Variants
The construction of a code tree for the Huffman coding is based on a certain probability distribution.
Three different variants result from the question about the determination of this distribution:
 static probability distribution
 dynamic probability distribution
 adaptive probability distribution
At the time of the encoding the probability distribution is unknown and can only be determined by analysing the entire set of data. This requires on the one hand an additional access to the complete data volume before starting the encoding process. On the other hand information about this distribution must be provided in addition to the contents for decoding purposes.
Moreover the distribution usually is not constant for the entire data set what negatively affects the
compression efficiency.
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