EP O 1 79 291 B1 T8ble l T. _ Two-d__ens_onal code table _ _ode Ele_ent_ to be coded Notat_on COde WOrd pass b l, bz P OOO l . Hor_zontal aoal, ala2 H OOl?_(aoa l)_M(8 la2) _ Vert_cal al _ us t under b l a lb l = O V (,O) l __ . al to the right of b l alb l -- l Vg( l) O. _l l alb l -- 2 Vg(2) OOOO l l _ a lb l = 3 Vg(3) OOOOO l l a l to the left of b l alb l E l VL( l) O IO . alb l _ 2 VL (2) OOOOIO _ _ alb l E 3 VL (3) OOOOO IO Extens_on 2-D (extens_ons) OOOOOOlxxx l-D (extens_ons) OOOOOOOO IXXX _5 Referring to Fig. 2, an exemplary- panern is shown for describ_ing the coding scheme wherein the pel Ipi CtUre element) ''ao'' fep FeSentS the Feferen Ce OF Sta_ing element on the COdíng linel the ''a_'' representS _ the ne Xt Changing element tO the Fight Of ao on the COd._ng l._nel and the ''b_'' fepfeSentS the fifSt Changing element On the feferen Ce l__ne tO the right Of ao and Of OppOSite COIOUF tO ao. AS appafent ffOm Table 1, the code words for la_b_ l _ 3 are of relatively short length. __ 50 Describing the basic concept of a first embodiment of the present invention with reference to Figs. 3A thFOUgh 6D, the inVentiOn deteCtS a Chang__ng element C_ in a fiFSt SCan line, a Chang._ng element C2 in a SeCOnd SCan l._ne and a Changing element C_ in a thi Fd sCan line. F__gs. 3A-B, QA-D, 5A-D 6A-D show panerns which are pre-processed in accordance with the pfeSent._nVention, and _ 55 Fig. 7 shows a circuit block diagram for performing the pre-process in accordance with the present _invention. Fig. 8 shows an example of an oríginal image used for the descr__ption of a second embodiment of the pfeSent invention. _ Fig. 9 shows panerns which are pre-processed in the second embod__ment ofthe present invention, and 6o Fig. IO shows the pre-process operation in the second embodiment of the present __nvention. . J Descripton of First Embodiment The invent__on performs a pre-process of bi-level image data to reduce the amount of compressed data, wh._ch are compressed under a conventional two-dimensional coding scheme, such as provided bv the 65 CCl_ Recommendatíon T.Q. _ _.3_-_ _,... . . .