Method, device, and computer program for optimizing transmission of motion vector related information when transmitting a video stream from an encoder to a decoder

Abstract

The invention relates to the encoding or decoding of at least one portion of an image by predicting the at least one portion using at least one predictor, the at least one predictor being determined as a function of at least one reference image portion and as a function of values of a plurality of items of motion information. After having obtained a value of a first item of the plurality of items, a value of a second item is evaluated as a function of the obtained value of the first item, the second item being an item of the plurality of items and being distinct from the first item. Next, the at least one predictor is determined as a function of the at least one reference image portion and as a function of the first and second items.

1 . A method for encoding or decoding at least one portion of an image by predicting the at least one portion using at least one predictor, the at least one predictor being determined as a function of at least one reference image portion and as a function of values of a plurality of items of motion information, the method comprising:
 obtaining a value of a first item of the plurality of items;   evaluating a value of a second item as a function of the obtained value of the first item, the second item being an item of the plurality of items and being distinct from the first item;   determining the at least one predictor as a function of the at least one reference image portion and as a function of the first and second items.   
     
     
         2 . The method according to  claim 1 , further comprising a step of obtaining a value of a third item, the third item being an item of the plurality of items and being distinct from the first and the second item, the step of evaluating the value of the second item as a function of the obtained value of the first item being carried out as a function of the obtained value of the third item. 
     
     
         3 . The method according to  claim 2  wherein the third item comprises a prediction mode of which the value indicates that the at least one portion and the at least one reference image portion belong to at least two different images. 
     
     
         4 . The method according to  claim 1  wherein the plurality of items comprises at least one motion vector, the first item comprising a resolution of the at least one motion vector. 
     
     
         5 . The method of  claim 1  wherein the plurality of items comprises at least one motion vector and wherein the second item comprises a number of motion vector predictors used to predict the at least one motion vector. 
     
     
         6 . The method according to  claim 4  wherein the plurality of items comprises at least one motion vector and wherein the second item comprises a number of motion vector predictors used to predict the at least one motion vector and further comprising a step of obtaining the number of motion vector predictors if the obtained value of the first item is equal to a predetermined value. 
     
     
         7 . The method according to  claim 1  wherein the second item comprises a number of reference lists from which the at least one predictor is derived. 
     
     
         8 . The method according to  claim 1  wherein the first item or the second item comprises a prediction mode. 
     
     
         9 . The method of  claim 8  according to which the first item comprises a prediction mode, wherein the plurality of items comprises at least one motion vector and wherein the second item comprises a number of motion vector predictors used to predict the at least one motion vector, wherein the second item comprises a number of reference lists from which the at least one predictor is derived, wherein the plurality of items comprises at least one motion vector, the second item comprising a resolution of the at least one motion vector, or wherein the second item comprises a reference frame index. 
     
     
         10 . The method of  claim 1  wherein the step of obtaining the value of the first item comprises a step of setting the value of the first item to a predetermined value if the value of the first item is not received along with encoded data. 
     
     
         11 . The method of  claim 1  wherein the step of evaluating the value of the second item as a function of the obtained value of the first item comprises a step of obtaining a value of a third item if the obtained value of the first item is equal to a predetermined value, the third item being an item of the plurality of items and being distinct from the first and the second item, the value of the second item being evaluated as a function of the obtained value of the third item. 
     
     
         12 . The method of  claim 1  wherein the value of the second item is chosen from among a set of obtained values as a function of the obtained value of the first item and/or wherein the value of the second item is associated with one prediction unit of the at least one portion. 
     
     
         13 . The method of  claim 12  according to which the value of the second item is associated with one prediction unit of the at least one portion, wherein the second item is associated with one prediction unit of the at least one portion or with a plurality of prediction units of a plurality of portions of the image depending on a coding mode. 
     
     
         14 . A method for encoding or decoding at least a first portion and a second portion of an image by predicting the first and the second portions using predictors, the predictors being determined as a function of at least one reference image and as a function of motion vectors, the at least one reference image being distinct from the image to which belongs the first and second portions, a first resolution of motion vectors being associated with a prediction unit of the first portion and a second resolution of motion vectors being associated with a prediction unit of the second portion, the first resolution being different from the second resolution, the method comprising:
 obtaining motion vector information;   evaluating at least one first motion vector associated with the first portion and at least one second motion vector associated with the second portion, as a function of the obtained motion vector information; and   determining at least one first predictor for the first portion and at least one second predictor for the second portion.   
     
     
         15 . The method of  claim 14  wherein at least one motion vector predictor used to evaluate the at least one first motion vector is not rounded or wherein at least one motion vector predictor used to evaluate the at least one first motion vector is not rounded when no residual motion vector value associated with the at least one motion vector predictor is used to evaluate the at least one first motion vector. 
     
     
         16 . The method of  claim 14  wherein a number of first motion vector predictors used to predict the first portion, a number of reference frame indexes used to predict the first portion, or a prediction mode used to predict the first portion is determined as a function of the first motion vector resolution. 
     
     
         17 . The method of  claim 14  wherein the first motion vector resolution, a number of reference frame indexes used to predict the first portion, and/or a number of reference frame indexes used to predict the first portion are determined as a function of a prediction mode. 
     
     
         18 . The method of  claim 14  wherein the first resolution is different from the second resolution only for the Adaptive Motion Vector Prediction mode. 
     
     
         19 . A computer readable storage medium storing a program for carrying out the method of  claim 1 . 
     
     
         20 . A device for encoding or decoding at least one portion of an image by predicting the at least one portion using at least one predictor, the at least one predictor being determined as a function of at least one reference image portion and as a function of values of a plurality of items of motion information, the device comprising at least one microprocessor configured for carrying out the steps of:
 obtaining a value of a first item of the plurality of items;   evaluating a value of a second item as a function of the obtained value of the first item, the second item being an item of the plurality of items and being distinct from the first item;   determining the at least one predictor as a function of the at least one reference image portion and as a function of the first and second items.