1. A method of processing, comprising: accepting an ordered series of quantized transform coefficients of a block of image data, the quantized transform coefficients being generated according to a quantization parameter of the block; classifying the accepted series to form a classified series having a class of a plurality of pre-defined classes, the classifying being according to one or more factors including the size of the block of image data, the classifying comprising: first-stage classifying the accepted series to form a first-stage classified series having a first class of a plurality of pre-defined first classes, the first-stage classifying being according to the size of the block; and second-stage classifying the first-stage classified series to form the classified series having the first class and further having a second class of one or more second classes pre-defined for the first class, the second-stage classifying being according to one or more factors including the quantization parameter of the block, such that the class of the accepted series is defined by at least the first class and the second class; and applying one of a plurality of pre-defined entropy coding methods to the accepted ordered series to form a sequence of codewords, the entropy coding method applied being according to the class of the accepted series, wherein for at least two different pre-defined classes of ordered series of different sizes, different pre-defined entropy coding methods are applied to the different pre-defined classes.