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        "description": "The variational model assumes brightness constancy and global flow smoothness with a chosen regularization strength. Aperture ambiguity, illumination change, discontinuities and non-small motion limit the inference. It is not guaranteed recovery of true physical motion in arbitrary video. Iteration/stopping and later robust flow models remain separate.",
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      "statement": "# Horn and Schunck: estimate image motion by linking neighboring pixels\n\nA brightness-change constraint combined with spatial smoothness yields a global variational optical-flow model and an iterative neighbor-coupled velocity estimate.\n\nA moving camera image does not tell us both components of motion at every pixel. Along a straight edge, movement parallel to the edge can remain invisible. Horn and Schunck combined the brightness-change equation with a preference for neighboring velocities to vary smoothly. Their iterative method propagates information across the image, including patches with little visible texture. This is a useful modeling choice, not a guarantee that apparent brightness motion equals physical surface motion. Reflections, changing light and occlusions can violate the assumptions; smoothness can blur genuine motion boundaries. The paper tested synthetic image sequences with noise and quantization and reported its largest errors near occluding boundaries. The reported experiments have not been independently reproduced here.\n\n## Scientific scope\n\nThe variational model assumes brightness constancy and global flow smoothness with a chosen regularization strength. Aperture ambiguity, illumination change, discontinuities and non-small motion limit the inference. It is not guaranteed recovery of true physical motion in arbitrary video. Iteration/stopping and later robust flow models remain separate.\n\n## People and systems\n\nBerthold K.P. Horn; Brian G. Schunck\n\n\n\n## Original sources\n\n- [Berthold K.P. Horn and Brian G. Schunck: Determining Optical Flow (1981)](https://people.csail.mit.edu/bkph/papers/Optical_Flow_OPT.pdf)\n",
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