Motion Estimation Techniques

2.3.1. Brightness constancy motion model and the optical flow equation 10 2.3.2. Glossary 2D motion vector field: the 2D motion vector field is defined as the projection of the 3D objects motion onto the 2D image plane. Aperture problem: when observing a moving structure through a small aperture, different physical motions appear indistinguishable Block matching: Motion estimation algorithms based on the matching of blocks between two frames, with the objective to minimize a dissimilarity measure. Brightness constancy: Assumption that a pixel intensity remains constant along a motion trajectory. In other words, variations in time of the pixel intensity are exclusively due to the objects displacements. Dense motion field: Motion field which represents motion by assigning one motion vector to each image pixel. Lambertian reflectance: An ideal diffusely reflecting surface, whose apparent brightness is the same regardless of an observer view angle. Motion compensation: To perform temporal processing on pixels along motion trajectories, i.e. shifted by a motion vector, instead of on co-located pixels. In video coding, motion compensated prediction refers to the prediction of a block by using a shifted previously encoded block, where the shift correspond to the estimated motion vector. Motion trajectory: The path that a pixel follows through space and time when considering an image sequence as a three-dimensional continuous spatio-temporal field. Multi-resolution motion estimation: Techniques based on a multi-resolution or multi-scale data representation, which first compute a coarse estimate of the motion field at the lowest resolution level and then progressively refine it at successively higher resolution levels. Occlusion, Disocclusion: An occlusion refers to a region or object which is partially or fully hidden by another object closer to the camera. A disocclusion denotes a newly appearing region or object which was previously occluded. Optical flow: the optical flow is defined as the apparent motion of the brightness pattern. In other words, the optical flow captures the spatio-temporal variation of pixel intensities in an image sequence. Outlier: an outlier is sample which markedly deviates from the rest of the data samples. Sprite: a sprite, also known as mosaic or panoramic image, refers to a large composite image obtained by aligning and blending pixels from multiple displaced images Rate-distortion: in the context of lossy data compression, the optimal minimization of the date rate in order to be able to reconstruct the source without exceeding a given distortion, or reciprocally, the minimization of the reconstruction distortion for a …