Microsoft patents video coding method using base color index maps

1. One or more non-transitory computer-readable media having stored thereon computer-executable instructions for causing a computer system, when programmed thereby, to perform operations comprising: encoding a frame of a sequence, thereby producing encoded data, wherein the encoding the frame comprises, for a coding unit of the frame: setting a syntax element that indicates whether prediction mode for the coding unit is intra or inter; based at least in part on the prediction mode for the coding unit being intra, setting a flag value that indicates whether or not to use a base color index map mode for the coding unit; entropy coding the syntax element and the flag value; and encoding the coding unit using the base color index map mode, including: creating a base color table for the coding unit, the base color table having multiple index values, the base color table assigning one or more index values, among the multiple index values, to one or more corresponding base colors; creating an index map for the coding unit, the index map including at least one index value among the one or more index values, and the index map further including one or more exception values not representing any of the one or more corresponding base colors in the base color table, the one or more exception values being designated using a highest possible index value among the multiple index values of the base color table; encoding the base color table for the coding unit; and encoding the index map for the coding unit; and outputting the encoded data as part of a bitstream, wherein the encoded data includes the syntax element and the flag value.