Image analysis – Applications – Document or print quality inspection
Reexamination Certificate
1998-03-09
2001-08-14
Johns, Andrew W. (Department: 2621)
Image analysis
Applications
Document or print quality inspection
C358S406000
Reexamination Certificate
active
06275600
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to measuring image characteristics of printed output from a digital printer.
A digital printer receives electronic digital input data in the form of a bitmap (in which there is one bit per pixel), and outputs a printed sheet. The input data are typically received serially in a raster pattern and are used to control the deposit of toner from a drum to a sheet of paper.
Many factors can cause the print quality of a digital printer to deteriorate over time. Traditionally, assessments of this degradation have been done subjectively, as a user tries to match the printer's image quality with his or her subjective perception of ideal output.
Generally, printed sheets are manually inspected to determine quality. The user generates a test page and judges its quality by mentally recalling the appearance of the test page when the printer was new or last serviced. The user can also compare the test page to samples in a “limits” book, which defines the lower bounds for standard printer output. An actual printed image may have defects such as white pinholes in black areas, smears, or blurry edges. Some defects may be acceptable and some may fall below an acceptable quality level. Based on manual inspection, the user rejects printed sheets or makes adjustments to the printer.
A technician performing preventive maintenance may obtain readings of the print density uniformity by using a densitometer, which measures light reflected from a page. These readings only partially correlate with human judgments of print quality. Therefore, unless there is a dramatic shift in quality, or a noticeable defect such as streaking, users have difficulty detecting subtle or gradual changes in quality. With color output, detecting changes is even more difficult since the eye is poor at identifying absolute colors.
SUMMARY OF THE INVENTION
In one aspect, the invention features, in general, measuring image characteristics of printed output from a digital printer by sending test pattern data to the digital printer, generating a printed image of the test pattern data at the digital printer, scanning the printed image to obtain digital pattern data, and analyzing the digital pattern data of the printed image. The test pattern that is printed includes target objects designed to reveal specific printed image characteristics, and the analysis of the data from scanning the printed image includes the generation of one or more quantitative ratings with respect to printed image characteristics.
In other aspects, the invention features computer programs, print systems, digital printers, test instruments, and services that carry out the method of measuring print image characteristics just described.
Embodiments of the invention may include one or more of the following features. The quantitative ratings can include measurements of the black and white densities, uniformity, edge sharpness, resolution, and positional accuracy of the target objects. The measurements also detect defects, such as streaks and smears. Landmarks in the test pattern are used to correct for scanner error.
One or more quality ratings can be generated from the measurements. Using these ratings, one can automatically monitor and adjust the print image characteristics of a digital printer so that the printer is within allowable margins. For example, one can use the measurements to adjust print engine related parameters such as power and duration of the laser, and charging current. The method is applicable to black and white as well as color printing applications.
Other aspects and advantages of the invention will be apparent from the drawings taken together with the accompanying description.
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Banker Yigal J.
Monks David E.
Phillips Lee E.
Ting David M. T.
i.data International, Inc.
Jacobson & Holman PLLC
Johns Andrew W.
LandOfFree
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