Method and apparatus for eliminating lamp strobing in a digital input scanner
First Claim
1. In a scanning system including an illumination source having a time varying output controlled by a drive circuit and an image sensor driven by a pixel clock for scanning successive scan lines of an image, a method of eliminating strobing in the successive scan lines of the image comprising:
- determining a nominal scan line time and an associated scan line integration time for the image sensor;
determining a nominal illumination source light output period;
adjusting at least one of (i) the nominal scan line integration time and (ii) the nominal illumination source light output period such that the scan line integration time is equivalent to an integer number of illumination source light output periods.
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Accused Products
Abstract
A method of eliminating strobing in successive scan lines of an image includes determining a nominal scan line time and an associated scan line integration time for the image sensor. A nominal illumination light source output period is determined for the illumination source. In order to ensure that the scan line integration time is equivalent to an integer number of illumination source light output periods, at least one of the nominal scan line integration time and the nominal illumination source light output period is adjusted. A clock signal, derived from the pixel clock, drives both the frequency circuitry of the lamp drive circuit and the integration time of the image sensor. The present method provides a reliable means for eliminating lamp strobing independent of the relative phasing of the lamp oscillation phase with respect to the start of each scan line integration.
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Citations
14 Claims
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1. In a scanning system including an illumination source having a time varying output controlled by a drive circuit and an image sensor driven by a pixel clock for scanning successive scan lines of an image, a method of eliminating strobing in the successive scan lines of the image comprising:
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determining a nominal scan line time and an associated scan line integration time for the image sensor; determining a nominal illumination source light output period; adjusting at least one of (i) the nominal scan line integration time and (ii) the nominal illumination source light output period such that the scan line integration time is equivalent to an integer number of illumination source light output periods. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method of scanning a document, said method comprising:
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illuminating the document with a lamp having a time varying light output; scanning successive scan lines of the illuminated document with a line scanner; adjusting at least one of (i) a nominal light output period of the lamp and (ii) a nominal scan line integration time of the scanner such that the scan line integration time of the scanner is equivalent to an integer number of lamp light output periods; and driving the lamp and the scanner in accordance with the adjusted light output period and scan line integration time using a common pixel clock signal. - View Dependent Claims (8, 9, 10)
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11. A document scanner system for scanning a document comprising:
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a lamp having a time varying light output positioned to illuminate the document; a scanner configured to scan successive scan lines of the illuminated document; an adjustment system designed to adjust at least one of (i) a nominal light output period of the lamp or (ii) a nominal scan line integration time of the scanner, wherein the scan line integration time of the scanner is made equivalent to an integer number of lamp light output periods of the lamp; and a pixel clock configured to generate a pixel clock signal implemented to drive the lamp and the scanner in accordance with the adjusted light output period and scan line integration time using the pixel clock signal. - View Dependent Claims (12, 13, 14)
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Specification