensional transfer function to the scalars and gradient magnitudes of the volume data record to obtain a color value and an opacity value for each voxel of the volume data record; and displaying the volume data record with the respective color and opacity values of the voxels by way of a volume rendering technique; and carrying out a linear assignment of the opacity values to the scalars and the gradient magnitudes by the transfer function.