Device independent color controller and method

Details Device independent color controller and method Device independent color controller and method

1998-05-22

2001-05-22

Williams, Kimberly A (Department: 2622)

Facsimile and static presentation processing

Natural color facsimile

Color correction

C358S001900

Reexamination Certificate

active

06236474

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Related Applications
The subject matter of the present application is related to the subject matter of the applications “Automatic Colorant Mixing Method and Apparatus” and “Dynamic Device Independent Image Correction Method and Apparatus” filed by the same assignee, which are incorporated herein by reference.
2. Field of Invention
The present invention relates to controlling the output of a marking device, and in particular, to a device independent color controller and method that uses information detected from a color output image to control individual color separations.
3. Description of Related Art
Customers continue to demand faster, higher quality and more sophisticated marking devices (e.g., printers, copiers, etc.). Additionally, customers demand the ability to reproduce their desired input images to achieve accurate output that does not vary over time (e.g., between pages or when output again at a later time) or among various marking devices (e.g., among various printers on a network, between home and office marking devices, etc.). These considerations are more difficult to achieve with color marking devices because of the greater number of variables involved and the sensitivity of these devices to environmental conditions.
In addition to controlling other variables of the marking device subsystem, controlling the device independent marking device tone reproduction curves (TRCs) for a color marking device would also be desirable. Tone reproduction curves are stored plots of an input parameter value versus an output parameter value. A TRC is a monitonically increasing marking device function in input-output contone space, input-output density space or input-output byte space, or combinations thereof. In other words, a TRC indicates the value of the output parameter for a specific device that must be used to reproduce the input parameter.
It would be desirable to use controlled tone reproduction curves at different steps in the reproduction process. The controlled tone reproduction curve for any one of the marking device color separations would account for the variability in reproducing that color in the marking device.
Moreover, it would be desirable to provide controlled of tone reproduction curves on a real time basis, either between jobs or within a single job, to account for ongoing marking device variability.
SUMMARY OF THE INVENTION
According to a method of the invention, error in an output color of a colored output image in a marking device intended to match a desired image is corrected. The method includes the steps of detecting a current output color in the output image with a color sensing device, determining a difference between the current output color and a corresponding target color under standard conditions and automatically setting a marking device input-output relationship for a next output color based on the difference between the current output color and the corresponding target color under standard conditions to minimize the difference between the next output color and the corresponding target color.
The step of determining preferably includes obtaining the corresponding target color by accessing target color values stored in memory. Obtaining the corresponding target color preferably includes accessing a look-up table. Obtaining the corresponding target color preferably includes accessing a look-up table of target color spectra values.
The marking device input-output relationship is preferably a tone reproduction curve corrected for variability of the marking device. The step of setting preferably includes outputting a corrected tone reproduction curve for at least one of the color separations that the marking device is capable of outputting. Also, the step of determining preferably includes obtaining at least one nominal tone reproduction curve.
The step of determining preferably includes summing the at least one nominal tone reproduction curve and the processed difference between the current output color and the corresponding output color under standard conditions.
The step of determining preferably includes transforming spectra of the current output color from device independent space to control parameter space. The step of determining preferably includes transforming spectra of the target color from device independent space to control parameter space. The step of determining preferably includes calculating an error signal equal to the difference between the current output color and control parameter space and the corresponding target color under standard conditions in control parameter space.
The step of setting preferably includes obtaining a weighted error by multiplying the error signal by a gain matrix. The step of setting preferably includes integrating the weighted error with respect to an iteration number.
The step of determining preferably includes obtaining at least one nominal tone reproduction curve, and the step of setting preferably includes summing the integrated weighted error with the at least one tone reproduction curve to yield a corrected tone reproduction curve as the marking device input-output relationship.
The method preferably includes the step of outputting the marking device input-output relationship to at least one controller operating in a time hierarchical mode. The steps of detecting, determining and setting preferably occur while the marking device is outputting.
An apparatus for correcting error in an output color of a colored output image intended to match a desired image is also disclosed.


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