Method and apparatus for encoding image data is described. In an example, a memory stores bit-planes associated with the image data. Each of the bit-planes is partitioned into data units. A bit modeler communicates with the memory and produces modeled data in response to each of the data units for each of the bit-planes. An arithmetic coder communicates with the bit modeler and produces a coded data in response to each of the modeled data produced by the bit-modeler. In another example, the bit-modeler processes at least two of the bit-planes in parallel.