Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-06-29
2001-12-04
Lee, Cheukfan (Department: 2722)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S523000
Reexamination Certificate
active
06327052
ABSTRACT:
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection, subject to the provisions of 37 C.F.R. § 1.14, to the facsimile reproduction by any one of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
MICROFICHE APPENDIX
This application contains a Microfiche Appendix consisting of two (2) slides and 110 frames.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to post processing color data. More particularly, the present invention pertains to post processing possibly inaccurate color data to generate accurate color data.
2. Description of the Related Art
Processing and printing of color data has become an increasingly important area in both computer engineering and printing technology. Color data can currently be processed and printed on a wide variety of commonly available computer systems. Unfortunately, some computer based printing systems in common use do not provide high quality color prints. Color data printed by these conventional systems frequently have inaccurate color hues and excessive saturation values.
As an aid for understanding the limitations of conventional color data processing, it is desirable to describe here various concepts of color data processing. Color data typically is displayed on raster displays, such as the common cathode ray tube (CRT) monitor. The viewing surface of a raster display includes a rectangular array of picture elements (pixels). Each pixel comprises a smallest area on the display surface that can be assigned independent characteristics, such as color and radiant intensity. In typical displays, each pixel comprises a red R color dot, green G color dot, and blue B color dot, which when activated respectively emit red R, green G, and blue B light. The R, G, and B color dots of a pixel are in close proximity with one another so that light emitted from the color dots appears to mix. Consequently, by selectively varying the intensity of light emitted from each of the three color dots, the pixel can emit a broad range of colors over a broad range of radiant intensity.
To selectively control the appearance of a pixel, a color amount is produced for each color dot of the pixel. The color amounts can be represented in the form (r, g, b), where r controls illumination of the R color dot, g control illumination of the G color dot, and b controls illumination of the B color dot. The color amounts r, g, and b weight the amount of light to be emitted by color dots R, G, and B respectively. Such color amounts (r, g, b) are often referred to as RGB data. The totality of all possible color amounts for a given set of weighted colors forms a color space. Thus, for primary colors R, G, and B, the totality of possible color amounts (r, g, b) forms an RGB color space.
The RGB color space used for a particular display may reflect characteristics of that display. For example, the color amounts (r, g, b) for a CRT monitor typically have been raised by an exponent &ggr;, where &ggr; is referred to a gamma value for the CRT monitor. This exponentiation by &ggr; allows the perceived brightness of the CRT monitor to change in a somewhat linear manner. That is, a fixed magnitude change in a color amount r, g, or b appears to yield the same increase in radiant intensity of R, G, or B light regardless of the magnitudes of the color amounts r, g, and b prior to the change.
Printing of colors described using RGB data is complicated because displayed colors are additive whereas printed colors are subtractive. Displayed colors are additive because when two colors are combined together (added on a display), the result is a third color having a frequency distribution which is approximately the sum of the frequency distributions of the two colors. The third color may also be brighter than the other two colors. Printed colors are subtractive because when a printed color is illuminated with light IL, the printed color absorbs a given frequency distribution FD of the light IL, and appears to have the color of that portion of light IL-FD which is reflected. Thus, a printed color can appear to change colors when the color of an illuminating light is changed. Further, combining two printed colors results in a darker third color.
To print color data, a processor converts color amounts for each pixel to colorant amounts for each pixel. Typically, the colorant amounts have the form (c, m, y, k) and respectively weight amounts of cyan (C), magenta (M), yellow (Y) and black (K) colorants. Such colorants are affixed to a printable medium to produce printed colors. The totality of all colorant amounts for a given set of colorants comprises a colorant space. C, M, Y, K are referred to as primary colorants of a CMYK colorant space. Usually, a distinct set of colorant amounts (c, m, y, k) is used for printing each pixel.
The colorant amounts (c, m, y, k) determined by some conventional systems are inaccurate. For example, when conversion from color amounts (r, g, b) to colorant amounts (c, m, y, k) is accomplished in accordance with the protocol set forth by the POSTSCRIPT® LEVEL 1 Language as specified by ADOBE SYSTEMS, INCORPORATED, printed colorant amounts sometimes look too gray and desaturated, particularly for printing photographic data. Further, the pure colors RGB and colorants CMY are not inverts of one another. Thus, green G displayed a monitor is much lighter than correspondence cyan C plus magenta M on a print. Further, a green G plus blue B color has a light cyan C appearance when displayed on a monitor but prints as a much darker and somewhat bluer cyan C.
It can be difficult to avoid such inaccurate color conversions when managing color data. For example, in CORELDRAW® from COREL, retaining the original RGB data typically cannot be accomplished, and the user conventionally must print inaccurate colorant amounts determined according to the POSTSCRIPT® LEVEL 1 conversion protocol, or use the color management system in CORELDRAW® which may not be appropriate for a given printer.
There is thus a continuing need for an improved system and method for converting between color data formats. Such system and method should be compatible with conventional systems, and preferably should be able to convert possibly inaccurate colorant amounts (c, m, y, k) obtained with conventional systems to accurate colorant amounts for printing color data. Further, such system and method should preferably be easy to operate by end users.
SUMMARY OF THE INVENTION
According to the present invention, a color data processing system and color data processing method are provided for processing and printing color data. Computer readable media and data structures for implementing and performing such color data processing system and method are also provided in accordance with the present invention.
In accordance with a first aspect of the present inventions the color data processing system post processes an output signal which was produced from an input signal according to a first signal processing protocol. For example, the first signal processing protocol may be an inaccurate color to colorant conversion protocol. The color data processing system includes first and second color data processing subsystems. The first color data processing subsystem receives the output signal and produces an intermediate signal according to a second signal processing protocol. The second signal processing protocol preferably substantially inverts the first signal processing protocol. Thus, if the first signal processing protocol converts original color amounts to inaccurate colorant amounts, then preferably, the intermediate signal substantially represents the original color amount within limits of gamut. The second color data processing subsystem receives the intermediate signal from the first color data processing subsystem, and produces a final signal according to a third signal processing protocol.
Electronics For Imaging, Inc.
Glenn Michael A.
Lee Cheukfan
LandOfFree
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