Context-based Adaptive Binary Arithmetic Coding (CABAC) is the entropy coding module in the HEVC/H video coding standard. As in its predecessor. High Throughput CABAC Entropy Coding in HEVC. Abstract: Context-adaptive binary arithmetic coding (CAB-AC) is a method of entropy coding first introduced . Context-based Adaptive Binary Arithmetic Coding (CABAC) is a method of entropy coding which is widely used in the next generation standard of video coding.
|Published (Last):||4 October 2010|
|PDF File Size:||14.96 Mb|
|ePub File Size:||19.41 Mb|
|Price:||Free* [*Free Regsitration Required]|
Circuits and Systems for Video TechnologyVol.
Cahac context modeling provides estimates of conditional probabilities of the coding symbols. This so-called significance information is transmitted as a preamble of the regarded transform block followed by the magnitude and sign information of nonzero levels in reverse scanning order. It generates an initial state value depending on the given slice-dependent quantization parameter SliceQP using a pair of so-called initialization parameters for each model which cabaf a modeled linear relationship between the SliceQP and the model probability p.
The design of these four prototypes is based on a priori knowledge about hev typical characteristics of the source data to be modeled and it reflects the aim to find a good compromise between the conflicting objectives of avoiding unnecessary modeling-cost overhead and exploiting the statistical dependencies to a large extent.
However, in cases where the amount of data in the process of adapting to the true underlying statistics is comparably small, it is useful to provide some more appropriate initialization values for each probability model in order to better reflect its typically skewed nature. At that time – and also at a later stage when the scalable extension of H. From that time until completion of the first standard specification of H.
Arithmetic coding is finally applied to compress the data. This allows the discrimination of statistically different sources with the result of a significantly better adaptation to the individual statistical characteristics.
Note however that the actual transition rules, as tabulated in CABAC and as shown in the graph above, were determined to be only approximately equal to those gevc by hebc exponential aging rule.
Application-Specific Cache and Prefetching for HEVC CABAC Decoding
Probability estimation in CABAC is based on a table-driven estimator using a finite-state machine FSM approach with tabulated transition rules as illustrated above. The remaining bins are coded using one of 4 further context models:. CABAC is based on arithmetic codingwith a few innovations and changes to adapt it to the needs of video encoding standards: The specific features and the underlying design principles of the M coder can be found here. One of 3 models is selected for bin 1, based on previous coded MVD values.
Please enable it for full functionality and experience. These estimates determine the two sub-ranges that the arithmetic coder uses to encode czbac bin. Interleaved with these significance flags, a sequence of so-called last flags one for each significant coefficient level is generated for signaling the position of the last significant level within the scanning path.
If e k is small, then there is a high probability that the current MVD will have a small magnitude; conversely, if e k is large then it is more likely that the current MVD will have a large magnitude. As a consequence of these important criteria within any standardization effort, additional constraints have been imposed on the design of CABAC with the result that some of its original algorithmic components, like the binary arithmetic coding engine have been completely re-designed.
Since CABAC guarantees an inherent adaptivity to the actually given conditional probability, there is no need for further structural adjustments besides caabac choice of a binarization or context model hevcc associated initialization values which, as a first approximation, can be chosen in a canonical way by using the prototypes already specified in the CABAC design.
Related standard contributions in chronological order, as listed here: As an extension of this low-level pre-adaptation of probability models, CABAC provides two additional pairs of initialization parameters for each model that is used in predictive P or bi-predictive B slices.
Xabac design of CABAC involves the key elements vabac binarization, context modeling, and binary arithmetic coding.
For the specific choice of context models, four basic design types are employed in CABAC, where two of them, as further described below, are applied to coding of transform-coefficient levels, only. Hegc first converts all non- binary symbols to binary. It is a cxbac compression technique, although the video coding standards in which it is used are typically for lossy compression applications.
The arithmetic decoder is described in some detail in the Standard.
Context-adaptive binary arithmetic coding – Wikipedia
Binarization The coding strategy of CABAC is based on the finding that a very efficient coding of syntax-element values in a hybrid block-based video coder, like components of motion vector differences or transform-coefficient level values, can be achieved by employing a binarization scheme as a kind of preprocessing unit for the subsequent stages of context modeling and binary arithmetic coding.
Usually the addition of syntax elements also affects the distribution of already available syntax elements which, in general, for a VLC-based entropy-coding approach may require to re-optimize the VLC tables of the given syntax elements rather than just adding a suitable VLC code for the new syntax element s.
The design of binarization schemes in CABAC is based on a few elementary prototypes whose structure enables simple online calculation yevc which are adapted to some suitable model-probability distributions. It has three distinct properties:.
Context-Based Adaptive Binary Arithmetic Coding (CABAC)
Context-modeling for coding of binarized level magnitudes are based on the number of previously transmitted level magnitudes greater or equal to 1 within the reverse scanning path, which is motivated by the observation that levels with magnitude equal to 1 are statistical dominant at the end of the scanning path.
This is the purpose of the initialization process for context models in CABAC, which operates on two levels. Choose a context model for each bin. On the lowest level cwbac processing in CABAC, each bin value enters the binary arithmetic encoder, either in regular or bypass coding mode. CABAC has multiple probability modes for different contexts.
Context-adaptive binary arithmetic coding
By decomposing each syntax element value into a sequence of bins, further processing of each bin value in CABAC depends on the associated coding-mode decision, which can be either chosen as the regular or the bypass mode.
The coding strategy of CABAC is based on the finding that a very efficient coding of syntax-element values in a hybrid block-based video coder, like components of motion vector differences or transform-coefficient level values, can be hevd by employing a binarization scheme as a kind of preprocessing unit for the subsequent stages of context modeling and binary arithmetic coding. Utilizing suitable context models, a given inter-symbol redundancy can be exploited by switching between different probability models according to already-coded symbols in the neighborhood of the current symbol to encode.