Image color balance for scanners using an illumination spectral sensor

• US 7,251,065 B2
• Filed: 01/31/2002
• Issued: 07/31/2007
• Est. Priority Date: 01/31/2002
• Status: Active Grant

• Current Assignee: Kodak Alaris Inc (KPP (no. 2) Trustees Ltd.)
• Original Assignee: Eastman Kodak Company
• Inventors: Simmons, George O., Barton, Mark A.
• Primary Examiner(s): Lee; Cheukfan
• Application Number:
  US10/062,049
• Publication Number:
  US 20030147110A1
• Time in Patent Office: 2,007 Days
• Field of Search: 358/406, 358/504, 358/523, 358/509, 358/475, 358/487, 358/516, 358/505, 358/506, 358/445, 358/446, 250/214.C, 250/214.DC, 250/216
• US Class Current: 358/509
• CPC Class Codes: H04N 1/603 controlled by characteristics of the picture signal generator or the picture reproducer
• CPC Class Codes: H04N 1/6086 by scene illuminant, i.e. conditions at the time of picture capture, e.g. flash, optical filter used, evening, cloud, daylight, artificial lighting, white point measurement, colour temperature

Abstract

An image scanning system for producing an electronic version of a hardcopy element which is compensated for spectral content of an illumination source in the image scanning system, the image scanning system includes a sensor for receiving light containing the hardcopy element for forming and storing an electronic version of the hardcopy element; a spectral sensor for receiving light from the illumination source and storing an electronic version of spectral contents of the illumination source; and a conversion system for receiving the electronic versions of the illumination source and the hardcopy element and creating a compensation table that compensates subsequent hardcopy elements passed through the conversion system.

Claims

1. An image scanning system for producing an electronic version of a hardcopy which is compensated for variations in the spectral content of an illumination source in the image scanning system, the image scanning system comprising:

(a) a first sensor for receiving light reflected or transmitted from the hardcopy, and for forming and storing an electronic image version of the hardcopy;

(b) a second sensor for receiving light from the illumination source and for forming and storing an electronic version of the spectral contents of the illumination source; and

(c) a conversion system for receiving the electronic version of the illumination source, and computing the contents of a LUT (Look Up Table) such that subsequent electronic images passed through the LUT are properly compensated for the spectral content of the illumination.

2. The scanning system as in claim 1, wherein the conversion system is created from the equations:

$\begin{array}{c}{\mathrm{SensorOutput}}_c=<br><br>{\int <br><br>}_{\mathrm{\lambda <br><br>}<br><br><br><br>\min }^{\mathrm{\lambda <br><br>}<br><br><br><br>\max }<br><br>\mathrm{Illumination}<br><br><br><br>\left(\mathrm{\lambda <br><br>}\right)·<br><br>\mathrm{ReflectiveImage}<br><br>\left(\mathrm{\lambda <br><br>}\right)·<br><br>\\ <br><br>\mathrm{OpticalTransfer}<br><br><br><br>\left(\mathrm{\lambda <br><br>}\right)·<br><br>{\mathrm{SensorTransfer}}_c<br><br>\left(\mathrm{\lambda <br><br>}\right)<br><br>d<br><br><br><br>\mathrm{\lambda <br><br>}\\ {\mathrm{OptimalOutput}}_c=<br><br>{\int <br><br>}_{\mathrm{\lambda <br><br>}<br><br><br><br>\min }^{\mathrm{\lambda <br><br>}<br><br><br><br>\max }<br><br>\mathrm{Image}<br><br><br><br>\left(\mathrm{\lambda <br><br>}\right)<br><br>·<br><br>\mathrm{Color}<br><br><br><br>{\mathrm{SpaceTransfer}}_c<br><br><br><br>\left(\mathrm{\lambda <br><br>}\right)<br><br>d<br><br><br><br>\mathrm{\lambda <br><br>}\end{array}$

where,

SensorOutput_c(λ

) is an expected output of one channel of the image sensor;

Illumination(λ

) is a function that describes the spectral content of the light source as detected by the illumination sensor, as a function of wavelength;

ReflectiveImage(λ

) is a function that describes the color content of the image at the point of evaluation, compounded with the transmission or reflective process of the scanning path, as a function of wavelength;

OpticalTransfer(λ

) is a function that describes the transmission of the optical path, as a function of wavelength;

SensorTransfer_c(λ

) is a function that describes the sensitivity of the first sensor, as a function of wavelength;

OptimalOutput_c(λ

) is an ideal output of the scanning system at a given color of the reflective image;

Image(λ

) is a function that describes the color content of the image at the point of evaluation, as a function of wavelength;

ColorSpaceTransfer_c(λ

) is a function that describes the weighting of a given channel of a color space, as a function of wavelength; and

Subscript “

c”

denotes the sensor channel being evaluated.

3. The scanning system in claim 1, wherein the conversion system includes as a table or LUT for implementation.

4. The scanning system as in claim 3, wherein the conversion system includes a mathematical scheme that interpolate entries in the LUT or table.

5. An image scanning system for producing an electronic version of a hardcopy which is compensated for variations in the spectral content of an illumination source in the image scanning system, the image scanning system comprising:

(a) a color sensor for receiving light reflected or transmitted from the hardcopy, and for forming and storing an electronic version of the hardcopy;

(b) a spectral sensor for receiving light from the illumination source and for forming and storing an electronic version of the spectral contents of the illumination source;

(c) a conversion operator that compensates the electronic version of the hardcopy, wherein the conversion operator includes a LUT or table for implementation; and

(d) a conversion system for receiving the electronic version of the illumination source, wherein the conversion system compensates the electronic version of the hardcopy.

6. The scanning system as in claim 5, wherein the conversion operator is created from the equations:

$\begin{array}{c}{\mathrm{SensorOutput}}_c=<br><br>{\int <br><br>}_{\mathrm{\lambda <br><br>}<br><br><br><br>\min }^{\mathrm{\lambda <br><br>}<br><br><br><br>\max }<br><br>\mathrm{Illumination}<br><br><br><br>\left(\mathrm{\lambda <br><br>}\right)·<br><br>\mathrm{ReflectiveImage}<br><br>\left(\mathrm{\lambda <br><br>}\right)·<br><br>\\ <br><br>\mathrm{OpticalTransfer}<br><br><br><br>\left(\mathrm{\lambda <br><br>}\right)·<br><br>{\mathrm{SensorTransfer}}_c<br><br>\left(\mathrm{\lambda <br><br>}\right)<br><br>d<br><br><br><br>\mathrm{\lambda <br><br>}\\ {\mathrm{OptimalOutput}}_c=<br><br>{\int <br><br>}_{\mathrm{\lambda <br><br>}<br><br><br><br>\min }^{\mathrm{\lambda <br><br>}<br><br><br><br>\max }<br><br>\mathrm{Image}<br><br><br><br>\left(\mathrm{\lambda <br><br>}\right)<br><br>·<br><br>\mathrm{Color}<br><br><br><br>{\mathrm{SpaceTransfer}}_c<br><br><br><br>\left(\mathrm{\lambda <br><br>}\right)<br><br>d<br><br><br><br>\mathrm{\lambda <br><br>}\end{array}$

where,

SensorOutput_c(λ

) is an expected output of one channel of the image sensor;

Illumination(λ

) is a function that describes the spectral content of the light source as detected by the illumination sensor, as a function of wavelength;

ReflectiveImage(λ

) is a function that describes the color content of the image at the point of evaluation, compounded with the transmission or reflective process of the scanning path, as a function of wavelength;

OpticalTransfer(λ

) is a function that describes the transmission of the optical path, as a function of wavelength;

SensorTransfer_c(λ

) is a function that describes the sensitivity of the first sensor, as a function of wavelength;

OptimalOutput_c(λ

) is an ideal output of the scanning system at a given color of the reflective image;

Image(λ

) is a function that describes the color content of the image at the point of evaluation, as a function of wavelength;

ColorSpaceTransfer_c(λ

) is a function that describes the weighting of a given channel of a color space, as a function of wavelength; and

Subscript “

c”

denotes the sensor channel being evaluated.

7. The scanning system as in claim 5, wherein the conversion operator includes a mathematical scheme that interpolate entries in the LUT or table.