Image encoding device, image encoding method, and image encoding program, and image decoding device, image decoding method, and image decoding program

1. An image encoding device adapted to segment an image into blocks and encode the image in units of blocks resulting from segmenting the image, comprising:

a block segmentation unit that recursively segments the image into rectangles of a predetermined size to generate a target block subject to encoding; and

an encoding unit that encodes block segmentation information of the target block, wherein the block segmentation unit includes:

a quartering unit that quarters the target block in recursive segmentation in a horizontal direction and a vertical direction to generate four blocks; and

a halving unit that halves the target block in recursive segmentation in the horizontal direction or the vertical direction to generate two blocks,

wherein when a previous recursive segmentation is halving and the target block is of a predetermined size, the halving unit prohibits the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation and thereby prevents:

block segmentation that results in a rectangle further elongated in the same direction and

an increase in the memory bandwidth necessary for at least one of intra prediction or inter prediction, and

wherein the memory bandwidth necessary for the intra prediction is prevented from increasing when the target block is halved inside the target block, by restricting the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation.

2. An image encoding method adapted to segment an image into blocks and encode the image in units of blocks resulting from segmenting the image, comprising:

recursively segmenting the image into rectangles of a predetermined size to generate a target block subject to encoding; and

encoding block segmentation information of the target block, wherein the segmenting includes:

quartering the target block in recursive segmentation in a horizontal direction and a vertical direction to generate four blocks; and

halving the target block in recursive segmentation in the horizontal direction or the vertical direction to generate two blocks,

wherein when a previous recursive segmentation is halving and the target block is of a predetermined size, the halving prohibits the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation and thereby prevents:

block segmentation that results in a rectangle further elongated in the same direction, and

an increase in the memory bandwidth necessary for at least one of intra prediction or inter prediction, and

wherein the memory bandwidth necessary for the intra prediction is prevented from increasing when the target block is halved inside the target block, by restricting the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation.

3. A non-transitory computer-readable medium having an image encoding program adapted to segment an image into blocks and encode the image in units of blocks resulting from segmenting the image, the program comprising computer-implemented modules including:

a block segmentation module that recursively segments the image into rectangles of a predetermined size to generate a target block subject to encoding; and

an encoding module that encodes block segmentation information of the target block, wherein the block segmentation module includes:

a quartering module that quarters the target block in recursive segmentation in a horizontal direction and a vertical direction to generate four blocks; and

a halving module that halves the target block in recursive segmentation in the horizontal direction or the vertical direction to generate two blocks,

wherein when a previous recursive segmentation is halving and the target block is of a predetermined size, the halving module prohibits the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation and thereby prevents:

block segmentation that results in a rectangle further elongated in the same direction, and

an increase in the memory bandwidth necessary for at least one of intra prediction or inter prediction, and

wherein the memory bandwidth necessary for the intra prediction is prevented from increasing when the target block is halved inside the target block, by restricting the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation.

4. An image decoding device adapted to decode an image in units of blocks resulting from segmenting the image, comprising:

a block segmentation unit that generates a target block subject to decoding based on decoded recursive block segmentation information; and

a decoding unit that decodes the target block, wherein the block segmentation unit includes:

a quartering unit that quarters the target block in recursive segmentation in a horizontal direction and a vertical direction to generate four blocks; and

a halving unit that halves the target block in recursive segmentation in the horizontal direction or the vertical direction to generate two blocks,

wherein when a previous recursive segmentation is halving and the target block is of a predetermined size, the halving unit prohibits the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation and thereby prevents:

block segmentation that results in a rectangle further elongated in the same direction and

an increase in the memory bandwidth necessary for at least one of intra prediction or inter prediction, and

wherein the memory bandwidth necessary for the intra prediction is prevented from increasing when the target block is halved inside the target block, by restricting the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation.

5. An image decoding method adapted to decode an image in units of blocks resulting from segmenting the image, comprising:

generating a target block subject to decoding based on decoded recursive block segmentation information; and

decoding the target block, wherein

the segmenting includes:

quartering the target block in recursive segmentation in a horizontal direction and a vertical direction to generate four blocks; and

halving the target block in recursive segmentation in the horizontal direction or the vertical direction to generate two blocks,

wherein when a previous recursive segmentation is halving and the target block is of a predetermined size, the halving unit prohibits the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation and thereby prevents:

block segmentation that results in a rectangle further elongated in the same direction and

an increase in the memory bandwidth necessary for at least one of intra prediction or inter prediction, and

wherein the memory bandwidth necessary for the intra prediction is prevented from increasing when the target block is halved inside the target block, by restricting the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation.

6. A non-transitory computer-readable medium having an image decoding program adapted to decode an image in units of blocks resulting from segmenting the image, the program comprising computer-implemented modules including:

a block segmentation module that generates a target block subject to decoding based on decoded recursive block segmentation information; and

a decoding module that decodes the target block, wherein

the block segmentation module includes:

a quartering module that quarters the target block in recursive segmentation in a horizontal direction and a vertical direction to generate four blocks; and

a halving module that halves the target block in recursive segmentation in the horizontal direction or the vertical direction to generate two blocks,

wherein when a previous recursive segmentation is halving and the target block is of a predetermined size, the halving unit prohibits the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation and thereby prevents:

block segmentation that results in a rectangle further elongated in the same direction and

an increase in the memory bandwidth necessary for at least one of intra prediction or inter prediction, and

wherein the memory bandwidth necessary for the intra prediction is prevented from increasing when the target block is halved inside the target block, by restricting the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation.

7. The image encoding device of claim 1 , wherein at least one of a first flag indicating whether to quarter the target block is transmitted and received, and a second flag indicating whether to halve the target block is transmitted and received.

8. The image encoding device of claim 7 , wherein the second flag is set so that the previous recursive segmentation is halving and the target block is of the predetermined size, the halving unit prohibits the target block subject to current recursive segmentation from being segmented in the same direction as the direction in which the target block was segmented in the previous recursive segmentation.

9. The image encoding device of claim 7 , wherein when the second flag is set so that the last but one recursive segmentation is halving and the first flag is set so that a previous recursive segmentation is quartering, the block segmentation unit prohibits further segmentation of the target block.