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| Determining an alignment estimation between two (fingerprint) images |
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Inkjet printing: mask-rotation-only at page extremes; multipass modes for quality and throughput on plastic media
| Details |
Inventors: Cleveland, Lance; Hall, Corrina A. E.; Hilliard, William C.;
Assignee: Hewlett-Packard Company (Palo Alto, CA)
Primary Examiner: Barlow, Jr.; John E.
Assistant Examiner:
Attorney, Agent or Firm:
Images are printed using marks formed in pixel arrays by a scanning print head. For transparent and glossy media, with poor absorbance, drying is enhanced by a multipass (preferably six-pass) print mode in which the total number of ink drops or spots is allocated among correspondingly multiple masks, though some may be duplicates. To further hasten drying, heat is applied--through the medium, from the opposite side as that on which ink is deposited--but the amount of heat is strictly moderated, particularly for nontransparent glossy media, to accommodate the hypersensitivity of these media to heat-induced warping. Heating for glossy media is preferably restricted to about one-third the power used for drying plain paper. Convective drying too is promoted, by operating a fan over the printed image. Certain special techniques well-suited for plain-paper printing have been found undesirable for use with plastic media; these techniques include so-called "resolution-enhanced technology", bidirectional printing (particularly of black), and optical-density controlled printing speed. At top and bottom of each page or sheet of printing medium, where it is undesirable to operate with the pen partly off the edge of the sheet, and where also the printing medium is constrained from only one direction rather than being held taut beneath the pen, the print mask is rotated while the printing medium is held stationary--thereby entirely avoiding reliance upon accuracy of print-medium advance. |
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 1.
STEEPER DIAGONAL The print mask of the present invention forms diagonal lines that are skewed more toward the printing-medium advance direction than those of prior-art masks.
This is beneficial because in this direction there tends to be more error due to paper advancement and paper shrinkage.
In at least some commercial printers the above-mentioned largest permissible pattern, within the basic architectural constraint of the printing apparatus that is in use, is rectangular and vertically oriented--in other words, longer in the direction of the printing-medium advance.
In this case, preferably the diagonals formed by the invention approximate the longest diagonal line possible within that vertically oriented largest permissible pattern.
Within the previously mentioned eight-by-four pattern constraint of one Hewlett Packard printer, a particularly desirable print mode creates the following eight-by-three pattern cell or "base pattern".
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xoo
xoo
xoo
oxo base pattern
oxo or cell
oxo
oox
oox
012 .
rarw.
column number within the base pattern
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The resulting pattern still appears as diagonal lines when printed on the page, but now they are angled at roughly seventy degrees from the pen-scan axis--or, as it may be called, the "horizontal".
The pattern alignment is now more vertical than horizontal, and this more effectively camouflages dot dislocation due to error in printing-medium shrinkage or advance.
The diagram above shows that within the eight-row cell or base pattern there are three rows of the repeating subpattern "xoo" and three of the subpattern "oxo", but only two of the bottom subpattern "oox".
This asymmetry is without substantive consequence, or may possibly aid slightly in suppressing undesirable moire patterns and the like due to excessively regular cell structure.
The slope of the diagonal is probably best defined as the angle from any point (for example, the first dot) along the repeating unit to the same point on the next diagonally adjacent repeating unit
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Image Analysis 
