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Gamut correction with color separation and methods and apparatuses for performing same
| Details |
Inventors: Marsden, Jonathan; Samadani, Ramin;
Assignee: Electronics for Imaging, Inc. (Foster City, CA)
Primary Examiner: Cuchlinski, Jr.; William A.
Assistant Examiner: Marc-Coleman; Marthe
Attorney, Agent or Firm: Glenn; Michael A.
Methods and apparatuses for correcting gamut limitations of a color device. A method includes creating a predefined color space for use in gamut correction due to the gamut limitations of the color device, such as a color printer, and producing a set of color data values using the predefined color space. The set of color data values is for use in converting from a first color space (e.g., RGB) to a second color space (e.g., CMYK). A method in another embodiment includes creating a first color separation table, creating a predefined color space, creating a second color separation table for converting values of colors in the predefined color space to values in a colorant space, and creating a composite color separation lookup table by using a plurality of first values from the first color separation table and using a plurality of second values from the second color separation table. The predefined color space is typically based upon a set of redefined chromaticities which are used in a transformation function. Various apparatuses of invention, including data structures in computer readable media (e.g., LUTs) and hardware and/or software combinations, are described. Methods of using these apparatuses are also described. |
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DETAILED DESCRIPTION In one aspect of the present invention, an improved gamut mapping technique consists of redefining the red, green, and blue monitor chromaticities to values for which corresponding hues appear as intended.
This technique in effect defines a predefined color space for use in gamut correction where the predefined color space is based upon a set of redefined monitor chromaticities which are typically used in the transformation function for transforming color values from one color space, such as RGB, to another color space.
In a typical implementation of this aspect of the present invention, the technique consists of generating the appropriate color separation tables using a normal gamut mapping strategy with typical monitor chromaticities and again generating a color separation table, typically the same size as the first color separation table, using the new monitor chromaticity values.
A gamut surface generated using the original chromaticities is then used to determine what is in gamut and what is out of gamut.
The two color separation tables are then combined such that points which lie in gamut use the values from the first color separation table while points which lie out of gamut use values from the second color separation table.
To prevent potential harsh transitions between points lying near the gamut surface, one embodiment of the present invention uses a blending function to blend these points by combining values from the two separation tables.
Using this technique, colors which fall in gamut still appear as intended, while color values which are out of gamut now map to colors which subjectively more closely resemble the intended colors.
In another aspect of the present invention, two complete color separation lookup tables are created and then combined.
A first color separation table is created, where this table determines a conversion from a first set of color values to a first set of colorant values.
A second color separation table is also created, which table determines a conversion from the first set of color values to a second set of colorant values
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Image Analysis 
