Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1997-03-25
2001-08-28
Moore, David (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S529000
Reexamination Certificate
active
06281984
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is related by common inventorship and subject matter to copending patent application No. Ser. No. 08/823,596, entitled “A System, Method, and Program For Converting Three Dimensional Colorants To More Than Three Dimensional Colorants” filed on even date herewith, assigned to the Assignee hereof and entirely incorporated herein by this reference.
This application is related by common inventorship and subject matter to copending patent application No. Ser. No. 08/823,597 entitled “A System, Method, and Program For Converting An Externally Defined Four Dimensional Colorant (CMYK) Into An Equivalent Four Dimensional Colorant Defined In Terms Of The Four Inks (C′M′Y′K′) That Are Associated With A Given Printer” filed on even date herewith, assigned to the Assignee hereof, and entirely incorporated herein by this reference.
This application is related by common inventorship and subject matter to copending patent application No. Ser. No. 08/832,774 entitled “A System, Method, and Program For Converting An Externally Defined Four Dimensional Colorant (CMYK) Into An Equivalent Four Dimensional Colorant Defined In Terms Of The Four Inks (C′M′Y′K′) That Are Associated With A Given Printer By Using A Three Dimensional To Four Dimensional Conversion Process” filed on even date herewith, assigned to the Assignee hereof and entirely incorporated herein by this reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to color printing, and more specifically, to converting a four dimensional color (CMYK), defined in terms of a standard or another printer, into an equivalent four dimensional color defined in terms of the colors (i.e., inks, toners, etc.) that are uniquely associated with a printer that is to perform the actual printing.
2. Description of the Related Art
For additive color processes such as used in display monitors, red, green, and blue are primary colors. In theory, mixing red, green, and blue light in various combinations can produce any color. For example, cyan is a mixture of green and blue and magenta is a mixture of red and blue. Black is the absence of any red, green, or blue; while white contains all three. A display monitor involves an additive process of light, and therefore, any color it produces can be defined in terms of red (R), green (G), and blue (B).
In a printing process, inks are typically deposited on white paper which already reflects the full amount of red, green, and blue. Instead of adding red, green and blue (RGB) together to produce any color, quantities of red, green, and blue are removed to produce a desired color. To do this, filters or inks have to be produced which filter individual primary colors, while not affecting the other two. The filter colors which accomplish this are the colors which are the complement of the primary colors. For example, yellow is the complement of blue. A blue filter, one which filters out blue light, passes red and green and thus appears yellow. Yellow ink can be thought of as an ink which removes blue. Thus, the complement of blue is yellow; the complement of red is cyan; and the complement of green is magenta. As such, cyan, magenta, and yellow are the primary colors in the subtractive color system and are known as the process colors in the printing industry.
Theoretically, with only three colors of ink: cyan (C), magenta(M) and yellow (Y), a printer could print any color. White can be obtained by putting no ink on the paper; and black can be obtained by putting cyan, magenta, and yellow on the paper, blocking all light. Realistically, however, the color obtained when placing cyan, magenta, and yellow on paper may not be pure black. It may be brownish. Consequently, black ink is typically added to the printing process color set. The black ink not only insures a richer black color, but it also reduces the amount of ink that has to be used to produce most colors. For example, if at any one place on the paper, quantities of C, M, and Y are placed, there will be a gray component which can be removed and replaced with black. This reduces the total amount of ink on the paper and produces better grays and blacks. In addition, it increases the gamut of the color set.
As a theoretical example of this process called black substitution or gray component removal, consider the following:
A color requires
Cyan=20%
Magenta=40%
Yellow=60%
In theory, the above color has a 20% gray component, the least common denominator. As such, 20% of each color could be removed and replaced with 20% black. The following will theoretically produce the same color.
New color mix
Cyan=0%
Magenta=20%
Yellow=40%
Black=20%
In the above example, 120 units of ink are replaced with 80 units of ink. Thus ink is saved. Colored inks usually cost more than black ink; thereby saving even more.
As shown above, color can be expressed in several ways. A color can be expressed in terms of percents of RGB (red, green, blue), CMY, (cyan, magenta, yellow) or CMYK (cyan, magenta, yellow, black). None of these color spaces, as they are called, are defined as to what color is produced by mixing combinations of each. Generally, these color spaces are referred to as being device dependent, since the color produced by a given CMYK mix on one printer will not produce the same color on another.
An attempt has been made in the United States to standardize the process color inks so that the colors can be predicted. A standard called SWOP (Specification for Web Offset Publication) has been published which standardized the process ink colors. Recently, the standard has been taken a step further and 928 combinations of CMYK have been defined as to what color will result in a device independent color space (CIE XYZ or CIE L*a*b*). In Europe, a standard called Euroscale has been developed for four different paper surfaces. SWOP and Euroscale are very close, but not exactly the same.
In 1931, the organization called the Commission Internationale L'Eclairge (International Commission of Lighting), the CIE, met to try to establish a system of device independent color, color based on human sight. While attempting to define RGB, problems arose which persuaded the members to process the data through a matrix transform which produced a color space called CIE XYZ or XYZ. Since the XYZ color space is based on the human perception of color, any two different colors, even though the spectrum of these two colors may be different, will be perceived as the same color by a human if the XYZ values are the same under given lighting conditions.
From the XYZ color space, additional color spaces have been derived. One of these is called CIEL*a*b*, pronounced C Lab, or L*a*b*. This color space is based on XYZ of the color referenced to XYZ of the light source or paper. Most specifications such as the SWOP standard are specified in terms of XYZ and L*a*b* under a light source such as daylight D50. It is a three component color space with each color specified in terms of L*, a*, and b*. L* specifies the lightness; and the hue and saturation are determined from the values of a* and b*.
As previously discussed, a display monitor involves an additive process of light, and therefore, any color it produces can be defined in terms of RGB. However, a printing process is a subtractive process since it is printing on white paper, and therefore, color printers use cyan (C), magenta (M), and yellow (Y) or cyan, magenta, yellow and black (K), i.e., CMY or CMYK, to produce various colors. However, input files, such as a display monitors, scanners or other information used to print images are typically defined using RGB. Some input files can be defined in terms of CMY or CMYK. Input files may also be defined in device independent terms such as XYZ or L*a*b. Therefore, a conversion process has to take place in order to convert RGB, XYZ, or L*a*b* of an input file into CMY or CMYK for printing.
If the input file is RGB, XYZ, or L*a*b*, it
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