Bi-directional optical flow method with simplified gradient derivation

Abstract

A video coding device may be configured to perform directional Bi-directional optical flow (BDOF) refinement on a coding unit (CU). The device may determine the direction in which to perform directional BDOF refinement. The device may calculate the vertical direction gradient difference and the horizontal direction gradient difference for the CU. The vertical direction gradient difference may indicate the difference between the vertical gradients for a first reference picture and the vertical gradients for a second reference picture. The horizontal direction gradient difference may indicate the difference between the horizontal gradients for the first reference picture and the horizontal gradients for the second reference picture. The video coding device may determine the direction in which to perform directional BDOF refinement based on the vertical direction gradient difference and the horizontal direction gradient difference. The video coding device may perform directional BDOF refinement in the determined direction.

1 - 20 . (canceled) 
     
     
         21 . A device for video decoding, comprising:
 a processor configured to:   obtain a size of a video block;   determine a utilization status of an inter prediction technique for the video block;   determine whether to perform bi-directional optical flow (BDOF) for the video block based on the size of the video block and the utilization status of the inter prediction technique for the video block; and   decode the video block based on the determination of whether to perform BDOF for the video block.   
     
     
         22 . The device of  claim 21 , wherein the processor is further configured to compare the size of the video block and a value, and the determination of whether to perform BDOF for the video block is based on the comparison between the size of the video block and the value. 
     
     
         23 . The device of  claim 21 , wherein the inter prediction technique comprises advanced temporal motion vector prediction (ATMVP), and BDOF is determined not to be performed for the video block based on a determination that ATMVP is to be used to decode the video block. 
     
     
         24 . The device of  claim 21 , wherein the inter prediction technique comprises a sub-block prediction technique, BDOF is determined not to be performed for the video block based on a determination that the sub-block prediction technique is to be used to decode the video block. 
     
     
         25 . The device of  claim 21 , wherein the utilization status of the inter prediction technique indicates whether the inter prediction technique is to be performed for the video block. 
     
     
         26 . The device of  claim 21 , wherein the utilization status indicates that the inter prediction technique is not to be performed for the video block, the size of the video block is less than a value, and BDOF is determined to be performed for the video block. 
     
     
         27 . The device of  claim 21 , wherein BDOF is determined to be performed, and the processor is further configured to:
 determine a plurality of gradients based on a sample location in the video block;   determine a motion refinement based on the plurality of the gradients; and   obtain a sample value associated with the video block based on the determined motion refinement.   
     
     
         28 . The device of  claim 21 , wherein the inter prediction technique is spatial-temporal motion vector prediction (STMVP), frame-rate up conversion (FRUC), or an affine mode. 
     
     
         29 . A method for video decoding, comprising:
 obtaining a size of a video block;   determining a utilization status of an inter prediction technique for the video block;   determining whether to perform bi-directional optical flow (BDOF) for the video block based on the size of the video block and the utilization status of the inter prediction technique for the video block; and   decoding the video block based on the determination of whether to perform BDOF for the video block.   
     
     
         30 . The method of  claim 29 , wherein the method further comprises comparing the size of the video block and a value, and the determination of whether to perform BDOF for the video block is based on the comparison between the size of the video block and the value. 
     
     
         31 . The method of  claim 29 , wherein the inter prediction technique comprises advanced temporal motion vector prediction (ATMVP), and BDOF is determined not to be performed for the video block based on a determination that ATMVP is to be used to decode the video block. 
     
     
         32 . The method of  claim 29 , wherein the inter prediction technique comprises a sub-block prediction technique, and BDOF is determined not to be performed for the video block based on a determination that the sub-block prediction technique is to be used to decode the video block. 
     
     
         33 . A device for video encoding, comprising:
 a processor configured to:   obtain a size of a video block;   determine a utilization status of an inter prediction technique for the video block;   determine whether to perform bi-directional optical flow (BDOF) for the video block based on the size of the video block and the utilization status of the inter prediction technique for the video block; and   encode the video block based on the determination of whether to perform BDOF for the video block.   
     
     
         34 . The device of  claim 33 , wherein the processor is further configured to compare the size of the video block and a value, and the determination of whether to perform BDOF for the video block is based on the comparison between the size of the video block and the value. 
     
     
         35 . The device of  claim 33 , wherein the inter prediction technique comprises advanced temporal motion vector prediction (ATMVP), and BDOF is determined not to be performed for the video block based on a determination that ATMVP is to be used to encode the video block. 
     
     
         36 . The device of  claim 33 , wherein the inter prediction technique comprises a sub-block prediction technique, and BDOF is determined not to be performed for the video block based on a determination that the sub-block prediction technique is to be used to encode the video block. 
     
     
         37 . A method for video decoding, comprising:
 obtaining a size of a video block;   determining a utilization status of an inter prediction technique for the video block;   determining whether to perform bi-directional optical flow (BDOF) for the video block based on the size of the video block and the utilization status of the inter prediction technique for the video block; and   encoding the video block based on the determination of whether to perform BDOF for the video block.   
     
     
         38 . The method of  claim 37 , wherein the method further comprises comparing the size of the video block and a value, and the determination of whether to perform BDOF for the video block is based on the comparison between the size of the video block and the value. 
     
     
         39 . The method of  claim 37 , wherein the inter prediction technique comprises advanced temporal motion vector prediction (ATMVP), and BDOF is determined not to be performed for the video block based on a determination that ATMVP is to be used to encode the video block. 
     
     
         40 . The method of  claim 37 , wherein the inter prediction technique comprises a sub-block prediction technique, and BDOF is determined not to be performed for the video block based on a determination that the sub-block prediction technique is to be used to encode the video block.