Video coding system

Abstract

A motion estimation system for a video coder is disclosed. The system comprises an input for a video image ( 6 ) to be coded. It also comprises a series of motion estimators ( 2, 3 ) of varying complexity, for estimating a motion vector field between the received image ( 6 ) and a reference image ( 5 ). The subsequent motion estimator in the series is selected by a control means ( 4 ) if a prediction error associated with the motion vector field estimated by the currently selected motion estimator exceeds a predetermined threshold.

What is claimed is:  
     
         1 . A motion estimation system for a video coder comprising: 
 means for receiving a video frame to be coded;    a series of motion estimators of varying complexity, for estimating a motion vector field between the said received frame and a reference frame; and    control means for selecting the subsequent motion estimator in the series only if a prediction error associated with the motion vector field estimated by the currently selected motion estimator exceeds a predetermined threshold.    
     
     
         2 . A motion estimation system as claimed in  claim 1 , wherein the series of motion estimators comprises a series of motion models.  
     
     
         3 . A motion estimation system as claimed in  claim 2 , wherein the motion models are polynomial motion models.  
     
     
         4 . A motion estimation system as claimed in  claim 2  or  3 , wherein the series of motion models comprise a hierarchy inluding a translational motion model, a simplified linear model and a complete linear model.  
     
     
         5 . A motion estimation system as claimed in any of  claims 2  to  5 , wherein the series of motion models comprises any one, or any combination of, a zero motion model, a translational motion model, an affine motion model and a quadratic motion model.  
     
     
         6 . A motion estimation system as claimed in any preceding claim, wherein the series of motion estimators comprises a series of minimisers.  
     
     
         7 . A motion estimation system as claimed in  claim 6 , wherein the series of minimisers comprises a segment matching minimiser, a Newton minimiser and a Quasi-Newton minimiser.  
     
     
         8 . A motion estimation system as claimed in  claim 6  or  7 , wherein the series of minimisers comprises a full search minimiser and/or a Taylor expanded minimiser.  
     
     
         9 . A motion estimation system as claimed in any preceding claim, further comprising means for smoothing the received frame and for forwarding the smoothed frame to the series of motion estimators.  
     
     
         10 . A motion estimation system as claimed in  claim 9 , wherein the smoothing means comprises a series of low pass filters.  
     
     
         11 . A motion estimation system as claimed in  claim 9  or  10 , wherein the control means selects the level of smoothing during minimisation depending on the change in prediction error.  
     
     
         12 . A video coder comprising a motion estimation system as claimed in any preceding claim.  
     
     
         13 . A motion estimation method for coding a video frame, comprising: 
 receiving a video frame to be coded;    estimating a motion vector field between the said received frame and a reference frame, using a motion estimator from a series of motion estimators of varying complexity;    determining whether a prediction error associated with the motion vector field estimated by the currently selected motion estimator exceeds a predetermined threshold and, only if so, selecting the subsequent motion estimator in the series.