Edge delta runlength (EDRL) data stream decoder for bi-level graphics

1. An expander circuit to process an edge delta runlength (EDRL) encoded data stream of codewords to produce image line data, including:

an EDRL stream decoder responsive to the encoded data stream including,

a barrel shifter,

a decoder coupled to the barrel shifter,

an EDRL state machine responsive to the decoder and configured to produce data indicating codeword length; and

a feedback loop responsive to the data indicating a code length and arranged to control operation of the barrel shifter:

wherein the EDRL encoded data stream is entropy coded, and

wherein the feedback loop includes a bit offset circuit arranged to vary shifting of the barrel shifter on the basis of the data indicating code length.

2. An expander circuit according to claim 1 , wherein the bit offset circuit controls the barrel shifter so that an edge of the barrel shifter storing a most significant bit is aligned to a codeword boundary of the encoded data stream.

3. An expander circuit according to claim 2 , wherein the bit offset circuit is arranged to perform addition of a current codeword bit offset with a newly generated codeword bit offset from the EDRL state machine.

4. An expander circuit according to claim 3 , wherein the bit offset circuit performs modulo-n addition where n is the length of an input codeword bit pattern of said data stream.

5. A printer of a type having a micromechanical pagewidth printhead including an expander circuit according to claim 4 .

6. A printer including an expander circuit according to claim 1 .