Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-10-30
2004-12-21
Nguyen, Thinh (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S037000
Reexamination Certificate
active
06832824
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to machines and procedures for incremental printing or copying of text or graphics on printing media such as paper, transparency stock, or other glossy media; and more particularly to a machine and method that constructs—under direct computer control—text or images from individual colorant spots created on a printing medium, in a two-dimensional pixel array. For purposes of this document, by the phrases “incremental printing” and “incremental printer” it is meant to encompass all printers and copiers that perform computer-controlled construction of images by small increments.
Incremental printers thereby form images either directly on the print medium—as in the case of ink-jet, dot-matrix or wax-transfer systems—or on an electrostatically charged drum just before transfer to the medium as in the case of laser printers. Thus by “incremental printer” it is meant to exclude printing presses, which form a whole image from a previously prepared master negative or plate. The invention relates most particularly to hardware for use in calibration to optimize color effects, prevent overinking, and perform other functions directly related to image quality.
BACKGROUND OF THE INVENTION
1. Introduction
Printer users have a need for accurate color reproduction, for a very great variety of reasons. Many businesses depend on color for their image recognition and identification. Even the optimum maintenance of trademark rights in some situations can depend upon accurate presentation of the color portions of a mark.
Much more familiar motivations include the desire of hobby and home users to see natural flesh tones in printed reproductions of photographs, and to see colors in graphic designs that match their originals.
Colors machine-printed as arrays of ink dots are affected by a wide range of factors including temperature, humidity, ink viscosity, absorption by paper or other printing media, writing-mechanism wear, and many others. All these factors cause variation in inkdrop volume and thereby dot size on the media.
Efforts to analyze such factors and take them into account typically center about optical measurements of one type or another. These may be made at the factory for a complete line of printers, or made in the field for a single production unit—or skilfully devised combinations of these alternatives.
U.S. Pat. No. 5,537,516 of Sherman et al. offers (columns 2 and 3) a brief but helpful orientation as to the differences between measurements respectively made with a densitometer, a colorimeter and a scanner. Sherman also offers several proposals for using a scanner to calibrate a printer.
These proposals include various regimes of combined factory and field measurements, linked through specially constructed standard or customized target test patterns. Sherman also teaches defocusing or diffusing the targets to minimize adverse characteristics of scanners.
Although color accuracy of chromatic colors is of enormous importance commercially, for purposes of the present document (including the claims) the word “color” is used to encompass both chromatic and nonchromatic colors. Similarly the term “colorant” is used to encompass both chromatic and nonchromatic colorants.
General phrases such as “color measurement” are used to encompass both densitometry and colorimetry. In particular they encompass measurement of exclusively nonchromatic colors, as well as measurement of chromatic colors either alone or mixed with nonchromatic colors.
U.S. Pat. No. 5,272,518 of Vincent, assigned to the Hewlett Packard Company, describes a small handheld calorimeter for use in calibrating incremental printers and other image-related devices associated with computers. To exclude ambient light the device includes a hood that is meant to be manually brought down directly against a calibration test pattern.
Vincent at one point may seem to suggest too that a calorimeter such as his invention may be incorporated into the printer or other device to facilitate autocalibration; however, Vincent does not teach how to implement any such suggestion. In addition, Vincent teaches extensively the theoretical foundations of calibration for image-related devices of the type under consideration here.
It is known in handheld calorimeters and the like to use a gas-arc flashlamp, particularly for the benefits of the broad, relatively flat and somewhat controllable spectral emission of such a lamp. Neither the Vincent system, however, nor any known system of light measurement used in a printer, employs such a lamp.
2. Densitometry
For a given set of inks with known spectral values and a known printing medium, one can calculate a color table that maps a desired color in some color space into a set of values to be printed on the media. These values may be given as a percentage of the medium to cover with each of the inks.
A color table is created for each unique combination of ink and printing medium. To compensate for dot-size variation, the color table should be adjusted or calibrated for the current operating conditions.
One way to accomplish this is through a density measurement for each of the inks used, by first printing a series of swatches at various nominal (intended) densities, then measuring the actual density of the samples. What is measured is the fraction of the medium that is covered by the dots, and in most densitometer methodologies the actual color does not matter.
This process depends on the composition of the ink remaining constant, and likewise the spectral characteristics of the medium. Typically these tables are computed during development of a printer, and stored permanently in the printer—where they can be changed only by replacing the software storage component, typically a read-only memory (ROM) circuit board.
Through proper use of such measurements, it is possible to compensate for all the factors that affect dot size—thus making the color output of the printer more consistent—but the calibration is valid only for a current set of environmental conditions, inks and media. A change in temperature therefore would require a new calibration.
Later calibration is not possible with a different medium for which no color table exists. Also it is assumed that the colors do not interact—each ink is linearized independently of the others, in a one-dimensional calibration.
3. Colorimetry
To extend the calibration process to be more general, it is necessary to measure actual spectral values of ink at different levels of coverage on the desired medium. This accounts for interaction of inks and media, and makes the process independent of foreknowledge of ink and medium spectral characteristics.
In this process there is an interaction between the ink colors, because of the overlap between the spectra of the different inks. Although an ink is treated as contributing color in a single spectral band, essentially every ink actually has components in more than one part of the spectrum.
This is a multidimensional calibration. This process creates custom color tables for current ambient conditions and arbitary ink and media. In addition, such measurements in effect linearize the first type of calibration mentioned above.
4. Methods
At least two methodologies are known heretofore for calibration of incremental color printers:
(a) Off-line calibration—In this approach a user operates a spectrally discriminating optical sensing device, i. e. a calorimeter, to make measurements of a test pattern. The calorimeter readings are taken independently of the printer operation.
First the printer must be used to print the test pattern onto the desired medium. Modernly this process is controlled by an application program in a host computer or in an onboard microprocessor that is part of the printer itself. The pattern usually includes many color patches, typically between fifty and several hundred.
Then the user must operate a calorimeter—such as for example a small unit sometimes called a “color mouse”. (The term “color mouse” appears to be related to, but not one of, the trademark
Baker Thomas H.
Canal Josep Miguel
Moroney Nathan M.
Hewlett--Packard Development Company, L.P.
Huffman Julian D.
Lippman Peter I.
Nguyen Thinh
LandOfFree
Color-calibration sensor system for incremental printing does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Color-calibration sensor system for incremental printing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Color-calibration sensor system for incremental printing will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3274556