When a sensor of a scanning array is identified as "bad" (defective), data
from a neighboring "good" sensor is used to determine pixel data
nominally associated with the bad sensor. During a calibration procedure,
dark-offset and gain values are determined for each sensor to compensate
for individual differences between the sensors of the array. These values
are entered into a table in memory. During scanning of an actual image,
the values are used to determine digital image pixel data from the signal
data provided by the sensors. The calibration procedure also identifies
bad sensors, e.g., sensors that remain on or off, irrespective of the
illumination incident to them. Extreme offset and gain values are entered
into the table locations associated with the respective sensor. When the
extreme values are detected, the signal data for the respective sensor is
discarded, and the pixel data associated with the most recently processed
good sensor is used as the pixel data associated with the bad sensor.
Thus, instead of being all white or all dark, pixels associated with a
bad sensor match neighboring pixels. Generally, this result is far more
acceptable perceptually. Thus, a scanner can have a useful life beyond
the failure of one or more sensors of the scanning array.