Video coding using reference picture resampling supporting region of interest
Methods, systems, and bitstream syntax are described for canvas size, single layer or multi-layer, scalable decoding, with support for regions of interest (ROI), using a decoder supporting reference picture resampling. Offset parameters for a region of interest in a current picture and offset parameters for an ROI in a reference picture are taken into consideration when computing scaling factors to apply reference picture resampling. Syntax elements for supporting ROI regions under reference picture resampling are also presented.
1. A method to decode a coded bitstream with region of interest (ROI) support, the method performed by a processor and comprising:
receiving a coded bitstream comprising coded pictures and syntax parameters for one or more regions of interest (ROI) within the coded pictures, wherein the syntax parameters comprise a picture header with ROI picture header parameters and a slice header with ROI slice header parameters, wherein the ROI picture header parameters comprise an ROI enabling flag and ROI offset parameters for a scaling window, and the ROI slice header parameters comprise an ROI switch parameter denoting whether ROI scaling is enabled at a slice level and whether the ROI offset parameters in the picture header are applied to a reference picture or a current picture; and
decoding a coded region in a current picture in the coded bitstream, wherein decoding the coded region comprises:
for the current picture and an active reference picture in an Inter slice:
initializing a default scaling window in the Inter slice using values defined in a picture parameter set;
if detecting that the ROI enabling flag is set to 1:
overriding the parameters of the default scaling window based on the ROI offset parameters and the ROI switch parameter to generate an ROI scaling window; and
applying reference picture resampling using the ROI scaling window.
2. The method of claim 1 , wherein for the active reference picture, the ROI switch parameter comprises three values: 0, denoting to not override the default scaling window, 1, denoting to generate the ROI scaling window in the active reference picture, and 2, denoting to generate the ROI scaling window in the current picture.
3. The method of claim 1 , wherein the ROI offset parameters comprise absolute left, right, top, and bottom offsets for the scaling window which replace original offset values of the scaling window.
4. The method of claim 1 , wherein the ROI offset parameters comprise delta left, right, top, and bottom offsets for the scaling window which need to be added to original offset values of the scaling window.
5. A method to decode a coded bitstream with region of interest (ROI) support, the method performed by a processor and comprising:
receiving a coded bitstream comprising coded pictures and syntax parameters for one or more regions of interest (ROI) within the coded pictures, wherein the syntax parameters comprise a picture header with ROI picture header parameters and a slice header with ROI slice header parameters, wherein the ROI picture header parameters comprise an ROI switch parameter and ROI offset parameters for a scaling window, and the ROI slice header parameters comprise a slice ROI enable flag, wherein the ROI switch parameter denotes whether ROI scaling is enabled, and if enabled, whether the ROI offset parameters in the picture header are applied to a reference picture or a current picture; and
decoding a coded region in a current picture in the coded bitstream, wherein decoding the coded region comprises:
for the current picture and an active reference picture in an Inter slice:
initializing a default scaling window in the Inter slice using values defined in a picture parameter set;
if detecting using the ROI switch parameter that ROI scaling is enabled:
if detecting that the slice ROI enable flag is enabled:
overriding the parameters of the default scaling window based on the ROI offset parameters and the ROI switch parameters to generate an ROI scaling window; and
applying reference picture resampling using the ROI scaling window.
6. The method of claim 5 , wherein the ROI switch parameter comprises three values: 0, denoting no ROI scaling is enabled, 1, denoting to generate the ROI scaling window in the active reference picture, and 2, denoting to generate the ROI scaling window in the current picture.
7. The method of claim 5 , wherein the ROI offset parameters comprise absolute left, right, top, and bottom offsets for the scaling window which replace original offset values of the scaling window.
8. The method of claim 5 , wherein the ROI offset parameters comprise delta left, right, top, and bottom offsets for the scaling window which need to be added to original offset values of the scaling window.
9. A non-transitory computer-readable storage medium having stored thereon computer-executable instructions for executing with one or more processors a method in accordance with claim 1 .
10. An apparatus comprising a processor and configured to perform the method of claim 1 .