Method and system of decoded picture buffer for intra block copy mode
A method for a video encoder or decoder using an Intra Block Copy (IntraBC) mode is disclosed. If IntraBC mode is enabled and no loop filter is used for a current picture, a currently decoded reference picture for the current picture is marked as a long-term reference picture before and during decoding of the current picture. The currently decoded reference picture is assigned in reference picture list construction for IntraBC reference of the current picture and buffer fullness for the DPB is calculated before starting decoding the current picture by taking into account of only one reference picture buffer. According to another method, if the maximum DPB size is 1, a variable or a syntax element is set to a target value to impose restriction to use only one picture storage buffer in the DPB to store reference picture for encoding or decoding of a current picture.
1. A method of managing a DPB (decoded picture buffer) for a video encoder or decoder using coding modes including an Inter prediction mode and an Intra Block Copy (IntraBC) mode, comprising:
determining a total number of reference pictures for the DPB, wherein the DPB comprises short-term and long-term reference pictures;
allocating up to the total number of reference pictures in the DPB;
encoding or decoding a current picture using the reference pictures stored in the DPB; and
if the IntraBC mode is enabled, no loop filter is used for the current picture, and when only one version of a current decoded picture is used, marking the current decoded picture as being used for long-term reference at a beginning of or during a process of decoding the current picture, and marking the current decoded picture in the DPB as a short-term reference picture after decoding of the current picture.
2. The method of claim 1 , wherein the total number of reference pictures is calculated as a sum of a first total number of short-term RPS (reference picture set) that have POC (picture order count) values less than the POC value of the current picture, a second total number of short-term RPS that have the POC values greater than the POC value of the current picture, a third total number of long-term RPS, and a version value associated with information regarding whether two versions of the current decoded picture are used, and wherein the version value is 1 if two versions of the current decoded picture are used and the version value is 0 if one version of the current decoded picture is used.
3. The method of claim 2 , wherein if the total number of reference pictures is greater than a maximum required size of the DPB minus 1 specified in SPS (sequence parameter set), the total number of reference pictures is set to the maximum required size of the DPB minus 1 or smaller.
4. The method of claim 1 , further comprising marking the current decoded picture as a short-term reference picture and keeping the current decoded picture in the DPB after decoding the current picture.
5. The method of claim 1 , wherein information regarding whether two versions of the current decoded picture are used are determined based on a flag indicating no loop filter is used for the current picture and IntraBC mode is enabled.
6. A video encoder or decoder using coding modes including an Inter prediction mode and an Intra Block Copy (IntraBC) mode, comprising a DPB (decoded picture buffer) and one or more electronic circuits arranged to:
determine a total number of reference pictures for the DPB , wherein the DPB comprises short-term and long-terra reference pictures;
allocate up to the total number of reference pictures in the DPB;
encode or decode a current picture using the reference pictures stored in the DPB; and
if the IntraBC mode is enabled, no loop filter is used for the current picture, and when only one version of a current decoded picture is used, mark the current decoded picture as being used for long-term reference at a beginning of or during a process of decoding the current picture, and mark the current decoded picture in the DPB as a short-term reference picture after decoding of the current picture.