1. A method of generating a three dimensional representation of the shape of a subject from a depth image, the method comprising comparing a depth image of the subject with a plurality of representative images, wherein each representative image is associated with a respective parametric model for the shape and pose of a subject, each respective parametric model including numerical variables and the representative images being representations of a mean value of said variables for a cluster of possible shapes and poses of the subject; identifying a representative image of the plurality of representative images as a closest representative image to the depth image of the subject; selecting the parametric model for the shape and pose of the subject associated with the closest representative image to the depth image; and generating a three dimensional representation of the subject by fitting the selected parametric model to the depth image of the subject.