Abstract: A system for compressing image data, when input in the form of run length coded sequential lines of image data, encodes variable length segments of the current to-be-coded line two dimensionally in terms of the detected relationship between the constants of five registers. The run length code words of the current line and the immediately previous reference line are accessed sequentially and selectively from respective FIFO buffers under the control of switching logic which also establishes a pattern of connections, unique to the generated code representing the immediately previous current line segment, coupling the outputs of the registers and the buffers to the inputs of the registers through adders to establish the next set of five values in terms of which segment coding takes place. One dimensional coding can be accommodated.