# US 4,393,410 A · Multiple camera automatic digitizer and method

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- Number: US 4,393,410 A
- Document ID: US4393410A
- Status: Granted
- Kind: A
- Application number: 06/321,233
- Filed: 1981-11-13
- Granted: 1983-07-12
- Earliest claimed: 1981-11-13
- Assignees: Wespac
- Inventors: Warren J. Ridge; Dennis C. Roberts
- Web page: https://patentgrep.com/patent/US4393410A

## CPC

- H04N 1/19584: {Combination of arrays}
- H04N 1/195: the array comprising a two-dimensional [2D] array
- H04N 1/19594: {using a television camera or a still video camera}
- H04N 2201/0077: Types of the still picture apparatus
- H04N 2201/0414: Scanning an image in a series of overlapping zones
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

A multiple camera automatic digitizer includes a plurality of spaced video cameras mounted within a housing under a transparent digitizing surface. Multiplexing circuitry multiplexes video signals from a selected video camera into a video amplifier, the output of which is converted to a digital number representing the darkness of the point of the document most recently scanned by a presently selected one of the video cameras. In accordance with the invention, the automatic digitizer includes a microprocessor, system controls that allows selection of various ones of the video cameras to achieve digitizing of corresponding areas of a large document, and computes skew correction factors for each camera as the basis of digitizing of a plurality of permanent alignment marks on a bottom surface of a cover for the digitizing surface. The skew correction factors are used to skew correct the camera data produced by the corresponding camera. The skew corrected lateral offset of each camera is computed by the microprocessor on the basis of the digitized coordinates of the alignment points and is used to automatically compute skew corrected, offset corrected document coordinates for all of the video cameras.

## Claims

### Claim 1

A method of digitizing an item, said method comprising the steps of:
(a) operating a first video camera to effect producing camera coordinates of first and second alignment points in the field of view of said first video camera and to effect producing a first plurality of camera coordinates of a third alignment point, said third alignment point also being in the field of view of a second video camera;
(b) operating said second video camera to effect producing a second group of camera coordinates of said third alignment point, and to effect producing camera coordinates of a fourth alignment point in the field of view of said second video camera;
(c) computing skew corrected coordinates of said first alignment point from said camera coordinates of said first and second alignment points, said skew corrected coordinates of said first alignment point being referenced to a boundary of a skew corrected camera plane of said first video camera;
(d) computing a first plurality of skew corrected coordinates of said third alignment point from said camera coordinates of said third alignment point and said skew corrected coordinates of said first alignment point, said skew corrected coordinates of said third alignment point being referenced to said first alignment point;
(e) computing skew corrected, offset corrected coordinates of said third alignment point from both said skew corrected coordinates of said third alignment point and an offset number representing the distance of a boundary of a document plane to the boundary of said skew corrected camera plane of said first video camera, said skew corrected, offset corrected coordinates of said third alignment point being referenced to the boundary of said document plane;
(f) computing a second plurality of skew corrected coordinates of said third alignment point from said second group of camera coordinates of said third alignment point and said camera coordinates of said fourth alignment point, said second plurality of skew corrected coordinates of said third alignment point being referenced to a boundary of a skew coorected plane of said second video camera;
(g) operating said second video camera to effect producing of camera coordinates of a general point in the field of view of said second video camera, said general point being a point of the item to be digitized;
(h) computing skew corrected coordinates of said general point from said camera coordinates of said general point and said second plurality of skew corrected coordinates of said third alignment point, said skew corrected coordinates of said general point being referenced to said third alignment point;
(i) computing skew corrected, offset corrected coordinates of said general point from said skew corrected coordinates of said general point and said skew corrected, offset corrected coordinates of said third alignment point, said skew corrected, offset corrected coordinates of said general point being referenced to said boundary of said document plane;
(j) outputting said skew corrected, offset corrected coordinates of said general point as a digitized value representing the location of said general point on said document.

### Claim 2 (depends on 1)

The method of claim 1 wherein said first, second, third and fourth alignment points are disposed on a support surface that supports the item to be digitized and wherein said method includes placing the item to be digitized against the support surface between the support surface and said first and second video cameras after step (b) and before step (g).

### Claim 3 (depends on 2)

The method of claim 2 wherein the item to be digitized is a document, the document covering said first, second, third and fourth alignment marks when the document is placed on the support surface.

### Claim 4 (depends on 3)

The method of claim 3 including the method of storing said camera coordinates of said first, second, third and fourth alignment points.

### Claim 5 (depends on 4)

The method of claim 4 wherein steps (c), (d), (e), (f), (h) and (i) are effectuated by operating a microprocessor system.

### Claim 6 (depends on 5)

The method of claim 5 wherein steps (a), (b) and (g) are also effectuated by operating the microprocessor system.

### Claim 7 (depends on 1)

The method of claim 1 wherein step (c) includes computing said skew corrected coordinates of said first alignment point in accordance with the formulas
x'.sub.A =kx.sub.A and y'.sub.A =ky.sub.A
wherein x.sub.A and y.sub.A are the camera coordinates of said first video camera for said first alignment point and k is the ratio of the distance between said first and second alignment points and the difference between a y camera coordinate of said second alignment point and a y camera coordinate of said first alignment point.

### Claim 8 (depends on 7)

The method of claim 7 wherein step (d) includes computing said first plurality of skew corrected coordinates of said third alignment point in accordance with the formulas
x.sub.P '"=(x.sub.P -x.sub.A) cos .psi.+(y.sub.P -y.sub.A) sine .psi.
and
y.sub.P '"=-(x.sub.P -x.sub.A) sine .psi.+(y.sub.P -y.sub.A) cos .psi.
where x.sub.P and y.sub.P are the camera coordinates of said first video camera for said third alignment point, and .psi. is the angle by which said first video camera is skewed.

### Claim 9 (depends on 8)

The method of claim 8 wherein step (e) includes computing said skew corrected, offset corrected coordinates of said third alignment point in accordance with the formulas
x.sub.P ""=x.sub.P "'+x.sub.PD '
and
y.sub.P ""=y.sub.P "'+y.sub.PD '
where
x'.sub.PD is an offset number representing the distance between an x boundary of said document plane and said first alignment point and y'.sub.PD is an offset number representing the distance between a y boundary of said document plane and said first alignment point.

### Claim 10 (depends on 9)

The method of claim 9 wherein step (f) includes computing said second plurality of skew corrected coordinates of said third alignment point in accordance with the formulas
x.sub.P '=k.sub.2 x.sub.P' and y.sub.P '=k.sub.2 y.sub.P'
where
x.sub.p' and y.sub.P' are camera coordinates of said second video camera for said third alignment point and
k.sub.2 is the ratio between the distance between said third alignment point and a fourth alignment point and the difference between a y camera coordinate of said second video camera for said fourth alignment point and a y camera coordinate of said second video camera for said third alignment point.

### Claim 11 (depends on 10)

The method of claim 10 wherein step (h) includes computing said skew corrected coordinates of said general point in accordance with the formulas
x.sub.G '"=(x.sub.G -x.sub.P') cos .psi..sub.2 +(y.sub.G -y.sub.P') sine .psi..sub.2 and
y.sub.G '"=-(x.sub.G -x.sub.P) sine .psi..sub.2 +(y.sub.G -y.sub.P') cos .psi..sub.2
where x.sub.G and y.sub.G are camera coordinates of said second video camera for said general point, and .psi..sub.2 is the skew angle of said second video camera.

### Claim 12 (depends on 11)

The method of claim 11 wherein step (i) includes computing said skew corrected, offset corrected coordinates of said general point in accordance with the formulas
x.sub.G ""=x.sub.G "'+x.sub.GD '
y.sub.G ""=y.sub.G "'+y.sub.GD '
where x.sub.GD ' is an offset number representing the distance between said x boundary of said document plane and said third alignment point and y.sub.GD ' is an offset number representing the distance between said y boundary of said document plane and said third alignment point.

### Claim 13 (depends on 12)

The method of claim 12 including repeating steps (g) through (i) for all other general points on said document in the field of view of said second video camera.

### Claim 14 (depends on 1)

The method of claim 1 wherein said first, second, third and fourth alignment points are on the item to be digitized.

### Claim 15 (depends on 14)

The method of claim 14 including the steps of producing codes to represent different degrees of darkness of points scanned by said first and second video cameras, said first, second, third and fourth alignment points having a degree of darkness that is recognized for the purposes of steps (a) (b), (c), (d), (e) and (g) but is not recognized for the purposes of steps (h) and (i) to cause digitizing of all general points on said document and avoid digitizing alignment marks.

### Claim 16 (depends on 1)

The method of claim 1 wherein said first alignment point is located in the upper left corner portion of the field of view of said first video camera and said third alignment point is located in the upper left corner portion of said second video camera.

### Claim 17

A system for digitizing an item, said digitizing comprising in combination:
(a) first and second video cameras;
(b) first means for operating a first video camera to effect producing camera coordinates of first and second alignment points in the field of view of said first video camera and to effect producing a first plurality of camera coordinates of a third alignment point, said third alignment point also being in the field of view of a second video camera;
(c) second means for operating said second video camera to effect producing a second group of camera coordinates of said third alignment point, and to effect producing camera coordinates of a fourth alignment point in the field of view of said second video camera;
(d) third means for computing skew corrected coordinates of said first alignment point from said camera coordinates of said first and second alignment points, said skew corrected coordinates of said first alignment point being referenced to a boundary of a skew corrected camera plane of said first video camera;
(e) fourth means for computing a first plurality of skew corrected coodinates of said third alignment point from said camera coordinates of said third alignment point and said skew corrected coordinates of said first alignment point, said skew corrected coordinates of said third alignment point being referenced to said first alignment point;
(f) fifth means for computing skew corrected, offset corrected coordinates of said third alignment point from both said skew corrected coordinates of said third alignment point and an offset number representing the distance of a boundary of a document plane to the boundary of said skew corrected camera plane of said first video camera, said skew corrected, offset corrected coordinates of said third alignment point being referenced to the boundary of said document plane;
(g) sixth means for computing a second plurality of skew corrected coordinates of said third alignment point from said second group of camera coordinates of said third alignment point and said camera coordinates of said fourth alignment point, said second plurality of skew corrected coordinates of said third alignment point being referenced to a boundary of a skew corrected plane of said second video camera;
(h) seventh means for operating said second video camera to effect producing of camera coordinates of a general point in the field of view of said second video camera;
(i) eighth means for computing skew coordinates of said general point from said camera coordinates of said general point and said second plurality of skew corrected coordinates of said third alignment point, said skew corrected coordinates of said general point being referenced to said third alignment point;
(j) ninth means for computing skew corrected, offset corrected coordinates of said general point from said skew corrected coordinates of said general point and said skew corrected, offset corrected coordinates of said third alignment point, said skew corrected, offset corrected coordinates of said general point being referenced to said boundary of said document plane; and
(k) means for outputting said skew corrected, offset corrected coordinates of said general point as a digitized value representing the location of said general point on said item to be digitized.

### Claim 18 (depends on 17)

The digitizing system of claim 17 wherein said first, second, third and fourth alignment points are disposed on a support surface that supports the item to be digitized.

### Claim 19 (depends on 18)

The digitizing system of claim 18 wherein the item to be digitized is a document, the document covering said first, second, third and fourth alignment marks when said document is placed on the support surface.

### Claim 20 (depends on 19)

The digitizing system of claim 19 including means for storing said camera coordinates of said first, second, third and fourth alignment points.

### Claim 21 (depends on 20)

The digitizing system of claim 20 wherein said third, fourth, fifth, sixth, eighth and ninth means are implemented by means of a microprocessor system.

### Claim 22 (depends on 21)

The digitizing system of claim 21 wherein said first, second, and seventh means are implemented by means of said microprocessor system.

### Claim 23 (depends on 17)

The digitizing system of claim 17 wherein said third means computes said skew corrected coordinates of said first alignment point in accordance with the formulas
x'.sub.A +kx.sub.A and y'.sub.A =ky.sub.A
wherein x.sub.A and y.sub.A are the camera coordinates of said first alignment point and k is the ratio of the distance between said first and second alignment points and the difference between a y camera coordinate of said second alignment point and a y camera coordinate of said first alignment point.

### Claim 24 (depends on 23)

The digitizing system of claim 23 wherein said fourth means computes said first plurality of skew corrected coordinates of said third alignment point in accordance with the formulas
x.sub.P '"=(x.sub.P -x.sub.A) cos .psi.+(y.sub.P -y.sub.A) sine .psi.
y.sub.P '"=-(x.sub.P -x.sub.A) sine .psi.+(y.sub.P -y.sub.A) cos .psi.
where x.sub.P and y.sub.P are the camera coordinates of said third alignment point, and .psi. is the angle by which said first video camera is skewed.

### Claim 25 (depends on 24)

The digitizing system of claim 24 wherein said fifth means computes said skew corrected, offset corrected coordinates of said third alignment point in accordance with the formulas
x.sub.P ""=x.sub.P "'+x.sub.PD '
and
y.sub.P ""=y.sub.P "'+y.sub.PD '
where x'.sub.PD is an offset number representing the distance between a x boundary of said document plane and said first alignment point and y'.sub.PD is an offset number representing the distance between a y boundary of said document plane and said first alignment point.

### Claim 26 (depends on 25)

The digitizing method of claim 25 wherein said sixth means computes said second plurality of skew corrected coordinates of said third alignment point in accordance with the formulas
x.sub.P '=k.sub.2 x.sub.P' and y.sub.P '=k.sub.2 y.sub.P'
where
x.sub.P', and y.sub.P' are camera coordinates of said video camera for said third alignment point and
k.sub.2 is the ratio between the distance between said third alignment point and a fourth alignment point and the difference between a y camera coordinate of said second video camera for said fourth alignment point and a y camera coordinate of said second video camera for said third alignment point.

### Claim 27 (depends on 26)

The digitizing system of claim 26 wherein said eighth means computes said skew corrected coordinates of said general point in accordance with the formulas
x.sub.G '"=(x.sub.G -x.sub.P') cos .psi..sub.2 +(y.sub.G -x.sub.P') sine .psi..sub.2 and
y.sub.G '"=-(x.sub.G -x.sub.P') sine .psi..sub.2 +(y.sub.G -y.sub.P') cos .psi..sub.2
where x.sub.G and y.sub.G are camera coordinates of said second video camera for said general point, and .psi..sub.2 is the skew angle of said second video camera.

### Claim 28 (depends on 27)

The digitizing system of claim 27 wherein said ninth means computes said skew corrected, offset corrected coordinates of said general point in accordance with the formulas
x.sub.G ""=x.sub.G "'+x.sub.GD '
y.sub.G ""=y.sub.G "'+y.sub.GD '
where x.sub.GD ' is an offset number representing the distance between said x boundary of said document plane and an x plane of said skew corrected plane of said second video camera and y.sub.GD ' is an offset number representing the distance between said y boundary of said document plane and a y plane of said skew corrected plane of said second video camera.

### Claim 29 (depends on 17)

The digitizing system of claim 17 wherein said first, second, third and fourth alignment points are on the item to be digitized.

### Claim 30 (depends on 29)

The digitizing system of claim 29 including means for producing codes to represent different degrees of darkness of points scanned by said first and second video cameras, said first, second, third and fourth alignment points having a degree of darkness that is recognized by said first, second, third, fourth, sixth and seven means but is not recognized by said eighth and ninth means to cause said digitizing system to digitize all general points on said documents but to not digitize alignment points.

### Claim 31 (depends on 17)

The digitizing system of claim 17 wherein said first alignment point is located in the upper left corner portion of the field of view of said first video camera and said third alignment point is located in the upper left corner portion of said second video camera.

### Claim 32 (depends on 17)

The digitizing system of claim 17 including means for causing a reference surface to have a predetermined level of brightness, means for causing one of said video cameras to scan a first predetermined point of said reference surface, analog-to-digital conversion means for producing a reference code representing the brightness of said first predetermined point, means for storing said reference code, means for causing the other of said video cameras to scan a second predetermined point of said reference surface, means for causing said analog-to-digital conversion means to produce a brightness code representing the brightness of said second predetermined point, means for comparing said brightness code and said reference code, to produce adjustment information representing an amount of adjustment required to adjust said analog-to-digital conversion means to cause said analog-to-digital conversion means to produce a new value of said brightness code that is more nearly equal to said reference code, means for storing said adjustment information, and means for adjusting said analog-to-digital conversion means in response to said adjustment information.