Method and apparatus for reading images without need for self-generated illumination source

A method for reading images, comprising the steps of:

• collecting light and focusing said light onto a photosensor;
• generating a photosensor output signal in response to light focused onto said photosensor;
• removing common mode noise from said photosensor output signal, and generating a noise-reduced photosensor output signal thereby;
• and
• detecting edge transitions in said noise-reduced photosensor output signal, said edge transitions corresponding to transitions between lighter and darker portions of a read image;
• wherein said step of removing common mode noise from said photosensor output signal comprises the steps of
• charging a capacitor to a reset voltage for a predetermined period,
• after said predetermined period, applying said photosensor output signal to said capacitor, and
• sampling an output voltage of said capacitor.

An apparatus for reading encoded images comprising:

• a multi-focus imaging system;
• a charge-coupled device positioned so as to receive light collected by said multi-focus imaging system, and generating a CCD output signal thereby;
• means connected to said charge-coupled device for reducing common mode noise in said CCD output signal, and generating a noise-reduced CCD output signal thereby;
• and
• a decoder connected to said noise-reduced CCD output signal;
• wherein said means for reducing common mode noise in said CCD output signal comprises a correlated double sampling circuit, said correlated double-sampling circuit comprising circuitry selected from the group consisting of:
• a dual slope processor and a dual sampler processor.

A method for optical reading, comprising the steps of:

• collecting light using a multi-focus imaging system;
• focusing the collected light onto a charge coupled device, and generating a CCD output signal thereby;
• removing common mode noise from said CCD output signal, and generating a noise-reduced CCD output signal thereby;
• and
• adjusting an exposure time of said charge-coupled device in response to said CCD output signal;
• wherein said step of removing common mode noise from said CCD output signal comprises the steps of
• charging a capacitor to a reset voltage for a predetermined period,
• after said predetermined period, applying said CCD output signal to said capacitor, and
• sampling an output voltage of said capacitor.