IMAGE ENCODER, IMAGE DECODER, IMAGE ENCODING METHOD, AND IMAGE DECODING METHOD

1 . An image decoder comprising:

circuitry; and

a memory coupled to the circuitry;

wherein the circuitry, in operation, performs a boundary smoothing operation along a boundary between a first partition having a triangular shape and a second partition having a triangular shape that are split from an image block, the boundary smoothing operation including:

in response to determining to perform the boundary smoothing operation;

first-predicting first values of a set of pixels of the first partition along the boundary, using a first motion vector for the first partition;

second-predicting second values of the set of pixels of the first partition along the boundary, using a second motion vector for the second partition;

weighting the first values and the second values; and

decoding the first partition using the weighted first values and the weighted second values.

2 . The decoder of claim 1 , wherein the circuitry, in operation, performs:

parsing a first index indicative of the first motion vector and a second index indicative of the second motion vector;

selecting the first motion vector based on the first index; and

selecting the second motion vector based on the second index.

3 . The decoder of claim 2 , wherein the first motion vector is selected from a first set of motion vector candidates, and the second motion vector is selected from a second set of motion vector candidates.

4 . The decoder of claim 1 , wherein the circuitry, in operation, performs:

determining to perform the boundary smoothing operation based on an image block size condition.

5 . The decoder of claim 1 , wherein the circuitry, in operation, performs:

determining to perform the boundary smoothing operation based on a parameter indicative of performing the boundary smoothing operation.

6 . The decoder of claim 1 , wherein the circuitry, in operation, performs:

determining to perform the boundary smoothing operation based on a parameter indicative of a split direction applied to split the image block into the first partition and the second partition, wherein the split direction includes: from a top-left corner of the image block to a bottom-right corner thereof, and from a top-right corner of the image block to a bottom-left corner thereof.

7 . The decoder of claim 1 , wherein weights applied to the first values and weights applied to the second values are non-zero.

8 . The decoder of claim 1 , wherein a number of pixels in a row or in a column in the set of pixels is four.

9 . An image decoder comprising:

an entropy decoder which, in operation, receives and decodes an encoded bitstream to obtain quantized transform coefficients,

an inverse quantizer and transformer which, in operation, inverse quantizes the quantized transform coefficients to obtain transform coefficients and inverse transform the transform coefficients to obtain residuals,

an adder which, in operation, adds the residuals outputted from the inverse quantizer and transformer and predictions outputted from a prediction controller to reconstruct blocks, and

the prediction controller coupled to an inter predictor, an intra predictor, and a memory, wherein the inter predictor, in operation, generates a prediction of a current block based on a reference block in a decoded reference picture and the intra predictor, in operation, generates a prediction of a current block based on an decoded reference block in a current picture,

wherein

the image decoder, in operation, performs a boundary smoothing operation along a boundary between a first partition having a triangular shape and a second partition having a triangular shape that are split from an image block, the boundary smoothing operation including:

in response to determining to perform the boundary smoothing operation;

first-predicting first values of a set of pixels of the first partition along the boundary, using a first motion vector for the first partition;

second-predicting second values of the set of pixels of the first partition along the boundary, using a second motion vector for the second partition;

weighting the first values and the second values; and

decoding the first partition using the weighted first values and the weighted second values.

10 . The decoder of claim 9 , which, in operation, performs:

parsing a first index indicative of the first motion vector and a second index indicative of the second motion vector;

selecting the first motion vector based on the first index; and

selecting the second motion vector based on the second index.

11 . The decoder of claim 9 , which, in operation, performs:

determining to perform the boundary smoothing operation based on an image block size condition.

12 . The decoder of claim 9 , which, in operation, performs:

determining to perform the boundary smoothing operation based on at least one parameter selected from: a first parameter indicative of performing the boundary smoothing operation, and a second parameter indicative of a split direction applied to split the image block into the first partition and the second partition, wherein the split direction includes: from a top-left corner of the image block to a bottom-right corner thereof, and from a top-right corner of the image block to a bottom-left corner thereof.

13 . The decoder of claim 9 , wherein weights applied to the first values and weights applied to the second values are non-zero.

14 . An image decoding method of performing a boundary smoothing operation along a boundary between a first partition having a triangular shape and a second partition having a triangular shape that are split from an image block, the method comprising:

in response to determining to perform the boundary smoothing operation;

first-predicting first values of a set of pixels of the first partition along the boundary, using a first motion vector for the first partition;

second-predicting second values of the set of pixels of the first partition along the boundary, using a second motion vector for the second partition;

weighting the first values and the second values; and

decoding the first partition using the weighted first values and the weighted second values.

15 . The method of claim 14 , comprising:

parsing a first index indicative of the first motion vector and a second index indicative of the second motion vector;

selecting the first motion vector based on the first index; and

selecting the second motion vector based on the second index.

16 . The method of claim 15 , wherein the first motion vector is selected from a first set of motion vector candidates, and the second motion vector is selected from a second set of motion vector candidates.

17 . The method of claim 14 , comprising:

determining to perform the boundary smoothing operation based on an image block size condition.

18 . The method of claim 14 , comprising:

determining to perform the boundary smoothing operation based on a parameter indicative of performing the boundary smoothing operation.

19 . The method of claim 14 , comprising:

determining to perform the boundary smoothing operation based on a parameter indicative of a split direction applied to split the image block into the first partition and the second partition, wherein the split direction includes: from a top-left corner of the image block to a bottom-right corner thereof, and from a top-right corner of the image block to a bottom-left corner thereof.

20 . The method of claim 14 , wherein weights applied to the first values and weights applied to the second values are non-zero.