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Lucas and Kanade: align images with small gradient-guided steps

Spatial image gradients guide iterative local least-squares registration, reducing candidate searches and permitting translation, affine and brightness-adjustment extensions.

What is recorded here?

Spatial image gradients guide iterative local least-squares registration, reducing candidate searches and permitting translation, affine and brightness-adjustment extensions. To compare two camera views, a computer must find which patches show the same thing. Searching every possible position is expensive. Lucas and Kanade used the way image brightness changes across a patch to estimate a small corrective movement, then repeated the correction. Their least-squares formulation also extends to rotation, scaling, shear and simple brightness changes. This works locally: a good starting estimate and informative image gradients matter. A flat patch supplies no position information, and a single straight edge leaves motion along that edge ambiguous. Smoothing and coarse-to-fine matching can enlarge the useful range but can erase small details. The original stereo system required substantial human guidance. The reported stereo experiment has not been independently reproduced here.

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Scientific scope

The local iterative registration assumes a stated image relation, sufficiently small updates and informative gradients. A singular/poorly conditioned local matrix, large motion or changing appearance can defeat it. The algorithm is not guaranteed global registration of arbitrary image pairs. Pyramids, robust losses and later tracking variants are separate.

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People and systems

Bruce D. Lucas; Takeo Kanade

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English catalogue narrative

Lucas and Kanade: align images with small gradient-guided steps

Spatial image gradients guide iterative local least-squares registration, reducing candidate searches and permitting translation, affine and brightness-adjustment extensions.

To compare two camera views, a computer must find which patches show the same thing. Searching every possible position is expensive. Lucas and Kanade used the way image brightness changes across a patch to estimate a small corrective movement, then repeated the correction. Their least-squares formulation also extends to rotation, scaling, shear and simple brightness changes. This works locally: a good starting estimate and informative image gradients matter. A flat patch supplies no position information, and a single straight edge leaves motion along that edge ambiguous. Smoothing and coarse-to-fine matching can enlarge the useful range but can erase small details. The original stereo system required substantial human guidance. The reported stereo experiment has not been independently reproduced here.

Scientific scope

The local iterative registration assumes a stated image relation, sufficiently small updates and informative gradients. A singular/poorly conditioned local matrix, large motion or changing appearance can defeat it. The algorithm is not guaranteed global registration of arbitrary image pairs. Pyramids, robust losses and later tracking variants are separate.

People and systems

Bruce D. Lucas; Takeo Kanade

Original sources