Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1999-06-18
2004-11-23
Lee, Thomas D. (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S003090
Reexamination Certificate
active
06822757
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color transformation method and a recording medium with a color transformation program recorded thereon, and more particularly to a color transformation method for transforming device data in a first device space represented by a first color system into device data in a second device space represented by a second color system different from the first color system, as well as to the recording medium with a color transformation program recorded thereon.
2. Description of the Related Art
In recent years, in conjunction with the consolidation of communication facilities of open networks, in devices such as image displaying devices and printing devices connected to the networks, images are presented by using image source data including color information of other devices. In this case, it is necessary to transform image source data (hereafter referred to as the device data) including color information of the devices between color spaces (hereafter referred to as the device spaces) of the devices. For example, in a case where an image is color printed by using RGB data which is mainly used in image displaying devices, the RGB data must be transformed into CMYK data which is mainly used in the printing devices.
Conventionally, when transforming RGB data to CMYK data, the device spaces of RGB and CMK are temporarily mapped on a generally used color space (hereafter referred to as the colorimetric space) such as an L*a*b* color space or an XYZ color space. Then, a transformation from the RGB device space into the colorimetric space and a transformation from the colorimetric space into the CMYK device space are sequentially effected. Namely, it has been general practice to transform the RGB data into color information in the colorimetric space, and then the color information in the colorimetric space into the CMYK data.
However, the reproducible range, (also known as the gamut), in the colorimetric space, which corresponds to each device space, differs among the respective devices.
FIG. 13
shows a conceptual diagram illustrating the configurations and ranges of a gamut
90
of a device space (hereafter called the RGB device space) based on the RGB color system in the colorimetric space and a gamut
92
of a device space (hereafter called the RGB device space) based on the CMYK color system. As shown in
FIG. 13
, the gamut
90
and the gamut
92
differ from each other.
In a case where data conversion which temporarily undergoes the above-described mapping on the colorimetric space is effected between the RGB device space and the CMYK device space having different gamuts in the colorimetric space, in a forward direction (RGB device space ∃ colorimetric space), the gamut
90
in the RGB device space must be enlarged to a region (a region including both the gamut
90
and the gamut
92
) which includes a region
94
which is unnecessary as an actual gamut, whereas, in a reverse direction (colorimetric space ∃ CMYK device space), mapping must be effected on the CMYK device space by including a region
96
which is not required as a gamut in the CMYK device space.
For this reason, it is general practice to subject data corresponding to the gamut
90
and the gamut
92
in
FIG. 13
to processing such as space compression, expansion, truncation, and the like, and there is a possibility that reproduction accuracy declines in the case of color reproduced from data subjected to processing such as space compression, expansion, truncation, and the like. In addition, since it is difficult to uniformly effect mapping in the entire gamut of the destination CMYK device space to which the transformation is effected to, there is a possibility that maximum use cannot be made of the gamut of the CMYK device space (i.e., an effective gamut is lost).
In addition, since the device space and the L*a*b* color space do not exhibit complete agreement in discrete sampling characteristics and quantization characteristics, if the conversion which temporarily undergoes mapping on the L*a*b* color space is effected, discontinuous CMYK data is obtained with respect to the RGB data which continues at predetermined intervals, so that there is a possibility that the quality of the image which is printed out deteriorates.
Further, K data has a characteristic that it is equivalently replaced by a gray component which is represented by a predetermined amount of equivalent CMY data, and innumerable CMYK data which are equivalent to one arbitrary piece of CMYK data are present, as shown in FIG.
14
. Accordingly, when RGB data is converted to CMYK data, since innumerable combinations of CMYK device space can be obtained, there arises the need to set some restricting conditions on the conversion.
Further in actual printing, the reproduction of color and density must be ensured. In terms of physical properties of printing, the color reproduction characteristic does not necessarily follow an increase in the amount of ink linearly. Namely, the additive process with respect to the amount of ink does not hold, and an unstable gamut is unfailingly present. This is attributable to the fact that there is an upper limit to the ink accepting capacity of printing ink which is a reproducing medium. Therefore, in converting RGB data to CMYK data, it is desirable to develop the gamut by avoiding the aforementioned unstable gamut.
When the RGB device space represented by a monitor or the like is mapped on the CMYK device space peculiar to printing, it is difficult to isochromatically convert all the colors owing to their difference in the gamuts. Accordingly, as general color matching means, various methods shown below in Table 1 are adopted depending on purposes, each having their merits and demerits.
TABLE 1
What to
White
Gradation
Within
Outside
Method
preserve
point
conversion
gamut
gamut
Perceptual
Perceptual
relatively
effected
relatively
relatively
relative
moved
moved
moved
relation
of color
Saturation
chroma
relatively
effected
preserved
uniform
moved
chroma
Relative
chroma
relatively
effected
preserved
closest
colorimetric
moved
color
Absolute
chroma
absolute
not
preserved
closest
colorimetric
effected
color
In the perceptual method, all the colors are relatively converted within the gamut, but retention of isochroism with respect to data within the gamut and outside the gamut is not ensured, and in a case where the gamuts of the device space before and after conversion are substantially different, there is a possibility of the atmosphere of the image becoming entirely different due to the conversion. In addition, with respect to the remaining three methods in which measures are devised for mapping for only the region outside the gamut, in the case of the absolute colorimetric method, if the gamuts differ substantially, there is a high possibility that data corresponding to the region outside the gamut is truncated, while in the relative colorimetric system and the saturation method, the continuity of gradation in the target device space is not ensured.
SUMMARY OF THE INVENTION
The present invention has been devised to overcome the above-described problems, and it is an object of the present invention to provide a color transformation method capable of effecting transformation of the device data between different device spaces.
To this end, in accordance with a first aspect of the present invention, there is provided a color transformation method for transforming device data in a first device space represented by a first color system into device data in a second device space represented by a second color system different from the first color system, comprising the steps of: determining a first relationship of correspondence from the device data in the first device space to color information in a third color system different from the first and the second color systems and a second relationship of correspondence from the device data in the second device space to color information of the third color system; determining an inverse re
Nakata Shin
Usami Yoshinori
Brinich Stephen
Fuji Photo Film Co. , Ltd.
Lee Thomas D.
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