Image scanner with calibration mechanism to obtain full dynamic range and compensated linear output
First Claim
1. An image scanner comprising:
- a charge coupled device for receiving an image, said charge coupled device generating a first video output signal and a second video output signal;
a filter assembly including a plurality of color filters, said filer assembly including means for positioning a selected color filter from said plurality of color filters in front of said charge coupled device to generate a first selected color video output signal corresponding to said first video output signal and a second selected color video output signal corresponding of said second video output signal;
means or defining a non-clipping DC bias signal, said defining means includingmeans for assigning a threshold value,means for iteratively incrementing a temporary DC bias signal,means of iteratively applying said temporary DC bias signal to said first selected color video output signal and said second selected color video output signal until said first selected color video output signal is above said threshold and forms a first non-clipped video output signal and said second selected color video output signal is above said threshold and forms a second non-clipped video output signal;
means for iteratively defining a firs gain value and a second gain value;
means for adding said first gain value to said first non-clipped video output signal to provide a first non-saturated, non-clipped video output signal; and
means for adding said second gain value to said second non-clipped video output signal to provide a second non-saturated, non-clipped video output signal.
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Abstract
A calibrated scanner is disclosed. The calibrated scanner includes a sensor board with a Charge Coupled Device (CCD) having two output signals. The sensor board also includes two offset devices, a coarse offset and a fine offset, the coarse offset being connected to the two output signals, the fine offset being connected to one of the output signals. The offsets are adjusted to provide a nonclipping DC bias for the two output signals. The sensor board also includes two gain devices, one gain device being attached to each output signal. The gain devices are adjusted to balance the two output signals. After these adjustments, the saturation level of the CCD is determined. The saturation level information is then used in readjusting the gain and offset devices. After this calibration, a linear correction may be applied to the output signal of the sensor board. The linear correction is accomplished by determining dark and light values of the sensor board. These values, along with ideal dark and light values, are used to solve two linear equations to determine M and b values. The M and b values are then used to provide direct linear correction to the data leaving the sensor board.
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Citations
12 Claims
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1. An image scanner comprising:
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a charge coupled device for receiving an image, said charge coupled device generating a first video output signal and a second video output signal; a filter assembly including a plurality of color filters, said filer assembly including means for positioning a selected color filter from said plurality of color filters in front of said charge coupled device to generate a first selected color video output signal corresponding to said first video output signal and a second selected color video output signal corresponding of said second video output signal; means or defining a non-clipping DC bias signal, said defining means including means for assigning a threshold value, means for iteratively incrementing a temporary DC bias signal, means of iteratively applying said temporary DC bias signal to said first selected color video output signal and said second selected color video output signal until said first selected color video output signal is above said threshold and forms a first non-clipped video output signal and said second selected color video output signal is above said threshold and forms a second non-clipped video output signal; means for iteratively defining a firs gain value and a second gain value; means for adding said first gain value to said first non-clipped video output signal to provide a first non-saturated, non-clipped video output signal; and means for adding said second gain value to said second non-clipped video output signal to provide a second non-saturated, non-clipped video output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An image scanner comprising:
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a charge coupled device for receiving an time, said charge coupled device generating a firs video output signal and a second video output signal; means or combining said firs video output signal and said second video output signal to produce an analog video output signal; an analog-to-digital coercer for converting said analog video output signal to a digital video output signal; means for compensating said digital video output signal to establish a compensated digital video output signal with a linear dynamic range, wherein said compensating means includes means for gathering a light signal value (Xlight) produced by said charge coupled device when said charge coupled device is exposed to an illuminated object for a minimum exposure period; means for interpolating a dark signal value (Xdark) produced by said charge coupled device when said charge coupled device is exposed to a dark image for a minimum exposure period; means for defining an ideal no light value (NL); means for designating an ideal white light value (WL); and means for simultaneously solving a white light function and a no light function for an M variable and a b variable, said white light function and said no light function being respectively defined as
space="preserve" listing-type="equation">WL=M * X.sub.light +b
space="preserve" listing-type="equation">NL=M * X.sub.dark +b. - View Dependent Claims (11, 12)
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Specification