1. A method comprising: directing modulated light at an object in motion over at least one set time interval; using a beam splitter to direct a first portion of the modulated light after reflection from the object onto a range imager and a second portion of the modulated light onto an intensity imager so as to generate time-dependent, pixel-specific, intensity data and range data of the object; and using a processor to: perform pixel-level fusion of the intensity data and the range data, and calculate three-dimensional, pixel-level motion flow from the pixel-level fusion of the intensity data and the range data, wherein the pixel-level fusion is implemented by minimizing ∑ u ⁢ [ I ⁡ ( R ⁡ ( u , p + Δ ⁢ ⁢ p ) ) - T ⁡ ( u ) ] 2 such that pixel motion p is constrained within a planar patch as defined by [ ∂ u ⁢ Z ∂ u ⁢ X ∂ v ⁢ Z ∂ v ⁢ Y ⁢ ⁢ 1 ] ⁢ p T = Δ t ⁢ Z , wherein: T(u) is previously acquired frame, I(u) is an input image, R(u,p) is a warp function describing a motion of image elements between T and I, u refers to image pixel coordinates in terms of row and column, (u,v), p T is motion of image elements between T and I, and Δp is a change in p from a previously calculated value, ∂ u Z and ∂ u X are range image gradients along pixel row, u, ∂ v Z and ∂ v Y are range image gradients along pixel column, v, Δ t Z is partial derivative with respect to time, t, X, Y, Z refers to three-dimensional coordinates of range image expressed in pixel coordinates u, v, and t.