Selective Run-Length Encoding

Background. Run-Length Encoding (RLE) is one of the most fundamental tools in data compression. The basic idea is to represent each element only once, followed by its count within the run. For example, can be stored as (namely an encoded variable ) together with <1, 3, 2, 2, ...> (namely a run-control variable ). Yet, the compression power of RLE drops significantly if there lacks consecutive elements in the sequence. In extreme cases, the output of the encoder may require more space than the input (aka size inflation ).