Methods for palette size signaling and conditional palette escape flag signaling

A method of palette coding for a picture, wherein the picture is divided into multiple coding units (CUs), the method comprising:

• receiving input data associated with a current coding unit (CU);
• determining current palette size of a current palette table of the current CU, or both predicted palette size and new palette size associated with the current palette table, wherein the predicted palette size indicates a first number of entries of the current palette table that are predicted by a palette predictor and the new palette size indicates a second number of entries of the current palette table that are not predicted by the palette predictor;
• and
• performing one of:
• determining whether or not to signal a CU-level escape pixel presence flag according to the current palette size or both of the predicted palette size and the new palette size and signaling a CU-level escape pixel presence flag according to the determination of whether or not to signal the CU-level escape pixel presence flag, wherein the CU-level escape pixel presence flag indicates whether there is any sample in the current CU coded as an escape pixel;
• and
• determining whether or not to constrain the CU-level escape pixel presence flag to one according to the current palette size or both of the predicted palette size and the new palette size, and constrain the CU-level escape pixel presence flag to one according to the determination of whether or not to constrain the CU-level escape pixel presence flag to one.

A video coding system implementing palette coding for a picture, wherein the picture is divided into multiple coding units (CUs), the system comprising:

• a receiver configured to receive input data associated with a current coding unit (CU);
• a processor configured to determine current palette size of a current palette table of the current CU, or both predicted palette size and new palette size associated with the current palette table, wherein the predicted palette size indicates a first number of entries of the current palette table that are predicted by a palette predictor and the new palette size indicates a second number of entries of the current palette table that are not predicted by the palette predictor;
• and
• the processor further configured to perform one of:
• determining whether or not to signal a CU-level escape pixel presence flag according to the current palette size or both of the predicted palette size and the new palette size and signaling a CU-level escape pixel presence flag according to the determination of whether or not to signal the CU-level escape pixel presence flag, wherein the CU-level escape pixel presence flag indicates whether there is any sample in the current CU coded as an escape pixel;
• and
• determining whether or not to constrain the CU-level escape pixel presence flag to one according to the current palette size or both of the predicted palette size and the new palette size, and constrain the CU-level escape pixel presence flag to one according to the determination of whether or not to constrain the CU-level escape pixel presence flag to one.