Facsimile and static presentation processing – Natural color facsimile – Color correction
Reexamination Certificate
1997-10-21
2004-11-30
Coles, Edward (Department: 2622)
Facsimile and static presentation processing
Natural color facsimile
Color correction
C358S518000, C382S167000
Reexamination Certificate
active
06825958
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device and a method of fabricating a color conversion table, and a medium for recording a program for forming a color conversion table. In the invention grey scale color representing data, in a post-conversion color representing space, is corresponded to lattice points in a pre-conversion color representing space for converting grey scale color representing data between different color representing spaces.
2. Description of the Prior Art
There has conventionally been known as a color conversion table of this kind a color print system for performing color printing of a color image in a computer.
Inside the computer, the color image is displayed in a grey scale by the three primary colors of red, green and blue (R, G, B) for respective pixels arranged vertically and horizontally. In a general color printing device, printing is performed using the three colors of cyan, magenta and yellow (C, M, Y), or the four colors of (C, M, Y, K) added with black but with no grey scale. Accordingly, in performing color printing, there is an operation of color conversion from the three primary colors of red, green and blue (R, G, B) to the three colors of cyan, magenta and yellow (C, M, Y), and also an operation of grey scale conversion from grey scale display to display having no grey scale. Incidentally, although color space per se is one space, display has to differ depending on the definition of coordinates and accordingly, in the following, the space is referred to as a color representing space in accordance with the definition of coordinates, for convenience of explanation.
The color conversion from (R, G, B) display to (C, M, Y) display is not unequivocally determined by a conversion equation. Normally, a correspondence relationship is established, mutually, in respect of color spaces each having coordinates of respective grey scales. For convenience, the correspondence relationship may also be referred to as a corresponding relationship. The conversion is successively performed through this correspondence relationship. When a pre conversion (R, G, B) display is provided with 256 grey scales for each color, a color conversion table having elements of substantially 16,700,000 (256×256×256) must therefore be prepared.
For the sake of the efficient use of storage resources, the correspondence relationship is not prepared for all the coordinate values but, rather, for lattice points at pertinent discontinuous intervals. A interpolation calculation is thus used along therewith. That is, when it is intended to establish the correspondence relationship of a (C, M, Y) color representing space in respect of color of certain known coordinates in a (R, G, B) color representing space (i.e., RGB coordinates), a correspondence relationship among the lattice points surrounding the known coordinates is used. The correspondence relationship of the RGB and CMY coordinates is established after performing of linear interpolation or the like. The lattice points in each color space and their correspondence is stored as a color conversion table.
Such a color conversion table is generally provided along with a printer driver. Just one printer driver per se, including a color conversion table, is typically provided with a given color printing device. Therefore, a number of lattice points, determined based on storage constraints, is specified also in respect of the color conversion table.
The above-described conventional color conversion table, however, is not necessarily optimal with respect to a given user's environment. The color conversion table is formed by the provider the printer driver based on general storage constraints, but there may be a case where a table is too large or, sometimes a case where a larger size would be more suitable for the table, depending on the user's environment.
Furthermore, print quality may differ depending on the size of the color conversion table and, therefore, a constant size for the color conversion table may not be sufficient.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a device and a method for fabricating a color conversion table, capable of forming a color conversion table optimized to a given environment, such as that of a user or the like. It is also an object of the invention to provide a computer readable medium recording such a program for forming such an optimal color conversion table.
According to an aspect of the present invention, there is provided a device for fabricating a color conversion table in which a color conversion table corresponding grey scale color representing data in a post conversion color representing space to lattice points is formed in order to convert the grey scale color representing data between the different color representing spaces, the device including a pre conversion color conversion table for storing a corresponding relationship of conversion at a small number of lattice points and interpolating means for increasing the lattice points of the pre conversion color conversion table by an interpolation calculation and forming a color conversion table used in the conversion.
According to the present invention constituted as described-above, there is originally existed the pre conversion color conversion table having a small number of the lattice points, which requires little storage resource. Further, the interpolating means forms the color conversion table by increasing the lattice points of the pre conversion color conversion table by interpolation calculation and utilizes the formed color conversion table in color conversion.
The number of the lattice points in the pre conversion color conversion table may be relatively small in comparison with those in the formed color conversion table and has not necessarily to be an extremely small numerical value. Particularly, in the case of three-dimensional lattice points, the amount of lattice points is changed in a cubic ratio. That is, when the number of points is halved, the size of the color conversion table is reduced to ⅛ of the original and accordingly, enormous effect is achieved to storage resource only with a small difference therebetween.
Therefore, according to the present invention, the color conversion table is formed from the pre conversion color conversion table having a small size by increasing the lattice points and therefore, only minimum storage resource is needed when the color conversion is not performed whereas when the color conversion is performed, the color conversion table having a necessary magnitude can be formed and accordingly, the present invention can provide a further flexible device of fabricating a color conversion table. Naturally, the table may be spread when it is necessary and is not spread when it is not necessary or may be left in the spread state when there is allowance in storage resource.
In respect of the interpolation calculating means, various calculations are applicable. Hence, it is a further object of the present invention to provide a further specific constitution in respect of the interpolation calculating means.
According to a device of fabricating a color conversion table of the present invention, the interpolating means comprises nonlinear interpolation calculating means for performing an interpolation by a nonlinear interpolation calculation from a corresponding relationship of a plurality of lattice points.
According to the present invention constituted as described-above, the nonlinear interpolation calculating means of the interpolating means interpolates the lattice points by the nonlinear interpolation calculation from the corresponding relationship in the plurality of lattice points.
The corresponding relationship in the increased lattice points is accurately reproduced by performing the nonlinear interpolation calculation. Accordingly, a result having very excellent reproducing performance can be provided even with a small number of lattice points in the pre conversion
Fukasawa Kenji
Kasahara Hirokazu
Coles Edward
Pokrzywa Joseph R.
Seiko Epson Corporation
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