# US 9,001,399 B2 · Automatically compensating for color differences from side 1 to side 2 of a document scanning device

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- Number: US 9,001,399 B2
- Document ID: US9001399B2
- Status: Granted
- Kind: B2
- Application number: 13/799,526
- Filed: 2013-03-13
- Published: 2014-09-18
- Granted: 2015-04-07
- Earliest claimed: 2013-03-13
- Assignees: Xerox Corporation
- Applicants: Xerox Corporation
- Inventors: Mihai Cuciurean-Zapan; Michael John Wilsher
- Web page: https://patentgrep.com/patent/US9001399B2

## CPC

- H04N 1/60: Colour correction or control {(H04N1/54 takes precedence)}
- H04N 1/00013: {Reading apparatus}
- H04N 1/00023: {Colour systems}
- H04N 1/00031: {Testing, i.e. determining the result of a trial (H04N1/00029 takes precedence; using test signals for transmission mode changing H04N2201/33371)}
- H04N 1/00045: {using a reference pattern designed for the purpose, e.g. a test chart}
- H04N 1/00068: {Calculating or estimating}
- H04N 1/00087: {Setting or calibrating (picture signal circuits H04N1/40)}
- H04N 1/2032: {of two pictures corresponding to two sides of a single medium (refeeding a sheet for double-sided scanning H04N1/00572)}
- H04N 1/6033: {using test pattern analysis (H04N1/6055 takes precedence)}
- H04N 2201/0081: Image reader (H04N2201/0091 - H04N2201/0094 take precedence)
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

What is disclosed is a system and method for compensating for side 1 to side 2 differences in a document scanning device. In one embodiment, the present method involves selecting at least one solid area patch printed in at least one reference color of a color space. The scan head of side 1 scans the patch to capture a first set of color values. The scan head of side 2 scans the same patch to capture a second set of color values. A regression method generates a coefficient matrix which minimizes a ΔE color difference metric between the first and second sets of color values. An image processing module associated with the side 2 scanner is programmed with the coefficient matrix and uses the coefficient matrix to adjust a color response of the side 2 scanner to compensate for side 1 to side 2 differences.

## Claims

### Claim 1

A method for compensating for side 1 to side 2 scan head differences in a scanning device capable of scanning a document in a duplex mode, the method comprising:
scanning, using a side 1 scanner, at least one solid area patch printed in at least one reference color to capture a first set of color values;
scanning, using a side 2 scanner, said same solid area patch to capture a second set of color values;
generating, using a regression method, a matrix of coefficients, wherein multiplying each color value within said second set of color values by said matrix of coefficients minimizes a ΔE color difference metric between said first and second sets of color values;
scanning a first image using said side 1 scanner;
generating a first set of output color values corresponding to said first image, said first set of output color values comprising pixels within said first image multiplied by an identity matrix;
scanning a second image using said side 2 scanner; and
generating a second set of output color values corresponding to said second image, said second set of output color values comprising pixels within said second image multiplied by said matrix of coefficients.

### Claim 2 (depends on 1)

The method of claim 1, further comprising weighting any of said coefficients such that a color response of certain colors is enhanced.

### Claim 3 (depends on 1)

The method of claim 1, wherein said ΔE color difference metric comprises any of: a Euclidean distance between two colors, and a CIEDE2000 metric.

### Claim 4 (depends on 3)

The method of claim 3, wherein said Euclidean distance between two colors in a color space with coordinates expressed in terms of {L*, a*, b*}, comprises:
ΔE*ab=√{square root over ((ΔL*)2+(Δa*)2+(Δb*)2)}{square root over ((ΔL*)2+(Δa*)2+(Δb*)2)}{square root over ((ΔL*)2+(Δa*)2+(Δb*)2)}.

### Claim 5 (depends on 1)

The method of claim 1, wherein said regression method comprises any of: a linear regression method, and a least squares method.

### Claim 6 (depends on 1)

The method of claim 1, wherein one processor implements said generating a first set of output color values and said generating a first set of output color values.

### Claim 7 (depends on 1)

The method of claim 1, wherein said step of generating said matrix of coefficients are performed in response to a user initiated event on a user interface of a document reproduction system.

### Claim 8

A system for compensating for side 1 to side 2 scan head differences in a scanning device capable of scanning a document in a duplex mode, the system comprising:
a storage device storing a first set of color values acquired by scanning at least one solid area patch using image sensors of a side 1 scan head of said scanning device, said storage device further storing a second set of color values acquired by scanning said same solid area patch using image sensors of a side 2 scan head of said scanning device, said solid area patch having been printed in at least one reference color;
a processor in communication with said storage device, said processor executing machine readable program instructions for performing:
retrieving, from said storage device, said first and second sets of color values; and
executing a regression method that generates a matrix of coefficients, wherein multiplying each color value within said second set of color values by said matrix of coefficients minimizes a ΔE color difference metric between said first and second sets of color values;
a side 1 image processing module associated with said side 1 scan head, said image processing module configured to generate a first set of output color values corresponding to a first image, said first set of output color values comprising pixels within said first image multiplied by an identity matrix; and
a side 2 image processing module associated with said side 2 scan head, said side 2 image processing module configured to generate a second set of output color values corresponding to a second image, said second set of output color values comprising pixels within said second image multiplied by said matrix of coefficients.

### Claim 9 (depends on 8)

The system of claim 8, further comprising a second processor configured to implement said side 1 image processing module and said side 2 image processing module.

### Claim 10 (depends on 8)

The system of claim 8, wherein said regression method comprises any of: a linear regression method, and a least squares method.

### Claim 11 (depends on 8)

The system of claim 8, further wherein at least one of said side 1 image processing module and said side 2 image processing module is further configured to weight coefficients such that a color response of certain colors is enhanced.

### Claim 12 (depends on 8)

The system of claim 8, wherein said ΔE color difference metric comprises any of: a Euclidean distance between two colors, and a CIEDE2000 metric.

### Claim 13 (depends on 12)

The system of claim 12, wherein said Euclidean distance between two colors in a color space with coordinates expressed in terms of {L*, a*, b*}, comprises:
ΔE*ab=√{square root over ((ΔL*)2+(Δa*)2+(Δb*)2)}{square root over ((ΔL*)2+(Δa*)2+(Δb*)2)}{square root over ((ΔL*)2+(Δa*)2+(Δb*)2)}.