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Claims  |
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We claim:
1. In a desktop publishing application program for operating on a
publication comprising a first page object and a second page object, the
first page object having a higher Z-order than the second page object, a
method for trapping the first page object against the second page object
comprising the steps of:
decomposing the first page object into one or more first page object
components;
creating a first trap source list comprising one or more first trap
candidate segments from the first page object components, the trap
candidate segments comprising exposed edges of the first page object
components that intersect or abut the second page object;
for each of the first trap candidate segments in the first trap source
list:
detecting whether a potential adjacency trapping situation exists between
the first trap candidate segment and the second page object,
in response to detecting the potential adjacency trapping situation,
performing adjacency trapping between the first trap candidate segment and
the second page object to create a trap segment and to remove from the
first trap source list any portion of the first trap candidate segment
that maps to the trap segment, and
performing a color test to determine whether the trap segment is to be
added to a trap output list or deleted;
for each of the first trap candidate segments in the first trap source
list:
detecting whether a potential general-purpose trapping situation exists
between the first trap candidate segment and the second page object,
in response to detecting the potential general-purpose trapping situation,
performing general-purpose trapping between the first trap candidate
segment and the second page object to create a next trap segment and to
remove from the first trap source list any portion of the first trap
candidate segment that overlays the second page object, and
in response to creating the next trap segment, performing a color test to
determine whether the next trap segment is to be added to the trap output
list or deleted; and
rendering the trap segments from the trap output list onto appropriate
color plates to hide misregistration errors between the first page object
and the second page object.
2. A computer readable medium having stored thereon computer-executable
instruction for performing the method of claim 1.
3. The method of claim 1, wherein detecting whether the potential adjacency
trapping situation exists comprises:
determining that the second page object abuts the first page object;
decomposing the second page object into second page object components to
create a second trap source list comprising second trap candidate
segments;
comparing the first trap candidate segment to each second trap candidate
segment in the second trap source list according to the following steps:
comparing the rotation states of the first trap candidate segment and the
second trap candidate segment,
if the rotation states are equivalent, determining whether the first trap
candidate segment and the second trap candidate segment are separated by
less than a maximum adjacency trapping distance,
if the first trap candidate segment and the second trap candidate segment
are separated by less than a maximum adjacency trapping distance,
determining whether the first trap candidate segment overlaps the second
trap candidate segment in the direction corresponding to the rotation
states,
if the first trap candidate segment overlaps the second trap candidate
segment in the direction corresponding to the rotation states, determining
whether the shared extent of the first trap candidate segment and the
second trap candidate segment is greater than a predetermined length, and
if the shared extent of the first trap candidate segment and the second
trap candidate segment is greater than a predetermined length, determining
whether respective segment normal vectors for the first trap candidate
segment and the second trap candidate segment point in opposite
directions,
whereby a potential adjacency trapping situation exists if it is determined
that the respective segment normal vectors for the first trap candidate
segment and the second trap candidate segment point in opposite
directions.
4. The method of claim 3, wherein performing adjacency trapping between the
first trap candidate segment and the second page object comprises:
creating the trap segment along the shared extent of the first trap
candidate segment and the second trap candidate segment;
comparing the trap segment to the first trap candidate segment; and
removing from the first trap source list any portion of the first trap
candidate segment that maps to the trap segment.
5. A computer readable medium having stored thereon computer-executable
instruction for performing the method of claim 4.
6. The method of claim 1, wherein detecting whether the potential
general-purpose trapping situation exists comprises:
decomposing the second page object into second page object components to
create a second trap source list comprising second trap candidate
segments; and
determining whether the first trap candidate segment intersects any of the
second trap candidate segments.
7. The method of claim 6, wherein performing general-purpose trapping
between the first trap candidate segment and the second page object
comprises:
generating the next trap segment having a length equal to the extent of the
intersection between the first trap candidate and the second trap
candidate segment; and
removing from the first trap source list any portion of the first trap
candidate segment overlays the second page object component associated
with the second trap candidate segment.
8. A computer readable medium having stored thereon computer-executable
instruction for performing the method of claim 7.
9. The method of claim 1, wherein detecting whether the potential
general-purpose trapping situation exists comprises determining whether
the first trap candidate segment is contained entirely within the second
page object.
10. The method of claim 9, wherein performing general-purpose trapping
between the first trap candidate segment and the second page object
comprises:
generating the next trap segment having a length equal to the first trap
candidate segment; and
removing from the first trap source list any portion of the first trap
candidate segment overlays the second page object component associated
with the second trap candidate segment.
11. A computer readable medium having stored thereon computer-executable
instruction for performing the method of claim 10.
12. The method of claim 1, further comprising the step of self-trapping the
one or more first page object components against one another to create one
or more additional trap segments to be added to the trap output list.
13. A computer readable medium having stored thereon computer-executable
instruction for performing the method of claim 12.
14. In a desktop publishing application program for operating on a
publication comprising a first page object, a second page object and a
third page object, the second page object having a higher Z-order than the
first page object and the third page object having a lower Z-order than
the first page object, a method for trapping the first page object against
the second page object and the third page object comprising the steps of:
decomposing the first page object into one or more first page object
components;
self-trapping the one or more first page object components against each
other to create one or more trap segments to be added to a trap output
list;
creating a first trap source list comprising one or more first trap
candidate segments from the one or more first page object components, the
one or more first trap candidate segments comprising exposed edges of the
one or more first page object components that intersect or abut the second
page object or the third page object;
adjacency trapping the one or more first trap candidate segments against
the second page object to remove portions of the one or more first trap
candidate segments from the first trap source list;
adjacency trapping the one or more first trap candidate segments against
the third page object to remove portions of the one or more first trap
candidate segments from the first trap source list and to add additional
trap segments to the trap output list;
general-purpose trapping the one or more first trap candidate segments
against the second page object to remove portions of the one or more first
trap candidate segments from the first trap source list and to add further
trap segments to the trap output list; and
rendering the trap segments of the trap output list onto appropriate color
plates.
15. A computer readable medium having stored thereon computer-executable
instructions for performing the method of claim 14.
16. The method of claim 14, wherein the first page object is a text
containing page object; and
wherein the method further comprises trapping the text contained in the
first page object against the third page object.
17. The method of claim 16, wherein trapping the text contained in the
first page object against the third page object comprises:
determining the color of the text;
determining that the first page object is transparent;
rendering the text on the appropriate color plates as it would appear
without trapping;
obtaining outline information for each character comprising the text;
converting the outline information into line segments to be stored in a new
trap source list; and
general-purpose trapping the line segments of the new trap source list
against the third page object to create new trap segments to be added to
the trap output list.
18. A computer readable medium having stored thereon computer-executable
instructions for performing the method of claim 17.
19. The method of claim 16, wherein trapping the text contained in the
first page object against the third page object comprises:
determining the color of the text;
determining that the first page object is opaque;
determining the background color of the first page object;
performing a color calculation on the background color of the first page
object and the color of the text to determine that trapping between the
text and the first page object is appropriate;
using trapping heuristics to calculate a trap width and a trap color;
rendering the text on the appropriate color plates as it would appear
without trapping;
obtaining outline information for each character comprising the text, the
outline information defining the outlines of the characters; and
rendering the outlines of the characters on appropriate color plates in the
trap width and trap color.
20. A computer readable medium having stored thereon computer-executable
instructions for performing the method of claim 19.
21. The method of claim 14, further comprising the step of keepaway
trapping any of the one or more first trap candidate segments that do not
intersect with any other colored page object in the publication.
22. The method of claim 21, wherein keepaway trapping any of the one or
more first trap candidate segments that do not intersect with any other
colored page object in the publication comprises:
for each of the one or more first trap candidate segments, determining if
the first trap candidate segment is associated with a rich black colored
first page object component;
for each first trap candidate segment associated with a rich black colored
first page object component, rendering a corresponding thin white segment
on all color plates except a black color plate.
23. A computer readable medium having stored thereon computer-executable
instructions for performing the method of claim 22. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The present invention relates in general to improving the quality of
printing press output by hiding unwanted gaps between different colored
areas on a printed output page. More particularly, the present invention
relates to automatically calculating minimal traps for each page object in
a publication in a native desktop publishing application, prior to
converting the publication to a page description language.
BACKGROUND OF THE INVENTION
Printing presses are used to generate large volumes of high-quality printed
output pages. Most printing presses that generate multiple-color output do
so by laying down on a printed output page one color of ink at a time, in
a multi-pass process. Two types of color jobs that may be run on such
printing presses are: process color printing and spot color printing.
Process color printing involves four primary ink colors: cyan, magenta,
yellow and black. These four primary ink colors are commonly referred to
by their initials CMY and K. Cyan, magenta and yellow are subtractive
primary ink colors and may be combined to form most other ink colors. Spot
color printing involves application of solid areas of a pre-mixed ink
rather than overlapping four inks (CMY and K) to create colors. A spot
color ink is a specific color, such as a bright orange or a purple, that
is laid down on the printed output page in a single pass. Process color
printing and spot color printing may be combined, using CMY and K inks
along with one or more spot color inks.
As a printed output page moves through a printing press, different colored
inks for the printing job are laid down in successive passes. Each ink
color is applied by what is commonly called a color plate. Conceptually,
each page object of the publication is printed on the printed output page
in a back-to-front order. If a page object contains a percentage greater
than zero of the ink color corresponding to the current color plate, that
object is rendered in that percentage of color on the printed output page.
If a page object contains zero percent of the ink color of the current
color plate, a white area in the shape of that page object is generated on
the printed output page. Generation of a white area in the shape of a page
object is called a "knocking out" a color, or rendering a "knockout" of
the page object. As the printed output page moves through the printing
press, the succession of rendering and knocking out colors of the page
objects of the publication for each ink color produces the final printed
output. Those skilled in the art will recognize that the physical printing
process is somewhat different from the above conceptual description, but
that the net effect is equivalent.
Certain factors may cause defects to appear in the printed output pages
generated by a printing press. For example, liquid inks may be absorbed,
to some degree, into the printed output page and may cause the paper to
stretch and deform slightly. Also, because the printed output page moves
through the press at high speeds, it may bounce when it is stopped to have
an ink color pressed onto it. The effect of these and other factors may be
slight variances in the alignment of the various ink colors. Such
variances are commonly referred to as misregistration errors.
Misregistration errors result in gaps between areas of different color, or
areas where one process color ink appears to be out of alignment with
others process color inks. One solution to the problem of misregistration
errors is known as "trapping."
Trapping does not prevent misregistration errors. Instead, trapping is a
procedure that aims to reduce the visibility of misregistration errors.
Assuming that limitations of current ink, paper and printing press
technologies cannot be removed, trapping provides an effective stopgap
solution for hiding misregistration errors on printed output pages.
Through analysis of all page objects in a publication, it is possible to
determine which ink colors will end up being adjacent to one another on
the final printed output pages. Existing trapping heuristics may be used
to determine which color combinations, when adjacent to one another, are
likely to cause visible misregistration errors.
Trapping is the name given to the process of identifying adjacent color
pairs that are likely to cause misregistration errors and hiding the
misregistration errors by laying down an extra strip of ink, of a
calculated color and width, to cover any gap or misalignment that may
occur. Physically, an extra strip of ink only affects the color plate on
which it is placed. In other words, an extra strip of ink enlarges the
area of color on a particular color plate without causing a knockout of
additional white space on other color plates. Accordingly, when the
different color plates are composited onto the final printed output page,
the extra ink strip covers any gap or misalignment that will occur due to
misregistration.
Prior to the invention of the personal computer, trapping was performed
manually, by creating hand-doctored images of the printed output pages.
The advent of the personal computer and desktop publishing (DTP) software
gave rise to the possibility of automatic trapping solutions. Prior art
DTP applications typically perform trapping by performing a
post-processing step on an output file, such as a PostScript file. Also,
prior art DTP applications are not operable to perform trapping with a
high level of accuracy.
Certain prior art-high-end trapping applications are capable of trapping
with a high level of accuracy, i.e., performing multiple types of trapping
along the length of a page object. However, these high-end applications
also typically operate on page data in a post-processing manner. That is,
high-end trapping applications typically accept as input the page data
generated by a DTP application after it has been converted to an
intermediate format, such as PostScript or some other proprietary page
description language. Post-processing is an expensive and time consuming
effort.
Thus, there remains a need for a desktop publishing application that is
operable to perform trapping of page objects in the native application, so
as to avoid the need for post-processing.
There further remains a need for a desktop publishing application that is
operable to perform trapping of page objects in the native application
using precise position and color information,
SUMMARY OF THE INVENTION
The present invention meets the above-described needs by providing a
desktop publishing (DTP) application program with functionality for
automatically generating minimal traps for each page object in the native
DTP application program, prior to converting a publication to a page
description language. The present invention may leverage and/or build upon
the existing functionality of a DTP application program.
In one embodiment, a desktop publishing application program is configured
to generate minimal traps for a publication comprising a first page
object, a second page object and a third page object. In the exemplary
publication, the second page object has a higher Z-order than the first
page object and the third page object has a lower Z-order than the first
page object. The present invention traps the first page object against the
second page object and the third page object by decomposing the first page
object into one or more first page object components; self-trapping the
first page object components against each other to create one or more trap
segments to be added to a trap output list; creating a first trap source
list comprising one or more first trap candidate segments from the first
page object components, the first trap candidate segments comprising
exposed edges of the first page object components that intersect or abut
the second page object or the third page object; adjacency trapping the
first trap candidate segments against the second page object to remove
portions of the first trap candidate segments from the first trap source
list; adjacency trapping the first trap candidate segments against the
third page object to remove portions of the first trap candidate segments
from the first trap source list and to add additional trap segments to the
trap output list; general-purpose trapping the first trap candidate
segments against the second page object to remove portions of the first
trap candidate segments from the first trap source list and to add further
trap segments to the trap output list; and rendering the trap segments of
the trap output list onto appropriate color plates.
According to one embodiment of the present invention, adjacency trapping a
first trap candidate segments against a second page object having a lower
Z-order than the first page object involves: detecting whether a potential
adjacency trapping situation exists between the first trap candidate
segment and the second page object; in response to detecting the potential
adjacency trapping situation, performing adjacency trapping between the
first trap candidate segment and the second page object to create a trap
segment and to remove from the first trap source list any portion of the
first trap candidate segment that maps to the trap segment; and performing
a color test to determine whether the trap segment is to be added to a
trap output list or deleted.
In an exemplary embodiment, detecting a potential adjacency trapping
situation involves: determining that the second page object abuts the
first page object; decomposing the second page object into second page
object components to create a second trap source list comprising second
trap candidate segments; comparing the first trap candidate segment to
each second trap candidate segment in the second trap source list
according to the following steps: (1) comparing the rotation states of the
first trap candidate segment and the second trap candidate segment, (2) if
the rotation states are equivalent, determining whether the first trap
candidate segment and the second trap candidate segment are separated by
less than a maximum adjacency trapping distance, (3) if the first trap
candidate segment and the second trap candidate segment are separated by
less than a maximum adjacency trapping distance, determining whether the
first trap candidate segment overlaps the second trap candidate segment in
the direction corresponding to the rotation states, (4) if the first trap
candidate segment overlaps the second trap candidate segment in the
direction corresponding to the rotation states, determining whether the
shared extent of the first trap candidate segment and the second trap
candidate segment is greater than a predetermined length, and (5) if the
shared extent of the first trap candidate segment and the second trap
candidate segment is greater than a predetermined length, determining
whether respective segment normal vectors for the first trap candidate
segment and the second trap candidate segment point in opposite
directions, whereby a potential adjacency trapping situation exists if it
is determined that the respective segment normal vectors for the first
trap candidate segment and the second trap candidate segment point in
opposite directions. An exemplary method for adjacency trapping involves:
creating a trap segment along the shared extent of the first trap
candidate segment and the second trap candidate segment; comparing the
trap segment to the first trap candidate segment; and removing from the
first trap source list any portion of the first trap candidate segment
that maps to the trap segment.
According to an exemplary embodiment of the present invention,
general-purpose trapping involves: detecting whether a potential
general-purpose trapping situation exists between the first trap candidate
segment and the second page object; in response to detecting the potential
general-purpose trapping situation, performing general-purpose trapping
between is the first trap candidate segment and the second page object to
create a next trap segment and to remove from the first trap source list
any portion of the first trap candidate segment that overlays the second
page object; in response to creating the next trap segment, performing a
color test to determine whether the next trap segment is to be added to
the trap output list or deleted; and rendering the trap segments from the
trap output list onto appropriate color plates to hide misregistration
errors between the first page object and the second page object.
An exemplary method for detecting whether a potential general-purpose
trapping situation exists involves decomposing the second page object into
second page object components to create a second trap source list
comprising second trap candidate segments and determining whether the
first trap candidate segment intersects any of the second trap candidate
segments. An exemplary method for performing general-purpose trapping
between the first trap candidate segment and the second page object
involves: generating the next trap segment having a length equal to the
extent of the intersection between the first trap candidate and the second
trap candidate segment; and removing from the first trap source list any
portion of the first trap candidate segment overlays the second page
object component associated with the second trap candidate segment.
According to another aspect of the present invention, text contained within
a text-containing page object is also trapped against other page objects
in a publication. If the text-containing page object is opaque, the text
therein may be trapped against the background of the text-containing page
object. If the text-containing page object is transparent, the text
therein may be trapped against page objects beneath the text-containing
page object.
In an exemplary embodiment, trapping text contained in an opaque text
containing page object against the background of the text containing page
object involves: determining the color of the text; determining the
background color of the first page object; performing a color calculation
on the background color of the first page object and the color of the text
to determine that trapping between the text and the first page object is
appropriate; using trapping heuristics to calculate a trap width and a
trap color; rendering the text on the appropriate color plates as it would
appear without trapping; obtaining outline information for each character
comprising the text, the outline information defining the outlines of the
characters; and rendering the outlines of the characters on appropriate
color plates in the trap width and trap color.
In an exemplary embodiment, trapping text contained in a transparent text
containing page object against the lower Z-ordered page object involves:
determining the color of the text; rendering the text on the appropriate
color plates as it would appear without trapping; obtaining outline
information for each character comprising the text; converting the outline
information into line segments to be stored in a new trap source list; and
general-purpose trapping the line segments of the new trap source list
against the third page object to create new trap segments to be added to
the trap output list.
According to another aspect of the present invention, functionality is
provided for performing keepaway trapping on any of trap candidate
segments in a trap source list that do not intersect with any other
colored page object in the publication. In an exemplary embodiment,
keepaway trapping involves: determining if a trap candidate segment is
associated with a rich black colored first page object component; and if
the trap candidate segment is associated with a rich black colored first
page object component, rendering a corresponding thin white segment on all
color plates except a black color plate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1, comprising FIG. 1A, FIG. 1B, FIG. 1C, FIG. 1D and FIG. 1E, provides
illustrations of page objects to illustrate some basic trapping examples.
FIG. 2 illustrates an exemplary computing environment for implementation of
the exemplary embodiments of the present invention.
FIG. 3, comprising FIG. 3A and FIG. 3B, provides a flow chart of an
exemplary trapping method for an individual page object.
FIG. 4 is an illustration of a rectangle page object to accompany a
discussion of page object decomposition.
FIG. 5, comprising FIG. 5A, FIG. 5B and FIG. 5C, illustrates various
rectangle page objects providing examples of three potential adjacency
trapping situations.
FIG. 6, comprising FIG. 6A, FIG. 6B and FIG. 6C, provides a flow chart
illustrating an exemplary method for analyzing a potential adjacency
trapping situation.
FIG. 7 is a flow chart illustrating an exemplary general-purpose trapping
method.
FIG. 8, comprising FIG. 8A and FIG. 8B, is a flow chart illustrating an
exemplary method for performing a general polygon intersection
calculation.
FIG. 9 is a flow chart illustrating an exemplary method for trapping text
containing page objects.
DETAILED DESCRIPTION
The present invention provides a system and method for automated
intelligent trapping of page objects in desktop publishing software. The
present invention provides automatic trapping for all page objects in a
publication. Each page object is trapped as completely as possible.
Complete trapping means that each page object is subdivided into atomic
geometric and color components, each of which is then trapped against all
of the components from that same page object. The components of a page
object may then be trapped against all page objects beneath them on the
page and sometimes to page objects above them on the page. The page
objects beneath a component of a page object are all decomposed into
subparts as well. Page objects that are adjacent to one another are
trapped correctly, so as to avoid traps that negatively impact the
appearance of the printed output page. Text characters in the publication
may be trapped as well. The present invention also allows manual overrides
to be set for a page object and its associated components. Manual
overrides may be used to handle cases that are not effectively dealt with,
in the view of the printing professional, through automatic trapping.
In accordance with the present invention, when a trap is calculated for a
given page object, only the necessary portion of the trap is actually
drawn. Drawing only the necessary portion of each trap results in a
printed output page having highly accurate traps. The high trapping
accuracy of the present invention relies on precise size and color
information about each page object in a publication, including text
characters. Thus, the present invention may be configured to gather data
pertaining to each page object and its associated components, including
position and size information, rotation angle, and formatting (e.g.,
color, borders etc.). Using this gathered data, the present invention may
calculate precise intersection points for all page object components.
Precise intersection points allow the present invention to determine exact
locations on the printed output page where trapping will be required to
hide misregistration errors.
It should be understood that trapping calculations are based on both
geometric and color calculations. Color calculations are used to determine
what color ink to lay down in order to hide misregistration errors. Color
calculations depend on two things (1) the front-to-back relationship of
the page objects (known as the Z-order of the page objects); and (2) the
relative luminance of the colors (i.e., the perceived brightness or
darkness of the colors). The Z-order, in combination with information
about the position of each page object on the page, may be used to
determine which ink colors will end up being adjacent to one another on
the printed output page.
Over time, heuristics have been developed that use the Z-order and the
luminance of two colors to determine the trap color, if any, that should
be applied. By convention, there are four main types of traps based on
these color heuristics: spread traps, choke traps, centerline traps and
keepaway traps. Each of the four main trap types is designed to cover a
specific type or range of color combinations and Z-ordering. Also,
combinations of these trap types may be applied to any page objects in a
publication, including geometric shapes, pictures, gradient and pattern
fills and text. The following reference materials, which are herein
incorporated by reference, provide more detailed information regarding
trapping: (1) "Makeready: A Prepress Resource," by Dan Margulis,
MIS:Press, 1996; (2) "The Complete Guide to Trapping (Second Edition)," by
Brian P. Lawler, Hayden Books, 1995.
The following description will hereinafter refer to the drawing, in which
like numerals indicate like elements throughout the several figures. FIG.
1, which comprises FIG. 1A, FIG. 1B, FIG. 1C, FIG. 1D and FIG. 1E, and the
following description are intended to provide some basic trapping
definitions and examples.
Spread Traps
A spread trap is a trap created by drawing the foreground color or shape of
a page object slightly oversize. Spread trapping is generally employed
when the foreground page object is lighter than the background page
object, or when the background page object is an indeterminate color (such
as a photograph). For example, in FIG. 1A, the yellow triangle page object
102 is positioned on top of a blue rectangle page object 104. In a
colorized representation of FIG. 1A, the blue rectangle page object 104
would be visibly darker than the yellow triangle page object 102. Spread
trapping would result in the yellow triangle page object 102 being drawn
slightly larger than the corresponding knockout generated within the blue
rectangle page object 104. In other words, extra yellow ink would be laid
down to bridge any misregistration gaps between the yellow triangle page
object 102 and the blue rectangle page object 104, thereby improving the
quality of the printed output page.
Choke Traps
A choke trap is created by drawing a background page object or color
slightly oversize. Drawing the background page object slightly oversize
effectively reduces the size of the knockout of a higher Z-ordered page
object. Choke trapping is typically used when the background page object
is lighter in color than the foreground page object, or when the
foreground page object is an indeterminate page object such as a
photograph. By way of example, FIG. 1B shows a blue triangle page object
106 positioned on top of a yellow rectangle page object 108. Within the
yellow rectangle page object 108, application of extra yellow ink along
the boundary of the knockout corresponding to the blue triangle page
object 106 would create a choke trap.
Centerline Traps
A centerline trap uses colors from both foreground and background page
objects to hide misregistration errors. Colors that are close to one
another in luminance, but that would still potentially cause
misregistration errors are candidates for this centerline trapping. For
example, in FIG. 1C, an orange triangle page object 112 is positioned on
top of a green rectangle page object 114. If the calculated luminance of
the two colors (orange and green) are sufficiently close to each other, a
centerline trap is created by slightly enlarging the orange triangle page
object 112 and also by slightly shrinking the size of the corresponding
knockout within the green rectangle 114. Those skilled in the art will
recognize that physical process of centerline trapping is slightly more
complicated than the above description, but that the net effect is
analogous.
Keepaway Traps
Keepaway traps are used to deal with a special type of black ink, known as
rich black ink. Rich black ink is black ink that has had other color
components added thereto. Rich black inks are used when large patches of
black color are to be printed on the printed output page. Rich black inks
are used because they tend to look better than pure black ink.
As an example, rich black ink may be created in a process color print job
by adding 20 percent each of cyan, magenta and yellow ink to black ink.
Creation of rich black in this manner is accomplished by laying down
black, cyan, magenta and yellow inks successively. Accordingly,
misregistration errors may occur around the edges of rich black page
objects if the cyan, magenta or yellow colors "peek out" from the side of
a black page object. A keepaway trap prevents this type of misregistration
error from happening by reducing the size of the non-black components of
the page object. Reducing the size of the non-black components of the page
object allows the bulk of the page object to be seen in the desired rich
black color, while preventing misregistration errors from causing unwanted
effects at the edges of the page object.
Exemplary Operating Environment
FIG. 2 an | | |
