EP0889640A2
Expired / Lapsed
EP
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Sum and difference error diffusion
Assignee: Xerox Corp
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Filing: 1998-06-23
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Granted: —
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Expires: 2018-06-23
Abstract
Abstract A vector error diffusion system (16,18) for quantizing pixel value in color images, which initially determines whether any pixel should be white or colored, and subsequently determines for a CMYK printer (20) whether the pixel should be a primary color, a secondary color or black.
Inventors
- 👤 Steven J. Harrington
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 12:03
CPC Classifications
B; B41; B41B; B41B15/00; H; H04; H04N; H04N1/00; H04N1/46; H04N1/52
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
181 words
A halftoning processor for preparing documents for
printing at a color printer, said documents defined by
plural separations, each separation including a set of
color separation image signals describing optical density
therein with c density levels, for a destination color
printer rendering density with d density levels, the
processor comprising: a separation signal input for receiving separation
image signals corresponding to a selected discrete area of
the document; means for summing said separation image signals; comparison means for comparing said separation image
signals with each other; a separation counting logic means for using said sum
to identify a number of separation signals with d density
levels to be printed at the discrete area; a color determination logic means, responsive to said
separation counting logic means and said comparison means
to generate print signals whereby specific colorants are
deposited at said discrete area; and an error distribution means, determining any
differences between said received separation image signals
and said print signals, and adding the determined
difference, if any, to image signals corresponding to areas
adjacent to said discrete area, to be processed.
Claim 2
Dependent Claim
17 words
A processor according to claim 1, wherein the summing
and comparison means are provided by respective circuits.
Claim 3
Dependent Claim
163 words
A halftoning processor (16,18) for receiving groups of
separation signals defining optical density for
corresponding discrete areas of a document at c levels in
each separation, the processor including: a first calculating arrangement which receives as
inputs the groups of separation signals, for determining
the number of image signals that should be printed for said
discrete area of the document, a second calculating arrangement, responsive to said
determined number of image signals that should be printed,
and the values of the separation image signals, for
determining which printer colorants should be deposited at
said discrete area of the document, and generating print
signals responsive thereto, an error distribution arrangement, for determining any
differences between said received image signals and said
print signals, and adding the determined difference, if
any, to image signals corresponding to areas adjacent to
said discrete area, to be processed; and, an image processor for directing signals processed at
said halftone processor to a printer to print said
halftoned image.
Claim 4
Dependent Claim
55 words
A processor according to claim 3, wherein said first
calculating arrangement includes: a summing means for summing the receiving separation
signals; and a thresholding means for comparing sums to a set of
separation thresholds, said comparison identifying how many
separations should be printed for each discrete location,
and for producing an output signal indicative thereof.
Claim 5
Dependent Claim
47 words
A processor according to claim 3 or claim 4, wherein
said second calculating arrangement includes: means for determining any differences between
separation image signals directed thereto; and means for comparing differences to a color
determination threshold and for producing an output of
indicating colors to be printed.
Claim 6
Dependent Claim
52 words
A processor according to any of claims 3 to 5, wherein
said second calculating arrangement includes: means for determining any differences between
separation image signals directed thereto; and means for selecting thresholds responsive to said
first circuit determination, for comparing differences to
a color determination threshold and outputting printer
signals thereby derived.
Claim 7
Dependent Claim
45 words
A processor according to any of the preceding claims,
wherein said error distribution means determines
differences between said received image signals and said
print signals, as a function of the sum of separation
signals, and as a function of the differences between
selected separation signals.
Claim 8
Dependent Claim
90 words
A printing system, including a processor preparing
documents for printing at a color printer, said documents
defined by plural separations, each separation including a
set of color separation image signals describing optical
density therein with c density levels, for a destination
color printer rendering density with d density levels, the
system comprising: a color printer (20); a source (10) of separation image signals representing
optical density within the separation at one of c levels,
for a discrete area therein; and a halftoning processor
according to any of the preceding claims.
Claim 9
Independent Claim
157 words
A method of halftoning documents preparatory to
printing at a color printer said documents defined by
plural separations, each separation including a set of
color separation image signals describing optical density
therein with c density levels, for a destination color
printer rendering density with d density levels, the method
comprising: receiving separation image signals corresponding to a
selected discrete area of the document; summing said separation images signals for a discrete
location of the document; using said sum to identify a number of separation
signals with d density levels to be printed at the discrete
area; comparing said separation image signals with each
other; responsive to said summing and said comparison
generating print signals whereby specific colorants are
deposited at said discrete area; determining any differences between said received
separation image signals and said print signals, and adding
the determined difference, if any, to image signals
corresponding to areas adjacent to said discrete area, to
be processed.
Claim 10
Dependent Claim
60 words
A method according to claim 9, wherein for separation
image signals given as C, M, Y, said comparing said
separation image signals with each other includes the
substeps of: determining u= M-Y; determining t=C-M; determining t+u comparing the results of each determination with
others of said determinations, and generating print signals
indicative of colorants to deposit at said discrete area.
Claim 11
Dependent Claim
78 words
A method according to claim 9, wherein the separation
image signals are given as C, M, Y, and including the
substeps of: determining s=M+C+Y determining u=M+Y determining t=C-M determining u+t determining said differences between said received
separation image signals and said print signals as a
function of s, u, t and u+t, and adding the determined
difference, if any, to values of s, u, t, and u+t
corresponding to areas adjacent to said discrete area, to
be processed.
References Cited (Backward Citations)
No citation records indexed.
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