Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-09-03
2003-07-01
Tran, Huan (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C358S001900
Reexamination Certificate
active
06585340
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 construct—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” I mean 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 inkjet, dot-matrix or wax-transfer systems—or on an electro-statically charged drum just before transfer to the medium as in the case of laser printers. Thus by “incremental printer” I mean to exclude printing presses, which form a whole image from a previously prepared master negative or plate. The invention employs calibration techniques to optimize color quality and to prevent overinking.
BACKGROUND OF THE INVENTION
The invention deals with two well-known problems of computer-controlled incremental printers: color quality, and overinking. Color quality will be discussed first.
Reproduction of colors in inkjet printers is greatly affected by factors such as the volume of ink delivered, the type of printing medium, the environmental conditions, and the spatial and temporal rules used to place the colorant on the medium.
In combination, these factors result in a final color rendition that may be very different from what is specified by the computer application. This undesirable result can be further classified into two types of reproduction: lack of accuracy and poor consistency.
By “accuracy” I mean the ability of the printer to print the exact color that is requested by the application. By “consistency” I mean the ability of a population of printers to print always the same color for a given color specification received from the application.
While there are well-known methods to improve color accuracy (usually by providing a color dictionary or color map), color consistency is far more difficult. This is due to the occurrence of factors that vary in a wide range and cannot be predicted at the time of building such color maps.
(a) Inconsistent color—Two types of solutions have been used heretofore to reduce color-reproduction error due to poor consistency. The more-widely used method creates a so-called “calibration profile” (similar to the color maps mentioned above) that remains valid as long as all the above-mentioned environmental and operational factors remain constant.
Preparing such a calibration profile or color map is time consuming, because many color patches must be printed and measured. It is also relatively costly, because it uses a significant quantity of the final ink and printing media—which are expensive in some cases.
It is well worth the effort and cost to prepare such a profile or map once, at the factory, for an entire printer product line, and to ship such a generic profile with each printer produced. This approach, however, has important limitations.
First, such a map preestablished at the factory, if generic to a product line, is inaccurate at the outset for many or most of the printers in the line. Second and more important, even if prepared for each individual printer, a map becomes obsolete whenever any of the printheads is replaced and whenever environmental or operational conditions change.
Third, setting up a printer to automatically make a complete color map for itself in the field—that is, after shipment to final users and perhaps even after each change of printhead, or of environmental parameters—is generally unacceptable because of the great time consumption and cost mentioned above. The present market is so highly competitive and demanding as to make the delay and cost alone appear prohibitive.
A known alternative to the use of complete maps or profiles consists of automatically printing—in the field—a much smaller number of color patches with each of the printheads, and automatically measuring them with an optical sensor in the printer. Results of these measurements are then incorporated into so-called “transfer functions”, one for each printhead, which reconcile the expected and measured values.
The transfer functions are then applied, immediately before printing, to color data provided by the application. This second method is far faster and less costly than building complete color maps, but still takes several minutes and still wastes printing medium and ink.
Furthermore, as with the first method, the calculated correction rapidly becomes obsolete with changes in environmental or operating conditions. As a consequence, the process must be repeated very often if the desired consistency in color reproduction is to be maintained. Even with these burdens, the transfer-function approach is less complete than the use of calibration profiles, and therefore inferior in terms of final image quality.
Some prior systems are believed to have included an automatically followed protocol for deciding when to calibrate, for instance when an operator commands it or when an inkjet pen or laser toner cartridge is changed, or when the printing medium is changed. Even with such automatic procedures—and an optical sensor built into the printer so that the user does not have to actively participate in performance of the map-making—delay and cost in the present competitive market greatly handicap the transfer-function approach too.
Representative of the second (transfer function) approach is U. S. Pat. No. 5,107,332 of Chan. He teaches use of automatically, continuously field-maintained transfer functions to “continuously update an initial full scale look up table which was initially prepared from a full scale color gamut.”
It is not completely clear what Chan means by “continuously”, since it would not appear practical to implement that description literally while at the same time printing a desired output image. Presumably his invention instead makes its small test patterns automatically between image printouts or perhaps once a day, or every time a certain number of images has been printed.
It is not my intention to criticize the Chan system, since it undoubtedly functions very well and serves an excellent purpose. As can be seen, however, it does leave some room for further improvement.
Of particular interest are two printer-control languages that have previously been created or adapted for Hewlett Packard (HP) inkjet printers, and particularly large printer/plotters. One of these languages was developed by HP and is known as “HP-GL/2”; the other, developed by the Adobe company, is called “PostScript®”. These languages heretofore have remained subject to undesirable print-quality inconsistencies, as discussed above, arising from environmental and operational variations.
The PostScript system has historically employed a transfer-function approach. HP-GL/2 has not.
For printing color images, the PostScript system enables a user to define such functions for whatever purpose the user wishes. A typical usage is for linearization of each ink individually—or to linearize a display device with respect to a scanner, or as between two different display devices. Any such defined transfer function is applied by PostScript to the desired image data—after those data have been interpreted using a principal color calibration profile that nominally interfaces a known image-data source with a known printer.
(b) Inconsistent ink-limiting requirements—The known technique of ink limiting is used to avoid depositing excessive amounts of ink in some special situations, particularly when printing in certain chromatic inks on certain media, such as glossy stock. For example, it appears that particular inkjet inks contain relatively large pigment molecules that are not readily absorbed into the relatively smaller pores of some glossy media.
To achieve vivid colors in
Hewlett--Packard Development Company, L.P.
Huffman Julian D.
Lippman Peter I.
Tran Huan
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