Image decoding device, image encoding device, and data structure of encoded data

Abstract

Memory required during decoding is reduced. A video image decoding device ( 1 ) is equipped with main direction deriving means ( 1453 A) that references a prediction mode definition DEFPM( 1 ), and from a prediction mode number, derives a main direction of a prediction direction corresponding to a prediction mode, and a gradient deriver ( 1453 B) that references a gradient definition table DEFANG( 1 ), and derives a gradient of the prediction direction.

1 . An image decoding device that decodes an image from encoded data by generating a predicted image with an intra prediction method associated with a prediction mode, characterized in that
 for an intra prediction method of directional prediction, a prediction mode corresponding to a prediction direction is associated with a prediction mode number for specifying the prediction mode,   the image decoding device comprising:   decoding means including reference pixel configuring means that determines whether or not the prediction mode number is less than or equal to a designated threshold, and configures reference pixels on the basis of the determined result, in which the decoding means conducts a designated decoding process in accordance with the configured reference pixel.   
     
     
         2 . An image decoding device that decodes an image from encoded data by generating a predicted image with an intra prediction method associated with a prediction mode, characterized in that
 for an intra prediction method of directional prediction, an association between a prediction mode corresponding to a prediction direction expressed by a main direction and gradient, and a prediction mode number for uniquely specifying the prediction mode, has a property enabling a designated feature related to at least one of the main direction and the gradient to be specified from the prediction mode number,   the image decoding device comprising:   feature specifying means that specifies the feature from the prediction mode number decoded from the encoded data, on the basis of the association; and   decoding means that conducts a designated decoding process in accordance with the feature.   
     
     
         3 . The image decoding device according to  claim 2 , characterized in that
 the feature specifying means specifies an absolute value of the gradient of the prediction direction as the feature, and   the decoding means derives a prediction direction corresponding to the prediction mode by deriving the main direction of the directional prediction, and also deriving the gradient of the prediction direction on the basis of the absolute value of the gradient of the prediction direction, as the decoding process.   
     
     
         4 . The image decoding device according to  claim 2 ,
 characterized in that   the feature specifying means specifies an absolute value of the gradient of the prediction direction as the feature, and   the decoding means selects a filter to apply to reference pixels used in predicted image generation on the basis of the absolute value of the gradient as the decoding process.   
     
     
         5 . The image decoding device according to  claim 2 , characterized in that
 the feature specifying means specifies a sign of the gradient of the prediction direction as the feature, and   the decoding means decides a scan order in which to decode transform coefficients on the basis of the sign of the gradient as the decoding process.   
     
     
         6 . An image decoding device that decodes an image that has been encoded by generating a predicted image with an intra prediction method associated with a prediction mode, characterized by comprising:
 arithmetic decoding means that, to decode a prediction mode of a target prediction unit, decodes, from encoded data by arithmetic decoding, an estimated prediction mode flag indicating whether or not to use an estimated prediction mode, and an estimated prediction mode index for designating one of a plurality of estimated prediction modes;   estimated prediction mode deriving means that derives the plurality of estimated prediction modes from already-decoded prediction modes assigned to a plurality of nearby prediction units near the target prediction unit; and   prediction mode decoding means that, in a case in which context for arithmetic decoding of the estimated prediction mode index is not configured, selects an estimated prediction mode indicated by the estimated prediction mode index if the estimated prediction mode flag indicates a match with an estimated prediction mode, and uses a swapping process for the plurality of estimated prediction modes if the estimated prediction mode flag does not indicate a match with an estimated prediction mode.   
     
     
         7 . The image decoding device according to  claim 6 , characterized in that
 if the estimated prediction mode flag does not indicate a match with an estimated prediction mode, the prediction mode decoding means executes an estimated prediction mode swapping process on the basis of a magnitude comparison of prediction mode numbers corresponding to the plurality of prediction modes.   
     
     
         8 - 11 . (canceled)