Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
1999-11-10
2002-10-01
Luu, Matthew (Department: 2672)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S589000, C345S591000, C345S604000, C348S223100, C348S602000, C348S649000, C348S655000, C358S516000, C358S518000, C358S519000, C358S520000, C382S162000, C382S167000
Reexamination Certificate
active
06459436
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image processing method and apparatus, and more particularly, to an image processing method and apparatus for performing color matching according to ambient light.
FIG. 1
is a conceptual view of general color matching.
Input RGB data is converted by an input profile to XYZ data of a color space which does not depend on any devices. Since an output device cannot express colors outside the color reproduction range of the output device, gamut mapping is performed on the inputted data, which has been converted to the data in the device-independent color space, such that all colors of the inputted data fall within the color reproduction range of the output device. After the gamut mapping is performed, the inputted data is converted from the device-independent color space to CMYK data of a color space which is dependent on the output device.
In color matching, a reference white point and ambient light are fixed. For instance, according to a profile specified by the International Color Consortium (ICC), Profile Connection Space (PCS) for associating profiles uses XYZ values or Lab values based on a D
50
characteristic. Therefore, correct color reproduction is guaranteed when an inputted original document and a printout are viewed under an illuminant of the D
50
characteristic. Under an illuminant of other characteristics, correct color reproduction is not guaranteed.
When a sample (e.g., an image) is viewed under different illuminants, XYZ values of the viewed sample naturally vary. The XYZ values under various illuminants are predicted by conversion methods such as (1) ratio conversion, (2) Von Kries conversion, and (3) prediction formula using a color perception model.
In the ratio conversion method, XYZ values under a reference white point W
1
are converted to XYZ values under a reference white point W
2
at a ratio of W
2
/W
1
. If this conversion method is applied to the Lab uniform color space, the Lab values under W
1
become equal to the Lab values under W
2
. Assuming that XYZ values of a sample under W
1
(Xw
1
, Yw
1
, Zw
1
) are (X
1
, Y
1
, Z
1
) and XYZ values of the sample under W
2
(Xw
2
, Yw
2
, Zw
2
) are (X
2
, Y
2
, Z
2
), the following relations are obtained by the ratio conversion:
X2
=
Xw2
Xw1
X1
Y2
=
Yw2
Yw1
Y1
Z2
=
Zw2
Zw1
Z1
}
(
1
)
According to the Von Kries conversion, XYZ values under the reference white point W
1
are converted to XYZ values under the reference white point W
2
at a ratio of W
2
′/W
1
′ in a human color perception space PQR. If this conversion method is applied to the Lab uniform color space, the Lab values under W
1
do not become equal to the Lab values under W
2
. Assuming that XYZ values of a sample under W
1
(Xw
1
, Yw
1
, Zw
1
) are (X
1
, Y
1
, Z
1
) and XYZ values of the sample under W
2
(Xw
2
, Yw
2
, Zw
2
) are (X
2
, Y
2
, Z
2
), the following relations are obtained by Von Kries conversion:
[
X2
Y2
Z2
]
=
[
inv_Mat
]
[
Pw2
Pw1
0
0
0
Qw2
Qw1
0
0
0
Rw2
Rw1
]
[
Mat
]
[
X1
Y1
Z1
]
(
2
)
where
[
Pw2
Qw2
Rw2
]
=
[
Mat
]
[
Xw2
Yw2
Zw2
]
(
3
)
[
Pw1
Qw1
Rw1
]
=
[
Mat
]
[
Xw1
Yw1
Zw1
]
(
4
)
[
inv_Mat
]
=
[
1.85995
-
1.12939
0.21990
0.36119
0.63881
0
0
0
1.08906
]
(
5
)
[
Mat
]
=
[
0.44024
0.70760
-
0.08081
-
0.22630
1.16532
0.04570
0
0
0.91822
]
(
6
)
To convert XYZ values under a viewing condition VC
1
(including W
1
) to XYZ values under a viewing condition VC
2
(including W
2
), the prediction formula using a color perception model, which is a conversion method such as CIE CAM 97s using the human color perception space QMH (or JCH) is employed. Herein, Q for QMH represents brightness, M represents colorfulness, and H represents hue quadrature or hue angle. J for JCH represents lightness, C represents chroma, and H represents hue quadrature or hue angle. If this conversion method is applied to the Lab uniform color space, the Lab values under W
1
are not equal to the Lab values under W
2
, similarly to the case of the Von Kries conversion. Assuming that XYZ values of a sample under W
1
(Xw
1
, Yw
1
Zw
1
) are (X
1
, Y
1
, Z
1
) and XYZ values of the sample under W
2
(Xw
2
, Yw
2
, Zw
2
) are (X
2
, Y
2
, Z
2
), the prediction formula using color appearance model performs the following conversion:
(
X
1
,
Y
1
,
Z
1
)→[forward conversion of
CIE CAM
97
s
]→(
Q, M, H
) or (
J, C, H
)→[inverse conversion of
CIE CAM
97
s
] (
X
2
,
Y
2
,
Z
2
)
In other words, if it is assumed that XYZ values under a reference white point which varies depending on a ratio conversion can be converted, the contour lines of hue in the Lab color spaces under various reference white points are always the same. However, if human color perception is taken into consideration, such as in the Von Kries conversion or prediction formula using a color perception model, the contour lines of hue in the Lab color spaces under different reference white points vary depending on the reference white points.
For the above reason, if gamut mapping (hue restoration) defined under one Lab color space is applied to color matching under different reference white points, the human vision perceives the hue as inconsistent.
Moreover, in the current ICC profile, since the PCS is limited to XYZ values or Lab values based on the D
50
characteristic, color matching corresponding to ambient light cannot be performed.
SUMMARY OF THE INVENTION
The present invention is made in consideration of the above situation, and has as its object to provide an image processing method and apparatus for realizing excellent color reproduction regardless of viewing conditions.
Another object of the present invention is to provide an image processing method and apparatus for realizing excellent color reproduction particularly by performing partial adaptation processing.
Furthermore, another object of the present invention is to provide an image processing method and apparatus which enable adjustment of partial adaptation processing so as to adjust chromatic adaptability processing to obtain a result desired by a user.
In order to attain the above objects, the present invention provides an image processing method for performing chromatic adaptability conversion processing on input image data based on a viewing condition, wherein the chromatic adaptability conversion processing performs partial adaptation processing in accordance with ambient light and an illuminant, and at least one parameter of the partial adaptation processing can be adjusted.
Furthermore, in order to attain the above objects, the present invention provides an image processing apparatus comprising conversion means for at least performing chromatic adaptability conversion processing on input image data based on a viewing condition, wherein the chromatic adaptability conversion processing performs partial adaptation processing in accordance with ambient light and an illuminant, and at least one parameter of the partial adaptation processing can be adjusted.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
REFERENCES:
patent: 5208911 (1993-05-01), Newman et al.
patent: 5276779 (1994-01-01), Statt
patent: 5432906 (1995-07-01), Newman et al.
patent: H1506 (1995-12-01), Beretta
patent: 5532848 (1996-07-01), Beretta
patent: 5583666 (1996-12-01), Ellson et al.
patent: 5754448 (1998-05-01), Edge
patent: 5754682 (1998-05-01), Katoh
patent: 5920358 (1999-07-01), Takemura
patent: 6157735 (2000-12-01), Holub
patent: 6225974 (2001-05-01), Mardsen et al.
patent: 6229916 (2001-05-01), Ohkubo
patent: 6243059 (2001-06-01), Greene
patent: 6249315 (2001-06-01), Holm
patent: 6340975 (2002-01-01), Mardsen et al.
patent: 7-222196 (1995-08-01), None
patent: 9-093451 (1997-0
Kumada Shuichi
Ohga Manabu
Luu Matthew
Sajous Wesner
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