The Arithmetic Decoding Engine
The arithmetic decoder is described in some detail in the Standard. It has three distinct properties:
1. Probability estimation is performed by a transition process between 64 separate probability states for “Least Probable Symbol” (LPS, the least probable of the two binary decisions “0” or “1”).
2. The range R representing the current state of the arithmetic coder is quantized to a small range of pre-set values before calculating the new range at each step, making it possible to calculate the new range using a look-up table (i.e. multiplication-free).
3. A simplified encoding and decoding process is defined for data symbols with a nearuniform probability distribution. The definition of the decoding process is designed to facilitate low-complexity implementations of arithmetic encoding and decoding. Overall, CABAC provides improved coding efficiency compared with VLC at the expense of greater computational complexity.
Read more about this topic: Context-adaptive Binary Arithmetic Coding
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