Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1999-11-29
2004-10-26
Coles, Edward (Department: 2622)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S001100, C358S504000
Reexamination Certificate
active
06809837
ABSTRACT:
FIELD OF THE INVENTION
The subject invention pertains to the art of color management and image/text printing or display systems, and is especially applicable to a method and apparatus wherein a sensor monitors a color print output for on-line construction of an analytical model of printer operation. More particularly, the invention relates to system controls for modeling the printer by implementating an adaptive algorithm for estimation of analytical model parameters based upon processing of a relatively small number of control samples, target colors or other input signals, whereby the model is then useful for calibrating, diagnosing or standardizing operations of the printer.
Color correction and/or control should not be confused with color registration systems and sensors for insuring that colors are positioned properly, printed accurately, superposed correctly and/or adjacent to one another.
BACKGROUND OF THE INVENTION
In today's business and scientific world, color has become essential as a component of communication. Color facilitates the sharing of knowledge and ideas. Companies involved in the development of digital color print engines are continuously looking for ways to improve the total image quality of their products. One of the elements that affects image quality is the ability to consistently produce the same quality image output on a printer from one day to another, from one week to the next, month after month. Colors on a printer tend to drift over time due to ink/toner variations, temperature fluctuations, type of media used, environment, etc. There has been a long felt commercial need for efficiently maintaining print color predictability, particularly as electronic marketing has placed more importance on the accurate representation of merchandise in illustrative print or display media.
Color perception is a psychological and physiological phenomenon that involves three elements: light, object and observer. Color changes as light, medium (i.e., paper, monitor) and observer interact. Color may be perceived differently under different types of lighting. Light sources that affect color include incandescent and fluorescent light. The first makes color seem more red and orange while the second emphasizes green and yellow tones. Different types of media also affect color perception. Paper is a medium that reflects color ink. In other cases the medium can be transmissive or emissive. Transparencies are an example of a transmissive medium while a computer monitor is emissive. The third element in the phenomenon is the observer. Different people may see the same color slightly differently. In order to characterize color image quality, the interaction of these elements must be understood so that when colors are intended to be matched, i.e., monitor to printer, scanner to printer, etc., acceptable appearance results.
For automatic control systems spectral data is often used to represent color perception as a pattern of wavelengths that leave the object before being interpreted by a viewer. Spectral data defines color independent of light and observer influence. A spectrophotometer is a sensing device used to measure spectral data.
There are different ways of representing color. One way color is described consists of the following parameters: hue, lightness and saturation. Hue represents the actual color wavelength (red, blue, etc.), lightness corresponds to the white content while saturation captures the richness or amplitude in color. Another way of describing color uses the three dominant primary colors red, blue and green (RGB). By combining these primary colors, in different intensities, most colors visible to humans can be reproduced. Monitors and scanners use the additive RGB color process. Printers use the subtractive CMYK (cyan, magenta, yellow and black) color process based on light reflected from inks coated on a substrate. The color representations described above fail to reproduce color predictably because they are observer or device dependent.
The functional models presented in this specification use a device independent color space to consistently track a set of target colors. L*, a*, b* are the CIE (Commission Internationale de L'éclairage) color standards utilized in the modeling. L* defines lightness, a* corresponds to the red/green value and b* denotes the amount of yellow/blue.
On-line model prediction is also known as “system identification” in automatic controls literature. It is the terminology used for the process of characterizing a given control system. Characterization of the system can be done in two ways; non-parametric and parametric. In non-parametric system identification, the profile of the device can be measured by printing specific target colors as specified by the known standards. This profile is used as it is (without constructing any model of the device) while making rendering decisions/viewing of the customer colors on the monitor. This is one time measurement and does not use the historical information to construct any model. Whereas in the parametric system identification, predetermined target colors can be printed as chronological jobs in the banner sheet/header sheet or else the target colors can be extracted from the customer image and measured either by measuring straight from the output image or by rendering subset of customer colors as target color patches in banner or header page. (c.f. copending Xerox application D/99511Q1—L. K. Mestha, inventor, for a control system using dual mode banner color test sheets, herein incorporated by reference.) Using the target colors and their measured counterparts, parameters of the model are adjusted on-line during each measurement. The intention in the parametric system identification is to adjust the parameters of the model and refine it over time by using past and present color data so that the model is what customers can use in their desktops. If such models can be incorporated on the smart color sensor, then the model can be exported to customer workstations.
As business and scientific environments continue to require increasingly complex printing capabilities, and especially more consistent and accurate color matching outputs, there is a continuing need for improved on-line modeling and calibrating of color printing devices. Prior systems which have suggested color modeling (c.f., U.S. Pat. No. 5,612,902 to Stokes) have been unable to recursively converge the model parameters continuously and efficiently. Current needs are better served with analytical model processing in a way that accurate parameters of a parametric model can be quickly identified through a recursive computation scheme. In a network printing environment such a need is particularly apparent for multiple prints which can come from different sources to different printers all networked to one another. Multiple printers could be of the same or different color marking technologies/colorants/materials linked to the same or different color gamuts. The multiple printer outputs being compared could even come from different types of printers, such as black and white, highlight color and process color printers. The principal problems exist when all of the prints from these different types of printers will not match or even be consistent from day-to-day. The problem domain grows by several orders of magnitude when the images are viewed under different lighting sources/viewing angles and are printed on different paper with non-optimum originals. Color differences produced on documents could also be due to stochastic errors on the images as they are produced by the devices of varying types, technology and media.
The subject invention is particularly useful to provide solutions to the foregoing color problems for a wide range of color workflow practices and particularly in customer environments with complex printing requirements. Printing and product enhancements are provided that would enable customers to manipulate color documents on a screen before even printing/displaying an output on different output devices in way
Mestha Lingappa K.
Ramirez Olga Y.
Coles Edward
Fay Sharpe Fagan Minnich & McKee LLP
Sanbet Zebene
Xerox Corporation
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