Information reading apparatus

Claim 1

An information reading apparatus, comprising: (a) a manuscript reader for producing a photoelectronically converted analog signal; (b) an A/D converter for converting said analog signal into digital data including picture image data and shading correction reference image density data; (c) memory means for storing said digital data corresponding to the output of said manuscript reader with no light input to said manuscript reader; (d) subtracting means for subtracting said data stored in said memory means from both picture image data and shading correction reference density data so as to effect a base level correction of both said data; and (e) shading correction means for effecting a predetermined shading correction based on said picture image data and said shading correction reference density data, base levels of both data having been corrected by said subtracting means, said shading correction means comprising: (i) logarithmic converting means for converting an output signal of said subtracting means into a logarithmic value; (ii) other memory means for storing a shading correction reference density data of said logarithmic value, and (iii) other subtracting means for subtracting said logarithmic value of said shading correction reference density data stored in said other memory means from said picture image data converted into a logarithmic value by said logarithmic converting means.