A system and method are provided for packing compressed image data into a format suitable for encoding. The system includes a plurality of sub-band state registers, which store compressed image data from a corresponding sub-band. A bit packer receives a stream of bits of compressed image data, and concatenates the input bits with bits stored in one of the sub-band state registers. If a length of the concatenated bits is less than a width of an output data bus, the bit packer stores the concatenated bits in the sub-band state register. If the length of the concatenated bits is greater than or equal to the width of the output data bus, the bit packer outputs the concatenated bits via the output data bus.