EP0963105A2
Expired / Lapsed
EP
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Threshold matrix, and method and apparatus of reproducing gray level using threshold matrix
Assignee: Canon Inc
•
Filing: 1999-06-02
•
Granted: —
•
Expires: 2019-06-02
Abstract
Abstract The present invention provides a threshold matrix that can obtain high-quality images with a uniform dot distribution using small masks and that can obviate the need to increase the mask size for a high-definition printer to reduce the memory capacity required to store the masks, as well as a gray-level reproduction method and apparatus using this threshold matrix. A threshold matrix is formed so that (1) a dot pattern generated by executing gray level processing using the threshold matrix has a set of element pixel blocks having in all gray levels the same dot distribution in each element pixel block corresponding to each element mask, so that (2) a low irregularity or pseudo periodicity is introduced into one of the low gray levels after the first gray level, so that (3) in all gray levels, the number of dots is equal for all element pixel blocks, and so that (4) every 4n ((n) is an integer) gray levels, the number of dots is equal for four partial element pixel blocks each obtained by dividing each element pixel block into four.
Inventors
- 👤 Takashi Suzuki
- 👤 Keiji Okinaka
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 14:45
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/405; H04N1/4051
Claims Analysis
Total Claims: 23
Claim 1
Independent Claim
133 words
A method of reproducing a gray level for representing
density of each pixel of an output image by binary or
multivalue data by corresponding each pixel of an original
image one to one to each pixel of a threshold matrix (a mask),
comprising the steps of: having non-blue noise properties at every gray level
of dot patterns generated in a pixel block of a reference
size using a mask of a size smaller than the reference size
of the pixel block; and generating in an output image no moire having visually
undesired contrast and an artifact such as a constant
repetitive pattern, etc. caused by the mask itself when an
input image receives a gray level process and the image is
output through an output device having a resolution of over
600 dpi.
Claim 2
Dependent Claim
34 words
The method according to claim 1, wherein said dot
pattern generated only by the mask has a value equal to or
larger than 1dB as a mean value of anisotropy at every gray
level.
Claim 3
Independent Claim
98 words
A method of reproducing a gray level for representing
density of each pixel of an output image by binary or
multivalue data by corresponding each pixel of an original
image one to one to each pixel of a threshold matrix (a mask),
comprising the steps of: having non-blue noise properties at every gray level
of dot patterns generated only by the mask; and generating in an output image no moire having visually
undesired contrast and an artifact such as a constant
repetitive pattern, etc. caused by the mask itself when an
input image receives a gray level process.
Claim 4
Independent Claim
130 words
A method of reproducing a gray level for representing
density of each pixel of an output image by binary or
multivalue data by corresponding each pixel of an original
image one to one to each pixel of a threshold matrix (a mask),
comprising the steps of: having a plurality of independent spectra, of a
two-dimensional domain frequency spectrum of a dot pattern
generated only by the mask, caused by periodicity of the mask
at every gray level; and generating in an output image, which has received a gray
level process, no visually undesired artifacts by
introducing low irregularity (perturbation) to distribution
of dots at a plurality of gray levels, and by assigning noise
elements having a small amount of low frequency elements to
a spectrum in a one-dimensional radius direction.
Claim 5
Independent Claim
192 words
A method of reproducing a gray level using a relatively
small threshold matrix having the same threshold array
corresponding to an entire original image in a two-dimensional
and regular array to represent density of each
pixel of an output image by binary or multivalue data by
corresponding each pixel of an original image one to one to
each pixel of a threshold matrix (a mask), comprising the
steps of: said mask having a size of an arrangement of a plurality
of masks (element masks) of a size used in dispersed-dot
dithering, and dot pattern generated by said mask: (1) having a set of element pixel blocks in which
distribution of dots in each element pixel block
corresponding to each element mask is the same at every gray
level; (2) having low irregularity or pseudo-periodicity at
any low gray level at a first level or thereafter; (3) having an equal number of dots in all element pixel
blocks at every level; and (4) having an equal number of dots in four partial
element pixel blocks each having a quarter of each element
pixel block at every 4n (n indicates an integer) gray level.
Claim 6
Independent Claim
26 words
The method according to any of claims 1 through 5,
wherein adjacent masks are shifted along a boundary when said
masks are two-dimensionally and repeatedly used.
Claim 7
Independent Claim
15 words
The method according to claims 1 through 6, wherein said
mask is different from quadrilateral.
Claim 8
Independent Claim
77 words
The method according to any of claims 5 through 7,
wherein said low irregularity or pseudo-periodicity is
implemented by providing, at all or part of predetermined
positions in each element pixel block corresponding to each
element mask, a small pixel block having a number of pixels
equal to or smaller than a quarter (1/4) of a total number
of pixels in the section, and by selecting one pixel for a
dot in each of small pixel blocks.
Claim 9
Independent Claim
73 words
The method according to any of claims 1 through 8,
wherein repulsive potential is assigned to all dots when a
dot pattern is determined for a specific gray level as a
method of determining a dot pattern at each gray level to
generate the mask, and a dot is placed to determine a dot
pattern for a next gray level at a pixel having lowest
potential determined as a sum of potential values.
Claim 10
Independent Claim
52 words
A method of reproducing a gray level of color image to
which the method according to any of claims 1 through 9 is
applied, wherein a color image is analyzed into a plurality
of color elements; and an original image having at least one
of the color elements is an input image.
Claim 11
Independent Claim
179 words
An apparatus of reproducing a gray level for
representing density of each pixel of an output image by
binary or multivalue data by corresponding each pixel of an
original image one to one to each pixel of a threshold matrix
(a mask), comprising: storage means for storing a threshold matrix; comparison means for comparing a value of the threshold
matrix as a threshold with density of each pixel of an
original image; and output means for outputting a binary or multivalue dot
pattern based on a comparison result of said comparison means,
wherein said threshold matrix has a size smaller than the
reference size of the pixel block, dot patterns generated
in a pixel block of a reference size have non-blue noise
properties at every gray level, no moire having visually
undesired contrast nor an artifact such as a constant
repetitive pattern, etc. caused by the mask itself is
generated in an output image when an input image receives
a gray level process and the image is output through an output
device having a resolution of over 600 dpi.
Claim 12
Independent Claim
148 words
An apparatus of reproducing a gray level for
representing density of each pixel of an output image by
binary or multivalue data by corresponding each pixel of an
original image one to one to each pixel of a threshold matrix
(a mask), comprising: storage means for storing a threshold matrix; comparison means for comparing a value of the threshold
matrix as a threshold with density of each pixel of an
original image; and output means for outputting a binary or multivalue dot
pattern based on a comparison result of said comparison means,
wherein said threshold matrix has dot patterns generated only
by the mask having non-blue noise properties at every gray
level, and generates in an output image no moire having
visually undesired contrast or an artifact such as a constant
repetitive pattern, etc. caused by the mask itself when an
input image receives a gray level process.
Claim 13
Independent Claim
182 words
An apparatus of reproducing a gray level for
representing density of each pixel of an output image by
binary or multivalue data by corresponding each pixel of an
original image one to one to each pixel of a threshold matrix
(a mask), comprising: storage means for storing a threshold matrix; comparison means for comparing a value of the threshold
matrix as a threshold with density of each pixel of an
original image; and output means for outputting a binary or multivalue dot
pattern based on a comparison result of said comparison means,
wherein said threshold matrix has a plurality of independent
spectra, of a two-dimensional domain frequency spectrum of
a dot pattern generated only by the threshold matrix, caused
by periodicity of the threshold matrix at every gray level,
and generates in an output image, which has received a gray
level process, no visually undesired artifacts by
introducing low irregularity (perturbation) to distribution
of dots at a plurality of gray levels, and by assigning noise
elements having a small amount of low frequency elements to
a spectrum in a one-dimensional radius direction.
Claim 14
Independent Claim
213 words
An apparatus of reproducing a gray level for
representing density of each pixel of an output image by
binary or multivalue data by corresponding each pixel of an
original image one to one to each pixel of a threshold matrix
(a mask), comprising: storage means for storing a threshold matrix; comparison means for comparing a value of the threshold
matrix as a threshold with density of each pixel of an
original image; and output means for outputting a binary or multivalue dot
pattern based on a comparison result of said comparison means,
wherein said threshold matrix mask has a size of an arrangement
of a plurality of masks (element masks) of a size used in
dispersed-dot dithering, and a generated dot pattern has: (1) a set of element pixel blocks in which distribution
of dots in each element pixel block corresponding to each
element mask is the same at every gray level; (2) low irregularity or pseudo-periodicity at any low
gray level at a first level or thereafter; (3) an equal number of dots in all element pixel blocks
at every level; and (4) an equal number of dots in four partial element pixel
blocks each having a quarter of each element pixel block at
every 4n (n indicates an integer) gray level.
Claim 15
Dependent Claim
107 words
A threshold matrix for use in converting density of each
pixel of an original image into binary or multivalue data,
wherein said threshold matrix has a size smaller than the
reference size of the pixel block, dot patterns generated
in a pixel block of a reference size have non-blue noise
properties at every gray level, no moire having visually
undesired contrast nor an artifact such as a constant
repetitive pattern, etc. caused by the mask itself is
generated in an output image when an input image receives
a gray level process and the image is output through an output
device having a resolution of over 600 dpi.
Claim 16
Dependent Claim
77 words
A threshold matrix for use in converting density of each
pixel of an original image into binary or multivalue data,
wherein said threshold matrix has dot patterns generated only
by the threshold matrix having non-blue noise properties at
every gray level, and generates in an output image no moire
having visually undesired contrast or an artifact such as
a constant repetitive pattern, etc. caused by the mask itself
when an input image receives a gray level process.
Claim 17
Dependent Claim
110 words
A threshold matrix for use in converting density of each
pixel of an original image into binary or multivalue data,
wherein said threshold matrix has a plurality of independent
spectra, of a two-dimensional domain frequency spectrum of
a dot pattern generated only by the threshold matrix, caused
by periodicity of the threshold matrix at every gray level,
and generates in an output image, which has received a gray
level process, no visually undesired artifacts by
introducing low irregularity (perturbation) to distribution
of dots at a plurality of gray levels, and by assigning noise
elements having a small amount of low frequency elements to
a spectrum in a one-dimensional radius direction.
Claim 18
Dependent Claim
141 words
A threshold matrix for use in converting density of each
pixel of an original image into binary or multivalue data,
wherein said threshold matrix mask has a size of an
arrangement of a plurality of masks (element masks) of a size
used in dispersed-dot dithering, and a generated dot pattern
has: (1) a set of element pixel blocks in which distribution
of dots in each element pixel block corresponding to each
element mask is the same at every gray level; (2) low irregularity or pseudo-periodicity at any low
gray level at a first level or thereafter; (3) an equal number of dots in all element pixel blocks
at every level; and (4) an equal number of dots in four partial element pixel
blocks each having a quarter of each element pixel block at
every 4n (n indicates an integer) gray level.
Claim 19
Dependent Claim
179 words
A computer-readable storage medium storing a control
program for controlling a gray level reproducing process for
representing density of each pixel of an output image by
binary or multivalue data by corresponding each pixel of an
original image one to one to each pixel of a threshold matrix
(a mask), comprising: a threshold matrix having a size smaller than the
reference size of the pixel block, dot patterns generated
in a pixel block of a reference size having non-blue noise
properties at every gray level, wherein no moire having
visually undesired contrast nor an artifact such as a
constant repetitive pattern, etc. caused by the mask itself
is generated in an output image when an input image receives
a gray level process and the image is output through an output
device having a resolution of over 600 dpi; and a module for comparing a value of the threshold matrix
as a threshold with density of each pixel of an original image
for each pixel, and controlling an output of binary or
multivalue dot patterns depending on a comparison result.
Claim 20
Dependent Claim
145 words
A computer-readable storage medium storing a control
program for controlling a gray level reproducing process for
representing density of each pixel of an output image by
binary or multivalue data by corresponding each pixel of an
original image one to one to each pixel of a threshold matrix
(a mask), comprising: a threshold matrix having dot patterns generated only
by the threshold matrix having non-blue noise properties at
every gray level, wherein no moire having visually undesired
contrast or an artifact such as a constant repetitive pattern,
etc. caused by the mask itself is generated when an input
image receives a gray level process; and a module for comparing a value of the threshold matrix
as a threshold with density of each pixel of an original image
for each pixel, and controlling an output of binary or
multivalue dot patterns depending on a comparison result.
Claim 21
Dependent Claim
183 words
A computer-readable storage medium storing a control
program for controlling a gray level reproducing process for
representing density of each pixel of an output image by
binary or multivalue data by corresponding each pixel of an
original image one to one to each pixel of a threshold matrix
(a mask), comprising: a threshold matrix having a plurality of independent
spectra, of a two-dimensional domain frequency spectrum of
a dot pattern generated only by the threshold matrix , caused
by periodicity of the threshold matrix at every gray level,
wherein no visually undesired artifacts is generated in an
output image, which has received a gray level process, by
introducing low irregularity (perturbation) to distribution
of dots at a plurality of gray levels, and by assigning noise
elements having a small amount of low frequency elements to
a spectrum in a one-dimensional radius direction; and a module for comparing a value of the threshold matrix
as a threshold with density of each pixel of an original image
for each pixel, and controlling an output of binary or
multivalue dot patterns depending on a comparison result.
Claim 22
Dependent Claim
212 words
A computer-readable storage medium storing a control
program for controlling a gray level reproducing process for
representing density of each pixel of an output image by
binary or multivalue data by corresponding each pixel of an
original image one to one to each pixel of a threshold matrix
(a mask), comprising: a threshold matrix mask having a size of an arrangement
of a plurality of masks (element masks) of a size used in
dispersed-dot dithering, wherein a generated dot pattern
has: (1) a set of element pixel blocks in which distribution
of dots in each element pixel block corresponding to each
element mask is the same at every gray level; (2) low irregularity or pseudo-periodicity at any low
gray level at a first level or thereafter; (3) an equal number of dots in all element pixel blocks
at every level; and (4) an equal number of dots in four partial element pixel
blocks each having a quarter of each element pixel block at
every 4n (n indicates an integer) gray level; and a module for comparing a value of the threshold matrix
as a threshold with density of each pixel of an original image
for each pixel, and controlling an output of binary or
multivalue dot patterns depending on a comparison result.
Claim 23
Dependent Claim
108 words
A gray scale reproducing apparatus of associating each
pixel of an original image with each pixel of a threshold
matrix (mask) on a one-to-one correspondence to reproduce
the density of each pixel of an output image using binary
or multivalue data, wherein: in the anisotropy of dot
patterns generated only by a threshold matrix, the dot
pattern has a spectrum having a mean value of 3 dB or more
at every gray level and a maximum value of 10 dB or more,
and no moire having visually undesired contrast or no
artifact such as a constant repetition pattern caused by the
mask is generated in an output image.
References Cited (Backward Citations)
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