Facsimile and static presentation processing – Natural color facsimile – Color correction
Reexamination Certificate
1998-03-24
2001-11-27
Lee, Cheukfan (Department: 2722)
Facsimile and static presentation processing
Natural color facsimile
Color correction
C358S518000
Reexamination Certificate
active
06323969
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims priority of a Japanese Patent Application No. 09-206741 filed Jul. 31, 1996, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color converting apparatus and method. In particular, to a device and method suitable for accurately converting a color signal represented in a different formats by different devices so that a color image from one device may be accurately reproduced by a different device.
2. Description of the Related Art
In recent years, printers, facsimile machines, and related devices have acquired the ability to output data in full color and have become widely available. As a result of this growth in color reproduction devices a need has developed for sharing color picture images among different devices. However, since different devices reproduce images differently, when color picture images are shared with different devices the colors of a transmitted picture may be different from the colors of a picture that are received at the reception site.
The reason for this color mismatch is that in devices such as printers and scanners, colors are handled as color signals comprising a CMY signal and an RGB signal. For example, in a printer of which the minimum value and maximum a color signal is equal to a value of 0 to 255, respectively, all output colors are represented by a combination of values ranging from 0 to 255 of the CMY signal. In this case, even if the same value of the CMY signal is input, the color that is printed depends on the type of the printer. Thus, the method of representing colors with the CMY signal is device-dependent.
In the prior art, a color signal in the device-dependent format is represented in an intermediate format that is device-independent. Using this method, color reproducibility is obtained in different devices.
For example, an L*a*b* signal and an XYZ signal have been used as a color representation method in which colors are represented in a device-independent format. Colors represented in these formats are uniquely defined. Thus, these formats are used as intermediate color representing systems and colors are converted among different devices.
In reality, a picture that is input from a scanner and represented with an RGB signal is converted into a picture represented with an L*a*b* signal. Thereafter, the L*a*b* signal is converted into a CMY signal. The CMY signal is output to a printer. When the representing formats of these color signals are accurately converted, colors can be matched between devices.
To convert the format of a color signal, the value of a color signal in one format must be converted into the appropriate value of a color signal in another format. In order to convert the value of a color signal, a color conversion table that represents the relation between colors in respective color device is used. In this color signal converting method using a color conversion table, when a color signal registered in the color conversion table is converted, the relationship of colors registered in the color conversion table is used. When converting a color signal that does not exist in the color conversion table, a color signal listed in the color conversion table is interpolated to provide a corresponding color signal.
FIG. 38
is a schematic diagram for a two-dimensional registering method of a conventional color conversion table in a color space in the prior art.
In
FIG. 38
shows L*a*b* values at grid points P
1
to P
16
in an L*a*b* space corresponding to CMY values at points Q
1
to Q
16
in a CMY space. The relationship between L*a*b* grid points is listed in the color conversion table. Assuming that CMY values at points Q
1
, Q
2
, Q
5
, Q
9
, and Q
13
are out of the color reproducible range of the device, CMY values at points Q
1
′, Q
2
′, Q
5
′, Q
9
′, and Q
13
′that are in the color reproducible range of the device are substituted for points Q
1
, Q
2
,
05
, Q
9
, and Q
13
, respectively. The substituted CMY values are then registered to the color conversion table.
This color converting method using the conventional color conversion table with numeric values will now be discussed in further detail. In this example, the printer or other related device has a color conversion (CMY values) in the color reproducible range from 0 to 255 (from an L*a*b* signal to a CMY signal). However, it should be noted that the device may be other than a printer and that a color signal other than the L*a*b* signal and CMY signal may be used.
As shown in
FIG. 39
, a table depicting the structure of a conventional color conversion table is provided. The color conversion table shows the relation between an L*a*b* color signal and a CMY color signal. With the color conversion table, the L*a*b* color signal can be converted into the CMY color signal in the color reproducible range of the printer.
In
FIG. 39
, the relation between the L*a*b* color signal and the CMY color signal in the color reproducible range of the printer is 0≦L*≦100, −128≦a*≦128, and −128≦b*≦128, where the values of the L* signal are discretely registered at intervals of 12.5 and the values of the a* signal and b* signal are discretely registered at intervals of 32. This occurs because all values cannot be listed in the color conversion table. In the color conversion table shown in
FIG. 39
, L*a*b* values are distributed at equal intervals.
Thus, CMY values corresponding to L*a*b* values registered in the color conversion table can be directly obtained from the color conversion table.
CMY values corresponding to L*a*b* values that are not in the color conversion table are obtained by interpolation calculations relating L*a*b values and CMY values registered in the color conversion table. In this case, when L*a*b* values are regularly distributed and registered in the color conversion table, interpolation calculations can be easily performed.
When an L*a*b* value equal to (0, −128, −64) is input, since it has been registered in the color conversion table shown in
FIG. 39
, a CMY value equal to (255, 240, 253) corresponding to the L*a*b* value of (0, −128, −64) can be directly obtained with reference to the color conversion table shown in FIG.
39
.
However, when an L*a*b* value equal to (1, −128, −64) is input, since it has not been registered in the color conversion table shown in
FIG. 39
, a CMY value corresponding to the L*a*b* value of (1, −128, −64) is obtained by interpolating a CMY value corresponding to the L*a*b* value equal to (1, −128, −64).
In the conventional color conversion table, CMY values registered therein are values in the range of the color signal of the device in use. When the color conversion table is used for a printer that handles CMY values ranging from 0 to 255, CMY values corresponding to L*a*b* values out of the color range of the printer are substituted to CMY values ranging from 0 to 255 and then registered to the color conversion table.
In the case when L* values represent a black color and the printer reproduces black colors above a value of 18 and cannot output darker colors, CMY values that correspond to the color reproducible represented by L*a*b* values in the color range of the printer are registered. For example, a CMY value=(228, 224, 208) is registered corresponding to an L*a*b* value=(25, 0, 0).
Colors represented by L*a*b* values out of the color range of the printer are substituted with CMY values that can be reproduced by the printer and are registered in the color conversion table. For example, if a CMY value corresponding to an L*a*b* value equal to (12.5, 0, 0) is desired, a black color of an L* value equal to 12.5 cannot be produced as indicated above. Therefore, the darkest CMY value is selected corresponding to a CMY value equal to (255, 255, 255) is registered.
When an L*a*b* value which is not listed in the c
Semba Satoshi
Shimizu Masayoshi
Suzuki Shoji
Fujitsu Limited
Lee Cheukfan
Staas & Halsey , LLP
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