Automatic D.C. offset control for image scanners

Claim 2

In a scanner having a photosensitive scanning array for producing a series of analog image signals containing a video component which is characteristic of a scanned image and a D.C. offset component which is characteristic of the scanning array; improved means for restoring the image signal to a known D.C. level from which the video component is referenced, said improved means comprising: means for periodically scanning a reference region of known reflectivity to produce a scanned value signal; means for comparing said scanned value signal to a predetermined value to produce an offset value signal; means for periodically producing a signal characteristic of the D.C. offset component of the scanning array; means for producing an offset voltage signal from the D.C. offset component signal and said offset value signal; and means responsive to said offset voltage signal for modifing the image signals.

Claim 3

The improved signal restoring means of claim 1 wherein the photosensitive scanning array is an array of charge coupled devices having dark reference cells; and said means for producing said D.C. offset component signal samples the dark reference cells on the scanning array.

Claim 4

The improved signal restoring means of claim 1 further comprising means for averaging a plurality of signals from different positions on the reference region, wherein said scanned value signal is the average of a plurality of signals from different positions of the reference region.

Claim 5

The improved signal restoring means of claim 1 wherein said scanning array scans a document line by line, and said D.C. offset component of the scanning array is produced each scan line.

Claim 6

The improved signal restoring means of claim 1 wherein said predetermined value is that value that represents the expected value corresponding to the known reflectivity of the reference region.

Claim 7

The improved signal restored means of claim 1 wherein the reference region is substantially black.

Claim 8

The improved signal restoring means of claim 1 further comprising a platen for original documents to be scanned, wherein said reference region is located along one edge of the platen.

Claim 9

The improved signal restoring means of claim 5 wherein said reference region is along a crosstrack edge of the platen.

Claim 10

In a scanner having a photosensitive scanning array for producing a series of analog image signals containing a video component which is characteristic of a scanned image and a D.C. offset component which is characteristic of the scanning array; improved means for restoring the image signal to a known D.C. level from which the video component is referenced, said improved means comprising: means for periodically scanning a substantially black reference region to produce a scanned value signal; means for comparing said scanned value signal to a predetermined value to produce an offset value signal; means for producing a signal characteristic of the D.C. offset component of the scanning array; means for subtracting the D.C. offset component signal from said offset value signal to produce an offset voltage signal; and means for adding the offset voltage signal to the image signals to modify the image signals.

Claim 11

In a scanner having a photosensitive scanning array for producing a series of analog image signals containing a video component which is characteristic of a scanned image and a D.C. offset component which is characteristic of the scanning array; improved means for restoring the image signal to a known D.C. level from which the video component is referenced, said improved means comprising: means for periodically scanning a substantially black reference region to produce a scanned value signal; means for comparing said scanned value signal to a predetermined value to produce an offset value signal; means for producing a signal characteristic of the D.C. offset component of the scanning array; means for subtracting the D.C. offset component signal from said offset value signal to produce an offset voltage signal; and means for adding the offset voltage signal to the image signals to modify the image signals.

Claim 12

The improved signal restoring means of claim 9 wherein the photosensitive scanning array is an array of charge coupled devices having dark reference cells; and said means for producing said D.C. offset component signal samples the dark reference cells on the scanning array.

Claim 13

The improved signal restoring means of claim 9 further comprising means for averaging a plurality of signals from different positions on the reference region wherein said scanned value signal is the average of a plurality of signals from different positions of the reference region.

Claim 14

The improved signal restoring means of claim 9 wherein said scanning array scans a document line by line, and said D.C. offset component of the scanning array is produced each scan line.

Claim 15

The improved signal restoring means of claim 9 wherein said predetermined value is that value that represents the expected value corresponding to the reflectivity of the reference region.

Claim 16

The improved signal restoring means of claim 9 wherein the reference region is substantially black.

Claim 17

The improved signal restoring means of claim 9 further comprising a platen for original documents to be scanned, wherein said reference region is located along one edge of the platen.

Claim 18

The improved signal restoring means of claim 15 wherein said reference region is along a crosstrack edge of the platen.

Claim 19

A process for restoring a series of scanned image signals containing a video component and a D.C. offset component to a known D.C. level from which the video component is referenced, said process comprising the steps of: periodically scanning reference region of known reflectivity to produce a scanned value signal; comparing said scanned value signal to a predetermined value to produce an offset value signal; periodically producing a signal characteristic of the D.C. offset component of the scanning array; producing an offset voltage signal from the D.C. offset component signal and said offset value signal; and for modifing the image signals in response to said offset voltage signal.

Claim 20

A process for restoring a series of scanned image signals containing a video component and a D.C. offset component to a known D.C. level from which the video component is referenced, said process comprising the steps of: periodically scanning reference region of known reflectivity to produce a scanned value signal; comparing said scanned value signal to a predetermined value to produce an offset value signal; periodically producing a signal characteristic of the D.C. offset component of the scanning array; producing an offset voltage signal from the D.C. offset component signal and said offset value signal; and for modifing the image signals in response to said offset voltage signal.

Claim 21

The process of claim 17 further comprising the step of averaging a plurality of signals from different positions on the reference region wherein said scanned value signal is the average of a plurality of signals from different positions of the reference region.

Claim 22

The process of claim 17 wherein said D.C. offset component is produced each scan line.

Claim 23

The process of claim 17 wherein said predetermined value is that value that represents the expected value corresponding to the reflectivity of the reference region.

Claim 24

A process for restoring a series of scanned image signals containing a video component and a D.C. offset component to a known D.C. level from which the video component is referenced, said process comprising the steps of: periodically scanning a reference region of known reflectivity to produce a scanned value signal; comparing said scanned value signal to a predetermined value to produce an offset value signal; producing a signal characteristic of the D.C. offset component of the scanning array; subtracting the D.C. offset component signal from said offset value signal to produce an offset voltage signal; and adding the offset voltage signal to the image signals to modify the image signals.

Claim 25

A process for restoring a series of scanned image signals containing a video component and a D.C. offset component to a known D.C. level from which the video component is referenced, said process comprising the steps of: periodically scanning a reference region of known reflectivity to produce a scanned value signal; comparing said scanned value signal to a predetermined value to produce an offset value signal; producing a signal characteristic of the D.C. offset component of the scanning array; subtracting the D.C. offset component signal from said offset value signal to produce an offset voltage signal; and adding the offset voltage signal to the image signals to modify the image signals.

Claim 26

The process of claim 21 further comprising the step of averaging a plurality of signals from different positions on the reference region wherein said scanned value signal is the averge of a plurality of signals from different positions of the reference region.

Claim 27

The process of claim 21 wherein said D.C. offset component is produced each scan line.

Claim 28

The process of claim 21 wherein said predetermined value is that value that represents the expected value corresponding to the reflectivity of the reference region.