Fig. 2.

a and b Serve to illustrate the composite transform following registration after two levels. Please note that a and b have the same initial and final positions. (a) The initial positions (unfilled gray circles) are deformed to intermediate positions (filled gray circles) by using transform T₀ (stored as ω), followed by deformation to final positions (filled dark circles) by further use of transform T₁. The aggregate operation represents the composite transform (dashed line) of Eq. (2). (b) The initial positions (unfilled gray circles) are deformed to intermediate positions (filled black triangles) by using transform T₁, followed by deformation to final positions (filled dark circles) by further use of transform T₀, stored as the warping image ω at voxel centers. The aggregate operation represents the composite transform (dashed line) of Eq. (3).