Method and apparatus for reading images without need for self-generated illumination source
First Claim
1. An apparatus for reading encoded images comprising:
- focusing optics for collecting light;
a photosensor positioned so as to receive light collected by said focusing optics, and generating a photosensor output signal thereby;
a correlated double sampling circuit connected to said photosensor output signal, said correlated double sampling circuit comprising circuitry selected from the group consisting of;
a dual slope processor and a dual sampler processor; and
a decoder connected to said correlated double sampling circuit.
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Accused Products
Abstract
A method and apparatus for reading bar codes or other images while reducing or eliminating the need for self-generated illumination. An image reader is preferably embodied as a handheld unit and comprises an efficient optical collection system including an aperture with a high aspect ratio and/or a multi-focal lens or lenses. An optically transmissive spacer affixed to the front of the handheld unit allows ambient light to be collected at close range, and a diffuser may be used to reflect ambient light from the handheld unit to provide additional illumination at close range. A masked CCD detector with rectangular pixels receives collected light and is coupled to an adaptive exposure circuit for preventing saturation of the CCD detector at high illumination levels. A correlated double sampling circuit coupled to the adaptive exposure circuit rejects common mode noise and allows operation in lower light levels. The correlated double sampling circuit is connected to a signal processor which uses a derivative based technique for detecting edges of the image. A decoder uses the edge detection information to decode encoded information from the image.
234 Citations
21 Claims
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1. An apparatus for reading encoded images comprising:
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focusing optics for collecting light; a photosensor positioned so as to receive light collected by said focusing optics, and generating a photosensor output signal thereby; a correlated double sampling circuit connected to said photosensor output signal, said correlated double sampling circuit comprising circuitry selected from the group consisting of;
a dual slope processor and a dual sampler processor; anda decoder connected to said correlated double sampling circuit. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method for reading images, comprising the steps of:
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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. - View Dependent Claims (11, 12, 13, 14, 15)
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16. An apparatus for reading encoded images comprising:
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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. - View Dependent Claims (17, 18, 19)
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20. A method for optical reading, comprising the steps of:
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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. - View Dependent Claims (21)
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Specification