referring to fig3 there is shown a preferred embodiment of a filling system in accordance with the present invention . outline coordinate data generated by an outline generator 100 is divided into outline start position data and outline end position data by a start / end data divider 101 . the outline start position data and the outline end position data are stored in the form of a line data into an outline start position memory 102 and an outline end position memory 103 , respectively . the start / end data divider 101 discriminates between the outline start position data and the outline end position data , depending on which a differential value of the outline coordinate data is positive or negative . a controllable adder - subtracter 104 receives an addition control signal and a subtraction control signal from the outline start position memory 102 and the outline end position memory 103 , respectively . the addition control signal is comprised of the outline start position data and the subtraction control signal is comprised of the outline end position data . receiving these control signals , the controllable adder - subtracter 104 performs an addition operation when the addition control signal indicative of an outline start position is input and performs a subtraction operation when the subtraction control signal indicative of an outline end position is input . through these addition and subtraction operations , the controllable adder - subtracter 104 outputs a value of 1 or more in the region between the first outline start position and the last outline end position of a certain scanning line and outputs a value of 0 at positions other than that region . a filled image data generation circuit 105 receives the output value of the controllable adder - subtracter 104 for each scanning line and fills regions having a value of 1 or more . all of the filled regions are replaced , for example , by ` 1 `, and output to an image data memory 106 . the image data memory 106 stores therein the filled line data in sequence and forms bit map image data . fig4 illustrates a case in which the outline generator 100 generates the outline coordinate data in which two outlines are synthesized . since , as shown in the figure , a start position and an end position of each image outline exist on a certain scanning line , two start positions and two end positions are stored in the outline start position memory 102 and the outline end position memory 103 , respectively . note that the outline coordinate data is divided by the start / end data divider 101 such that the number of start positions is always equal to the number of end positions on any line . such start position data and end position data are output in scanning lines to the controllable adder - subtracter 104 as addition and subtraction parameters . as shown in fig5 the output status of the controllable adder - subtracter 104 is increased by one unit each time bit data ` 1 ` indicative of a start position is input , and is decreased by one unit each time bit data ` 1 ` indicative of an end position is input . therefore , the output value of the controllable adder - subtracter 104 is incremented from &# 34 ; 0 &# 34 ; to &# 34 ; 1 &# 34 ; by the first start position s1 and further incremented by the next start position s2 , and the output value goes to &# 34 ; 2 &# 34 ;. the output value is decremented by the first end position e1 and is returned to &# 34 ; 0 &# 34 ; by the last end position e2 . the region having output values of 1 or more is therefore formed on the scanning line between the first start position s1 and the last end position e2 , and the region are to be filled . the above - described operation of the controllable adder - subtracter 104 is applicable not only to the synthesis of two image outlines but also to the synthesis of an arbitrary number of image outlines . more particularly , since the number of start positions ( also end positions ) is equal to that of synthesized image outlines , an output value of the controllable adder - subtracter 104 is incremented each time a start position is input and decremented each time an end position is input , and , finally , the output value is returned to &# 34 ; 0 &# 34 ;. therefore , only the inside positions of the outermost outline of a synthesized outline have an output value of 1 or more , and such a region is to be filled . the controllable adder - subtracter 104 may be comprised of a single controllable adder - subtracter and can also be comprised of a plurality of controllable adder - subtracters which are connected in series . the number of data bits of any scanning line is a multiple of the number of the controllable adder - subtracters . note that since , in the case of a plurality of controllable adder - subtracters , the addition and subtraction operations are required repeatedly to cover all of the data bits of one line , a latch circuit is further required to be connected to the controllable adder - subtracters in series . a circuit construction in which a frame of image data is 8 bits × 8 lines and four controllable adder - subtracters are used will hereinafter be described as a concrete example of this embodiment to make the description simpler . as shown in fig6 the controllable adder - subtracter 104 comprises a single latch circuit 201 and four controllable adders 202 to 205 . the latch circuit 201 comprises a flip - flop , and output terminals f0 to f3 are connected to input terminals b10 to b13 of the adder 202 , respectively . the adders 202 to 205 are likewise connected in series . output terminals a40 to a43 of the last adder 205 are connected to input terminals e0 to e3 of the latch circuit 201 , respectively . output terminals d10 to d13 of the outline start position memory 102 are connected to the addition control terminals of the adders 202 to 205 , respectively , and output terminals d20 to d23 of the outline end position memory 103 are connected to the subtraction control terminals of the adders 202 to 205 , respectively . the filled image data generation circuit 105 comprises 0r gates 206 to 209 . output terminals a10 to a13 of the adder 202 are connected to the input terminals of the or gate 206 , respectively . likewise , the output terminals of the adders 203 to 205 are connected to the input terminals of the or gates 207 to 209 , respectively . also , the respective output terminals d20 to d23 of the outline end position memory 103 are connected to the input terminals of the or gates 206 to 209 . the output terminals of the or gates 206 to 209 are connected to input terminals d30 to d33 of the image data memory 106 , respectively . a controller 107 outputs latch control signal c1 to the latch circuit 201 , data read control signal c2 to the outline start position memory 102 , data read control signal c3 to the outline end position memory 103 , and image data write control signal c4 to the image data memory 106 . an operation in a case where the two image outlines shown in fig7 a and 7b are synthesized as shown in fig7 c will be described . among the image outline coordinate data generated by the outline generator 101 , the outline start position data is stored in the outline start position memory 102 , as shown in fig8 a , and the outline end position data is stored in the outline end position memory 103 , as shown in fig8 b . for 4th line of the outline data shown in fig8 a and 8b , the filling operation of this embodiment will hereinafter be described with reference to fig9 . first , the controller 107 outputs the respective read control signals c2 and c3 to the outline start position memory 102 and the outline end position memory 103 . this causes the outline start position memory 102 and the outline end position memory 103 to output the respective line data 301 and 302 ( in this example , of the fourth line ) to the controllable adder - subtracter 104 . as shown in fig9 the line data 301 of ` 0110 ` is output from the output terminals d10 to d13 of the outline start position memory 102 , and the line data 302 of ` 0000 ` is output from the output terminals d20 - d23 of the outline end position memory 103 . since an initial output value of the latch circuit 201 is &# 34 ; 0 &# 34 ; 4 - bit data ` 0000 ` is input to the input terminals b10 - b13 of the adder 202 . a first bit data ` 0 ` of the line data 301 is output from the output terminal d10 of the outline start position memory 102 to the addition control terminal of the adder 202 , and a first bit data ` 0 ` of the line data 302 is output from the output terminal d20 of the outline end position memory 103 to the subtraction control terminal of the adder 202 . therefore , the adder 202 does not perform any addition or subtraction operation , outputting 4 - bit data ` 0000 ` from the output terminals a10 - a13 and , consequently , the or gate 206 will output a bit data ` 0 `. similarly , since the adder 203 receives 4 - bit data ` 0000 ` from the adder 202 , a bit data ` 1 ` of d11 at the addition control terminal , and a bit data ` 0 ` of d21 at the subtraction control terminal , the adder 203 performs the addition operation and outputs 4 - bit data ` 0001 `, or decimal numeral &# 34 ; 1 &# 34 ;, from the output terminals a20 - a23 . therefore , the or gate 207 will output a bit data ` 1 `. since the adder 204 receives decimal numeral &# 34 ; 1 &# 34 ; from the adder 203 , a bit data ` 1 ` of d12 at the addition control terminal , and a bit data ` 0 ` at the subtraction control terminal , the addition operation is performed to output 4 - bit data ` 0010 `, i . e . , decimal numeral &# 34 ; 2 &# 34 ;, from the output terminals a30 - a33 . therefore , the or gate 208 will output a bit data ` 1 `. finally , since the adder 205 receives a decimal numeral &# 34 ; 2 &# 34 ; from the adder 204 , a bit data ` 0 ` of d13 at the addition control terminal , and a bit data ` 0 ` of d23 at the subtraction control terminal , the adder 205 does not perform any addition or subtraction operation , therefore outputs 4 - bit data ` 0010 `, i . e ., decimal numeral &# 34 ; 2 &# 34 ;, from the output terminals a40 - a43 . therefore , the or gate 209 will output a bit data ` 1 `. in this way , the respective output bits of the or gates 206 to 209 are ` 0 `, ` 1 `, ` 1 `, and ` 1 ` and output as filled image data 303 to the input terminals d30 to d33 of the image data memory 106 . the filling operation for the first half of the 4th line data is completed . subsequently , the controller 107 outputs the latch control signal c1 to the latch circuit 201 so that the output ` 0010 ` of the adder 205 is latched . the controller 107 further outputs the read control signals c2 and c3 to the outline start position memory 102 and the outline end position memory 103 . in response to these signals c2 and c3 , the respective memories 102 and 103 output the remaining line data 401 and 402 to the controllable adder - subtracter 104 . since the current output value of the latch circuit 201 is ` 0010 `, or decimal numeral &# 34 ; 2 &# 34 ;, the adder 202 receives the output data ` 0010 ` at the input terminals b10 - b13 . a first bit data ` 0 ` of the line data 401 is output from the output terminal d10 of the outline start position memory 102 to the addition control terminal of the adder 202 , and a first bit data ` 0 ` of the line data 402 is output from the output terminal d20 of the outline end position memory 103 to the subtraction control terminal of the adder 202 . therefore , the adder 202 does not perform any addition or subtraction operation , outputting 4 - bit data ` 0010 ` from the output terminals a10 - a13 and , consequently , the or gate 206 will output a bit data ` 1 `. similarly , since the adder 203 receives the 4 - bit data ` 0010 ` from the adder 202 , a bit data ` 0 ` of d11 at the addition control terminal , and a bit data ` 1 ` of d21 at the subtraction control terminal , the adder 203 performs the subtraction operation and outputs 4 - bit data ` 0001 `, or decimal numeral &# 34 ; 1 &# 34 ; from the output terminals a20 - a23 . therefore , the or gate 207 will output a bit data ` 1 `. since the adder 204 receives decimal numeral &# 34 ; 1 &# 34 ; from the adder 203 , a bit data ` 0 ` of d12 at the addition control terminal , and a bit data ` 1 ` of d22 at the subtraction control terminal , the subtraction operation is performed to output 4 - bit data ` 0000 `, i . e ., decimal numeral &# 34 ; 0 &# 34 ;, from the output terminals a30 - a33 . however , since the or gate 208 receives bit data ` 1 ` from the terminal d22 of the end position memory 103 , the output of the or gate 208 is ` 1 `. finally , since the adder 205 receives a decimal numeral &# 34 ; 0 &# 34 ; from the adder 204 , bit data ` 0 ` of d13 at the addition control terminal , and bit data ` 0 ` of d23 at the subtraction control terminal , the adder 205 does not perform any addition or subtraction operation , therefore outputs the 4 - bit data ` 0000 `, i . e ., decimal numeral &# 34 ; 0 &# 34 ; from the output terminals a40 - a43 since the or gate 209 inputs bit data &# 34 ; 0 &# 34 ; from the terminal d23 of the end position memory 103 , the or gate 209 outputs bit data ` 0 `. in this way , the respective output bits of the or gates 206 to 209 are ` 1 `, ` 1 `, ` 1 ` and ` 0 ` and output as filled image data 403 to the input terminals d30 to d33 of the image data memory 106 . the - filling operation for the second half of the 4th line data is completed . through the above - described first and second steps , the filling operation of the 4th line data is performed to fill the region from the first outline start position ( the 2nd data bit ) to the last outline end position ( the 7th data bit ). the above - described filling operation is repeated from the 1st line to the 8th line so that the entire inside of the synthesized outline will be filled as shown in fig1 . although only one embodiment of the present invention has been described herein , it will be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention . for example , even if a frame of image data is comprised of 100 bits × 100 lines , it would be apparent that the filling operation can be executed with the same configuration as in fig6 . in addition , although , in this embodiment , two image outlines have been synthesized , the present invention is not limited to this . even if a number of image outlines were synthesized , the filling operation would be executed in the same way as in fig6 .