exemplary embodiments of a bar - code reader , a method , and a computer program relating to reading a bar - code according to the present invention are explained in detail below with reference to the accompanying diagrams . fig1 is a block diagram of the bar - code reader according to an embodiment of the present invention . this bar - code reader includes an optical scanner 2 , an analog processor 3 , an ad converter 4 , and a reading processor 5 . the optical scanner 2 includes a laser diode ( ld ) 2 a and a polygon mirror 2 b . the ld 2 a emits a light beam . a mirror that reflects the light beam emitted from the ld 2 a forms the polygon mirror 2 b . the direction of reflection of the light beam is changed by rotating the polygon mirror 2 b using a motor ( not shown in the diagram ). thus , the polygon mirror 2 b provides a plurality of scanning patterns . using the optical scanner 2 , the light beam emitted from the ld 2 a is radiated , due to the rotation of the polygon mirror 2 b , on a bar code 1 that is held on a reading surface . the light beam is irradiated in a direction from a to b in the diagram . a light receiving section of the analog processor 3 receives light reflected from the bar code 1 . the analog processor 3 performs opto - electric conversion of the light received and converts it to an electric signal . the amplitude of this electric signal depends on the intensity of the light . the analog processor 3 then amplifies the signal according to the requirement . the ad converter 4 performs digital sampling of the opto - electrical signal amplified by the analog processor 3 , and outputs it as a digital signal . the reading processor 5 specifies bar - code characters based on the digital signal that is received from the ad converter 4 and outputs the signal . the reading processor 5 includes an extractor 5 a , a narrow - band differential processor 5 b , a module - frequency extractor 5 c , a module - point extractor 5 d , a module - timing extractor 5 e , an edge - emphasizing processor 5 f , an eql processor 5 g , a ternary judgment section 5 h , and a bar - code demodulator 5 i . the extractor 5 a extracts , from the opto - electrical signal , only a signal that is apparently a bar code signal , to reduce the load of processing in the latter part . concretely , the opto - electrical signal is in the form of a wave with time on the vertical axis and amplitude on the horizontal axis . therefore , the extractor 5 a extracts a part of the waveform as illustrated in fig2 a . the module - frequency extractor 5 c extracts a module - frequency that is equivalent to a basic module of a bar code signal . the narrow - band differential processor 5 b performs the narrow - band differentiation of the opto - electrical signal based on the module - frequency . therefore , the narrow - band differential processor 5 b extracts a waveform of an edge as illustrated in fig2 b . concretely , when a black bar in the bar code 1 is followed by a white bar , a plus ( positive ) edge is developed and when a white bar in the bar code 1 is followed by a black bar , a minus ( negative ) edge is developed . the module - timing extractor 5 e extracts timing for extracting a module point , based on the module - frequency extracted by the module - frequency extractor 5 c . the module - point extractor 5 d extracts a module point according to the timing that is extracted by the module - timing extractor 5 e as illustrated in fig2 c . the edge - emphasizing processor 5 f is a processor peculiar to the present invention and emphasizes amplitude of a module point that fulfils a predetermined condition , among module points that are extracted by the module - point extractor 5 d . the edge - emphasizing processor 5 f outputs edge - emphasizing output as illustrated in fig2 d . the edge - emphasizing processor 5 f emphasizes amplitude of a module point when a thick black bar or a thick white bar that forms the bar code 1 is detected . the reason for performing the edge emphasizing is as follows . a module point has a positive amplitude that changes from a black bar to a white bar of the bar code 1 or a negative amplitude that changes from a white bar to a black bar . in spite of the module point having the positive amplitude or the negative amplitude , the amplitude of the module point decreases due to practical problems like a thick black bar developed due to spreading of ink during printing of a bar code . edge emphasizing is performed to prevent a case that is not regarded as an edge that changes from a black bar to a white bar or an edge that changes from a white bar to a black bar . concretely , in a case of a thick black bar or a thick white bar of the bar code 1 a beam diameter 31 is smaller than the basic width of a black bar or a white bar ( see ( a ) in fig3 ). therefore , substantial amplitude of the signal subjected to opto - electric conversion is acquired and also the amplitude of the module point increases . however , if there is a thick black bar in the bar code 1 , the diameter of the beam becomes greater than the basic width of a black bar or a white bar ( see ( b ) in fig3 ). therefore , substantial amplitude of the signal subjected to opto - electric conversion is not acquired and the amplitude of the module point decreases . a similar phenomenon occurs when there is a thick white bar . therefore , when a thick black bar or a thick white bar is identified , the edge - emphasizing process is performed . in this process , the edge is shifted by the amount of excessive width of a black or a white bar . thus , by checking the position of the edge it can be judged whether there is a thick black bar or a thick white bar . the eql processor 5 g automatically equalizes the amplitude of a module point that has undergone edge emphasizing and a module point that has not undergone edge emphasizing . the ternary judgment section 5 h makes a judgment of whether each module point is a ‘ 1 ’ or a ‘ 0 ’ or a ‘− 1 ’ using the amplitude of the module point equalized by the eql processor 5 g . a module point that has a value ‘ 1 ’ denotes an edge that is changed from a black bar to a white bar , a module point that has a value ‘ 0 ’ denotes an edge that is changed from a white bar to a black bar , and a module point that has a value ‘− 1 ’ denotes an edge without any change ( in other words ‘ a case of no change ’). the bar - code demodulator 5 i specifies the combination of black bars and white bars that forms the bar code 1 and outputs bar - code characters corresponding to the specified combination . fig4 is a flow chart of the process executed by the reading processor 5 . first , the extractor 5 a extracts , from the signal that is subjected to opto - electric conversion , a part that is apparently a bar - code signal ( step s 101 ). then , the narrow - band differential processor 5 b performs narrow - band differentiation of the signal using the module frequency that is extracted by the module - frequency extractor 5 c and extracts a waveform of an edge from the signal extracted by the extractor 5 a ( step s 102 ). moreover , the module - point extractor 5 d extracts a module point from a waveform of an edge by using the module - timing that is extracted by the module - timing extractor 5 e ( step s 103 ). thus , when a module point is extracted from the waveform of an edge , the edge - emphasizing processor 5 f detects a thick black bar or a thick white bar , then emphasizes the edge of the corresponding part , and increases the amplitude of the module point ( step s 104 and s 105 ). then , the eql processor 5 g performs automatic equalization ( step s 106 ). based on the result of the automatic equalization , the ternary judgment section 5 h makes a judgment of whether the module point is a ‘ 1 ’ or a ‘ 0 ’ or a ‘− 1 ’ ( step s 107 ). using this judgment , the bar - code demodulator 5 i demodulates the signal to obtain bar - code characters ( step s 108 ). following is a concrete description of the edge - emphasizing processor 5 f with reference to fig5 to fig8 . a transversal filter that has five delays is considered here . fig5 is a block diagram of a transversal filter . the transversal filter is a digital filter in which setting a tap coefficient can set filter characteristics . the transversal filter includes five delays ( t ), five multiplying units , five tap coefficients ( c 1 to c 5 ), and a summing unit ( σ ). by passing the amplitude of the module point of the edge waveform through the transversal filter , an output signal ( y 1 , y 2 , . . . ) that depends on the value of a coefficient ( shown in a formula below ) can be acquired . the tap coefficients ( c 1 to c 5 ) of the transversal filter are assigned while considering a relationship with the thickness . for convenience of description , as illustrated in fig6 , the tap coefficients c 1 and c 5 are assumed to be 0 , the tap coefficients c 2 and c 4 are assumed to be − 0 . 5 , and the tap coefficient c 3 is assumed to be 1 . where y is the output signal , c is a tap coefficient , x is a delay signal , and n and i are suffixes . a case in which the amplitude of the module point is applied to the transversal filter is examined concretely . fig7 illustrates a waveform of an edge in a case of a thick black bar . the amplitude of module points a 1 to a 5 is decreased as compared to the adjacent amplitudes . the decrease in the amplitude is caused by the presence of a thick black bar . if we assume that the amplitude of the module point a 1 is 0 . 04254 , the amplitude of the module point a 2 is − 0 . 05176 , the amplitude of the module point a 3 is 0 . 04260 , the amplitude of the module point a 4 is − 0 . 04767 , and the amplitude of the point a 5 is 0 . 04688 , these amplitude values are set in the delays x 1 to x 5 of the transversal filter as shown in fig8 . y 3 = x 1 · c 1 + x 2 · c 2 + x 3 · c 3 + x 4 · c 4 + x 5 · c 5 , y 3 = 0 . 092315 . since the output y 3 is an output corresponding to x 3 , it can be seen that the amplitude is increased as compared to the original amplitude of 0 . 4260 . thus , by using the transversal filter , the edge - emphasizing can be performed to increase the amplitude of the module points having their amplitude decreased due to a thick black bar or a thick white bar . when the excessive width is less than a threshold value 1 or when the amplitude of x 3 is less than a threshold value 2 , the tap coefficients c 1 , c 2 , c 4 , and c 5 are assumed to be 0 and the tap coefficient c 3 is assumed to be 1 . when the excessive width is more than the threshold value 1 and the amplitude of x 3 is more than the predetermined threshold value 2 , the tap coefficients that are shown in fig6 may be used . moreover , by changing the tap coefficients dynamically , in accordance with the thick black bar or a thick white bar , the emphasizing characteristics that emphasize the amplitude of the edge can be changed . thus , in this embodiment , the extractor 5 a extracts , from the signal that is subjected to opto - electric conversion , a part that is apparently a bar - code signal . the narrow - band differential processor 5 b performs narrow - band differentiation using the module frequency and forms the edge waveform . further the module - point extractor 5 d extracts the module point from the edge waveform . then , the edge - emphasizing processor 5 f detects a thick black bar or a thick white bar and emphasizes the edge of the corresponding part , thereby increasing the amplitude of the module point . due to such structure , even in a case of a thick black bar or a thick white bar , the amplitude of the corresponding part can be emphasized . in this embodiment , the edge is emphasized when there is a thick black bar or a thick white bar . however , when an edge that has amplitude greater than the predetermined threshold value is detected , the amplitude of the edge can be emphasized . in this case , in the transversal filter in fig5 , if the amplitude of x 3 is less than the predetermined threshold value , the tap coefficients c 1 , c 2 , c 4 , and c 5 are assumed to be 0 and the tap coefficient c 3 is assumed to be 1 . and if the amplitude of x 3 is not less than the predetermined threshold value , the tap coefficients that are shown in fig6 may be used . moreover , if an edge for which the frequency of the module is more than the predetermined threshold value is detected , the amplitude of the edge that is included in this module can be emphasized . in this case , in the transversal filter in fig5 , when the module frequency is less than the threshold value 1 or when the amplitude of x 3 is less than the predetermined threshold value 2 , the tap coefficients c 1 , c 2 , c 4 , and c 5 are assumed to be 0 and the tap coefficient c 3 is assumed to be 1 . when the frequency of the module is not less than the threshold value 1 and the amplitude of x 3 is not less than the threshold value , the tap coefficients that are shown in fig6 may be used . by changing the tap coefficients dynamically , in accordance with the thick black bar and the thick white bar , the emphasizing characteristics that emphasize the amplitude of the edge included in the module can be changed . moreover , in this embodiment , a case of using an optical system that irradiates a bar code by a light beam to acquire reflected light is described . however , the present invention is not restricted to this case only and can also be applied similarly for a case of using an optical system in which extraneous light such as a charged coupled device ( ccd ) is used . furthermore , while realizing the bar - code reader by a computer program , each section ( processor ) in the reading processor 5 illustrated in fig1 may be stored in a read only memory ( rom ) as a program and each program may be executed by a central processing unit ( cpu ). thus , the present invention provides a bar - code reader , a method of reading a bar code , and a computer program for realizing the method according to the present invention on a computer that enables efficient and accurate reading of a bar code . although the invention has been described with respect to a specific embodiment for a complete and clear disclosure , the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth .