# US 7,746,509 B2 · Method for removing defects in scanned images

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- Number: US 7,746,509 B2
- Document ID: US7746509B2
- Status: Granted
- Kind: B2
- Application number: 11/641,731
- Filed: 2006-12-20
- Published: 2008-06-26
- Granted: 2010-06-29
- Earliest claimed: 2006-12-20
- Assignees: Xerox Corporation
- Inventors: Eugene A. Rogalski, Jr.; Roger Triplett
- Web page: https://patentgrep.com/patent/US7746509B2

## CPC

- H04N 1/4095: {Correction of errors due to scanning a two-sided document, i.e. show-through correction}
- H04N 1/407: Control or modification of tonal gradation or of extreme levels, e.g. background level
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

A method for removing show-through defects in scanned document images is provided by adjusting the scanner's image sensor calibration gain in the area of a drive roll gap. The method will also compensate for drive roll contamination. The invention uses a modified calibration scheme in conjunction with a document transmission sensor in the document handler to measure radiant energy transmitted through the document, i.e., transmission. The scanner adjusts the calibration gain factors to simulate a uniform background with knowledge of the gap and the input document's transmission thus a uniform scanner response is determined and presented to the image processing. A device for carrying out the method is also provided.

## Claims

### Claim 1

A method for removing show-through defects in document images scanned against background having a dark region, comprising:
(a) identifying pixels affected by said dark region;
(b) measuring radiant energy transmitted though the document;
(c) calculating a dark region gain factor for each pixel as a function of radiant energy transmitted though the document; and
(d) correcting pixel gain for the affected pixels by said dark region gain factor.

### Claim 2 (depends on 1)

The method of claim 1, wherein step (a) is performed by a setup scan of the roll during scanner initialization.

### Claim 3 (depends on 1)

The method of claim 1, wherein step (a) is performed by identifying pixels that will be substantially darker because of said dark region.

### Claim 4 (depends on 1)

The method of claim 1, wherein step (b) is performed by a sensor measuring the radiant energy transmitted through the document.

### Claim 5 (depends on 1)

The method of claim 1, wherein step (c) is performed as follows:
g=1+c T2, where g is the dark region dark factor, c is a constant depending upon document transmission, and T is the measured radiant energy transmitted through the document.

### Claim 6 (depends on 1)

The method of claim 1, wherein step (c) further comprises identifying pixels at the edge of the dark region and interpolating the dark region gain factor.

### Claim 7 (depends on 1)

The method of claim 1, wherein said step (d) further comprises calculating a desired image sensor response (y) for each pixel (i), as follow:
yi=gi*mi*xi+bi
where g, is the dark region gap factor
m, is a gain factor
b, is an offset factor
x, is an image sensor response.

### Claim 8 (depends on 1)

The method of claim 1, wherein the background is a surface of a document transport roller, and wherein the dark region of the background is a gap in the surface of the roller.

### Claim 9 (depends on 1)

The method of claim 1, wherein background is a surface of a document transport roller, and wherein the dark region of the background is contamination factors.

### Claim 10 (depends on 1)

The method of claim 1, further comprising measuring the input document reflectance (Rp).

### Claim 11 (depends on 10)

The method of claim 10, wherein step (c) is performed as follows:
g=1+c1T2/Rp−c2T2,
where g is the dark region dark factor, c1 and c2 are constants depending upon document transmission, and T is the measured radiant energy transmitted through the document.

### Claim 12

A system for removing show-through defects in document images scanned against a background having a dark region comprising:
(a) a device for identifying pixels affected by said dark region;
(b) a sensor for measuring radiant energy transmitted through the document (T);
(c) a device for calculating a dark region gain factor as a function of the radiant energy transmitted through the document; and
(d) a device for correcting pixel gain for the affected pixels by said dark region gain factor.

### Claim 13 (depends on 12)

The system of claim 12, wherein said sensor is a transmittance sensor.

### Claim 14 (depends on 12)

The system of claim 12, wherein said sensor is a dual function sensor which measures both transmission and reflectance of said document.

### Claim 15 (depends on 12)

The system of claim 12, further comprising a sensor for measuring the reflectance (Rp) of said document.

### Claim 16 (depends on 12)

The system of claim 12, wherein said system is part of a xerographic system.