Computer vision

Werkhoven P., Toet A. & Koenderink J.J. (1990). Displacement estimates through adaptive affinities.  IEEE Transactions on Pattern Analysis and Machine Intelligence  12(7), 658‑663.  Algorithms for the computation of optic flow from image sequences by means of "local constraint" (relating spatial to temporal gray value variations in the image plane) often postulate an additional "oriented smoothness constraint" (assuming that the flow vector field varies smoothly). Oriented smoothnes in addition to "local constraint" proves to be a mathematical foundation for many iterative algorithms that compute optic flow. In this correspondence we present a new technique that is functionally equivalent to the oriented smoothness concept and reduces numerical complexity and computational costs by eliminating the smoothness requirement from the iteration process. We applied local affine transformations for propagating uniquely computed flow vectors into homogeneous regions and along edges, in a single step. The window within which the local affine transformation is performed, is adaptive to the local structure of the intensity pattern, which is accordance with the oriented smoothness concept as formulated by Nagel.

 Werkhoven P. & Koenderink J.J. (1990).  Extraction of motion parallax structure in the visual system I.  Biological Cybernetics  63, 185‑191.  We present a paradigm to estimate local affine motion parallax structure from a varying image irradiance pattern. The method is based on a matching of jets of irradiance rather than the local image irradiance pattern or features of it. It does not put any constraints on the structure of the image irradiance pattern. Moreover, the aperture problem does not arise and additional ad hoc constraints on the velocity field like the 'smoothness constraint'' are superfluous. An implementation is designed such that the affine structure of the local motion parallax field is represented through simple combinations of the outputs of physiologically plausible receptive fields and their temporal derivatives.

Werkhoven P. & Koenderink J.J. (1990).  Extraction of motion parallax structure in the visual system II.  Biological Cybernetics  63, 193‑199.  We have developed an algorithm to extract local affine motion parallax structure of a varying image irradiance pattern in part I. In part II, we present computational results of this algorithm for situations where the information about the affine structure is contained in only two successive images. This applies to a large class of problems (e.g. two-image motion sequences and stereoscopic vision). The results show the effects of spatio-temporal discretisation and internal noise on the performance of this algorithm.