U.S. patent application number 12/885163 was filed with the patent office on 2011-01-13 for halftone dot formation method and apparatus for reducing layer thickness of coloring material inside halftone dots, and image formation apparatus.
This patent application is currently assigned to FUJI XEROX CO., LTD.. Invention is credited to Akira Ishii, Yoshifumi Takebe.
Application Number | 20110007363 12/885163 |
Document ID | / |
Family ID | 37566793 |
Filed Date | 2011-01-13 |
United States Patent
Application |
20110007363 |
Kind Code |
A1 |
Ishii; Akira ; et
al. |
January 13, 2011 |
Halftone Dot Formation Method and Apparatus for Reducing Layer
Thickness of Coloring Material Inside Halftone Dots, and Image
Formation Apparatus
Abstract
An image processing method generates a halftone-dot image by
forming a halftone dot, which is represented by a set of one or
plural output dots and corresponds to an intensity of an input
image signal, while making a part of the dots constituting the
halftone dot to be an actual non-output dot so as to reduce an
amount of a coloring material of the halftone-dot portion. When the
intensity of the image signal exceeds a predetermined value and is
in a predetermined range, while maintaining contour dots, which are
output dots contribute to formation of a contour of the halftone
dot, to be the output dot, the image processing method makes a part
of dots inside the contour dots to be the actual non-output
dot.
Inventors: |
Ishii; Akira; (Kanagawa,
JP) ; Takebe; Yoshifumi; (Kanagawa, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
FUJI XEROX CO., LTD.
Tokyo
JP
|
Family ID: |
37566793 |
Appl. No.: |
12/885163 |
Filed: |
September 17, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11357950 |
Feb 22, 2006 |
|
|
|
12885163 |
|
|
|
|
Current U.S.
Class: |
358/3.06 |
Current CPC
Class: |
H04N 1/4055
20130101 |
Class at
Publication: |
358/3.06 |
International
Class: |
H04N 1/405 20060101
H04N001/405 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 22, 2005 |
JP |
2005-045107 |
Feb 9, 2006 |
JP |
2006-032016 |
Claims
1. An image forming apparatus for generating a halftone-dot image
by forming a halftone dot, which is represented by a set of one or
plural output dots and corresponds to an intensity of an input
image signal, while making a part of the dots constituting the
halftone dot to be an actual non-output dot so as to reduce an
amount of a coloring material of the halftone-dot portion, the
image processing apparatus comprising: a binarization processing
section that, when the intensity of the image signal exceeds a
predetermined value and is in a predetermined range, while
maintaining contour dots, which are output dots contribute to
formation of a contour of the halftone dot, to be the output dot,
makes a part of dots inside the contour dots to be the actual
non-output dot; and an image recording section that forms the
halftone-dot image including the actual non-output dot in the
halftone dot, on a basis of the binarized data generated by the
binarization processing section.
2. The image forming apparatus according to claim 1, further
comprising: a first halftone-dot image generating section that
generates binarized data representing the halftone dot, which is
represented by the plural dots and corresponds to the intensity of
the input image signal; a second halftone-dot image generating
section that generates binarized data representing a set of the
real non-output dot in response to the intensity of the image
signal exceeding the predetermined value; and a calculation
processing section that makes the part of dots inside the contour
dots to be the non-output dot on a basis of the binarized data,
which is generated by the first halftone-dot image generating
section and represents the halftone dot, and the binarized data,
which is generated by the second halftone-dot image generating
section and represents the set of real non-output dot, wherein: the
image recording section comprises a recording energy control
section that executes image recording on a basis of the binarized
data, which is generated by the calculation processing section and
makes the part of dots inside the contour dot be the non-output
dot.
3. The image forming apparatus according to claim 1, further
comprising: a first halftone-dot image generating section that
generates binarized data representing the halftone dot, which is
represented by the plural dots and corresponds to the intensity of
the input image signal; and a second halftone-dot image generating
section that generates binarized data representing a set of the
real non-output dot in response to the intensity of the image
signal exceeding the predetermined value, wherein: the image
recording section comprises: a modulation control section that
generates output modulation data with using the binarized data,
which is generated by the first halftone-dot image generating
section and represents the halftone dot, as an on/off control input
and using the binarized data, which is generated by the second
halftone-dot image generating section and represents the set of
real non-output dot, as a modulation control input; and a recording
energy control section that executes image recording on a basis of
the output modulation data generated by the modulation control
section.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a Division of application Ser. No. 11/357,950 filed
Feb. 22, 2006. The disclosures of the parent application and
Japanese Patent Application No. 2005-45107 filed on Feb. 22, 2005
and Japanese Patent Application No. 2006-32016 filed on Feb. 9,
2006, including the specifications, claims, drawings and abstracts
are incorporated herein by reference in their entirety.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to an image processing method,
an image processing apparatus, and an image forming apparatus. More
specifically, the invention relates to a binarization processing
technique for generating a halftone-dot image by forming a halftone
dot having a predetermined size corresponding to an intensity of an
input image signal, the halftone dot which is used to record a
halftone-dot image on an image recording medium in a printing
technique such as an electrophotographic method and an inkjet
method.
[0004] 2. Description of the Related Art
[0005] As one of the techniques for generating a halftone-dot image
using binary data, there has been known a binarization processing
method (particularly referred to as a halftone processing method)
in which colored dots called halftone dots (set of individual
halftone output dots), each having a predetermined size
corresponding to an intensity of an input image signal, are formed
to thereby reproduce the density of a gradation image in a pseudo
manner by the size of each colored dot.
[0006] For example, a color printed matter is obtained by printing
respective inks, each having one of four colors composed of yellow
(Y), magenta (M), cyan (C), and black (K) colors, on a recording
medium (printing paper) with the inks superposed on one another
subsequently, using four printing plates for the inks. On the
printing plates are recorded halftone plate images in which
gradation of continuous-tone images of a color manuscript is
reproduced with a set of microscopic halftone dots.
[0007] FIG. 12 is a diagram illustrating an example (A) of the
above-mentioned halftone processing and an example (B) of halftone
dots generated by the halftone processing. For example, when
generating a halftone plate image in a printing technique using an
electrophotographic method, a comparator compares multilevel-image
signals (multilevel data) representing the gradation of an image of
a color document with predetermined screen pattern data (each
threshold-value data in a threshold-value matrix) as shown in FIG.
12(A), to generate binarized recording signals.
[0008] Further, the halftone plate images are exposed on an image
formation member (for example, a photoconductor drum) by
controlling on/off of a light beam for exposure according to
halftone dot signals, using the binarized recording signals as
on/off signals (halftone dot signals) for each record pixel. Then,
toner (powder) is sprayed onto the image formation member to
visualize an image on the image formation member (a latent image)
as a toner image. Thereafter, the toner image is transferred and
fixed onto the image recording medium to form an image having
halftone dots having a size corresponding to the density of the
image as shown in FIG. 12(B).
[0009] Here, when the halftone dots are used in the
electrophotographic method, in general, one or two grains (1.5
grains in average) of toner are piled up, reaching a height in a
range of ten and several .mu.m before a toner image is fixed. Since
the height of the piled-up toner is in many cases determined by an
amount of toner required for the maximum density of the image, it
may be an excessive amount of toner for halftone reproduction. In
particular, since the size of a halftone dot is small in a
highlight tone area (low density region), there are high
possibilities that this problem occurs.
[0010] For color reproduction, a thin halftone-dot toner image is
needed in the transfer process of toner because deterioration of
image quality during the transfer process increases as the
thickness of a halftone-dot toner image is larger. In addition, for
a multi-transfer for the color reproduction, more attention should
be paid to the deterioration of image quality. However, it is
difficult that the amount of toner needed for the maximum density
is compatible with the amount of toner appropriate for the halftone
dot reproduction.
[0011] Further, a non-fixed toner image having a thickness in the
range of ten and several .mu.m is crushed into a fixed toner image
having a thickness of several .mu.m after it is fixed. When the
toner fixed on paper absorbs light, density reproduction by the
toner occurs. In order to enhance the light absorption efficiency,
it is required to efficiently expose a coloring material containing
a thin toner layer to light. However, as described above, in the
halftone-dot structure for the halftone reproduction, the toner
layer may become excessively thick in many cases, and therefore,
the toner which makes a low contribution to light absorption exists
on the paper.
[0012] On the other hand, in a field of a printing technique, such
as an inkjet method, using ink as a coloring material, there is a
technique of controlling the amount of ink adhesion for forming
halftone dots for the purpose of adjusting the thickness of the
halftone dots called a dot gain or transferability of ink (coloring
material).
[0013] [Patent Document 1] WO 00/72580
[0014] [Patent Document 2] U.S. Pat. No. 6,532,082
[0015] For example, for the purpose of reducing the dot gain of a
stochastic screen (stochastic printing), mechanism disclosed in the
patent document 1 is a technique for appropriately reducing the
density of a binarized image by further stochastically thinning out
an image binarized with the stochastic screen.
[0016] In addition, mechanism disclosed in the patent document 2 is
a technique for appropriately reducing the density of a binarized
image by stochastically thinning out the image binarized by a
normal halftone process, premised on halftone dots of clustered
dots.
[0017] More specifically, in the mechanism disclosed in the patent
document 1, with respect to the stochastic screen called an FM
screen; and in the mechanism disclosed in the patent document 2,
with respect to a regular halftone screen called an AM screen, the
dot gain and the amount of ink are adjusted by non-periodically
thinning out some of the halftone dots. That is, halftone dots and
gap dots are asynchronously generated.
[0018] However, in the FM screen such as the mechanisms disclosed
in the patent document 1, since the density of the image is
reproduced with a minute density of dots, which are invisible (30
.mu.m or less), some of the integrated (clustered) minute halftone
dots may be thinned out and areas of colored pixels may be too
small to reproduce dots stably.
[0019] On the other hand, in the AM screen such as the mechanism
disclosed in the patent document 2, when some of the halftone dots
are non-periodically thinned out, there may occur a case where some
of the halftone dots are thinned out inside the halftone dots and a
case where some of the halftone dots are thinned out outside the
halftone dots. Accordingly, there may occur a phenomenon that the
crush of some of the halftone dots is different from the crush of
other halftone dots, which may result in image noises. In addition,
a coloring material in a halftone dot portion may be made thin when
many pixels are thinned out inside the halftone dots. However, when
many pixels are thinned out outside the halftone dots, since the
size reduction of the halftone dots is significant but an operation
of thinning out the coloring material in the halftone dot portion
is weakened, an effect of making the halftone dots uniformly thin
can not be expected. In particular, since the size of the halftone
dots becomes small in highlight tone area (low density area), there
are high possibilities that the above-mentioned problems occur.
SUMMARY
[0020] The invention provides mechanism, which can thins a
coloring-material layer in a halftone-dot portion while suppressing
errors in densities of the output image and preventing image
quality from deteriorating when density of a halftone-dot image is
reproduced in a pseudo manner by using halftone dots, regardless of
a printing method such as an electrophotographic method using
powder as a coloring material or an inkjet method using ink as a
coloring material.
[0021] An image processing method according to one embodiment of
the invention for generating a halftone-dot image by forming a
halftone dot, which is represented by a set of one or plural output
dots and corresponds to an intensity of an input image signal,
while making a part of the dots constituting the halftone dot to be
an actual non-output dot so as to reduce an amount of a coloring
material of the halftone-dot portion, the image processing method
includes when the intensity of the image signal exceeds a
predetermined value and is in a predetermined range, while
maintaining contour dots, which are output dots contribute to
formation of a contour of the halftone dot, to be the output dot,
making a part of dots inside the contour dots to be the actual
non-output dot.
[0022] An image processing apparatus according to another
embodiment of the invention is suitable for implementing the image
processing method according to the invention, and includes a
binarization processing section that, when the intensity of the
image signal exceeds a predetermined value and is in a
predetermined range, while maintaining contour dots, which are
output dots contribute to formation of a contour of the halftone
dot, to be the output dot, makes a part of dots inside the contour
dots to be the actual non-output dot.
[0023] An image forming apparatus according to a further another
embodiment of the invention has a function of the image processing
apparatus, which is suitable for implementing the image processing
method according to the invention, and includes a binarization
processing section that, when the intensity of the image signal
exceeds a predetermined value and is in a predetermined range,
while maintaining contour dots, which are output dots contribute to
formation of a contour of the halftone dot, to be the output dot,
makes a part of dots inside the contour dots to be the actual
non-output dot, and an image recording section that forms the
halftone-dot image including the actual non-output dot in the
halftone dot, on a basis of the binarized data generated by the
binarization processing section.
[0024] For example, as a shape of an original halftone dot, which
is a process target, there are a so-called dot-shaped halftone dot
(so-called dot screen), that is, an output dot growing into a
substantially circle shape in response to density, and a
line-shaped halftone dot having a structure in which a halftone dot
is continued in a line shape in a range where the input image
signal has a density equal to or larger than a predetermined
density (so-called line screen). The dot screen is easy in forming
a halftone dot, but is easily affected by disturbance at the time
of image formation and color moire. To the contrary, the line
screen has an advantage that it is less affected by the disturbance
at the time of the image formation and the color moire.
[0025] If the invention of this application is applied to the
dot-shaped halftone dot, the dot-shaped halftone dot becomes a
ring-shaped halftone dot. Also, in the case of applying the
invention of this application to the line-shaped halftone dot, for
example, non-output dots are made to be continued in a line shape
in the line-shaped halftone dot in a predetermined density range.
That is, two methods can be adopted representatively; one is the
case where gap is grown in the line-shaped structure to form a
double line structure and the other is the case where non-output
dots are maintained to be isolated in the line-shaped halftone dot,
that is, the non-output dots are not continued in a line shape in
the line-shaped halftone dot. The latter is better in
reproducibility of the line structure.
[0026] Also, a pure-electronic mechanism may be configured so that
the part of dots inside the contour dots is made to be a real
non-output dot on electronic data representing the halftone dot,
that is that an image recording signal inside the halftone dot is
thinned out. Alternatively, a mechanism may be configured to
modulate recording energy of the non-output dot inside the contour
dots of the halftone dot on a basis of the binarized data generated
by the binarization processing section so as to reduce an amount of
coloring material.
[0027] It is noted that a functional portion regarding the
binarized data processing in the image processing apparatus and the
image forming apparatus may be implemented by an electronic
calculator (computer) in a software manner. Therefore, a program
and a recording medium storing the program can be extracted as the
invention. The program may be supplied with being stored in a
computer readable storage medium or distributed by means of wired
or wireless communication means.
[0028] According to the above configuration, only when the
intensity of the image signal exceeds the predetermined value and
is in the predetermined range, while the contour dots, which are
the output dots contribute to the formation of the contour of the
halftone dot, are maintained to be the output dot, the part of dots
inside the contour dots is made to be the actual non-output dot.
Therefore, a layer thickness of the coloring material inside the
halftone dot can be reduced without the contour shape of the
halftone dot made of the toner or ink being deformed.
[0029] Thereby, without deterioration of the image quality, the
coloring material of the halftone-dot portion can be thinned
effectively. Also, since a ratio of an amount of the coloring
material contributing to light absorption is increased, the
consumption amount of the coloring material can be reduced. Also,
since the generation of the halftone dot and the generation of the
gap are synthesized, control required for generating the gap dots
inside the halftone dot is easy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a diagram illustrating an overall outline of an
image forming apparatus according to a first embodiment.
[0031] FIG. 2 is a diagram illustrating a configuration of a
binarization processing section according to the first
embodiment.
[0032] FIG. 3 is a diagram showing an example of a gap size profile
representing characteristics of threshold data for gap
formation.
[0033] FIG. 4 is a diagram showing an example of an image (A)
generated by a usual binarization process, and images (B) and (C)
generated by using the gap size profile shown in FIG. 3 according
to this embodiment.
[0034] FIG. 5 is a flow chart illustrating an outline of a
halftone-dot processing procedure by the binarization processing
section of the first embodiment.
[0035] FIG. 6 is a diagram illustrating a procedure for generating
ring-shaped halftone dots by the halftone dot process of the first
embodiment.
[0036] FIG. 7 is a diagram showing an example of an output of
halftone dots when an image recording process is performed
according to the halftone-dot processing procedure performed by the
binarization processing section of the first embodiment.
[0037] FIG. 8 is a diagram showing a comparison in an electronic
image between halftone dots according a conventional method and the
halftone dots generated in the process procedure according to the
first embodiment
[0038] FIG. 9 is a diagram illustrating a configuration of a
binarization processing section according to a second
embodiment.
[0039] FIG. 10 is a flow chart illustrating an outline of a
halftone-dot processing procedure used in an image forming
apparatus according to the second embodiment.
[0040] FIG. 11 is a diagram illustrating a process of generating
ring-shaped halftone dots according to the halftone-dot process of
the second embodiment.
[0041] FIG. 12 is a diagram illustrating a conventional and general
halftone-dot process and a halftone-dot image.
[0042] FIG. 13 is diagram illustrating a line-shaped halftone dot
(line screen).
[0043] FIG. 14 is a diagram illustrating a process of generating a
non-output dot (gap) with respect to the line-shaped halftone
dot.
[0044] FIG. 15 is a first example of generating gap with respect to
the line-shaped halftone dot according to a halftone-dot process
procedure of the third embodiment.
[0045] FIG. 16 is a second example of generating gap with respect
to the line-shaped halftone dot according to a halftone-dot process
procedure of the third embodiment.
DETAILED DESCRIPTION OF EMBODIMENTS
[0046] Hereinafter, embodiments of the invention will be described
in detail with reference to the accompanying drawings.
Overall Configuration of Image Forming Apparatus
First Embodiment
[0047] FIG. 1 is a diagram illustrating an overall outline of an
image forming apparatus according to a first embodiment, with
focusing attention on an image processing section (an image
processing apparatus), which is involved in a binarization process,
and an image recording section in a printing apparatus employing an
electrophotographic method, an inkjet method or the like. As shown
in the figure, an image forming apparatus 1 according to the first
embodiment includes a color-separation-signal generating section
10, a binarization processing section 20, a binary-data storage
section 30, an image recording section 40, and a profile switch
commanding section 50. The color-separation-signal generating
section 10, the binarization processing section 20, and the
binary-data storage section 30 make up the image processing section
(image processing apparatus), which is involved in the binarization
process.
[0048] The color-separation-signal generating section 10 acquires
image data Din having a relatively high number of bits (for
example, 8 to 10 bits) for each of the color components of red (R),
green (G), blue (B), for example, from an image input terminal such
as a personal computer connected through an image reading unit or a
communication interface (not shown) provided at a previous stage of
the color-separation-signal generating section 10, and converts the
acquired image data Din_R, Din_G, and Din_B for each of the color
components into color separation data for each of the color
components of C (cyan), M (magenta), Y (yellow), K (black)
(hereinafter, referred to as multilevel image data DMV)
corresponding to the toner colors, which are to be processed by the
image recording section 40. For example, multilevel digital data R,
G and B, each having several bits, is converted into multilevel
digital data C, M, Y and K each having the same several bits. This
color conversion process employs a process step of RGB
data.fwdarw.Lab data.fwdarw.YMCK data.
[0049] In addition, in stages previous or next to the
color-separation-signal generating process (a stage prior to the
binarization processing), specific image processes (pre-processes)
such as a background removal process, a magnification control
process, a contrast adjustment (density adjustment) process, a
color correction process, a filtering process, a TRC (Tone
Reproduction Control) correction process (also referred to as
gradation correction process) and the like are performed. These
processes are well known in the related art, and therefore,
explanation thereof will be omitted.
[0050] The binarization processing section 20 applies a screen
process to the respective multilevel image data DMV_C, DMV_M,
DMV_Y, and DMV_K for the respective input color components to
generate binarized data (one bit data). For example, the
binarization processing section 20 generates a binarized recording
signal Dout, which represents the density of a gradation image in a
pseudo manner by the size of the colored dots called halftone dots,
from the multilevel digital data C, M, Y and K, which are
multilevel image information having density gradation, and stores
the generated binarized recording signal Dout in the binary-data
storage section 30.
[0051] The image recording section 40 has a marking engine section
44 for reading out the binarized recording signal Dout generated by
the binarization processing section 20 from the binary-data storage
section 30 and then performing an image recording process. The
marking engine section 44 may use various methods such as an
electrophotographic method in which an electrostatic latent image
is formed by exposure and then the latent image is developed,
transferred and fixed by using toner as the coloring material, an
inkjet method of using ink as the coloring material, or a plate
printing method (for example, lithographic method) of transferring
ink on the recording paper using a prepared printing plate.
Configuration of Binarization Processing Section
First Embodiment
[0052] FIG. 2 is a diagram illustrating a configuration of the
binarization processing section 20 (binarization processing section
20 of the first embodiment) used in the image forming apparatus 1
according to the first embodiment. In addition, FIGS. 3 and 4 are
diagrams explaining basic characteristics of a gap formation
process executed in the binarization processing section 20
according to the first embodiment.
[0053] Here, FIG. 3 is a diagram showing an example of a gap-size
profile, which represents characteristics of threshold-value data
for gap formation and is used in the gap formation process
according to this embodiment. Further, FIG. 4(A) is a diagram
showing an example of an image generated by a binarization process
of a related art. FIG. 4 is a diagram showing an example of an
image (A) generated by a usual binarization process, and images (B)
and (C) generated by using the gap size profile shown in FIG. 3
according to this embodiment. Either figures show the case where
the binarization processing section 20 processes a dot-shaped
halftone dot whose output dot grows to have a substantially circle
shape in accordance with the density.
[0054] In FIGS. 3(A) and 3(B), reference numerals C1 and C3 each
denote a density giving a gap-formation starting point on a
low-density side, and reference numerals C2 and C4 each denote a
density giving a gap-formation starting point on a high-density
side. In addition, in FIG. 3(B), reference numeral Ccnt denotes a
density giving the maximum value of the number of gaps, that is, a
density at which the number of gaps changes from increase to
decrease. In particular, the reference numeral Ccnt is the first
value at which all binarization data representing halftone dots
output by the first comparing process section 21 has become output
dots, when the intensity of the multilevel image data DMV
(corresponding to the density of an input image) representing the
input image is changed from the low-intensity side.
[0055] The setting of densities C1 and C3, which gives the
gap-formation starting point on the low-density side, may be
considered to be essential to arrange the white dots (non-output
dots) inside the halftone dots while maintaining the outside of the
halftone dots formed of a set of black dots (output dots) as the
black dots (output dots). On the other hand, densities C2 and C4
giving the gap-formation starting point on the high-density side
are set to arrange white dots (non-output dots) within the halftone
dots only in an intermediate density region, but the densities C2
and C4 are not essential to the invention of this application. A
density range in which white dots (non-output dots) are arranged
inside the halftone dots may be in a range from the densities C1
and C3 giving the gap-formation starting point on the low-density
side to the maximum density Cmax.
[0056] The binarization processing section 20 according to the
first embodiment has features that it includes a plurality of sets
of comparators for binarization and threshold-value matrixes, and
that a plurality of calculation processors for performing a logic
operation for binary data output from the comparators, as compared
with conventional examples. In addition, the respective sets of the
comparators for binarization and the threshold-value matrixes are
modules, which can form the same halftone-dot structures, but are
characterized by the values of the threshold-value matrixes.
[0057] Specifically, as shown in the figure, the binarization
processing section 20 according to the first embodiment includes
three comparing sections 21, 22 and 23 for performing a comparison
process for binarization by referring to the multilevel data to be
processed and the threshold-value matrix, two binary calculating
process sections 26 and 27 for performing a logic operation for
binary data output from the comparing sections 21, 22 and 23, and a
threshold-value-matrix storage section 29.
[0058] The first comparing process section 21 corresponds to a
first halftone-dot processing section. A second halftone-dot
processing section includes the second and third comparing sections
22 and 23 and the first binary calculating process section 26. In
addition, a gap forming process section 28 for forming gaps in the
center portion of the halftone dots generated by the first
comparing process section 21 while maintaining a contour of the
halftone dots includes the second and third comparing sections 22
and 23 and the first and second binary calculating process sections
26 and 27.
[0059] Further, an algorithm for generating the halftone-dot image
in the second halftone-dot processing section including the second
and third comparing sections 22 and 23 and the first binary
calculating process section 26 is basically similar to an algorithm
for generating a halftone-dot image (black dots) as in the first
comparing process section 21 (that is, the first halftone-dot
processing section), even though threshold-value matrixes MTX1
referred to by these algorithms are different.
[0060] The threshold-value-matrix storage section 29 outputs
threshold values corresponding to coordinate values within the
matrixes. For example, the threshold-value-matrix storage section
29 has a halftone-dot profile storage section 29a and a gap-profile
storage section 29b.
[0061] The halftone-dot profile storage section 29a stores profile
data fundamental to forming the halftone dots. Specifically, the
halftone-dot profile storage section 29a stores a first
threshold-value matrix MTX1, which defines halftone-dot sizes
corresponding to densities of the input image, that is, defines the
densities of the input image for generating the halftone dots. The
first threshold-value matrix MTX1 gives a halftone-size profile
including a set of threshold-value data for formation of halftone
dots used in the halftone-dot forming process. Although the first
threshold-value matrix MTX1 is prepared so that a dot pattern
similar to a conventional halftone-dot growth can be basically
output, the first threshold-value matrix MTX1 is different from the
conventional halftone-dot growth in that the number of output dots
increases gradually within a unit halftone-dot region until the
density of the input image reaches from "0" to a transition-point
density Ccnt, and that all the dots within the unit halftone-dot
region become output dots after the density of the input image
exceeds the transition-point density Ccnt.
[0062] The gap-profile storage section 29b stores profile data,
which defines gap sizes corresponding to the densities of an input
image, that is, defines the densities of the input image for
generating the gaps. Specifically, the gap-profile storage section
29b stores second and third threshold-value matrixes MTX2 and MTX3
giving gap-size profile including a set of threshold-value data for
gap formation used in the gap forming process.
[0063] Here, the gap-size profile data (that is, threshold-value
data) stored in the gap-profile storage section 29b makes the gap
forming process section 28 to be able to generate halftone dots
having gaps of a size according to the gap-size profile data.
[0064] For example, the second threshold-value matrix MTX2 mainly
defines gap sizes on the low-density side in a middle density
region of the multilevel image data DMV. The third threshold-value
matrix MTX3 mainly defines gap sizes on the high-density side in
the middle density region of the multilevel image data DMV. A
combination of the both matrixes defines gap sizes in the entire
middle density region of the multilevel image data DMV.
"Combination of the both matrixes" in the first embodiment actually
refers to a logic synthesis for a result of the comparison with
reference to the threshold-value matrixes MTX2 and MTX3.
[0065] The gap-size profile has a basic characteristic that when an
input density exceeds a predetermined density, some of halftone
dots (black dots: output dots) are made to be white dots
(non-output dots) to form gaps, to thereby reduce an amount of
coloring material on the entire halftone dots. In other words, the
gap-size profile has a characteristic that gaps are not formed
within integrated (clustered) minute halftone dots by not forming
the gaps until the density of the input image exceeds the
predetermined density. Reproducibility of halftone dots
deteriorates when gaps are generated in a highlight tone area where
a dot size is small. This problem can be overcome by forming the
gaps with setting a relatively high density as the gap-formation
starting point.
[0066] In particular, as shown in the right upper portion of FIG.
3(A), within the unit halftone-dot region, while maintaining a
contour of a halftone dot, that is, while maintaining the outmost
output dots in lateral, longitudinal, and oblique directions
(hereinafter, referred to as "outline dots"), which contribute to
the formation of a contour of the halftone dots, as output dots,
the gaps are formed by making some dots inside the outline dots be
real non-output dots. That is, while maintaining coloring material
of contour portion of the halftone dots to a predetermined amount,
the amount of coloring material inside the contour portion of
halftone dots can be appropriately reduced.
[0067] Further, in a case in which a plurality of non-output dots
are formed inside the outline dots, if the non-output dots are
isolated from one another inside the outline dots, pixels to be
thinned out inside the halftone dots are scattered, which may
reduce an effect of making the coloring material of the halftone
dots thin. To avoid this problem, it is preferable to gather the
plurality of non-output dots into a cluster such that the plurality
of non-output dots are connected to one another, if at all
possible, without isolating the plurality of non-output dots from
one another. In addition, since output dots are scattered if output
dots of the halftone dots exist in a cluster composed of the
non-output dots, it is preferable to form the cluster with only the
non-output dots. Also, from a point of view of maintaining contour,
it is preferable to make the shape of a cluster composed of
non-output dots resemble the shape of the outline of the halftone
dots as much as possible.
[0068] For example, since halftone dots having sizes corresponding
to the densities are formed by increasing output dots such that a
set of black dots (output dots) has a roughly circular shape, it is
preferable to circularly thin out the recording signals (output
dots) inside the halftone dots having the roughly circular shape,
that is, to increase the number of non-output dots gradually from
the center of the halftone dots such that the set of non-output
dots has a roughly circular shape. For example, when four
non-output dots are formed inside the halftone dots, it is not
preferable that four non-output dots are not arranged in line in
the lateral, longitudinal, or inclined direction, but preferable
that two non-output dots are arranged in the lateral direction and
the other two non-output dots in the longitudinal direction.
Internal output dots are converted (thinned out) into non-output
dots such that the output dots are arranged in a roughly ring shape
when viewing the entire "halftone dots having gaps" as a final
result.
[0069] For example, the gap-profile storage section 29b stores
profile data according to one or both of a gap-size fixed system
shown in FIG. 3(A) and a gap-size variable system shown in FIG.
3(B). The value of the gap size b shown in FIG. 3(A) is an example,
and a plurality of profiles having various values obtained by
modifying the gap size b may be prepared. Similarly, a
characteristic line shown in FIG. 3(B) is an example, and a
plurality of profiles obtained by modifying the variation amount
(including maximum value) of the characteristic line in various
ways may be prepared. In any cases, a certain correspondence
relationship should exist between the density of the input image
and the gap size.
[0070] Further, when the plurality of profiles are stored, in
actuality, one of the profiles is selected and used according to
its application on the basis of a user's instruction through the
profile switch commanding section 50. Halftone-dot images with gaps
having different characteristics can be easily generated by
changing the used profile.
[0071] Here, the gap-size fixed system refers to a system of
forming a gap having a fixed size b0 at nearly a center inside the
halftone dots in a specific range (C1 to C2) of the middle density
region of density values of the multilevel image data DMV. On the
other hand, the gap-size variable system refers to a system of
dynamically (almost continuously) varying the gap size according to
a density as shown by a solid line in FIG. 3(B), in a specific
range (C3 to C4) of the middle density region of density values of
the multilevel image data DMV such that the gap size increases
gradually to the maximum value and decreases gradually after
reaching the maximum value.
[0072] In the gap-size fixed system, since one kind of a gap size
b0 may only be designated in the specific range (C1 to C2) of the
middle density region, a profile is relatively simple. However, a
pseudo outline may occur at a position where gap is generated even
though its generation mechanism is not evident. As one solution to
this problem, the gap-size variable system for designating
different gap sizes for different densities is employed.
[0073] Moreover, if relatively large (but smaller than halftone
dots) gaps are formed within relatively small halftone dots, that
is, if there are too many pixels thinned out inside the halftone
dots, the coloring material of halftone dot portions may become too
thin. To avoid this problem, in connection with variation
characteristics of the gap size from the densities C1 and C3 giving
the gap-formation starting point on the low-density side to the
transition-point density Ccnt, it is preferable to smoothly
increase the gap size. It is needless to say that the gap-size
fixed system is employed to give such a characteristic.
[0074] Further, in FIG. 3(B), the characteristic line (solid line)
is shown as a smooth curve varying substantially continuously.
However, when gaps are actually formed within the halftone dots,
the solid line has a multi-step characteristic because any dot
having a predetermined size in the threshold-value matrix is output
or not output.
[0075] Furthermore, as shown by a dotted line in FIG. 3(B), as an
intermediate system between the gap-size fixed system and the
gap-size variable system, a system of varying the gap size with
several steps according to a density such that the gap size
increases gradually to the maximum value and decreases gradually
after reaching the maximum value in the specific range of the
middle density region of density values of the multilevel image
data DMV can be employed.
[0076] Each of the comparing sections 21, 22, and 23, which is an
example of a density/threshold-value comparing section, compares
the multilevel image data DMV representing the density of an input
image, that is, the density of an input multilevel image, with the
threshold value of each of the threshold-value matrixes MTX1, MTX2
and MTX3 stored in the threshold-value-matrix storage section 29 to
then output an binary image.
[0077] For example, the first comparing process section 21 compares
the multilevel image data DMV to be processed with the first
threshold-value matrix MTX1. The second comparing process section
22 compares the multilevel image data DMV to be processed with the
second threshold-value matrix MTX2. The third comparing process
section 23 compares the multilevel image data DMV to be processed
with the third threshold-value matrix MTX3.
[0078] The first binary calculating process section 26 performs a
predetermined logic operation (specifically, difference process)
between second binary data Do2 output from the second comparing
process section 22 and third binary data Do3 output from the third
comparing process section 23.
[0079] The second binary calculating process section 27 performs a
predetermined logic operation (specifically, difference process)
between first bitmap data BM1, which is the first binary data Do1
output from the first comparing process section 21, and second
bitmap data BM2, which is a result of the logic operation output
from the first binary calculating process section 26.
[0080] A result of the logic operation executed in the second
binary calculating process section 27 is temporarily held as a
binarized recording signal Dout in the binary-data storage section
30. Then, the marking engine section 44 of the image recording
section 40 uses the binarized recording signal Dout in the image
recording process. That is, the marking engine section 44 serves as
a recording-energy control section for recording images on the
basis of the binarized recording signal Dout, which is binarization
data making some dots inside the outline dots generated by the
second binary calculating process section 27 become actual
non-output dots.
Procedure of the Halftone-Dot Process
First Embodiment
[0081] FIG. 5 and FIGS. 6(A) to 6(E) are diagrams illustrating the
binarization process (specifically, halftone-dot process) executed
in the binarization processing section 20 according to the first
embodiment. Here, in the case where the binarization processing
section 20 forms non-output dot with the dot-shaped halftone dot
(dot screen) being a process target, the following description will
be given by assuming that the gap-profile storage section 29b
stores the gap-size profile data of the gap-size variable system
shown in FIG. 3(B).
[0082] FIG. 5 is a flow chart illustrating an outline of a process
of the halftone-dot process by the binarization processing section
20 according to the first embodiment. FIGS. 6(A) to 6(E) are
diagrams illustrating a process of generating ring-shaped halftone
dots according to the halftone-dot process performed by the
binarization processing section 20 of the first embodiment. For
example, FIG. 6(A) shows an example of the first binary data Do1
output from the first comparing process section 21, that is, the
first bitmap data BM1. FIG. 6(B) shows an example of the second
binary data Do2 output from the second comparing process section
22. FIG. 6(C) shows an example of the third binary data Do3 output
from the third comparing process section 23. FIG. 6(D) shows an
example of the second bitmap data BM2 output from the first binary
calculating process section 26. FIG. 6(E) shows an example of the
binarized recording signal Dout output from the second binary
calculating process section 27.
[0083] The binarization processing section 20 according to the
first embodiment has a first feature that when multilevel image
data DMV having a density gradation is reproduced in a pseudo
manner by the size of colored dots called halftone dots, the amount
of coloring material is reduced by forming gaps inside the halftone
dots if density of an input image lies within the density range
from the gap-formation starting point on the low-density side to
that on the high-density side.
[0084] Further, the binarization processing section 20 according to
the first embodiment has a second feature that it employs a method
of thinning out information inside the halftone dots on the
binarized recording signal Dout, that is, a method in which two
images, i.e., a normal halftone-dot image and an image representing
a gap are generated and then a logic synthesis for the two images
is performed in order to reduce the amount of coloring material
inside the halftone dots.
[0085] Furthermore, the binarization processing section 20
according to the first embodiment has a third feature that it
generates the halftone dots having a halftone-dot size and a gap
size according to the profile by referring to profile data in which
the halftone-dot size and the gap size for each density are
recorded, in order to reduce the amount of the coloring material by
using, for example, a method of forming gaps in a central portion
of dots in the density specified by generating two images.
[0086] The first comparing process section 21 sets the first
threshold-value matrix MTX1 so as to output a halftone-dot pattern
having a size in accordance with the density of the multilevel
input image information (multilevel image data DMV) up to the
transition density Ccnt as in the conventional halftone-dot growth,
and compares with the multilevel image data DMV. Thereby, first
bitmap data BM1 shown in FIG. 6(A) is generated (S10).
[0087] The second comparing process section 22 sets the second
threshold-value matrix MTX2 so that dots of the second binary data
Do2 grow in a pattern where a dot follows another dot of the first
binary data Do1 from the inside of dots of the first binary data
Do1 (=the first bitmap data BM1) toward the outside thereof where
the density of the multilevel image data DMV is in a range of from
a density C3 (first density) giving the gap-formation starting
point on the low-density side to the transition-point density Ccnt
and that the second binary data Do2 maintains the state of the
transition-point density Ccnt, and compares with the multilevel
image data DMV. Thereby, the second comparing process section 22
generates the second binary data Do2 shown in FIG. 6(B).
[0088] The third comparing process section 23 sets the third
threshold-value matrix MTX3 so that dots are grown in a pattern
where the inside of dots of the second binary data Do2 is filled
with the dots from the outer side to the inner side of dots when
the density of the multilevel image data DMV exceeds the density
(the transition-point density) Ccnt, which gives the maximum value
of the number of gaps, and compare the third threshold-value matrix
MTX3 with the multilevel image data DMV. Thereby, the third
comparing process section 23 generates the third binary data
Do3.
[0089] The first binary calculating process section 26 generates
the second bitmap data BM2 shown in FIG. 6(D) by performing a
binary logic operation (logic subtraction process), which is
"Do2-Do3", between the second binary data Do2 output from the
second comparing process section 22 and the third binary data Do3
output from the third comparing process section 23.
[0090] A series of processes performed by the second halftone-dot
processing section including the second comparing process section
22, the third comparing process section 23, and the first binary
calculating process section 26 is to form gaps inside the halftone
dots according to the gap-size variable system (in this embodiment)
or the gap-size fixed system when the gaps are formed in the
halftone dots with the input density lying within the middle
density region C3 to C4, and are processes for making the gap size
correspond to the density of the input image. The purpose of the
processes is as follows.
[0091] For example, according to the gap-size variable system, when
the density of the multilevel input image information (multilevel
image data DMV) is less than the first density C3, the second
bitmap data BM2 is generated in such a manner that all outputs of
the second bitmap data BM2 are turned off (0; zero.fwdarw.white
dot/non-output dot) (S20-NO, S30). When the density of the
multilevel image data DMV is equal to or larger than the first
density C3 and less than the transition-point density Ccnt, the
second bitmap data BM2 is generated so that dots are turned on
(1.fwdarw.black dot/output dot) in accordance with the value of
density exceeding the first density C3 (S20-YES, S22-NO, S32).
[0092] In addition, when the density of the multilevel input image
information (multilevel image data DMV) is equal to or larger than
the transition-point density Ccnt at which all signals of the first
bitmap data BM1 are turned on (1.fwdarw.black dot/output dot) and
less than the second density C4, on-pixels (1.fwdarw.black
dot/output dot) in the second bitmap data BM2 are sequentially
turned off (0; zero.fwdarw.white dot/non-output dot) according to
the value of density exceeding the transition-point density Ccnt
(S22-YES, S24-NO, S34). Further, when the density of the multilevel
input image information (multilevel image data DMV) exceeds the
second density C4, all outputs of the second bitmap data BM2 are
turned off (0; zero.fwdarw.white dot/non-output dot) (S24-YES,
S36).
[0093] Thus, in the second bitmap data BM2, which is an output
result of the second halftone-dot processing section, as shown in
FIG. 6(D), a halftone-dot image is generated so that black dots
increase gradually in the specific range C3 to C4 of the middle
density region of the density values of the multilevel image data
DMV and decrease gradually after reaching the maximum value at the
transition-point density Ccnt. That is, halftone dots corresponding
to subsequent gaps (non-output dot) (a result of process in the
second binary calculating process section 27) can be dynamically
changed according to the density.
[0094] That is, in the second halftone-dot processing section
including the second comparing process section 22, the third
comparing process section 23, and the first binary calculating
process section 26, the second bitmap data BM2 are generated as
binarization data indicating non-output dots, which are represented
by a set of output dots and dynamically corresponds to the
intensities of the multilevel image data DMV (corresponding to the
densities of the input image) in a range from the first density C3
to the second density C4.
[0095] In particular, in this example, while the gap-size variable
system is employed, gaps are formed inside the halftone dots only
in the middle density region. Therefore, the number of non-output
dots takes its maximum value at the transition-point density Ccnt
at which the first bitmap data BM1 all become "1," and the number
of non-output dots gradually decreases from the maximum value
before and after the transition-point density (from C3 to Ccnt and
from Ccnt to C4). Thereby, the number of the non-output dots is
made to dynamically correspond to the input image density.
[0096] Thereafter, the second binary calculating process section 27
generates the binarized recording signal Dout shown in FIG. 6(E) by
performing a binary logic operation (logic subtraction process),
which is "BM1-BM2=Do1-(Do2-Do3)", between the first bitmap data BM1
(the first binary data Do1) output from the first comparing process
section 21 and the second bitmap data BM2 output from the first
binary calculating process section 26 (S38).
[0097] As shown in FIG. 6(E), the binarized recording signal Dout
output from the second binary calculating process section 27 is
binary data having a gap inside the halftone dot in the middle
density region. In other word, the binarization processing section
20 makes a part of dots inside the contour dots to be non-output
dots, on the binarized recording signal Dout, which is electronic
data representing the halftone dot.
[0098] Further, in this embodiment, since the gap-size variable
system is employed, it is possible to obtain the profile shown in
FIG. 3(B) in which the gap size varies according to the density so
that the gap size becomes a maximum at substantial center of the
middle density region and gradually decreases in the density region
before and after the substantial center.
[0099] Furthermore, even though not shown, according to the
gap-size fixed system, the second bitmap data BM2 is generated in
such a manner that all outputs of the second bitmap data BM2 are
turned off (0; zero.fwdarw.white dot/non-output dot) when the
density of multilevel input image information (multilevel image
data DMV) is less than the first density C1 and dots the number of
which corresponds to the gap size b are turned on (1.fwdarw.black
dot) when the density of the multilevel input image information
(multilevel image data DMV) is equal to or larger than the first
density C1 and less than the second density C2, without the
determination process on the transition-point density and processes
on the basis of the determination result in the gap-size variable
system. In addition, when the density of the multilevel input image
information (multilevel image data DMV) exceeds the second density
C2, all outputs of the second bitmap data BM2 are turned off (0;
zero.fwdarw.white dot).
[0100] According to the halftone-dot processing procedure executed
by the binarization processing section 20 according to the first
embodiment, it is possible to reliably generate the binarized
recording signal Dout having a gap inside the halftone dot without
damaging the contour shape of the halftone dots. Also, it is
possible to remove the coloring material inside the halftone dots
or to reduce the layer thickness in an output image by means of
gaps inside the halftone dot in data. Thus, a high transferability
of the coloring material and an improved image quality can be
obtained. Also, since a ratio of the amount of coloring material
contributing to light absorption can increase, it is possible to
reduce the amount of coloring material consumption.
[0101] That is, since gaps are reliably formed inside the halftone
dots without damaging the contour shape of the halftone dots, it is
possible to make the coloring material layer of the halftone dots
thin while preventing deterioration of image quality. For example,
since dots are not thinned out at ends of the halftone dots, there
is no possibility that the shapes of the halftone dots to be
reproduced are changed. Accordingly, image noises due to the gaps
are not generated.
[0102] Further, when the coloring material of the halftone dots is
made to be thin by adjusting the number of pixels to be thinned out
inside the halftone dots, that is, by adjusting the number of gaps
inside the halftone dots, the contour shape of the halftone dots is
not damaged, that is, gaps are not formed at the ends of the
halftone dots. Therefore, there is no adverse effect in which the
size of halftone dots is reduced. Accordingly, it is possible to
make the halftone dots uniformly thin.
[0103] Furthermore, when the density of the input image signal
exceeds the first density, the amount of coloring material is
reduced inside the halftone dots. Therefore, dot inside the
integrated (clustered) minute halftone dot is not thinned out as
shown in the uppermost figure in FIG. 6(E). As a result, there is
no possibility that dot reproduction in the halftone dot portion
will become unstable due to excessive reduction of the coloring
pixel area. That is, the amount of toner consumption can be reduced
while maintaining the reproducibility of the highlight tone area.
In particular, when the gap-size variable system for optimization
of the gap size for each density is employed, it is possible to
effectively improve the maintenance of image quality and to
effectively reduce the amount of toner consumption while
suppressing a pseudo outline at a position where gaps are
generated.
[0104] In addition, at first two images are generated, i.e., a
normal halftone-dot image and an image representing a gap are
generated. Then, a logic synthesis for the two images is executed
so as to form gaps inside the halftone dots. Thereby, the amount of
coloring material inside the halftone dots can be reduced.
Therefore, there is an advantage in that the gaps can be formed
relatively simply inside the halftone dots by using a digital
signal processing.
[0105] Moreover, the profile data (i.e., threshold-value data)
defining the gap sizes corresponding to the densities of the input
image is stored in the gap-profile storage section 29b, and the
gaps are formed by comparing the threshold-value data with the
multilevel image data DMV. Therefore, only by changing the profile,
a single processing device can generates a halftone-dot image with
gaps having different characteristics. Accordingly, even when the
gap size or the density at which the gaps are generated changes,
there is no need to re-design parameters for the binarization
processing. As a result, parameters for gap generation can be
efficiently designed.
Example of Output of Halftone Dots According to the First
Embodiment
[0106] FIG. 7 are diagrams showing an example of output of halftone
dots when an image recording process is performed according to the
procedure of the halftone-dot process executed by the binarization
processing section 20 of the first embodiment. Those examples show
design examples of ring-shaped halftone dots having a 190 lines/18
degree structure. FIG. 7(A) shows an output example of the first
bitmap data BM1 (the first binary data Do1) output from the first
comparing process section 21. FIG. 7(B) shows an output example of
the second binary data Do2 output from the second comparing process
section 22. FIG. 7 (C) shows an output example of the binarized
recording signal Dout output from the second binary calculating
process section 27 with respect to the multilevel image data DMV
corresponding to FIGS. 7(A) and 7(B). FIG. 7(D) shows an output
example of the binarized recording signal Dout when the multilevel
image data takes further higher density.
[0107] FIGS. 8(A) to 8(C) are diagrams showing a comparison in an
electronic image between halftone dots according to a related-art
method and the halftone dots generated according to the process
procedure executed by the binarization processing section 20 of the
first embodiment. This example also shows a design example of
ring-shaped halftone dots having a 190 line/18 degree structure.
Here, FIG. 8(A) shows a state of halftone-dot growth by a
related-art technique. FIG. 8(B) shows a state of halftone-dot
growth by the binarization processing section 20 according to the
first embodiment. FIG. 8(C) shows a state after fixing the toner
image to which the image recording section 40 applies the image
recording process on the basis of the binarized recording signal
Dout, which is generated from the input image of 25% density by the
binarization processing section 20 according to the first
embodiment.
[0108] As can be seen from a comparison of FIG. 8(B) with FIG.
8(C), when the binarization processing section 20 according to the
first embodiment performs the halftone-dot process, by performing
the binary calculation process to reduce the layer thickness of the
coloring material inside the halftone dots without damaging the
contour shape of the halftone dots due to toner or ink, it is
possible to obtain a halftone-dot image the inside of which is
filled up in an actual toner image even though ring-shaped halftone
dots having gaps thereinside are formed in an electronic image,
that is, in the binarized recording signal Dout. This means that it
is possible to reduce the amount of toner of the halftone-dot image
by applying the halftone-dot process according to the first
embodiment.
Overall Configuration of Image Forming Apparatus
Second Embodiment
[0109] FIG. 9 is a diagram illustrating an overall outline of an
image forming apparatus according to a second embodiment, with
focusing attention on the binarization process in a printing
apparatus employing an electrophotographic method, an inkjet method
or the like. The second embodiment provides a method of reducing
the amount of coloring material inside the halftone dots. The
second embodiment is characterized by employing a method of
modulating recording energy of non-output dots inside an outline
halftone dot on the basis of the first bitmap data BM1 and the
second bitmap data BM2 generated by the binarization processing
section 20, in order to reduce the amount of the coloring
material.
[0110] In the first embodiment, a completely electronic process is
performed to make some dots inside the outline dots become
non-output dots in the binarized recording signal Dout, which is
electronic data representing the halftone dots. To the contrary, in
the second embodiment, the control of the recording energy in the
image recording section 70 is additionally performed.
[0111] Specifically, as shown in FIG. 9, an image forming apparatus
1 according to the second embodiment includes a
color-separation-signal generating section 10, a binarization
processing section 60, a binary-data storage section 30, and an
image recording section 70.
[0112] Even though not shown, the binarization processing section
60 of the second embodiment has a configuration in which the second
binary calculating process section 27 in the binarization
processing section 20 of the first embodiment is removed.
[0113] The image recording section 70 has a modulation controlling
section 72 for generating output modulation data DEX for recording
and a marking engine 74 for performing an image recording process
on the basis of the output modulation data DEX generated by the
modulation controlling section 72.
[0114] The binarization processing section 60 provides the first
bitmap data BM1 (the first binary data Do1) output from the first
comparing process section 21 to an on/off control input terminal
72a of the modulation controlling section 72 through the
binary-data storage section 30. Also, the binarization processing
section 60 provides the second bitmap data BM2 output from the
first binary calculating process section 26 to a modulation control
terminal 72b of the modulation controlling section 72 through the
binary-data storage section 30.
[0115] The modulation controlling section 72 generates the output
modulation data DEX by using the first bitmap data BM1 as an on/off
control signal for exposure and using the second bitmap data BM2 as
output modulation control data.
[0116] In the image recording section 70 as configured above, the
marking engine 74 controls the recording energy of the halftone
dots on the basis of the output modulation data DEX so that the
coloring material inside the halftone dots is reduced. That is, the
marking engine 74 serves as a recording-energy control section for
recording an image on the basis of the output modulation data DEX
generated by the modulation controlling section 72.
[0117] For example, in the case where the marking engine 74 employs
an electrophotographic process, the marking engine 74 controls
exposure energy with using the output modulation data DEX as the
exposure modulation data so that the coloring material inside the
halftone dots is reduced. In addition, in the case where the
marking engine 74 employs an inkjet method, the marking engine 74
controls the amount of ink with using the output modulation data
DEX as ink amount modulation data so that the coloring material
inside the halftone dots is reduced.
Procedure of the Halftone-Dot Process
Second Embodiment
[0118] FIG. 10 and FIGS. 11(A) to 11(D) are diagrams illustrating a
binarization process (specifically, halftone-dot process) in the
image forming apparatus according to the second embodiment. Here,
it is assumed that the marking engine 74 employs the
electrophotographic method.
[0119] FIG. 10 is a flow chart illustrating an outline of a
procedure of the halftone-dot process executed by the image forming
apparatus 1 according to the second embodiment. FIGS. 11(A) to
11(D) are diagrams illustrating steps for generating ring-shaped
halftone dots according to the halftone-dot process executed by the
image forming apparatus 1 of the second embodiment. For example,
FIG. 11(A) shows an example of the first binary data Do1 output
from the first comparing process section 21, that is, the first
bitmap data BM1. FIG. 11(B) shows an example of the second binary
data Dot output from the second comparing process section 22. FIG.
11(C) shows an example of the third binary data Do3 output from the
third comparing process section 23. FIG. 11(D) shows an example of
the second bitmap data BM2 output from the first binary calculating
process section 26. FIGS. 11(A) to 11(D) are similar to FIGS. 6(A)
to 6(D), respectively.
[0120] The first comparing process section 21 serving as a first
halftone-dot processing section generates the first bitmap data
BM1, which forms halftone dots having a size corresponding to the
density of multilevel input image information (multilevel image
data DMV) (S10), similar to the first embodiment. The first
comparing process section 21 provides the generated first bitmap
data BM1 to the on/off control input terminal 72a of the modulation
controlling section 72 (S42).
[0121] Further, in the second halftone-dot processing section
including the second comparing process section 22, the third
comparing process section 23, and the first binary calculating
process section 26, the second bitmap data BM2, which forms
halftone dots corresponding to gaps having a size corresponding to
the density of the multilevel input image information (the
multilevel image data DMV), is generated (S20 to S36) according to
the same procedure as in the first embodiment. The second
halftone-dot processing section provides the generated second
bitmap data BM2 to the modulation control terminal 72b of the
modulation controlling section 72 (S44).
[0122] The modulation controlling section 72 generates the output
modulation data DEX with using the first bitmap data BM1 as the
on/off control signal for exposure and using the second bitmap data
BM2 as the output modulation control data (S46).
[0123] Here, in the configuration of the second embodiment, when
the image recording section 70 forms a toner image on a portion
exposed by light, the image recording section 70 performs an
exposure if the first bitmap data BM1 (on/off control signal) is
turned on (a hatched dot portion in FIG. 11(A)).
[0124] At this time, the image recording section 70 performs a 100%
exposure when the second bitmap data BM2 (output modulation data)
is "0; zero (a while dot portion in FIG. 11(D))", and performs an
exposure with a small amount of light (for example, less than 50%)
when the second bitmap data BM2 (output modulation data) is "1 (a
hatched dot portion in FIG. 11(D))".
[0125] Thus, it is possible to make dots having the second bitmap
data (output modulation data) of "1" become substantial non-output
dots. In addition, the real non-output dots in the first embodiment
and the substantial non-output dots are collectively called
substantial non-output dots.
[0126] The second bitmap data BM2 (output modulation data) is
obtained by the same process as in the first embodiment. If an
exposure is performed on the second bitmap data BM2 when only the
first bitmap data BM1 (on/off control signal) is turned on, it is
possible to obtain a printed pattern having gaps inside the
halftone dots in the middle density region, as shown in FIG.
6(E).
[0127] Thus, in actuality, it is possible to obtain the same
halftone-dot output image as in the first embodiment. Moreover, in
the output image, it is possible to remove the coloring material
inside the halftone dots or to reduce the layer thickness by
reducing the amount of exposure inside the halftone-dot image.
Accordingly, a high transferability of the coloring material and an
improved image quality can be obtained. Also, since a ratio of the
amount of coloring material contributing to light absorption can
increase, it is possible to reduce the amount of coloring material
consumption.
[0128] Further, the first embodiment has an advantage in that the
gaps can be formed relatively simply inside the halftone dots by
using a digital signal processing because the gaps are formed
inside the halftone dots by generating two images, i.e., the normal
halftone-dot image and the image representing gaps, and then
performing the logic synthesis for the two images. However, in the
first embodiment, since the density of gaps in the electronic data
(binarized recording signal Dout) becomes "0; zero", it is
essentially impossible to freely adjust the density of gaps.
Accordingly, in order to adjust the degree of thinness of the
coloring material inside the halftone dots, there may arise a need
to adjust the number of pixels to be thinned out inside the
halftone dots.
[0129] On the contrary, in the second embodiment, since it is
possible to adjust the amount of exposure when the second bitmap
data BM2 (output modulation data) becomes "1 (a hatched dot portion
in FIG. 11(D))", there is an advantage in that the density of gaps
can be freely adjusted even though the modulation controlling
section 72 is needed. Also, it is possible to adjust the degree of
thinness of the coloring material inside the halftone dots while
the number of pixels thinned out inside the halftone dots remains
unchanged.
Halftone-Dot Processing Procedure
Third Embodiment
Basic
[0130] FIGS. 13 and 14 are diagrams showing binarization processing
of a third embodiment (specifically, a halftone-dot processing).
The binarization processing of the third embodiment has a feature
in that what has a line-shaped halftone dot (line screen) as its
original halftone-dot structure is taken as a process target, and
the binarized processing section 20 generates non-output dots in
accordance with a predetermined rule.
[0131] Here, FIG. 13 is diagram illustrating a line-shaped halftone
dot (line screen), and FIG. 14 is a diagram illustrating a process
of generating a non-output dot (gap) with respect to the
line-shaped halftone dot. FIGS. 14(A) to (E) correspond to FIGS.
6(A) to 6(E), respectively.
[0132] In the process of generating the line-shaped halftone dot, a
comparator compares input multilevel data, which is the process
target (see FIG. 13(A)) and a threshold-value matrix for the
line-shaped halftone dot (see FIG. 13(B)) as shown in FIG. 13(C),
to thereby generate binarized recording signal Dout. In this case,
as shown in FIG. 13(D), although a shape of the halftone dot does
not have a line shape (line shape) at a low density (for example:
8), the dots are grown in a single direction as shown in FIG. 13
(E) as density increases to thereby connect in the line shape.
[0133] That is, as shown in an example of a line screen of 190
lines/72 degrees, in the line-shaped screen processing, an isolated
dot is generated in a low-density region, dots are grown therefrom
in a single direction, and dots, which are adjacent at low density,
are connected to form the line shape.
[0134] Here, as shown in FIG. 14, as in the first embodiment where
the dot-shaped halftone dot is dealt with, when an intensity of an
image signal exceeds a predetermined value and is in a
predetermined range, the binarized processing section 20 can thin
out a signal inside a halftone dot (in this case, meaning inside of
the line) by a synthesizing processing of binary data, which makes
a part of dots inside the contour dots to be actual non-output dot
while maintaining the contour dots, which are output dots
contributing to formation of the contour of such a line-shaped
halftone dot, that is, maintaining the line shape in accordance
with the flowchart shown in FIG. 5, which is a processing
procedure.
[0135] By applying the invention of this application to the
line-shaped halftone dot (line screen), the same effect as the
first embodiment can be enjoyed while an advantage of the
line-shaped halftone dot such as the fact that the line-shaped
halftone dot is strong against disturbance at the time of image
formation and color moire can be enjoyed, and a layer thickness of
coloring material inside the halftone dot can be thinned without a
contour shape of the halftone dot made of toner or ink being
deformed. The coloring material of the halftone-dot portion can be
thinned effectively without deterioration of the image quality, and
a consumption amount of the coloring material can be reduced.
Output Example 1 of Halftone Dot of Third Embodiment
[0136] FIG. 15 is a first example of generating gap with respect to
the line-shaped halftone dot according to a halftone-dot process
procedure of the third embodiment. This first example shows the
case where the third embodiment is applied to the line screen of
190 lines/72 degrees. FIG. 15(A) shows multilevel image data DMV,
FIG. 15(B) shows a first example of binarized image data of a line
screen structure and FIG. 15(C) shows a first example of gap
generation with respect to the line screen. Respective diagrams
show 12.5%, 25%, 50%, 75% and 100 in density.
[0137] If parameters of FIGS. 14(B), (C) and (D) take certain
parameters and multilevel image data DMV takes lower density (in
this case, 12.5% to 15%), gap exists in the line structure.
However, if the multilevel image data DMV takes further higher
density and is in a predetermined density range (in this example,
50% to 75%), non-output dots (gap) can be continued in a line shape
in the line-shaped halftone dot, that is, the gap is grown in the
line-shaped structure to form a double line structure
(particularly, refers to as "perfect hollow double line
structure).
[0138] However, in this case, since the gap becomes narrow on the
high-density side (noticeable at 75%), if number of screen lines
are a certain value and image is output with toner, the gap is
filled with the toner and a problem of the gradation
reproducibility arises. That is, in the case where the line-shaped
gap is provided in the line structure, as the number of screen
lines increases, if the perfect hollow double line structure is
employed, the line structure become too narrow and reproducibility
of the making process may be deteriorated.
Output Example 2 of Halftone Dot of Third Embodiment
[0139] FIG. 16 is a second example of generating gap with respect
to the line-shaped halftone dot according to a halftone-dot process
procedure of the third embodiment. This second example shows the
case where the third embodiment is applied to the line screen of
190 lines/72 degrees as well. FIGS. 16(A) to (C) correspond to
FIGS. 15(A) to (C), respectively.
[0140] By changing parameters of the FIGS. 14(B), (C) and (D), the
third embodiment can be applied as shown in the image example of
the second example, unlike the image example of the first example.
In this second example, if the multilevel image data DMV takes
lower density (in this case, 12.5% to 15%), gap exists in the line
structure. However, if the multilevel image data DMV takes further
higher density and is in a predetermined density range (in this
example, 50% to 75%), it is maintained that the non-output dots are
in an isolated state. That is, it is possible that the non-output
dots are not continued in the line-shaped halftone dot.
[0141] In this case, unlike the first example, the non-output dots
(gap) having a size to some extent can be generated surely even on
the high-density side. Therefore, even in the case where the number
of screen lines becomes large, the phenomenon that the gap becomes
narrow on the high-density side can be prevented by maintaining the
non-output dots to be in the isolated state in the line-shaped
halftone dot so that the gap is not continued in a line shape in
the line-shaped halftone dot. As a result, even in the case where
the image is actually output with toner, the phenomenon that the
gap is filled with the toner can be prevented and the
reproducibility of the line structure is enhanced. Therefore, the
reproducibility of the gradation can be kept good.
[0142] Having described the invention by way of exemplary
embodiments, it should be understood that the technical scope of
the invention is not limited thereto, but various changes and
modifications thereof can be made without departing from the spirit
of the invention. Also, it should be understood that the invention
covers such a modification or improvement.
[0143] Further, the embodiments are not intended to limit the
invention recited in claims. Furthermore, all combinations of
features described in the embodiments are not essential to the
solving means of the invention. The embodiments include various
inventions at various stages. Thus, various inventions may be made
by appropriate combining a plurality of described elements. In
addition, even if a few elements are removed from the overall
elements of the embodiments, a configuration from which the removed
few elements are excluded may be established as the invention as
long as an effect of the invention can be obtained.
[0144] For example, in the first and second embodiments, when the
image representing the gaps shown in FIG. 6(D) is generated, the
second threshold-value matrix MTX 2 defining the gap size on the
low density side and the third threshold-value matrix MTX 3
defining the gap size on the high density side are prepared and
then the gap size in the entire middle density region of the
multilevel image data DMV is specified by a combination of the both
threshold-value matrixes. However, gap threshold-value matrixes
(for example, putting two threshold values on the low and high
density sides into one coordinate) giving the halftone dot pattern
shown in FIG. 6(D) defining the gap size in the entire middle
density region of the multilevel image data DMV may be stored in
advance in the gap-profile storage section 29b. The binarization
process may be performed in the first binary calculating process
section 26 by using the gap threshold-value matrixes. With such
configuration, it is possible to reduce the number of
threshold-value matrixes to be used.
[0145] In addition, in the first embodiment, the gaps are formed
inside the halftone dots by generating two images, i.e., the normal
halftone-dot image shown in FIG. 6(A) and the halftone-dot image
representing the gaps shown in FIG. 6(D), and then performing the
logic synthesis for the two images. However, the binarization
process may be performed after the threshold values or density of
the input image is converted beforehand to form the halftone-dot
image having the gaps shown in FIG. 6(E).
[0146] With such configuration, it is possible to omit the
plurality of binarization processing sections for generating a
basic halftone-dot image (an example of the binary image) and
halftone-dot images (an example of the binary image; corresponding
to FIG. 6(D)) corresponding to the gap image (an example of the
binary image) for forming the gaps inside the halftone dots.
Accordingly, it is possible to efficiently generate the
halftone-dot images having the gaps.
Configuration Using Computer
[0147] Further, the above-described halftone dot process structure
may be configured not only by a hardware processing circuit but
also by software run by a computer on the basis of program codes
for implementing a function.
[0148] Accordingly, it is possible to consider, as a part of the
invention, a program or a computer-readable recording medium in
which the program is stored to implement the image processing
method, the image processing apparatus, or the image forming
apparatus according to the invention, by means of software run by
the computer. By employing a structure performed by the software,
there is an advantage in that a process order and the like can be
easily modified without modifying the hardware.
[0149] When the computer executes a series of halftone dot
processes by using software, programs constituting the software are
installed from a recording medium into a computer (for example,
built-in microcomputer) built in a dedicated hardware, or a SOC
(System On Chip) for implementing a desired system by mounting
various functions such as a CPU (Central Processing Unit), logic
circuits, memories and the like on a single chip, or a
general-purpose personal computer which is capable of performing
various functions by installing various programs into the computer,
and the like.
[0150] The recording medium changes the state of energy, such as
magnetism, light, electricity and the like, according to
description contents of the program by using a reading unit
included in a hardware resource of the computer, and delivers the
description contents of the program to the reading unit according
to a format of the signal corresponding to the change of the state
of energy.
[0151] For example, the recording medium may include a magnetic
disk (including a flexible disc (FD)) having a program recorded
thereon, an optical disc (CD-ROM (Compact Disc-Read Only Memory)),
a DVD (Digital Versatile Disc), an optical magnetic disc (including
a MD (Mini Disc)), or a transportable package media composed of
semiconductor memories and the like, all of which are distributed
to users to provide a program separately from a computer, or a ROM
or a hard disc having a program recorded thereon, which is provided
to users in a condition in which it is installed beforehand in a
computer. Also, the program constituting the software may be
provided to users through a wired or wireless communication
network.
[0152] For example, when a recording medium, which stores program
codes of software for implementing the halftone processing
function, is provided to a system or an apparatus and then a
computer (or CPU or MPU) of the system or apparatus reads out and
executes the program codes stored in the recording medium, it is
possible to achieve the same effect as that obtained by a hardware
processing circuit. In this case, the program codes themselves read
out from the recording medium implements the halftone process
functions.
[0153] Furthermore, not only the halftone process functions can be
implemented when the computer executes the read program codes, but
also, the halftone process functions can be implemented when OS
(Operating System) running on the computer performs some or all of
the actual processes on the basis of instructions of the program
codes.
[0154] In addition, after the program codes read from the recording
medium are written onto a memory installed in a function extension
card inserted into a computer or a function extension unit
connected to a computer, the halftone process functions can be
implemented when a CPU or the like installed in the function
extension card or the function extension unit performs some or all
of the actual processes on the basis of instructions of the program
codes.
[0155] Moreover, the program may be provided as a file in which the
program codes for implementing the halftone process functions are
described. In this case, the program may be provided as individual
program modules according to the hardware configuration of a system
constituted by the computer without being limiting to being
provided as a collective program file.
* * * * *