Image Morphing versus 3D Morphing

Image morphing, the construction of an image sequence depicting a gradual transition between two images, has been extensively investigated [21] [2] [6] [16]. For images generated from 3D models, there is an alternative to morphing the images themselves: 3D morphing generates intermediate 3D models, the morphs, directly from the given models; the morphs are then rendered to produce an image sequence depicting the transformation. 3D morphing overcomes the following shortcomings of 2D morphing as applied to images generated from 3D models:

• In 3D morphing, creating the morphs is independent of the viewing and lighting parameters. Hence, we can create a morph sequence once, and then experiment with various camera angles and lighting conditions during rendering. In 2D morphing, a new morph must be recomputed every time we wish to alter our viewpoint or the illumination of the 3D model.
• 2D techniques, lacking information on the model's spatial configuration, are unable to correctly handle changes in illumination and visibility. Two examples of this type of artifact are: (i) Shadows and highlights fail to match shape changes occuring in the morph. (ii) When a feature of the 3D object is not visible in the original 2D image, this feature cannot be made to appear during the morph; for example, when a singing actor needs to open her mouth during a morph, pulling her lips apart thickens the lips instead of revealing her teeth.