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Head pose estimation without manual initialization

Head pose estimation without manual initialization. Paul Fitzpatrick. Life without manual initialization. Yaw *. Pitch *. Roll *. Translation in X, Y, Z. Manual initialization gives mapping from relative pose to absolute pose Initial orientation Shape parameters

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Head pose estimation without manual initialization

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  1. Head pose estimationwithout manual initialization Paul Fitzpatrick

  2. Life without manual initialization Yaw* Pitch* Roll* Translation in X, Y, Z • Manual initialization gives mapping from relative pose to absolute pose • Initial orientation • Shape parameters • If automated, replacement is likely to be weakest link • Otherwise, it would be a complete pose estimation system in itself • So initialization drives design * Nomenclature varies

  3. Opportunistic initialization • Use frontal view as reference pose • Eyes, nose are well-defined, stable, symmetric • Head outline is less well-defined, but always present and relatively easy to find • Use outline to guide search for eye region

  4. Head outline and eye location • Track head using :- • Color histogram • Grouped motion • Match against ellipse model • “ellipse-specific direct least-square fitting” (M. Pilu et al) • Histogram initialized from grouped motion of ellipse • Eyes located using a blob detector • Trade off detection rate for low false positives • Only search for eyes where orientation can be determined

  5. Tracking pose changes • Establish a mesh of trackers on the face • Prune mesh by head outline, comparative motion • As head rotates, occluded trackers are destroyed and new ones created • Tracking mesh gives 2D translation, in-plane rotation, and relative scale • When eyes are detected, establish a coordinate system on nearby trackers • Purpose of mesh is to allow eye location to be maintained across large excursions in yaw and pitch

  6. Mesh coordinate system • Mesh coordinate system is that of “flattened head” surface • Ideally interacts with image coordinates only where surface is parallel to image plane • Represents the remaining 2 dimensions • Must lead to inconsistencies, especially without good knowledge of head size • Still, useful in two important cases :- • When part of mesh remains visible throughout, serving as landmark • When movement is somewhat degenerate, e.g. look away, then look back Point of interaction shifts when head rotates in depth If movement lies within a 2D strip, Euclidean geometry survives

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