Method and apparatus of palette index map coding for screen content coding

An apparatus for encoding video data in a video encoding system, the apparatus comprising one or more electronic circuits or processors arranged to:

• receive input data including a current block of the video data;
• determine a coding mode for the current block of the video data, wherein the coding mode is selected from a set of coding modes including a palette coding mode;
• if the palette coding mode is selected for the current block of the video data:
• map pixels in the current block of the video data to palette indices according to a palette table;
• determine a variable related to a total number of palette indices in the current block of the video data;
• determine a Rice parameter (k) for the current block of the video data;
• if the Rice parameter is equal to or greater than log-base-2 of current block size, binarizing the variable into a binary string using a fixed-length (FL) code with bit length equal to the log-base-2 of current block size;
• if the Rice parameter is smaller than the log-base-2 of current block size, binarize the variable into the binary string comprising a prefix part and a suffix part, wherein the prefix part is generated using a TR (Truncated Rice) binarization process with input information including the Rice parameter and the suffix part is generated using another binarization process, and the suffix part is allowed to be empty;
• and
• include the binary string representing the variable in a bitstream for the video data.

A method of decoding video data for a video decoding system, the method comprising:

• receiving a video bitstream comprising coded data including a current block of video data;
• determining from the video bitstream a coding mode for the current block of the video data, wherein the coding mode is selected from a set of coding modes including a palette coding mode;
• if the palette coding mode is used for the current block of the video data:
• determining a Rice parameter from coded information in the video bitstream;
• if the Rice parameter is equal to or greater than log-base-2 of current block size:
• parsing from the video bitstream a binary string corresponding to a fixed-length (FL) code with bit length equal to the log-base-2 of current block size for a variable related to a total number of palette indices in the current block of the video data;
• and
• determining the total number of palette indices in the current block of video data by decoding the variable based on the fixed-length (FL) code;
• and
• if the Rice parameter is smaller than the log-base-2 of current block size:
• parsing from the video bitstream the binary string for the variable related to the total number of palette indices in the current block of the video data, wherein the binary string comprises a prefix part and a suffix part, and wherein the prefix part is generated using a TR (Truncated Rice) binarization process with input information including the Rice parameter and the suffix part is generated using another binarization process, and the suffix part is allowed to be empty;
• and
• decoding the prefix part using a Truncated Rice de-binarization process with the Rice parameter and the suffix part is decoded using another de-binarization process if the suffix part is not empty;
• and
• determining the total number of palette indices in the current block of the video data by decoding the variable based on the prefix part and the suffix part of the binary string;
• and
• applying palette decoding to the current block of the video data using information including the total number of palette indices in the current block of the video data and a palette table.

An apparatus for encoding video data in a video encoding system, the apparatus comprising one or more electronic circuits or processors arranged to:

• receive a video bitstream comprising coded data including a current block of the video data;
• determine from the video bitstream a coding mode for the current block of the video data, wherein the coding mode is selected from a set of coding modes including a palette coding mode;
• if the palette coding mode is used for the current block of the video data:
• determine a Rice parameter (k) from coded information in the video bitstream, wherein value of the Rice parameter is dependent on a size of the current block of the video data;
• if the Rice parameter is equal to or greater than log-base-2 of current block size:
• parse from the video bitstream a binary string corresponding to a fixed-length (FL) code with bit length equal to the log-base-2 of current block size for a variable related to a total number of palette indices in the current block of the video data;
• and
• determine the total number of palette indices in the current block of video data by decoding the variable based on the fixed-length (FL) code;
• and
• if the Rice parameter is smaller than the log-base-2 of current block size:
• parse from the video bitstream the binary string for the variable related to the total number of palette indices in the current block of the video data, wherein the binary string comprises a prefix part and a suffix part, and wherein the prefix part is generated using a TR (Truncated Rice) binarization process with input information including the Rice parameter and the suffix part is generated using another binarization process, and the suffix part is allowed to be empty;
• and
• decode the prefix part using a Truncated Rice de-binarization process with the Rice parameter and the suffix part is decoded using another de-binarization process if the suffix part is not empty;
• and
• determine the total number of palette indices in the current block of the video data by decoding the variable based on the prefix part and the suffix part of the binary string;
• and
• apply palette decoding to the current block of the video data using information including the total number of palette indices in the current block of the video data and a palette table.