Image decoder and decoding method

1. A non-transitory computer readable medium including instructions which, when loaded to an image decoder, cause the image decoder to perform a process including:

receiving and decoding an encoded bitstream to obtain quantized transform coefficients and a first parameter and a second parameter;

deriving a partition mode based on the first and second parameters;

inverse-quantizing the quantized transform coefficients to obtain transform coefficients and inverse-transforming the transform coefficients to obtain residuals;

generating a prediction of a current block based on a reference block in a decoded reference picture or based on an encoded reference block in a current picture; and

adding the residuals and the predictions to reconstruct blocks;

wherein,

responsive to the derived partition mode being a first partition mode, the process includes executing the first partition mode including:

splitting a block of a picture, in a vertical direction or in a horizontal direction, into a plurality of first blocks, the plurality of first blocks including a N×2N block sized N pixels by 2N pixels;

splitting the N×2N block, wherein a ternary split is allowed to split the N×2N block in the vertical direction, which is a direction along the 2N pixels, into a plurality of sub blocks including at least one sub block sized N/4×2N, while a binary split is not allowed to split the N×2N block in the vertical direction into two sub blocks that are equally sized N/2×2N; and

decoding the plurality of sub blocks.

2. The computer readable medium according to claim 1 , wherein the first partition mode includes splitting the N×2N block in the vertical direction into two sub blocks sized N/4 pixels by 2N pixels and one sub block sized N/2 pixels by 2N pixels.

3. The computer readable medium according to claim 2 , wherein the first partition mode includes splitting the N×2N block in the vertical direction into a first sub block sized N/4 pixels by 2N pixels, a second sub block sized N/2 pixels by 2N pixels, and a third sub block sized N/4 pixels by 2N pixels, wherein the second sub block is interposed between the first sub block and the third sub block.

4. The computer readable medium according to claim 1 , wherein the first partition mode includes splitting the N×2N block in the vertical direction into one sub block sized N/4 pixels by 2N pixels and one sub block sized 3N/4 pixels by 2N pixels.

5. The computer readable medium according to claim 1 , wherein the process includes:

parsing the encoded bitstream to obtain the first and second parameters.

6. An image decoder comprising:

an entropy decoder which, in operation, receives and decodes an encoded bitstream to obtain quantized transform coefficients and a first parameter and a second parameter;

a block partition determiner which, in operation, derives a partition mode using based on the first and second parameters;

an inverse quantizer and transformer which, in operation, inverse quantizes the quantized transform coefficients to obtain transform coefficients and inverse transforms 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 encoded reference block in a current picture,

wherein,

the block partition determiner, responsive to deriving the derived partition mode being a first partition mode, executes the first partition mode including:

splitting a block of a picture, in a vertical direction or in a horizontal direction, into a plurality of first blocks, the plurality of first blocks including a N×2N block sized N pixels by 2N pixels;

splitting the N×2N block, wherein a ternary split is allowed to split the N×2N block in the vertical direction, which is a direction along the 2N pixels, into a plurality of sub blocks including at least one sub block sized N/4×2N, while a binary split is not allowed to split the N×2N block in the vertical direction into two sub blocks that are equally sized N/2×2N; and

decoding the plurality of sub blocks.

7. The image decoder according to claim 6 , wherein the first partition mode includes splitting the N×2N block in the vertical direction into two sub blocks sized N/4 pixels by 2N pixels and one sub block sized N/2 pixels by 2N pixels.

8. The image decoder according to claim 7 , wherein the first partition mode includes splitting the N×2N block in the vertical direction into a first sub block sized N/4 pixels by 2N pixels, a second sub block sized N/2 pixels by 2N pixels, and a third sub block sized N/4 pixels by 2N pixels, wherein the second sub block is interposed between the first sub block and the third sub block.

9. The image decoder according to claim 6 , wherein the first partition mode includes splitting the N×2N block in the vertical direction into one sub block sized N/4 pixels by 2N pixels and one sub block sized 3N/4 pixels by 2N pixels.

10. The image decoder according to claim 6 , wherein the entropy decoder, in operation:

parses the encoded bitstream to obtain the first and second parameters.

11. A decoding method comprising:

receiving and decoding an encoded bitstream to obtain quantized transform coefficients and a first parameter and a second parameter;

deriving a partition mode based on the first and second parameters;

inverse-quantizing the quantized transform coefficients to obtain transform coefficients and inverse-transforming the transform coefficients to obtain residuals;

generating a prediction of a current block based on a reference block in a decoded reference picture or based on an encoded reference block in a current picture; and

adding the residuals and the predictions to reconstruct blocks;

wherein,

responsive to the derived partition mode being a first partition mode, the decoding method comprises executing the first partition mode including:

splitting a block of a picture, in a vertical direction or in a horizontal direction, into a plurality of first blocks, the plurality of first blocks including a N×2N block sized N pixels by 2N pixels;

splitting the N×2N block, wherein a ternary split is allowed to split the N×2N block in the vertical direction, which is a direction along the 2N pixels, into a plurality of sub blocks including at least one sub block sized N/4×2N, while a binary split is not allowed to split the N×2N block in the vertical direction into two sub blocks that are equally sized N/2×2N; and

decoding the plurality of sub blocks.

12. The decoding method according to claim 11 , wherein the first partition mode includes splitting the N×2N block in the vertical direction into two sub blocks sized N/4 pixels by 2N pixels and one sub block sized N/2 pixels by 2N pixels.

13. The decoding method according to claim 12 , wherein the first partition mode includes splitting the N×2N block in the vertical direction into a first sub block sized N/4 pixels by 2N pixels, a second sub block sized N/2 pixels by 2N pixels, and a third sub block sized N/4 pixels by 2N pixels, wherein the second sub block is interposed between the first sub block and the third sub block.

14. The decoding method according to claim 11 , wherein the first partition mode includes splitting the N×2N block in the vertical direction into one sub block sized N/4 pixels by 2N pixels and one sub block sized 3N/4 pixels by 2N pixels.

15. The decoding method according to claim 11 ,

wherein, the deriving step includes parsing the encoded bitstream to obtain the first and second parameters.

16. The computer readable medium according to claim 1 ,

wherein the predetermined order of the plurality of partition modes is fixed or signaled in a bitstream.

17. The image decoder according to claim 6 ,

wherein the predetermined order of the plurality of partition modes is fixed or signaled in a bitstream.

18. The decoding method according to claim 11 ,

wherein the predetermined order of the plurality of partition modes is fixed or signaled in a bitstream.