Image encoding device, image encoding method, image decoding device, image decoding method, program, and storage medium
A prediction set determining section selects a prediction set from a prediction set group including a plurality of prediction sets having different combinations of prediction modes corresponding to different prediction directions. Further, a prediction mode determining section selects a prediction mode from the prediction set thus selected. An entropy encoding section encodes the prediction set thus selected, the prediction mode thus selected, and residual data between an input image and a predicted image formed on the basis of the prediction set and the prediction mode. This allows an image encoding device to carry out predictions from more various angles, thereby improving prediction efficiency.
1. An image decoder for decoding encoded data so as to form a decoded image, comprising:
a decoding circuit configured to decode, from the encoded data,
(i) an encode parameter including prediction mode information and
(ii) prediction residual data;
a first selecting circuit configured to select, from a plurality of prediction sets, one prediction set to be used with respect to each target block to be intra-predicted, wherein the prediction set includes , as prediction mode candidates, a plurality of prediction modes corresponding to respective direction predictions, wherein each of the plurality of prediction sets includes the same number of the plurality of prediction modes;
a second selecting circuit configured to select one prediction mode from the plurality of prediction modes included in the prediction set selected by the first selector;
a predicting circuit configured to form, on the basis of the prediction mode thus selected, a predicted image of the each target block to be intra-predicted; and
an adding circuit configured to form a decoded image of the each target block to be intra-predicted by adding the predicted image formed by the prediction section and the prediction residual data obtained by decoding the encoded data.
2. The image decoder as set forth in claim 1 , wherein prediction directions of the respective plurality of prediction modes corresponding to the respective direction predictions are unevenly distributed with a bias towards a specific direction.
3. The image decoder as set forth in claim 2 , wherein a plurality of prediction sets constituting the prediction set group are selectable with respect to a predetermined reference region which is referred to by the predictor in order to form the predicted image of the each target block to be intra-predicted.
4. The image decoder as set forth in claim 3 , wherein the predetermined reference region includes at least one of regions which are positioned on the left, on the upper left, and on the top, respectively, of the each target block to be intra-predicted.
5. The image decoder as set forth in claim 2 , wherein the specific direction is a horizontal direction or a vertical direction.
6. An image encoder for encoding an input image, comprising:
a determining circuit configured to determine a prediction mode to be used for forming a predicted image of a target block to be intra-predicted;
a selecting circuit configured to select, from a plurality of prediction sets, one prediction set with respect to each target block to be intra-predicted, wherein the prediction set includes, as prediction mode candidates, a plurality of prediction modes corresponding to respective direction predictions, wherein each of the plurality of prediction sets includes the same number of the plurality of prediction modes;
a prediction mode encoder configured to encode, with respect to the each target block to be intra-predicted and by use of the prediction set thus selected by the selector, the prediction mode thus determined;
a predicting circuit configured to form, on the basis of the prediction mode thus determined, a predicted image of the each target block to be intra-predicted; and
a residual data encoding circuit configured to encode residual data between the input image and the predicted image.
7. The image encoder as set forth in claim 6 , wherein prediction directions of the respective plurality of prediction modes corresponding to the respective direction predictions are unevenly distributed with a bias towards a specific direction.
8. The image encoder as set forth in claim 7 , wherein a plurality of prediction sets are selectable with respect to a predetermined reference region which is referred to by the predictor in order to form the predicted image of the each target block to be intra-predicted.
9. The image encoder as set forth in claim 8 , wherein the predetermined reference region includes at least one of regions which are positioned on the left, on the upper left, and on the top, respectively, of the each target block to be intra-predicted.
10. The image encoder as set forth in claim 7 , wherein the specific direction is a horizontal direction or a vertical direction.
11. An image decoding method for decoding encoded data so as to form a decoded image, the method comprising:
a decoding step of decoding, from the encoded data, (i) an encode parameter including prediction mode information and (ii) prediction residual data;
a first selecting step of selecting, from a plurality of prediction sets, one prediction set to be used with respect to each target block to be intra-predicted, wherein the prediction set includes, as prediction mode candidates, a plurality of prediction modes corresponding to respective direction predictions, wherein each of the plurality of prediction sets includes the same number of the plurality of prediction modes;
a second selecting step of selecting one prediction mode from the plurality of prediction modes included in the prediction set selected by the first selecting step;
a predicting step of forming, on the basis of the prediction mode thus selected, a predicted image of the each target block to be intra-predicted; and
an adding step of forming a decoded image of the each target block to be intra-predicted by adding the predicted image formed in the prediction step and the prediction residual data obtained by decoding the encoded data.
12. The image decoding method as set forth in claim 11 , wherein prediction directions of the respective plurality of prediction modes corresponding to the respective direction predictions are unevenly distributed with a bias towards a specific direction.
13. The image decoding method as set forth in claim 12 , wherein a plurality of prediction sets are selectable with respect to a predetermined reference region which is referred to by the predicting step in order to form the predicted image of the each target block to be intra predicted.
14. The image decoding method as set forth in claim 13 , wherein the predetermined reference region includes at least one of regions which are positioned on the left, on the upper left, and on the top, respectively, of the each target block to be intra-predicted.
15. The image decoding method as set forth in claim 12 , wherein the specific direction is a horizontal direction or a vertical direction.