Image data encoding and decoding

Abstract

An image encoding apparatus comprises a controller configured to select, from a set of prediction directions, a set of candidate prediction directions as a subset of the set of prediction directions, for a current image region of a current image in dependence upon one or more properties of a group of reference samples of the current image applicable to the current image region; and an intra-image predictor configured to predict samples of the current image region with respect to one or more of the group of reference samples of the same image according to a prediction direction between the current sample and a reference position amongst the reference samples; in which the intra-image predictor is configured to select the prediction direction for the current image region from the set of candidate prediction directions.

1 - 25 . (canceled) 
     
     
         26 . An image encoding apparatus comprising:
 a controller configured to select, from a set of prediction directions, a set of candidate prediction directions as a subset of the set of prediction directions, for a current image region of a current image in dependence upon one or more properties of a group of reference samples of the current image applicable to the current image region; and   an intra-image predictor configured to predict samples of the current image region with respect to one or more of the group of reference samples of the same image according to a prediction direction between the current sample and a reference position amongst the reference samples;   in which the intra-image predictor is configured to select the prediction direction for the current image region from the set of candidate prediction directions.   
     
     
         27 . The apparatus according to  claim 26 , in which the one or more properties represent at least one from the list consisting of:
 i. image activity of the group of reference samples, the selection of the subset of the prediction directions being weighted towards reference samples in the group of reference samples having higher image activity;   ii. position of the current image region within a picture; and   iii. availability of reference samples for prediction of the current image region.   
     
     
         28 . The apparatus according to  claim 26 , in which the controller is configured to supplement the set of candidate prediction directions with one or more additional prediction directions not forming part of the set of prediction directions. 
     
     
         29 . The apparatus according to  claim 28 , in which:
 the set of prediction directions each have associated direction identifiers; and   the controller is configured to assign the one or more additional prediction directions to respective direction identifiers associated with prediction directions which are in the set of prediction directions but not in the subset of prediction directions.   
     
     
         30 . The apparatus according to  claim 28 , in which the one or more additional prediction directions comprise one or more of:
 (i) a prediction direction lying between a respective pair of prediction directions in the set of candidate prediction directions; and   (ii) a prediction direction having an angle, between a current sample to be predicted and a reference position amongst the reference samples, which varies with a location, within the current region, of the current sample to be predicted.   
     
     
         31 . The apparatus according to  claim 26 , in which the set of candidate prediction directions includes at least a horizontal prediction direction and a vertical prediction direction. 
     
     
         32 . The apparatus according to  claim 26 , in which the controller is configured to encode data identifying the prediction direction selected for each sample or region of the image. 
     
     
         33 . The apparatus according to  claim 32 , in which the controller is configured to detect, as further candidate prediction directions, one or more likely prediction directions in response to those commonly used for one or more previously encoded image regions and to encode the data identifying the prediction direction as either: (i) data indicating that the prediction direction is a detected likely prediction direction, or (ii) data identifying the prediction direction amongst the remaining candidate prediction directions. 
     
     
         34 . Video storage, capture, transmission or reception apparatus comprising apparatus according to  claim 26 . 
     
     
         35 . An image decoding apparatus comprising:
 a controller configured to select, from a set of prediction directions, a set of candidate prediction directions as a subset of the set of prediction directions, for a current image region of a current image in dependence upon one or more properties of a group of reference samples of the current image applicable to the current image region; and   an intra-image predictor configured to predict samples of the current image region with respect to one or more of the group of reference samples of the same image according to a prediction direction between the current sample and a reference position amongst the reference samples;   in which the intra-image predictor is configured to select the prediction direction for the current image region from the set of candidate prediction directions.   
     
     
         36 . The apparatus according to  claim 35 , in which the one or more properties represent at least one from the list consisting of:
 i. image activity of the group of reference samples, the selection of the subset of the prediction directions being weighted towards reference samples in the group of reference samples having higher image activity;   ii. position of the current image region within a picture;   iii. availability of reference samples for prediction of the current image region.   
     
     
         37 . The apparatus according to  claim 35 , in which the controller is configured to supplement the set of candidate prediction directions with one or more additional prediction directions not forming part of the set of prediction directions. 
     
     
         38 . The apparatus according to  claim 37 , in which:
 the set of prediction directions each have associated direction identifiers; and   the controller is configured to assign the one or more additional prediction directions to respective direction identifiers associated with prediction directions which are in the set of prediction directions but not in the subset of prediction directions.   
     
     
         39 . The apparatus according to  claim 37 , in which the one or more additional prediction directions comprise one or more of:
 (i) a prediction direction lying between a respective pair of prediction directions in the set of candidate prediction directions; and   (ii) a prediction direction having an angle, between a current sample to be predicted and a reference position amongst the reference samples, which varies with a location, within the current region, of the current sample to be predicted.   
     
     
         40 . The apparatus according to  claim 35 , in which the controller is configured to detect encoded data identifying the prediction direction selected for each sample or region of the image. 
     
     
         41 . The apparatus according to  claim 42 , in which the controller is configured to detect, as further candidate prediction directions, one or more likely prediction directions in response to those commonly used for one or more previously encoded image regions and to encode the data identifying the prediction direction as either: (i) data indicating that the prediction direction is a detected likely prediction direction, or (ii) data identifying the prediction direction amongst the remaining candidate prediction directions. 
     
     
         42 . Video storage, capture, transmission or reception apparatus comprising apparatus according to  claim 35 . 
     
     
         43 . An image encoding method comprising:
 selecting, from a set of prediction directions, a set of candidate prediction directions as a subset of the set of prediction directions, for a current image region of a current image in dependence upon one or more properties of a group of reference samples of the current image applicable to the current image region;   selecting a prediction direction for the current image region from the set of candidate prediction directions; and   intra-image predicting samples of the current image region with respect to one or more of the group of reference samples of the same image according to a prediction direction between the current sample and a reference position amongst the reference samples.   
     
     
         44 . An image decoding method comprising:
 selecting, from a set of prediction directions, a set of candidate prediction directions as a subset of the set of prediction directions, for a current image region of a current image in dependence upon one or more properties of a group of reference samples of the current image applicable to the current image region;   selecting a prediction direction for the current image region from the set of candidate prediction directions; and   intra-image predicting samples of the current image region with respect to one or more of the group of reference samples of the same image according to a prediction direction between the current sample and a reference position amongst the reference samples.   
     
     
         45 . A non-transitory computer readable medium including computer program instructions, which when executed by a computer causes the computer to perform the method of  claim 44 .