Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
1997-10-30
2001-01-23
Evans, Arthur G. (Department: 2722)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S001100
Reexamination Certificate
active
06178008
ABSTRACT:
MICROFICHE APPENDIX
An Appendix to this document consists of two device-state tabulations and a coversheet, running to a total 138 aggregate frames and representing data for two different printing media. The tabulations are explained at the end of the disclosure portion of this document.
FIELD OF THE INVENTION
This invention relates generally to machines and procedures for printing text or images (whether photo-like pictorial images or commercial-style graphics such as charts, graphs, color bands behind text, etc.) from individual colorant quanta, such as (e. g. in inkjet printing) ink spots, created in a two-dimensional pixel array on a printing medium such as paper, transparency stock, or other glossy media. The invention relates more particularly to preliminary procedures that prepare data assemblages for later use in guiding the operation of a printing machine and method, such as for example an inkjet machine and method, and most particularly to formation of lookup tables that enable such a machine and method to select inkdrop or other colorant combinations quickly, efficiently and ideally. The invention was made for use in printing by error-diffusion techniques.
In most of this document, merely for definiteness and for relative simplicity of language, the invention and its environment are described in terms of inkjet printing, inkdrops etc. It is to be understood, however, that such wording is for convenience and for tutorial purposes only, and that the invention and the appended claims are not thus limited but rather are more generally applicable to other kinds of printing technologies, colorants, and colorant quanta.
DEFINITIONS
For purposes of this document, particularly including the appended claims, the following special meanings are to be understood throughout.
The term “palette” means all available colors which a printing device or system—as actually configured for operation, taking into consideration all inherent limitations and purposefully imposed constraints of hardware, firmware and software—can print in one individual pixel by depositing an inkdrop or combinations of inkdrops in that pixel. (By this definition, there is no such thing as an unavailable color in a machine palette unless two different machines are under consideration at the same time.)
A “drop set” is a one-dimensional combination of primary-color inkdrops (including zero or one drop) that can be deposited in one pixel. In a system which uses inks that are plural different densities or dilutions of a common basic ink color—for instance dark cyan drops and light cyan drops—a drop set may consist of zero or more drops of each of the plural densities or dilutions of that common ink color, e. g. one dark cyan drop plus three light cyan drops.
“Ramp” means a series of drop sets of a common basic ink color that are arranged in a substantially monotonic sequence by some color parameter such as lightness.
A “drop-set combination” is a two- or three-dimensional combination of, respectively, two or more drop sets. For example a particular drop-set combination may consist of two dark cyan drops plus one light cyan drop, plus three dark magenta drops and two yellow drops; or may consist of all those plus a black drop; or may consist of one yellow drop (since magenta, cyan and black drop sets may be zero); or may consist of no drops at all (since each one of three or four different drop sets may be zero); or may consist of four black drops only.
A “device state” is a drop-set combination that has been designated for inclusion in the palette of a certain printing device. (By this definition, there is no such thing as a “prohibited device state”—rather, prohibited drop-set combinations simply are not device states.)
A “color number” is a tag or code number that identifies a particular drop set within a ramp. Our color numbers have a very simple physical meaning:
for basic ink colors in which only one darkness or dilution is used, the color number is simply the number of inkdrops of that color (or for certain purposes a multiple of that number of drops, as will be seen); and
for basic ink colors in which light and dark drops are used together, the color number is the number of light drops plus a selected constant times the number of dark drops.
The constant is nominally equal to the number of light-drop states (e.g. five, including the state “zero”). For certain purposes it is preferable to offset the color-number values by one, so that the range begins with one rather than zero, as will be seen. We have found it preferable to avoid attaching any deeper significance to the color number, although intuitively it may seem appealing to say that, for instance, it represents the number of all light drops that would have the same lightness—subject to an assumption about equivalence between one dark drop and some number of light drops. Since lightness (or darkness) is not truly linear in ink loading, the above-mentioned “physical meaning” of the color number is not quantitative lightness as such, but will be related to lightness empirically. As examples, in a machine that will be allowed to print up to four drops of any ink in any pixel: (1) if only one darkness of yellow ink will be used, a color number for yellow may be any number from zero through four (or if preferred one through five); (2) if two different dilutions of cyan ink will be used, the color number for cyan is defined as nC
D
+C
L
, where the constant n is at least preferably an integer. If we select the constant n=5, then the color number is 5C
D
+C
L
and may take on any value from zero through twenty-four. Again, we advise against the temptation to identify one dark cyan drop 1C
D
as nominally equivalent in lightness to five light cyan drops 5C
L
(i. e., to write 1C
D
≡5C
L
), since any such equivalency is at best only roughly correct very close to one end of a ramp (e. g., for very small color numbers), and fails dramatically elsewhere. Using these examples, a color number of “zero” means no drop of either dilution. Correspondingly a cyan color number of “twenty-four” identifies the maximum allowable pixel load of cyan, namely four drops of dark cyan 4C
D
plus four drops of light cyan 4C
L
—because there are twenty-four possible nonzero combinations of two inks with five states each. (Alternatively the color-number range can be restated or redefined as one through twenty-five if preferred.)
An “index” (plural “indices”) is a one-dimensional color-coordinate value that is used to find an entry in a run-time color lookup table, based upon an input color specification that has been received or generated. For instance in a three-dimensional machine or perceptual space such as a cyan-magenta-yellow space, an index may be an individual C, M, or Y number on a 0-to-255 scale. Thus an index may be one building-block or element of a one-dimensional lookup table, or (if concatenated with other indices, for other color dimensions) a lookup table of more than one dimension. Intuitively an “index” is related to a “color number” in the sense that each represents a point in a one-dimensional color scale, but as a practical matter the two are very different: an index represents a one-dimensional color on a near-continuum that approximates the whole range of possible values along a color axis, and is used at run time during operation of a printer, after lookup table construction is complete—whereas a color number is a uniquely quantized label for a particular closely defined drop set, and is used only early-on in the process of constructing color-lookup tables. In addition the two are used (or are “read”) in opposite directions: the index at run time to help find a drop-set combination by its already-associated color specification, and the color number derived from a drop set to identify the drop set and so facilitate initial association of a color specification.
An “entry” is a triad of respective indices for three color dimensions—for example a triplet of CMY or RGB numbers on a 0-255,0-255,0-255 scale, or a triplet of La*b* numbers in a C
Bockman Francis E.
Li Guo
Evans Arthur G.
Hewlett--Packard Company
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