System and method for improving the signal to noise ratio of a CCD sensor in an optical scanner
AssigneeHewlett-Packard Company
InventorsGreg A. Degi, Gerald L. Meyer, Steven L. Webb
Life of this patent
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Abstract
A system and method for improving the signal to noise ratio of a CCD sensor within an optical scanner varies the exposure time of the CCD sensor. Exposure time is varied by clocking the CCD sensor a number of times equal to the number of pixels in the CCD sensor plus an additional number of clock cycles to create a delay. The additional exposure time maximizes the magnitudes of the charges produced by the CCD sensor. The required delay is computed during a pre-scan calibration step.
Claims8
An image capture system comprising:
- a charge coupled device sensor including
- an analog shift register, and
- an array of N sensing elements configured to produce a plurality of charges in response to light incident thereon and to dump said charges into said analog shift register upon receipt of a dump signal,
- wherein said charges are read out of said analog shift register with an N-cycle clock signal, said N-cycle clock signal defining an exposure time of said charge coupled device sensor and the delay between consecutive dump signals;
- means for comparing a magnitude of one of said charges generated by said charge coupled device sensor to a reference value;
- and
- calibration means for changing the number of clock cycles of said N-cycle clock signal based on said comparison of one of said charges and said reference value to adjust said exposure time of said charge coupled device sensor.
An image capture system comprising:
- a charge coupled device sensor having an array of N photoelectric sensing elements and an analog shift register, each of said N photoelectric sensing elements being configured to receive light from an image and to produce an electric charge corresponding to an intensity of the received light, said array of photoelectric sensing elements being configured to dump said electric charges to said analog shift register in response to a dump signal, said analog shift register being configured to sequentially shift one of said electric charges out of said charge coupled device in response to a clock signal;
- amplifier means for receiving an electric charge from said analog shift register and for producing an analog voltage corresponding thereto;
- conversion means for receiving an analog voltage from said amplifier means and for digitizing said analog voltage to produce a digitized voltage;
- memory means for storing said digitized voltage;
- and
- control means for generating M clock cycles, for providing said M clock cycles to said analog shift register, and for generating said dump signal at a conclusion of said M clock cycles, wherein M is greater than N and wherein a difference between M and N is equal to an increased exposure period for said photoelectric sensing elements of said charge coupled device sensor.
A method for digitizing and storing an image using a charge coupled device sensor having a linear array of photoelectric sensing elements and an N-length shift register for receiving charge values from the linear array, the method comprising the steps of:
- (a) determining a calibrated exposure time required to achieve a desired charge magnitude from the array:
- (b) exposing the array to the image for said calibrated exposure time to produce a digital representation of a line of said image, wherein said calibrated exposure time is implemented by changing an N-cycle clock signal applied to the N-length shift register to an M-cycle clock signal, wherein M is greater than N;
- (c) storing said digital representation of said line in a memory;
- and
- (d) repeating steps (b) and (c) until the image has been digitized and stored.
Dependencies are inferred from the claim text.