Computer graphics processing and selective visual display system – Computer graphics processing – Graph generating
Reexamination Certificate
1996-11-18
2001-01-09
Powell, Mark R. (Department: 2779)
Computer graphics processing and selective visual display system
Computer graphics processing
Graph generating
Reexamination Certificate
active
06172681
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for converting color data from a certain colorimetric system into another colorimetric system.
2. Description of the Related Art
When a user picks up an image by an image pick up device, the user sometimes desires to print out the picked up image with a color printer. Color data produced by the image pick up device is generally defined in an RGB colorimetric system. In order to print out the color data (referred to as RGB color data) by the color printer, the RGB color data has to be converted into CMY color data defined in a CMY colorimetric system.
SUMMARY OF THE INVENTION
It is conceivable that in order to subject the RGB color data to the conversion operation, the RGB color data is first transferred to a computer. The user then adjusts the RGB color data while observing the color state of the RGB color data as being displayed on a CRT display provided to the computer. The computer then converts the user's adjusted RGB color data into CMY color data in accordance with a theoretical relationship between the RGB colorimetric system and the CMY colorimetric system. In this case, however, table (LUT) in which a plurality of CMY parameters defined in the CMY colorimetric system are stored in correspondence with a plurality of Lab parameters defined in the L*a*b* colorimetric system. Each CMY parameter is determined as control data that can control the color printer to reproduce a color the same as that defined by a corresponding Lab parameter. The look up table is therefore prepared in accordance with the characteristic of the color printer. Accordingly, the computer converts the Lab color data into CMY color data while using the Lab parameters and the CMY parameters stored in the look up table.
According to the above-described color conversion method, however, the color state is adjusted in the HVC colorimetric system. Therefore, the original color data has to be converted four times: (1) from the RGB system into the L*a*b* system; (2) from the L*a*b* system to the HVC system; (3) from the HVC system back to the L*a*b* system; and (4) from the L*a*b* system into the CMY system. The final conversion is performed easily with using the look up table. However, the first through third conversions include calculations with square roots, cube roots, reverse trigonometric functions, and the like. Accordingly, it takes a long time to perform the respective conversion operations. Because each color image is comprised of a plurality of sets of color data (i.e., a plurality of picture elements), it there is a possibility that the obtained CMY color data may not accurately reproduce the color displayed on the CRT display. This problem occurs due to the respective characteristics of the image pick up device, the CRT display, the color printer, and the color inks used by the color printer.
In order to solve this problem, the computer may be controlled to convert the original RGB color data first into Lab color data defined in a L*a*b* colorimetric system which is representative of a uniform color space. The computer further converts the Lab color data into HVC color data defined in a Munsell colorimetric system. The Munsell colorimetric system indicates color in accordance with human's visual sense. The Munsell colorimetric system will be referred to as a HVC colorimetric system hereinafter because the Munsell colorimetric system indicates color by hue data H, value (lightness) data V, and chroma (saturation) data C. The user adjusts the HVC color data in the HVC colorimetric system. The user can therefore easily adjust the HVC color data into his/her desired color state because the HVC system is defined in accordance with the human's visual sense. When this adjustment is completed, the HVC color data is reconverted into Lab color data in the L*a*b* system.
The computer previously stores therein a look up takes a very long time to process the entire image. Especially when the user performs the color adjustment operation many times, the entire processing time length will become quite long.
In order to shorten the processing time length, it is conceivable to convert color data only through two conversion processes: (1) from the RGB system into the L*a*b* system; and (2) from the L*a*b* system into the CMY system. The final conversion is performed with using the look up table. When the user desires to adjust the color state of the color data, the user may input color adjustment amounts indicative of his/her desired adjustment degrees defined in the HVC colorimetric system. In accordance with the inputted color adjustment amounts, the computer changes all the parameters stored in the look up table. The final conversion is then performed with the thus adjusted look up table. This conceivable method can perform an entire process within a shorter period of time because this method does not include the conversion steps between the L*a*b* system and the HVC system.
It is noted, however, that the data amount of the look up table is relatively large. Accordingly, it still takes a relatively long time to change all the parameters in the look up table into newly-adjusted parameters. Every time the user sets his/her desired color adjustment amounts, the computer has to change all the parameters in the look up table. The computer is required to have a relatively large memory area for storing the thus newly-adjusted look up table.
It is therefore, an object of the present invention to overcome the above-described drawbacks, and to provide an improved color conversion method wherein it becomes unnecessary to change the look up table and which can still perform an entire conversion operation within a short period of time.
Another object of the present invention is to provide an improved color conversion device which can perform the improved color conversion method.
In order to attain these and other objects, the present invention provides a color converting method for converting color data from a first colorimetric system into a second colorimetric system, the method comprising the steps of: inputting a desired color adjustment amount; changing, dependently on the inputted color adjustment amount, a characteristic value indicative of relationship between first parameters defined in a first colorimetric system and second parameters defined in a second colorimetric system stored in a predetermined table; and converting color data, defined in the first colorimetric system, into color data in the second colorimetric system, in accordance with the table and the changed characteristic value.
According to another aspect, the present invention provides a color conversion device for converting color data defined in a first colorimetric system into color data in a second colorimetric system, the device comprising: color data input means for inputting color data defined in a first colorimetric system; adjustment input means for inputting a desired color adjustment amount; table storing means for storing a predetermined table in which first parameters defined in the first colorimetric system and second parameters defined in a second colorimetric system are stored in correspondence with each other at a predetermined relationship; characteristic value storing means for storing a predetermined characteristic value indicative of a relationship between the first and second parameters stored in the table; changing means for changing the predetermined characteristic value based on the inputted color adjustment amount; and conversion means for converting the inputted color data from the first colorimetric system to the second colorimetric system based on both the table and the changed characteristic value.
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Brother Kogyo Kabushiki Kaisha
Good-Johnson Motilewa
Oliff & Berridg,e PLC
Powell Mark R.
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