Arithmatic Coding

My implementation for Arithmetic Coding algorithm.

Getting Started

You can view testSample.py code to get an idea about how to use the ArithmaticCoding class.

Prerequisites

• Python 2.7

Basic Arithmetic Coding Algorithm

I have implemented the algorithm from Fundamentals of Multimedia book, the algorithms are Algorithm 7.5, Procedure 7.2, Algorithm 7.6.

Arithmetic Coding Encoder

BEGIN
  low = 0.0; high = 1.0; range = 1.0;
  initialize symbol;     // so symbol != terminator

  while (symbol != terminator)
  {
    get (symbol);
    low = low + range * Range_low(symbol);
    high = low + range * Range_high(symbol);
    range = high - low;
  }
  output a code so that low <= code < high;
END

Generating Codeword for Encoder

BEGIN
  code = 0;
  k = 1;
  while (value(code) < low)
  {
    assign 1 to the kth binary fraction bit;
    if (value(code) > high)
      replace the kth bit by 0;
    k = k + 1;
  }
END

Arithmetic Coding Decoder

BEGIN
  get binary code and convert to decimal value = value(code);
  Do
  {
    find a symbol s so that
      Range_low(s) <= value < Range_high(s);
    output s;
    low = Rang_low(s);
    high = Range_high(s);
    range = high - low;
    value = [value - low] / range;
  }
  Until symbol s is a terminator
END

Notes

I have not handled any exceptions, just the basic algorithm.

References

• Fundamentals of Multimedia

License

This project is licensed under the MIT License - see the LICENSE.md file for details