Image analysis – Color image processing
Reexamination Certificate
1999-04-16
2002-08-13
Grant, II, Jerome (Department: 2624)
Image analysis
Color image processing
C382S167000, C382S274000
Reexamination Certificate
active
06434268
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to data processing used for a full-color printing related equipment such as a printer, a video printer, a scanner or the like, an image processor for forming computer graphic images or a display device such as a monitor. More specifically, the invention relates to a color conversion device and a color conversion method for performing color conversion for image data of three colors of red, green and blue in accordance with an equipment used.
Color conversion in printing is an indispensable technology for compensating for deterioration of image quality such as that due to color mixing properties caused by factors such as that the ink is not of a pure color, or non-linearity (in the hue) of the image-printing, and to output a printed image with a high color reproducibility. Also, in a display device such as a monitor or the like, color conversion is performed in order to output (display) an image having desired color reproducibility in accordance with conditions under which the device is used or the like when an inputted color signal is to be displayed.
Conventionally, two methods have been available for the foregoing color conversion: a table conversion method and a matrix calculation method.
The table conversion method is a method for inputting image data of red, green and blue (referred to “R, G and B”, hereinafter) and obtaining image data of R, G and B stored beforehand in a memory such as ROM or complementary color data of yellow, magenta and cyan (referred to as “Y, M and C”, hereinafter). Since an arbitrary conversion characteristic can be employed, this table conversion method has an advantageous capability of executing color conversion with good color reproducibility.
However, in a simple structure for storing data for each combination of image data, a large-capacity memory of about 400 Mbit must be used. For example, even in the case of a compression method for memory capacity disclosed in Japanese Patent Kokai Publication No. S63-227181, memory capacity is about 5 Mbit. Therefore, a problem inherent in the table conversion system is that since a large-capacity memory is necessary for each conversion characteristic, it is difficult to implement the method by means of an LSI, and it is also impossible to deal with changes in the condition under which the conversion is carried out.
On the other hand, in the case of the matrix calculation method, for example, for obtaining printing data of Y, M and C from image data of R, G and B, the following formula (27) is used as a basic calculation formula.
[
Y
M
C
]
=
(
Aij
)
[
R
G
B
]
(
27
)
Here, i=1 to 3, and j=1 to 3.
However, by the simple linear calculation of the formula (27), it is impossible to provide a good conversion characteristic because of a non-linearity of an image-printing or the like.
A method has been proposed for providing a conversion characteristic to improve the foregoing characteristic. This method is disclosed in Japanese Patent Application Kokoku Publication H2-30226, directed to “color correction calculation device, and employs a matrix calculation formula (28) below.
[
Y
M
C
]
=
(
Dij
)
[
R
G
B
R
*
G
G
*
B
B
*
R
R
*
R
G
*
G
B
*
B
N
]
(
28
)
Here, N is a constant, i=1 to 3, and j=1 to 10.
In the foregoing formula (28), since image data having a mixture of an achromatic component and a color component is directly used, mutual interference occurs in computation. In other words, if one of the coefficients is changed, influence is given to the components or hues other than the target component or hue (the component or hue for which the coefficient is changed). Consequently, a good conversion characteristic cannot be realized.
A color conversion method disclosed in Japanese Patent Application Kokai Publication H7-170404 is a proposed solution to this problem.
FIG. 29
is a block circuit diagram showing the color conversion method for conversion of image data of R, G and B into printing data of C, M and Y, disclosed in Japanese Patent Application Kokai Publication H7-170404. A reference numeral
100
denotes a complement calculator;
101
, an minimum and maximum calculator;
102
, a hue data calculator;
103
, a polynomial arithmetic unit;
104
, a matrix calculator;
105
, a coefficient generator; and
106
, a synthesizer.
Next, the operation will be described. The complement calculator
100
receives image data R, G and B, and outputs complementary color data Ci, Mi and Yi which have been obtained by determining 1's complements. The minimum and maximum calculator
101
outputs a maximum value &bgr; and a minimum value &agr; of this complementary color data and an identification code S for indicating, among the six hue data, data which are zero.
The hue data calculator
102
receives the complementary color data Ci, Mi and Yi and the maximum and minimum values &bgr; and &agr;, and outputs six hue data r, g, b, y, m and c which are obtained by executing the following subtraction: r=&bgr;−Ci, g=&bgr;−Mi, b=&bgr;−Yi, y=Yi−&agr;, m=Mi−&agr;, and c=Ci−&agr;. Here, among the six hue data, at least two assume the value zero.
The polynomial arithmetic unit
103
receives the hue data and the identification code, selects, from r, g and b, two data Q
1
and Q
2
which are not zero and, from y, m and c, two data P
1
and P
2
which are not zero. Based on these data, the polynomial arithmetic unit
103
computes polynomial data: T
1
=P
1
*P
2
, T
3
=Q
1
*Q
2
, T
2
=T
1
/(P
1
+P
2
), and T
4
=T
3
/(Q
1
+Q
2
), and then outputs the results of the calculation.
The coefficient generator
105
generates calculation coefficients U(Fij) and fixed coefficients U(Fij) for the polynomial data based on information regarding the identification code S. The matrix calculator
104
receives the hue data y, m and c, the polynomial data T
1
to T
4
and the coefficients U, and outputs a result of the following formula (29) as color ink data C
1
, M
1
and Y
1
.
[
C1
M1
Y1
]
=
(
Eij
)
[
c
m
y
]
+
(
Fij
)
[
c
*
m
m
*
y
y
*
c
r
*
g
g
*
b
b
*
r
c
*
m
/
(
c
+
m
)
m
*
y
/
(
m
+
y
)
y
*
c
/
(
y
+
c
)
r
*
g
/
(
r
+
g
)
g
*
b
/
(
g
+
b
)
b
*
r
/
(
b
+
r
)
]
(
29
)
The synthesizer
106
adds together the color ink data C
1
, M
1
and Y
1
and data &agr; which is the achromatic data, and outputs printing data C, M and Y. Accordingly, the following formula (30) is used for obtaining printing data.
[
C
M
Y
]
=
(
Eij
)
[
c
m
y
]
+
(
Fij
)
[
c
*
m
m
*
y
y
*
c
r
*
g
g
*
b
b
*
r
c
*
m
/
(
c
+
m
)
m
*
y
/
(
m
+
y
)
y
*
c
/
(
y
+
c
)
r
*
g
/
(
r
+
g
)
g
*
b
/
(
g
+
b
)
b
*
r
/
(
b
+
r
)
]
+
[
α
α
α
]
(
30
)
The formula (30) shows a general formula for a group of pixels.
FIG. 30A
to
FIG. 30F
, which are schematic diagrams, show relations between six hues of red (R), green (G), blue (B), yellow (Y), cyan (C) and magenta (M) and hue data y, m, c, r, g and b, and each hue data relates to three hues.
FIG. 31A
to
FIG. 31F
, which are schematic diagrams, show relations between the six hues and product terms y*m, r*g, c*y, g*b, m*c and b*r, and it is seen that each hue data relates to specified hue among the six hues.
Thus, each of the six product terms y*m, m*c, c*y, r*g, g*b and b*r relates to only specific hue among the six hues of red, blue, green, yellow, cyan and magenta. In other words, only y*m is an effective product term for red; m*c for blue; c*y for green; r*g for yellow; g*b for cyan; and b*r for magenta.
Also, each of the six fraction terms y*m/(y+m), m*c/(m+c), c*y/(c+y), r*g/(r+g), g*b/(g+b) and b*r/(b+r) in the formula (30) relates to only a specific hue among the six hues.
As apparent from the foregoing, according to the color conversion method shown in
FIG. 29
, by changing coefficients for the product terms and the fraction terms regarding the specific hue, only the target hue can be adjusted without influencing to other hues.
Each of the foregoing produ
Asamura Masako
Hatano Yoshiko
Kagawa Shuichi
Maeshima Kazuya
Okamoto Takashi
Grant II Jerome
Mitsubishi Denki & Kabushiki Kaisha
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