If the Global Color Table Flag is set to 1, the value in this field
is used to calculate the number of bytes contained in the Global
Color Table. To determine that actual size of the color table,
raise 2 to [the value of the field + 1].
Even if there is no Global Color Table specified, set this field
according to the above formula so that decoders can choose the best
graphics mode to display the stream in.
Declaration Syntax
Remarks
This is the value of the globalColourTableSizeBits parameter passed
to the constructor.