Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1998-09-09
2003-04-01
Grant, II, Jerome (Department: 2624)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S001500
Reexamination Certificate
active
06542258
ABSTRACT:
MICROFICHE APPENDIX
The appendix of seventy-two frames is a program definition document for firmware and software discussed herein. The second and third frames are a table of contents.
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.
The invention advances the art of both printmasks and halftoning or so-called “dither” masks. For the sake of simplicity the invention will be described primarily with respect to printmasks, but it is to be understood that in many cases this term equivalently encompasses halftoning or dither masks. Without further elaboration, a person of common skill in the art will readily understand when such equivalency is present and when it is not.
The invention employs printmode and dithering techniques to optimize image quality vs. operating time and data-storage costs, and is particularly but not exclusively beneficial in scanning thermal-inkjet machines and methods. For definiteness the discussion in this document will refer to inkdrops, coalescence and other features and phenomena associated with inkjet printers; however, it is to be understood that equivalent characteristics of other printer types are encompassed within that discussion.
BACKGROUND OF THE INVENTION
Inkjet printers, and certain other types of incremental printers, are inherently capable of a very limited number of tonal levels. To achieve a moderate range of tonal variations in such printers, halftoning or dither masks are used to transform or “render” input variations in intensity in the form of spatially varying densities.
The eye integrates the spatial variations to, in effect, reconstruct a semblance of continuous-tone capability. The halftoning process, in incremental printers, sometimes employs masks known as dither masks or halftone masks, and the preparation of these masks is a matter of importance in terms of preparation time, data storage, and final output image quality.
To achieve vivid colors in inkjet printing with aqueous inks, and to substantially fill the white space between addressable pixel locations, ample quantities of ink must be deposited. Doing so, however, requires subsequent removal of the water base—by evaporation (and, for some printing media, absorption)—and this drying step can be unduly time consuming.
In addition, if a large amount of ink is put down all at substantially the same time, within each section of an image, related adverse bulk-colorant effects arise. These include so-called “coalescence” and “bleed” of one color into another (particularly noticeable at color boundaries that should be sharp), “blocking” or offset of colorant in one printed image onto the back of an adjacent sheet with consequent sticking of the two sheets together (or of one sheet to pieces of the apparatus or to slipcovers used to protect the imaged sheet), and “cockle” or puckering of the printing medium. Various techniques, discussed below, are known for use together to moderate these adverse drying-time effects and bulk- or gross-colorant effects.
(a) Prior Heat-application Techniques
Among these techniques is heating the inked medium to accelerate evaporation of the water base or carrier. Heating, however, has limitations of its own; and in turn creates other difficulties due to heat-induced deformation of the printing medium.
Glossy stock warps severely in response to heat, and transparencies too can tolerate somewhat less heating than ordinary paper. Accordingly, heating has provided only limited improvement of drying characteristics for these plastic media.
As to paper, the application of heat and ink causes dimensional changes that affect the quality of the image or graphic. Specifically, it has been found preferable to precondition the paper by application of heat before contact of the ink; if preheating is not provided, so-called “end-of-page handoff” quality defects occur—this defect takes the form of a straight image-discontinuity band formed across the bottom of each page when the page bottom is released.
Preheating, however, causes loss of moisture content and resultant shrinking of the paper fibers. To maintain the paper dimensions under these circumstances the paper may be held in tension, but this too induces still other types of image defects requiring yet further innovation to overcome them.
(b) Printmode Techniques
Another useful technique is laying down in each pass of the pen only a fraction of the total ink required in each section of the image—so that any areas left white in each pass are filled in by one or more later passes. This tends to control bleed, blocking and cockle by reducing the amount of liquid that is all on the page at any given time, and also may facilitate shortening of drying time.
The specific partial-inking pattern employed in each pass, and the way in which these different patterns add up to a single fully inked image, is known as a “print mode”. Heretofore most efforts in design of print modes have focused upon difficulties introduced by regularity or repetition of patterns previously regarded as inherent in printmode techniques.
For example, some print modes such as square or rectangular checkerboard-like patterns tend to create objectionable moire effects when frequencies or harmonics generated within the patterns are close to the frequencies or harmonics of interacting subsystems. Such interfering frequencies may arise in dithering subsystems sometimes used to help control the paper advance or the pen speed.
More recently, however, attention has turned to use of random or more-properly “randomized” patterns. These are introduced in the coowned patent documents listed earlier and will be discussed in greater detail shortly.
(c) Known Technology of Printmodes: General Introduction
The pattern used in printing each nozzle section is known as the “printmode mask” or “printmask”. The term “printmode” is more general, usually encompassing a description of a mask, the number of passes required to reach full density and the number of drops per pixel defining “full density”.
One particularly simple way to divide up a desired amount of ink into more than one pen pass is the checkerboard pattern mentioned above: every other pixel location is printed on one pass, and then the blanks are filled in on the next pass. This pioneering strategy was quickly recognized as inadequate for highly demanding competitive modern printers because of ink coalescence along diagonals, inability to correct moire phenomena, and also the appearance of so-called “banding” or evident boundaries between abutting ink swaths.
To reduce such horizontal banding problems (and sometimes minimize the moire patterns) discussed above, a print mode may be constructed so that the paper advances between each initial-swath scan of the pen and the corresponding fill-swath scan or scans. In fact this can be done in such a way that each pen scan functions in part as an initial-swath scan (for one portion of the printing medium) and in part as a fill-swath scan.
This technique tends to distribute rather than accumulate print-mechanism error that is impossible or expensive to reduce. The result is to minimize the conspicuousness of—or, in simpler terms, to hide—the error at minimal cost.
All of these strategies are now well known and have been elaborated to a very great extent, including the use of space- and sweep-rotated printmode masks, autorotating printmode masks (in which rotation occurs even though the pen pattern is consistent over the whole pen array and is never changed between passes), and steeply an
Bonner Matt
Garcia Joan Manel
Hickman Mark
Serra Josep Maria
Ashen & Lippman
Grant II Jerome
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