Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-03-31
2001-03-27
Rogers, Scott (Department: 2724)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S451000, C358S535000, C382S270000, C382S275000
Reexamination Certificate
active
06208431
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the rendering of images in a digital printing process, and more particularly, to methods and devices for eliminating artifacts in multi-cell color levels, including gray levels.
BACKGROUND OF THE INVENTION
Artifacts are printed pixel patterns which appear objectionable for a given solid color area. More specifically, artifacts appear as low frequency patterns in the color level. These patterns make the color level appear as a distinct combination of two or more colors and patterns rather than a uniform single color level. Conversely, artifact-free color levels have fine dot patterns which are difficult to observe.
Artifacts arise from the fact that most display devices such as, for example, printers, do not have enough available color levels to render all the color levels desired for a high quality image. Accordingly, such display devices must employ some type of halftoning to render all of the required color levels. Consequently, some of the halftone patterns employed by such devices for the required color levels include artifacts. The result is often a rendered image which has one or more areas appearing un-natural or “grainy” rather than smooth.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a method of selecting artifact-free color levels, including gray levels, for rendering images is provided. The method includes, for example, the steps of establishing a threshold matrix with a large number of color levels (preferably greater than 256) for each color, then examining at least one color level for artifacts and removing or modifying the color level in the threshold matrix if it has artifacts. The method further includes the steps of examining a range of color levels for artifacts, removing or modifying the color levels from the threshold matrix which have artifacts, and distributing the remaining color levels over a range of color levels from a first color level to a last color level. Once the threshold matrix is defined or optimized, it is then integrated or stored into a printer or display device.
According to another embodiment of the present invention, a method of selecting artifact-free gray levels for rendering images is provided. The method includes the steps of, for example, establishing a threshold matrix by examining at least one gray level for an artifact and if the gray level has an artifact, identifying the gray level for removal by modifying the threshold matrix. The step of examining at least one gray level for an artifact includes the step of digitally acquiring the gray level, performing a two dimensional Fourier transform to determine the spectral components of the gray level, and comparing at least one spectral component to a visual sensitivity threshold function to determine if the gray level has artifacts.
According to another embodiment of the present invention, a method of selecting artifact-free gray levels by employing an optical density measurement is provided. The method includes, for example, the steps of establishing a threshold matrix by examining the optical density power spectrum of at least one gray level for an artifact and if the gray level has an artifact, identifying the gray level for removal or modification in the threshold matrix. The step of examining the optical density power spectrum of at least one gray level for an artifact includes the step of optically scanning at least one gray level along at least a first dimensional component to arrive at a gray level optical density power spectrum. A Fourier analysis of the digital gray level image is performed to determine the gray level optical density power spectrum and spectral components. The spectral components of the gray level optical density power spectrum are compared to a visual sensitivity power spectrum for determining whether artifacts are present.
In all embodiments, color levels are flagged as either having artifacts or as being artifact-free. Once all of the color levels are examined and flagged, one of several color level removal procedures may be implemented to generate an artifact-free threshold matrix or an optimized threshold matrix.
It is, therefore, an advantage of the present invention to provide for the high quality rendering of images.
It is another advantage of the present invention to provide a method of generating artifact-free threshold matrices for display devices.
It is a further advantage of this invention to provide artifact-free multi-cell halftone threshold matrices.
REFERENCES:
patent: 4653926 (1987-03-01), Fukui
patent: 5406379 (1995-04-01), Kingsley et al.
patent: 5442461 (1995-08-01), Levien
patent: 5452403 (1995-09-01), Miller
patent: 5463720 (1995-10-01), Granger
patent: 5553200 (1996-09-01), Accad
patent: 5737452 (1998-04-01), Schiller
patent: 5854882 (1998-12-01), Wang
“Visual Contrast Sensitivity”, By: D.H. Kelly, published in 1977 (Optica Acta 24, No. 2, pp. 107-129.
“Optical and Retinal Factors Affecting Visual Resolution”, By: F. W. Campbell and D. G. Green, published in J. Physiol. 181, pp. 576-593 (1965).
“Periodic image artifacts from continuous-tone laser scanner”, published in Applied Optics, vol. 25, No. 21, pp. 3880-3884, Nov. 1986.
“A continuous-Tone Laser Color Printer”, Journal of Imaging Technology, vol. 14, No. 3, Jun. 1988, pp. 18-88.
“The human visual system: A guide for the display technologist”, By: B. E. Rogowitz, Proceedings of the SED, vol. 24/3, 1983, pp. 235-252.
“Economic Display Design”, By: C. Calson, Information Display, vol. 4, No. 5, May 1988, pp. 16-19.
Lee Ho Chong
Stanich Mikel J.
Thompson Gerhard R.
Zable Jack L.
Daugherty Patrick J.
Driggs Lucas Brubaker & Hogg Co. L.P.A.
International Business Machines - Corporation
Rogers Scott
LandOfFree
Method of eliminating artifacts in display devices does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of eliminating artifacts in display devices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of eliminating artifacts in display devices will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2461886