Amplification modulation screening method and apparatus
An amplitude modulation screening method is provided. The method comprises a step of utilizing regular hexagon screen dots to form a threshold matrix for amplitude screening. In embodiments of the present application, an amplitude modulation screening apparatus is also provided. The apparatus may comprise a matrix module configured to constitute a threshold matrix for amplitude screening using regular hexagon screen dots. Due to the threshold matrix formed with regular hexagon screen dots, the method and apparatus of the present application resolve the problem of the screen dots in the prior art, and improve the printing quality.
1. An amplitude modulation screening method, comprising:
utilizing regular hexagon screen dots to form a threshold matrix for amplitude screening, the step of utilizing comprising:
tiling the regular hexagon screen dots in the formed threshold matrix;
mapping each pixel of the threshold matrix onto each of the regular hexagon screen dots; and
setting a threshold for each pixel in each of the regular hexagon screen dots.
2. The method of claim 1 , wherein the step of tiling comprises:
dividing the threshold matrix into a plurality of tiled characteristic rectangles;
setting each of the characteristic rectangles to include:
one said regular hexagon screen dot D 0 at the center of the characteristic rectangle; and
four ¼ said regular hexagon screen dots D 1 , D 2 , D 3 , D 4 at corners of the characteristic rectangle, respectively, and being adjacent to D 0 ,
wherein the regular hexagon screen dot is divided into four portions in accordance with:
a first cutting line, which is a diagonal line along the tiling direction, and
a second cutting line, which passes through a center of the regular hexagon screen dot and being perpendicular to the first cutting line.
3. The method of claim 2 , wherein the step of mapping comprises:
drawing a line AA 1 which has an interaction angle with a line AB along the tiling direction and interacts with a line CD at a point A 1 ,
drawing a line BB 1 which is perpendicular to the line AA 1 and interacts with the line CD at a point B 1 ,
drawing a line segment CF which is perpendicular to the line BB 1 and interacts with the line BB 1 at a point F,
translating horizontally a right triangle BFC to the left X to obtain AGD,
translating vertically a trapezoid ABB 1 A 1 downwards Y−1 pixels to form a new trapezoid DCC 1 D 1 ,
extending AA 1 to interact with D 1 C 1 at a point A 2 , and BB 1 to interact with D 1 C 1 at a point B 2 ,
translating vertically a trapezoid A 1 B 1 B 2 A 2 downwards Y pixels to form a new trapezoid D 1 C 1 C 2 D 2 ,
repeating the above operations until the lines AA 1 and BB 1 interact at a point M in a new trapezoid D 3 C 3 C 4 D 4 ,
translating vertically a right triangle A 4 MB 4 downwards Y pixels to obtain D 4 PC 4 ,
extending the line AA 1 to interact with CP at a point N, extending the line BB 1 to interact with DP at a point Q, wherein a rectangle AMQG and a rectangle CFQP form a L-shaped area;
numbering uniquely screen dots in the L-shaped area; and
projecting the L-shaped area onto the rectangle ABCD.
4. The method of claim 2 , wherein the step of dividing the threshold matrix into a plurality of tiled characteristic rectangles comprises:
setting coprime length p and width q of the characteristic rectangle, where p/q≈√{square root over (3)}:1;
setting the tiling direction θ, wherein tgθ=a/b, and a and b are coprime;
setting a length and a width of the threshold matrix as follows:
X
=
Min
{
int
(
q
×
res
freq
×
a
2
+
b
2
〈
a
×
p
,
b
×
q
〉
)
,
int
(
p
×
res
freq
×
a
2
+
b
2
〈
a
×
p
,
b
×
q
〉
}
Y
=
Min
{
int
(
q
×
res
freq
×
a
2
+
b
2
〈
a
×
q
,
b
×
p
〉
)
,
int
(
p
×
res
freq
×
a
2
+
b
2
〈
a
×
q
,
b
×
p
〉
}
where Min{,} represents a minimized operation, <,> represents the greatest common divisor operation, the sign int( ) represents a rounding operation, Res represents a resolution of the printing device, and freq is the number of screening lines;
determining the number n of the regular hexagon screen dot as:
n
=
X
×
Y
/
(
res
freq
×
res
freq
)
=
p
×
q
×
(
a
2
+
b
2
)
〈
a
×
p
,
b
×
q
>
x
<
a
×
q
,
b
×
p
〉
.
5. The method of claim 4 , wherein set p=7, q=4, a=7, b=26.
6. The method of claim 2 , wherein the step of setting a threshold for each pixel comprises:
for each of the regular hexagon screen dots, determining a sorting value f i for each pixel based on a location of the pixel in the regular hexagon screen dot, wherein i=1, 2, . . . X×Y/n, X and Y represent the length and the width of the threshold matrix, respectively, and n represents the number of the hexagon screen dots;
establishing an array A based on the sorting value by rule of:
A
=
{
A
0
[
f
1
,
f
2
,
…
f
(
X
×
Y
/
n
)
]
A
1
[
f
1
,
f
2
,
…
f
(
X
×
Y
/
n
)
]
…
A
i
[
f
1
,
f
2
,
…
f
(
X
×
Y
/
n
)
]
…
A
n
[
f
1
,
f
2
,
…
f
(
X
×
Y
/
n
)
]
…
(
f
1
<
f
2
<
…
<
f
(
X
×
Y
/
n
)
)
where A i corresponds to each of the regular hexagon screen dots.
7. The method of claim 6 , wherein the step of determining the sorting value f i for each pixel comprises:
setting f i to be
{
f
i
=
(
2
×
y
i
)
/
q
,
if
k
<=
0
f
i
=
3
×
x
i
/
p
+
y
i
/
q
,
if
k
>
0
;
where k=3×q×x i −p×y i , x i , y i represent coordinates of pixel i in the regular hexagon screen dot,
wherein, for each of the regular hexagon screen dots, the center thereof is considered as the origin, and a diagonal line along the tiling direction is considered as the horizontal axis, and a line passing through the center of the regular hexagon screen dot and being perpendicular to the horizontal axis is considered as the vertical axis, so a coordinate system for each of the regular hexagon screen dots is created, and coordinates x i , y i of the pixel in each regular pixel screen dot are determined in the coordinate system.
8. The method of claim 7 , wherein for each of the regular hexagon screen dots, set the threshold of each pixel therein to be:
A
=
{
A
0
[
1
,
2
,
3
,
…
,
j
,
…
,
X
×
Y
/
n
]
A
1
[
1
,
2
,
3
,
…
,
j
,
…
,
X
×
Y
/
n
]
…
A
i
[
1
,
2
,
3
,
…
,
j
,
…
,
X
×
Y
/
n
]
…
A
n
-
1
[
1
,
2
,
3
,
…
,
j
,
…
,
X
×
Y
/
n
]
where, iε[0,n=1] and jε[0,X×Y/n−1].
9. The method of claim 8 , wherein the method further comprises:
generating random jitter table D[i], where iε[0,n−1]; and
setting A i [j]=D[i]*n+D[j], iε[0,n−1], jε[0,X×Y/n−1].
10. An amplitude modulation screening apparatus, comprising:
a matrix module configured to use regular hexagon screen dots to form a threshold matrix for amplitude screening, the matrix module comprising:
a tiling module configured to tile the regular hexagon screen dots in a threshold matrix;
a mapping module configured to map each pixel of the threshold matrix onto each of the regular hexagon screen dots; and
an assigning module configured to set a threshold for each pixel in each of the regular hexagon screen dots.
11. The apparatus of claim 10 , wherein the tiling module comprises:
a dividing module configured to divide the threshold matrix into a plurality of tiled characteristic rectangles; and
a creating module configured to set each characteristic rectangle to comprise:
one regular hexagon screen dot D 0 at the center of the characteristic rectangle; and
four ¼ said regular hexagon screen dots D 1 , D 2 , D 3 , D 4 at corners of the characteristic rectangle, respectively, and being adjacent to D 0 ,
wherein the regular hexagon screen dot is divided into four portions in accordance with,
a first cutting line, which is a diagonal line along the tiling direction, and
a second cutting line, which passes through a center of the regular hexagon screen dot and being perpendicular to the first cutting line.