Method and apparatus for providing sensor compensation in a document scanner

Claim 2

The method of claim 1 including the step of practicing said method prior to substantially every document scan.

Claim 3

The method of claim 2 including the steps of providing platen means (12) to support an edge of a document at a home position for scanning, and providing said target means adjacent said home position such that during the initial portion of a document scan, and prior to the scan of said document edge, a determination of said dark response and said light response may be made.

Claim 4

The method of claim 3 including the steps of scanning a portion of said target means while the same is not illuminated in order to determine said dark response, and scanning a portion of said target means while the same is illuminated in order to determine said light response.

Claim 5

The method of claim 4 including the step of scanning an illuminated document after the step of compensating for any variation in the dark response and/or in the light response of said individual sensor cells.

Claim 6

Document scanner apparatus (10) comprising, platen means (12) for supporting a document (11) to be scanned, said platen means having a beginning of scan area, target means (43) generally replicating the background color tone of documents to be scanned, and said target means being positioned adjacent to said beginning of scan area, moving light source means (16) for sequentially illuminating said target means and then said platen means when said light source means is energized, and as said light source means moves from said target means to said beginning of scan area, a light sensitive array (21) comprising a plurality of sensor cells (22) positioned to receive light from a document as the document is illuminated during a scan thereof, the sensor cells of said array each providing an output signal (50) in response to light received from individual document PELS during said scan, signal processing means (29) connected to receive the output signals of said sensor cells and to process the output signals provided thereby, first means (81, 82, 83, 84) for determining the dark response of said sensor cells as said array is subjected to said target means as said target means is not illuminated, and providing a dark response signal as a result thereof, second means (85, 87, 88, 89) for determining the light response of said sensor cells as said array is subjected to said target means as said target means is illuminated, and providing a light response signal as a result thereof, and means (54, 53) connecting said dark response signal and said light response signal as a controlling input to said signal processing means to thereby adjust the sensitivity of said signal processing means in a manner to compensate for any variation in the dark response and/or in the light response of said sensor cells.

Claim 7

The apparatus of claim 6 wherein the output signal of said sensor cells is an analog signal, wherein said first means for determining the dark response of said sensor cells and providing a dark response signal includes means responsive to said dark response signal for calculating first compensation data bits for each of said sensor cells, said first compensation data bits being representative of said dark response signal, wherein said second means for determining the light response of said sensor cells and providing a light response signal includes means responsive to said light response signal for calculating second compensation data bits for each of said sensor cells, said second compensation data bits being representative of said light response signal, data storage means (32), and means supplying said first and second compensation bits to said storage means to thereby store a compensation word for each individual sensor cell, for subsequent use during scan of a document, and wherein said signal processing means comprises convertor means (29) having control input means connected to receive sensor cell compensation words from said data storage means, and having signal input means connected to receive corresponding output signals from said sensor cells.

Claim 8

The apparatus of claim 7 wherein scan movement of said light source means begins with said light source means deenergized, so as to scan said target means while the same is not illuminated in order to determine said dark response, and wherein said target means is thereafter scanned while said light source means is energized in order to determine said light response.

Claim 9

The apparatus of claim 8 wherein said platen means is a substantially rectangular transparent member for supporting a document on the upper surface thereof, and said beginning of scan area comprises a leading edge of said rectangular member, wherein said target means is a linear, generally opaque member positioned adjacent the leading edge of said rectangular member, wherein said moving light source means is a line of light (24) on the surface of said rectangular member for sequentially illuminating PEL rows of a document as said line of light sequentially illuminates said opaque member and then the underside of said platen means from said beginning of scan area to an end of scan area, and wherein said array comprises N individual sensor cells arranged in a line that effectively extends parallel to the leading edge of said rectangular member, so as to receive light reflected from said opaque member and a document, and to thereby provide N PELS for each document row as the document is scanned, said compensation words comprising N compensation words stored for use during scan of a document, and one of said stored compensation words being provided to the control input of said convertor means in synchronism with the output signal of the corresponding sensor cell being provided to the signal input of said convertor means.

Claim 10

The apparatus of claim 9 wherein the control input of said convertor means is operable to control the transfer function of said convertor means in a manner so as to achieve the same output from said convertor for the same magnitude light reflected from a document PEL, independent of any sensitivity nonuniformity that may exist between the individual sensor cells of the array.