1. A method of decoding an image in a video or image decoder from a bitstream, the decoder having an arithmetic decoder to convert the bitstream into bins, and the decoder having a binarizer constructed based on a probability distribution associated with an alphabet of symbols, the method comprising: inverse binarizing, using the binarizer, a sequence of bins arithmetically decoded from the bitstream and corresponding to an encoded symbol from the alphabet of symbols, to produce a reconstructed symbol; updating the probability distribution based on the reconstructed symbol to produce an updated probability distribution; determining an updated binarizer based on the updated probability distribution for use in inverse binarizing a second sequence of bins to produce a second reconstructed symbol; and outputting the reconstructed symbols to be used in reconstructing the image.