Method for signaling of reference picture resampling with resampling picture size indication in video bitstream

1. A method of encoding a video bitstream using at least one processor, the method comprising:

determining that a conformance window is not used for reference picture resampling;

based on the determining that the conformance window is not used for the reference picture resampling, determining whether a reference picture resampling parameter is to be signaled;

based on determining that the reference picture resampling parameter is to be signaled, determining a plurality of reference region parameters to be used to calculate scaling for the reference picture resampling, the plurality of reference region parameters comprising at least a reference region left offset and a reference region top offset; and

encoding a current picture using the reference picture resampling parameter comprising the plurality of reference region parameters; and

generating an encoded video bitstream based on the encoded current picture, wherein the encoded video bitstream includes a flag indicating that the conformance window is not used for the reference picture resampling and the reference picture resampling parameter.

2. The method of claim 1 , wherein the flag is signaled in a picture parameter set.

3. The method of claim 1 , further comprising:

based on determining that a resampling picture size is to be signaled, determining a resampling ratio based on the resampling picture size,

wherein the resampling picture size is signaled in the encoded video bitstream as at least one of a width of the resampling picture size and a height of the resampling picture size.

4. The method of claim 3 , wherein the at least one of the width and the height is signaled in a picture parameter set.

5. The method of claim 3 , wherein the at least one of the width and the height is expressed as a number of luma samples included in the at least one of the width and the height.

6. The method of claim 3 , wherein the at least one of the width and the height is determined based on at least one offset distance between a border of the current picture and a predetermined luma sample of a reference region.

7. The method of claim 6 , wherein the at least one offset distance is signaled in a picture parameter set.

8. The method of claim 6 , wherein the at least one offset distance comprises at least one from among:

a horizontal offset distance between a left border of the current picture and a top-left luma sample of the reference region,

a vertical offset distance between a top border of the current picture and the top-left luma sample of the reference region,

a horizontal offset distance between a right border of the current picture and a bottom-right luma sample of the reference region, and

a vertical offset distance between a bottom border of the current picture and the bottom-right luma sample of the reference region.

9. A device for encoding a video bitstream, the device comprising:

at least one memory configured to store program code; and

at least one processor configured to read the program code and operate as instructed by the program code, the program code including:

first determining code configured to cause the at least one processor to determine that a conformance window is not used for reference picture resampling;

second determining code configured to cause the at least one processor to, based on the determining that the conformance window is not used for the reference picture resampling, determine whether a reference picture resampling parameter is to be signaled;

third determining code configured to cause the at least one processor to, based on determining that the reference picture resampling parameter is to be signaled, determine a plurality of reference region parameters to be used to calculate scaling for the reference picture resampling, the plurality of reference region parameters comprising at least a reference region left offset and a reference region top offset; and

encoding code configured to cause the at least one processor to encode a current picture using the reference picture resampling parameter comprising the plurality of reference region parameters; and

generating code configured to cause the at least one processor to generate an encoded video bitstream based on the encoded current picture, wherein the encoded video bitstream includes a flag indicating that the conformance window is not used for the reference picture resampling and the reference picture resampling parameter.

10. The device of claim 9 , wherein the flag is signaled in a picture parameter set.

11. The device of claim 9 , wherein the program code further comprises fourth determining code configured to cause the at least one processor to, based on determining that a resampling picture size is to be signaled, determine a resampling ratio based on the resampling picture size, and

wherein the resampling picture size is signaled in the encoded video bitstream as at least one of a width of the resampling picture size and a height of the resampling picture size.

12. The device of claim 11 , wherein the at least one of the width and the height is signaled in a picture parameter set.

13. The device of claim 11 , wherein the at least one of the width and the height is expressed as a number of luma samples included in the at least one of the width and the height.

14. The device of claim 11 , wherein the at least one of the width and the height is determined based on at least one offset distance between a border of the current picture and a predetermined luma sample of a reference region.

15. The device of claim 14 , wherein the at least one offset distance is signaled in a picture parameter set.

16. The device of claim 14 , wherein the at least one offset distance comprises at least one from among:

a horizontal offset distance between a left border of the current picture and a top-left luma sample of the reference region,

a vertical offset distance between a top border of the current picture and the top-left luma sample of the reference region,

a horizontal offset distance between a right border of the current picture and a bottom-right luma sample of the reference region, and

a vertical offset distance between a bottom border of the current picture and the bottom-right luma sample of the reference region.

17. A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by one or more processors of a device for encoding a video bitstream, cause the one or more processors to:

determine that a conformance window is not used for reference picture resampling;

based on the determining that the conformance window is not used for the reference picture resampling, determine whether a reference picture resampling parameter is to be signaled;

based on determining that the reference picture resampling parameter is to be signaled, determine a plurality of reference region parameters to be used to calculate scaling for the reference picture resampling, the plurality of reference region parameters comprising at least a reference region left offset and a reference region top offset; and

encode a current picture using the reference picture resampling parameter comprising the plurality of reference region parameters; and

generate an encoded video bitstream based on the encoded current picture, wherein the encoded video bitstream includes a flag indicating that the conformance window is not used for the reference picture resampling and the reference picture resampling parameter.

18. The non-transitory computer-readable medium of claim 17 , wherein the one or more instructions further cause the one or more processors to, based on determining that a resampling picture size is to be signaled, determine a resampling ratio based on the resampling picture size, and

wherein the resampling picture size is signaled in the encoded video bitstream as at least one of a width of the resampling picture size and a height of the resampling picture size.

19. The non-transitory computer-readable medium of claim 18 , wherein the at least one of the width and the height is expressed as a number of luma samples included in the at least one of the width and the height.

20. The non-transitory computer-readable medium of claim 18 , wherein the at least one of the width and the height is determined based on at least one offset distance between a border of the current picture and a predetermined luma sample of a reference region.