Patent Application
20090168116
The present invention relates generally to scanners, and more particularly to a method for calibrating a scanner having a scan bar including sensor elements.
Scanners are used to scan an image to create a scanned image which can be displayed on a computer monitor, which can be used by a computer program, which can be printed, which can be faxed, etc. One conventional scanner includes a scan bar and a white calibration strip. The scan bar has a fast-scan axis and a slow-scan axis aligned perpendicular to the fast-scan axis. The scan bar has an image sensor plane and includes a substantially-linear array of optical sensor elements, such as charge-coupled-device (CCD) elements substantially-aligned along the fast-scan axis. Each sensor element produces a signal proportional to the amount of light reaching the element. The proportion or “gain” of each element is related but not identical. In addition, the light source may not uniformly illuminate the document to be scanned. To get an image with a consistent representation, the elements should be individually calibrated using at least the calibration strip.
Calibration provides a revised gain for each sensor element to compensate for varying amounts of illumination produced by a scanner light source in different regions of the scanned image and to compensate for variations among the CCD elements of the scan bar. However, optical defects such as dust or debris on the calibration strip may cause the calibration of sensor elements which read the optical defects or blemishes to be inaccurate. When printing a scanned document, inaccurate calibration of a sensor element may result in streaking (i.e., a printed vertical column which will be brighter than neighboring columns).
For calibration, the calibration strip is imaged using at least a scanner lens to the image sensor plane of the scan bar. A calibration reading of the sensor elements is taken from the imaging of the calibration strip, and each sensor element is calibrated from at least one of the calibration readings using known calibration algorithms Scanners which allow the scan bar and/or the calibration strip to be moved will take an average of calibration readings of many (e.g., 255) different scan-bar lines of the calibration strip, wherein such averaging may make the optical defect insignificant However, some scanners have an automatic document feeder configuration for which the scan bar and the calibration strip are immobile. For these scanners, a calibration reading of the sensor elements can be taken from only a single scan-bar line of the calibration strip. A known technique for these scanners prevents streaking by using additional software to identify an invalid reading from an optical defect as an improbable sudden change in a calibration reading of the next sensor element and to replace such reading with a derived value based on valid sensor readings of neighboring sensor elements.
What is needed is an improved system and method for calibrating a scanner having a scan bar including sensor elements.
A first method of the present invention is for calibrating a scanner having a scan bar and a calibration strip. The scan bar has a fast-scan axis and a slow-scan axis aligned perpendicular to the fast-scan axis. The scan bar has an image sensor plane and includes a substantially-linear array of sensor elements substantially-aligned along the fast-scan axis. The first method includes imaging the calibration strip to the image sensor plane of the scan bar wherein the imaging is out of focus substantially-along the slow-scan axis. The first method also includes obtaining a calibration reading of the sensor elements from the imaging of the calibration strip.
A second method of the present invention is for calibrating a scanner having a scan bar and a calibration strip. The scan bar has a fast-scan axis and a slow-scan axis aligned perpendicular to the fast-scan axis. The scan bar has an image sensor plane and includes a substantially linear array of sensor elements substantially aligned along the fast-scan axis. The second method includes imaging the calibration strip to the image sensor plane of the scan bar wherein the imaging is optically widened substantially-along the slow-scan axis. The second method also includes obtaining a calibration reading of the sensor elements from the imaging of the calibration strip.
A scanner of the present invention includes a scan bar, a calibration strip, and a scanner lens. The scan bar has a fast-scan axis and a slow-scan axis aligned perpendicular to the fast-scan axis. The scan bar has an image sensor plane. The scanner also includes a cylindrical lens having an imaging-widening axis, wherein the cylindrical lens is disposed between at least one of the calibration strip and the scanner lens and the scanner lens and the image sensor plane, with the imaging-widening axis aligned substantially-parallel to the slow-scan axis.
Several benefits and advantages are derived from the first and/or second methods and from the scanner of the present invention. In one example, in a scanner having an automatic document feeder configuration with an immobile scan bar and an immobile calibration strip, the conventional need is avoided for additional software and computing time to identify an invalid reading from an optical defect as an improbable sudden change in a calibration reading of the next sensor element and to replace such reading with a derived value based on valid sensor readings of neighboring sensor elements.
A first method of the present invention, with reference to
It is noted that sensor element is to be understood as an optical sensor element such as, but not limited to a charge-coupled-device (CCD) element. It is also noted that the substantially linear array of sensor elements need not include every scan bar sensor element which lies substantially along the fast-scan axis of the scan bar. In one example, outlying sensor elements and/or defective sensor elements are not included, as can be appreciated by those skilled in the art. It is further noted that an image which is out of focus is blurred substantially along the slow-scan axis.
In one example of the first method, the imaging is of a white area of the calibration strip 14. In
In one implementation of the first method, the imaging is in focus substantially-along the fast-scan axis 16.
In one application of the first method, the scanner 10 has an automatic document feeder configuration (e.g., as represented in
In one enablement of the first method, the scan bar 12 and the calibration strip 14 are immobile when the scanner 40 is in the automatic document feeder configuration (such as the backside configuration of an automatic document feeder that is capable of a duplex scan). In one employment of the first method, the imaging and the calibration reading are performed when the scanner 40 is in the automatic document feeder configuration. In one extension of the first method, sensor elements 24 may be calibrated using at least one of calibration reading of the sensor elements 24. It is noted that while a calibration strip 14 is typically white in color, that some calibration techniques use a non-white light color instead of a white color calibration strip. In some embodiments, an additional calibration reading of the white (or light-colored) calibration strip with the lights off or an additional calibration reading of an additional black area of the otherwise white (or light-colored) calibration strip may be used in some calibration techniques, as is known to those skilled in the art.
A second method of the present invention is for calibrating a scanner 10 having a scan bar 12 and a calibration strip 14. The scan bar 12 has a fast-scan axis 16 and a slow-scan axis 18 aligned perpendicular to the fast-scan axis 16. The scan bar 12 has an image sensor plane 20 and includes a substantially linear array 22 of sensor elements 24 substantially aligned along the fast-scan axis 16. The second method includes, as summarized in block 36 of
In one implementation of the second method, the imaging is not optically widened substantially along the fast-scan axis 16.
It is noted that the applications, enablements, etc. of the first method are equally applicable to the second method.
A third method of the present invention is for calibrating a scanner 10 having a scan bar 12, a calibration strip 14, and a scanner lens 40. The scan bar 12 has a fast-scan axis 16 and a slow-scan axis 18 aligned perpendicular to the fast-scan axis 16. The scan bar 12 has an image sensor plane 20 and includes a substantially linear array 22 of sensor elements 24 substantially-aligned along the fast-scan axis 16. The third method includes, as summarized in block 42 of
It is noted that the implementations of the second method and the applications, enablements, etc. of the first method are equally applicable to the third method.
In one employment of the second and/or the third method, the imaging is optically widened at least two times. In one variation, the imaging is optically widened at least ten times. In one utilization of the third method, the cylindrical lens 44 is disposed between the calibration strip 14 and the scanner lens 32.
In one arrangement of the third method, the cylindrical lens 44 is disposed immediately in front of (i.e., to the left of in
In one illustration of the third method, an optical path 52 extends from the calibration strip 14, through the scanner lens 40, and to the image sensor plane 20, and the disposing of the cylindrical lens 44 is performed by swinging the cylindrical lens 44 into a position in the optical path 52 when a calibration reading of the sensor elements 24 is needed. In one variation, the third method also includes swinging the cylindrical lens 44 out of the optical path 38 when the calibration reading of the sensor elements 24 is completed, and a regular scan is to be performed. In one modification, mirrors (not shown) may also be used to create the optical path 52. In one modification, not shown, a mechanical swing arm may be employed to swing the cylindrical lens 44, wherein the mechanical swing arm is electronically controlled by a scanner control unit via a solenoid.
Several benefits and advantages are derived from the first, second, and/or third method of the present invention. In one example, in a scanner having an automatic document feeder configuration with an immobile scan bar and an immobile calibration strip, the conventional needs for additional software and computing time to identify an invalid reading from an optical defect as an improbable sudden change in a calibration reading of the next sensor element and to replace such reading with a derived value based on valid sensor readings of neighboring sensor elements may be avoided.
The foregoing description of several exemplary methods of the present invention has been presented for purposes of illustration. It is not intended to be exhaustive or to limit the invention to the precise actions and/or forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. It is intended that the scope of the present invention be defined by the claims appended hereto.
