Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
2002-03-22
2004-07-20
Bella, Matthew C. (Department: 2676)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
Reexamination Certificate
active
06765586
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a medium recording a color transformation lookup table for color transformation on printing, a printing apparatus and a printing method both using the color transformation lookup table, a medium recording a printing program, a color transformation apparatus, and a medium recording a color transformation program.
2. Description of the Prior Art
Image processing devices such as displays, printers have the device-dependent color gamut, that is, the range of colors producible by the device. When two image processing devices are compared in the aspect of colors, generally, some colors are producible on both devices; other colors are producible only on either device. For some image processing devices, despite having the ability of fine color reproduction, it was conventionally practiced to limit their color gamut to a certain extent enough to make their output look in homogenous colors to the human eyes. For example, assume that an image on a display is printed by a printer. In a color region where the color gamut of the display is wider than that of the printer, the colors visible on the display are mapped to fall within the color gamut of the display and the color gamut of the printer. Colors in another color region where the color gamut of the printer is wider than that of the display are not used when images are printed.
For conventional color transformation programs based on the above-described color-mapping method, a problem was posed which will be described below.
If an image presented on the display is printed, using the colors in a region that fall within both color gamuts of the display and of the printer, the colors of the printed image well match the colors of the image on the display. However, because colors out of the color reproducible range of the display are not produced by printing, best-quality print results are not always produced. For example, when printing a photograph including colors in the range of the green hue to the blue hue wherein the color gamut of the printer is wider in the direction of chroma rise, the colors of its print result will be poorer in tones than the colors of the actual subject.
SUMMARY OF THE INVENTION
To solve the problem, an object of the present invention is to provide a medium recording a color transformation lookup table, printing apparatus, printing method, a medium recording a printing program, a color transformation apparatus, and a medium recording a color transformation program, in order to permit an image processing device to produce desirable color image outputs by making more effective use of its color gamut.
In accordance with one aspect of the present invention, a medium recording a color transformation lookup table is provided. The color transformation lookup table is referenced for transformation of first color image data used on a first image processing device into second color image data used on a second image processing device and has a first set of values and a second set of values which represent a relationship between color gamuts of the first image processing device and the second image processing device,
wherein if there exists the region that is out of the color gamut of the first image processing device but falls within the color gamut of the second image processing device in a certain hue of the device-independent color space, the relationship is equivalent to the relationship of color gamut determined, based on gamut mapping in a predefined device-independent color space, through a process comprising:
a color gamut shift step to obtain the mapping which expands the shape of the color gamut of the first image processing device so as to be close to the shape of the color gamut of the second image processing device in a homogeneous hue range; and
a color gamut expansion step to obtain the mapping which expands a certain region of the resulting gamut processed at the color gamut shift step into the inside of color gamut of the second image processing device.
In the present invention of this aspect, by using a color transformation program that comprises the steps of inputting the first color image data for use on the first image processing device and transforming the first color image data into the second color image data for use on the second image output program, the first color image data is transformed into the second color image data, based on the relationship between color gamuts of the first image processing device and the second image processing device, which has been defined by the color gamut shift step. The color gamut shift step performs gamut mapping in which the shape of the color gamut of the first image processing device expands so as to be close to the shape of the color gamut of the second image processing device. In the predefined device-independent color space, this step is carried out in a hue in which a color region exists that is out of the color gamut of the first image processing device, but falls within the color gamut of the second image processing device.
When shifting the color gamut of the first image processing device, expansion rather than compression takes place so that the shape of the color gamut will be made close to the shape of the color gamut of the second image processing device. Consequently, if the color gamut of the second image processing device is wider than that of the first image processing device, the resulting gamut by shift maintains the characteristics of the color gamut of the first image processing device, while it is close to the characteristics of the color gamut of the second image processing device. Color gamut shift can take place without unnatural color transformation. By making the color gamut of the first image processing device close to the color gamut of the second image processing device, the region expands where the color gamut of the first image processing device overlaps with the color gamut of the second image processing device. This makes it possible to decrease the number of colors that are out of the color gamut of the second image processing device and increase the number of colors available on the second image processing device.
In order to obtain images with finer tones in a hue in which a color region exists that is out of the color gamut of the first image processing device, but falls within the color gamut of the second image processing device, following the color gamut shift step, the color gamut expansion step is carried out for gamut mapping in which a certain region of the resulting gamut after the color gamut shift further expands into the color gamut of the second image processing device. Consequently, the gamut obtained by shifting the color gamut of the first image processing device through the color gamut shift step is further modified to include colors that are out of the color gamut of the first image processing device, but fall within the color gamut of the second image output.
Color transformation of the first color image data into the second color image data, based on the finally obtained gamut, enables effective use of colors that are out of the color gamut of the first image processing device, but fall within the color gamut of the second image output. By using the color gamut shift step in combination with the color gamut expansion step as required, both unnatural color transformation prevention and effective use of the color gamut of the second image processing device can be achieved at the same time. The above-described process can be augmented by adding another step. For a region that still falls out of the color gamut of the second image processing device after the execution of the color gamut shift and color gamut expansion steps, it is advisable to compress the region into the color gamut and define the gamut mapping relationship between the first and second image processing devices.
In this way, according to the present invention, unnatural color transformation can be prevented with effective use of the color gamut of the secon
Fujino Makoto
Yamazaki Satoshi
Beyer Weaver & Thomas LLP
Richer Aaron M.
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