Registration results of high contrast organs for the normal subjects. The organ outlines are projected onto the X-ray and optical images, respectively. Different organs are distinguished with different colors; White, skin; Yellow, skeleton; Blue, lungs. (For interpretation of the references to colors in this figure, the reader is referred to the web version of this article.) (a) Two subjects with normal body sizes and standard postures. (b) Two subjects with irregular postures, and different open angles of the fore and hind limbs. (c) Two subjects with different body sizes: the upper one is underweight and the lower one is overweight.