Image color balance for scanners using an illumination spectral sensor
View Patent ↗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.
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:
SensorOutput
c
=
∫
λ
min
λ
max
Illumination
(
λ
)
·
ReflectiveImage
(
λ
)
·
OpticalTransfer
(
λ
)
·
SensorTransfer
c
(
λ
)
ⅆ
λ
OptimalOutput
c
=
∫
λ
min
λ
max
Image
(
λ
)
·
Color
SpaceTransfer
c
(
λ
)
ⅆ
λ
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:
SensorOutput
c
=
∫
λ
min
λ
max
Illumination
(
λ
)
·
ReflectiveImage
(
λ
)
·
OpticalTransfer
(
λ
)
·
SensorTransfer
c
(
λ
)
ⅆ
λ
OptimalOutput
c
=
∫
λ
min
λ
max
Image
(
λ
)
·
Color
SpaceTransfer
c
(
λ
)
ⅆ
λ
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.