Probability update method for binary arithmetic coding/decoding, and entropy coder/decoder using the same

A probability update method for binary arithmetic decoding, the method comprising:

• receiving a predetermined number of bins that are to be binary arithmetic decoded;
• obtaining entropy values indicating an average bit value of the bins by using a plurality of probability models having different scaling factors;
• determining a scaling factor of a probability model used to obtain a minimum entropy value among the plurality of probability models;
• updating a probability used in context-based adaptive binary arithmetic decoding by using the determined scaling factor;
• and
• performing context-based adaptive binary arithmetic decoding using the updated probability,
• wherein the updating a probability comprises:
• obtaining the updated probability by adding a first value and a second value, the first value being obtained by multiplying a value based on the at least one scaling factor by a probability of a previous bin, and the second value being obtained by multiplying the at least one scaling factor by a value of a current bin,
• wherein when a value of the current bin is y (y is 0 or 1), a probability previous to the current bin is p(t−1) (t is an integer), the updated probability is p(t), and the at least one scaling factor is α, the updated probability p(t) is obtained according to an equation P(t)=αy+(1−α)*P(t−1).

An entropy decoding apparatus comprising:

• an inverse binarizer configured to map values of predetermined syntax elements to bins of a binary value;
• a context modeler configured to receive a predetermined number of bins that are to be binary arithmetic decoded, obtain an autocorrelation value of each bin by using values of the received predetermined number of bins, determine at least one scaling factor used to update a probability of a binary value based on the autocorrelation value, and update a probability used in context-based adaptive binary arithmetic decoding by using the determined at least one scaling factor;
• and
• a regular coder configured to arithmetic decode a current bin by using the updated probability,
• wherein the context modeler obtains the updated probability by adding a first value and a second value, the first value being obtained by multiplying a value based on the at least one scaling factor by a probability of a previous bin, and the second value being obtained by multiplying the at least one scaling factor by a value of a current bin,
• wherein when a value of the current bin is y (y is 0 or 1), a probability previous to the current bin is p(t−1) (t is an integer), the updated probability is p(t), and the at least one scaling factor is α, the updated probability p(t) is obtained according to an equation P(t)=αy+(1−α)*P(t−1).