Certain embodiments provide a photo-realistic rendering apparatus and method. An illumination model is used that includes placing a synthetic or virtual light source adjacent a region of tissue of interest in order to visualize the thickness of the tissue by modeling how light from the virtual light source interacts with the tissue of interest, through effects including absorption and scattering, as light emitted from the light source travels through the tissue of interest to a view point of view plane. It is simulated how some light is absorbed making tissue regions that are thicker darker (since more of the light is absorbed and the intensity reduces) and more red (since tissue tends to absorb blue and green wavelengths more strongly than red wavelengths and this chromatic effect is incorporated in the illumination model). A 2D image can thus be provided in which the color and intensity of light propagating through the tissue provides visual feedback on the tissue thickness.