Restriction on sub-block size derivation for affine inter prediction

• US 10,609,384 B2
• Filed: 07/11/2018
• Issued: 03/31/2020
• Est. Priority Date: 09/21/2017
• Status: Active Grant

• Current Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Inventors: Chen, Huanbang, Yang, Haitao, Gao, Shan, Zhao, Yin, Zhou, Jiantong, Liu, Shan
• Primary Examiner(s): Habib, Irfan
• Application Number:
  US16/032,979
• Publication Number:
  US 20190089960A1
• Time in Patent Office: 629 Days
• CPC Class Codes: H04N 19/119 Adaptive subdivision aspects, e.g. subdivision of a picture into rectangular or non-rectangular coding blocks
• CPC Class Codes: H04N 19/139 Analysis of motion vectors, e.g. their magnitude, direction, variance or reliability
• CPC Class Codes: H04N 19/159 Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/52 by predictive encoding
• CPC Class Codes: H04N 19/54 using feature points or meshes

Abstract

A video coding device selects a current block for sub-block based affine inter-prediction, and derives a sub-block size for a sub-block of the current block. The sub-block size includes a sub-block width and a sub-block height. The device determines a unidirectional width threshold (TwU), a bidirectional width threshold (TwB), a unidirectional height threshold (ThU), and a bidirectional height threshold (ThB), where a total value of TwB and ThB exceeds a total value of TwU and ThU. The device determines that the affine inter-prediction is unidirectional inter-prediction or bidirectional inter-prediction. Based on the determination, the device applies the TwU or the TwB to the sub-block width, and applies the ThU or the ThB to the sub-block height. The device then derives a motion vector for the sub-block based on motion vectors for the current block, the sub-block width, and the sub-block height.

Claims

1. A method comprising:

selecting, by a processor at an encoder, a current block for sub-block based affine inter-prediction, the current block associated with a plurality of motion vectors;

deriving, by the processor, a sub-block size for a sub-block of the current block, the sub-block size including a sub-block width and a sub-block height;

determining, by the processor, a unidirectional width threshold (TwU), a bidirectional width threshold (TwB), a unidirectional height threshold (ThU), and a bidirectional height threshold (ThB), wherein a total value of TwB and ThB exceeds a total value of TwU and ThU, and wherein the total value of TwB and ThB is greater than the total value of TwU and ThU to ensure a minimum sub-block size for bidirectional inter-prediction exceeds a minimum sub-block size for unidirectional inter-prediction;

determining, by the processor, that the affine inter-prediction is unidirectional inter-prediction or bidirectional inter-prediction;

based on the determination of unidirectional inter-prediction or bidirectional inter-prediction, applying, by the processor, the TwU or the TwB to the sub-block width;

based on the determination, applying, by the processor, the ThU or the ThB to the sub-block height;

deriving, by the processor, a motion vector for the sub-block based on motion vectors for the current block, the sub-block width, and the sub-block height;

encoding, by the processor, prediction information for the sub-block in a bitstream, the prediction information based on the motion vector for the sub-block; and

transmitting, by a transmitter coupled to the processor, the bitstream toward a decoder for decoding and display.

2. The method of claim 1, wherein a value of TwB, a value of ThB, a value of TwU, and a value of ThU are predefined in a memory coupled to the processor.

3. The method of claim 1, further comprising encoding a value of TwB, a value of ThB, a value of TwU, a value of ThU, or combinations thereof, in a parameter set in the bitstream.

4. The method of claim 3, wherein the parameter set is a sequence parameter set (SPS), a picture parameter set (PPS), a slice header, or combinations thereof.

5. The method of claim 1, further comprising rounding the motion vector for the sub-block to a precision of one sixteenths accuracy.

6. The method of claim 1, wherein the sub-block size for the sub-block of the current block is derived according to:

7. An apparatus comprising:

a receiver to receive a bitstream;

a processor coupled to the receiver and configured to;

select a current block from the bitstream for decoding by sub-block based affine inter-prediction;

obtain a plurality of motion vectors for the current block from the bitstream;

derive a sub-block size for a sub-block of the current block, the sub-block size including a sub-block width and a sub-block height;

determine a unidirectional width threshold (TwU), a bidirectional width threshold (TwB), a unidirectional height threshold (ThU), and a bidirectional height threshold (ThB), wherein a total value of TwB and ThB exceeds a total value of TwU and ThU, and wherein the total value of TwB and ThB is greater than the total value of TwU and ThU to ensure a minimum sub-block size for bidirectional inter-prediction exceeds a minimum sub-block size for unidirectional inter-prediction;

determine that the affine inter-prediction is unidirectional inter-prediction or bidirectional inter-prediction based on the bitstream;

based on the determination of unidirectional inter-prediction or bidirectional inter-prediction, apply the TwU or the TwB to the sub-block width;

based on the determination, apply the ThU or the ThB to the sub-block height;

derive a motion vector for the sub-block based on motion vectors for the current block, the sub-block width, and the sub-block height;

employ the motion vector for the sub-block to reconstruct the sub-block based on a reference frame; and

forward a video sequence for display, the video sequence including the sub-block in a current frame.

8. The apparatus of claim 7, further comprising a memory coupled to the processor, the memory configured to store a value of TwB, a value of ThB, a value of TwU, and a value of ThU as predefined values.

9. The apparatus of claim 7, wherein the processor is further configured to obtain a value of TwB, a value of ThB, a value of TwU, a value of ThU, or combinations thereof, from a parameter set in the bitstream.

10. The apparatus of claim 9, wherein the parameter set is a sequence parameter set (SPS), a picture parameter set (PPS), a slice header, or combinations thereof.

11. The apparatus of claim 7, wherein the processor is further configured to round the motion vector for the sub-block to a precision of one sixteenths accuracy.

12. The apparatus of claim 7, wherein the sub-block size for the sub-block of the current block is derived according to:

13. A method comprising:

receiving, by a receiver, a bitstream;

selecting, by a processor, a current block from the bitstream for decoding by sub-block based affine inter-prediction;

obtaining, by the processor, a plurality of motion vectors for the current block from the bitstream;

deriving, by the processor, a sub-block size for a sub-block of the current block, the sub-block size including a sub-block width and a sub-block height;

determining, by the processor, a unidirectional width threshold (TwU), a bidirectional width threshold (TwB), a unidirectional height threshold (ThU), and a bidirectional height threshold (ThB), wherein a total value of TwB and ThB exceeds a total value of TwU and ThU, and wherein the total value of TwB and ThB is greater than the total value of TwU and ThU to ensure a minimum sub-block size for bidirectional inter-prediction exceeds a minimum sub-block size for unidirectional inter-prediction;

determining, by the processor, that the affine inter-prediction is unidirectional inter-prediction or bidirectional inter-prediction based on the bitstream;

based on the determination of unidirectional inter-prediction or bidirectional inter-prediction, applying, by the processor, the TwU or the TwB to the sub-block width;

based on the determination, applying, by the processor, the ThU or the ThB to the sub-block height;

deriving, by the processor, a motion vector for the sub-block based on motion vectors for the current block, the sub-block width, and the sub-block height;

employing, by the processor, the motion vector for the sub-block to reconstruct the sub-block based on a reference frame; and

forwarding, by the processor, a video sequence for display, the video sequence including the sub-block in a current frame.

14. The method of claim 13, wherein a value of TwB, a value of ThB, a value of TwU, and a value of ThU are stored as predefined values.

15. The method of claim 13, further comprising obtaining a value of TwB, a value of ThB, a value of TwU, a value of ThU, or combinations thereof, from a parameter set in the bitstream.

16. The method of claim 13, further comprising round the motion vector for the sub-block to a precision of one sixteenths accuracy.

17. The method of claim 13, wherein the sub-block size for the sub-block of the current block is derived according to: