Read-out level compensation in an optical reader system

An optical reader system comprising:

• a light source for illuminating an original sheet and a reference sheet;
• a plurality of sensor elements for detecting the light reflected at the surface of said original sheet and developing first output signals in response thereto,
• said sensor elements detecting the light reflected at the surface of said reference sheet and developing second output signals in response thereto;
• means for developing a picture signal in accordance with the first output signals derived from said plurality of sensor elements;
• and
• compensation means for performing a compensation operation on said picture signal thereby producing a compensated picture signal, said compensation means including;
• memory means for storing a reciprocal of the second output signals from said sensor elements in digital form therein;
• and
• analog-to-digital converter means connected to said sensor elements for receiving the second output signals from said sensor elements and developing digital second output signals in response thereto;
• reverse converter means for receiving the digital second output signals from said analog-to-digital converter means and developing a reciprocal of said digital second output signals in a digital form in response thereto, the reciprocal of said digital second output signals being presented to said memory means for storage therein when said optical reader system operates in said write mode;
• write means for introducing said reciprocal of said digital second output signals from said reverse converter means into said memory means when said optical reader system operates in said write mode;
• read means for developing said reciprocal of said digital second output signals from said memory means,
• digital-to-analog converter means for converting the reciprocal of said digital second output signals from said read means when said optical reader system operates in said read mode and for developing reciprocal analog second output signals in response thereto;
• multiplier means for multiplying the reciprocal analog second output signals from said digital-to-analog converter means by said picture signal thereby producing said compensated picture signal;
• switching means for connecting said write means to said memory means when said sensor elements scan said reference sheet, and for connecting said read means to said memory means when said sensor elements scan said original sheet,
• controller means connected to said memory means and including said write means and said read means for controlling said optical reader system to operate in said write mode and in said read mode to introduce said reciprocal into said memory means and to develop said reciprocal from said memory means, respectively;
• peak follower circuit means responsive to the output signals from said sensor elements for developing a peak output signal representative of the peak value of said output signals;
• comparator means responsive to said peak output signal and to said compensated picture signal for developing an output signal when the peak output signal is greater than or equal to said compensated picture signal;
• control signal generation means responsive to the output signal of said comparator for generating a first control signal and a second control signal, said control signal generation means including first and second control signal generating means, said first control signal generating means generating said first control signal when said output signal is generated twice in succession by said comparator means, said second control signal generating means generating said second control signal in response to the absence of said output signal for a predetermined time;
• and
• latch circuit means connected between said controller means and said memory means and responsive to said first and second control signals from the means for generating for storing an output signal from said controller means therein and for permitting said output signal from said controller means to enable said memory means in response to said first control signal and for preventing said output signal from said controller means for energizing said memory means in response to said second control signal.