Method and apparatus for generating multi-bit depth halftone amplitude-modulation dots
The present application discloses a method and an apparatus for generating multi-bit depth halftone amplitude-modulation dots. The method may comprise: scanning an input image to obtain a value of a current pixel P xy , where x represents a lateral position index of the current pixel, and y represents a vertical position index of the current pixel; obtaining g j from a preset multi-bit depth threshold matrix G by starting with i=0, and determining if P xy <g j , then providing a screening output gray level gradation value of the printer to Out=L−1−i; and otherwise, increasing i and repeating the determining and providing steps. L represents the number of a frequency-modulation screen gradation, L=2 e , e represents a bit depth value of the printer, i is an integer and i∈[0,L−1], h is an index number of an element g arranged sequentially in G and h is provided to h=(y % n)×m+(x % m)+i×m×n, and g j is the element value of i th line and j th row in G. The method and apparatus according to the present application can improve the speed for generating the multi-bit depth halftone amplitude-modulation dots.
1. A method for generating multi-bit depth halftone amplitude-modulation dots comprising:
scanning an input image to obtain a value of a current pixel P xy , where x represents a lateral position index of the current pixel, and y represents a vertical position index of the current pixel;
obtaining g j from a preset multi-bit depth threshold matrix G by starting with i=0, and
determining if P xy <g j ,
if yes, providing a screening output gray level gradation value of a printer Out=L−1−i; otherwise,
increasing i and repeating the determining and providing steps;
where L represents the number of a frequency-modulation screen gradation, L=2 e , e represents a bit depth value of the printer, i is an integer and i∈[0,L−1], h is an index number of an element g arranged sequentially in G and h is provided as h=(y % n)×m+(x % m)+i×m×n, and
g j is an element value of i th line and j th row in G.
2. The method according to claim 1 , wherein the multi-bit depth threshold matrix G is preset as
[
Line
1
:
g
1
,
g
2
,
g
3
,
…
g
n
×
m
Line
2
:
g
n
×
m
+
1
,
g
n
×
m
+
2
,
g
n
×
m
+
3
…
g
2
×
(
n
×
m
)
⋮
Line
i
:
…
g
j
Line
i
-
1
:
g
(
L
-
2
)
×
(
n
×
m
)
+
1
,
g
(
L
-
2
)
×
(
n
×
m
)
+
2
…
g
(
L
-
1
)
×
(
n
×
m
)
]
,
where m represents a width of the matrix, and n represents a height of the matrix.
3. The method according to claim 2 , wherein the multi-bit depth threshold matrix G is preset by:
1) setting initial parameters, comprising:
a) M=(L−1)×n×m, where M represents a maximum of G;
b) setting (L−1) cumulative arrays S i and initializing S i to S i =0; meanwhile, setting an index I of the cumulative arrays and an initial value of the index I is 0;
c) setting a cumulative threshold as C and the initial value of C is 1;
2) transferring logic are given as follows:
a) setting a=a xy ,
where x=I % m, if x>U i , x=U i , y=I(L−1);
when I %(n×m)=0, i=i+1, wherein % represents a modulo operation,
a xy represents a value of an element in x th line and y th row in a permutation matrix A i , U i represents a number of elements in i th line in the matrix A i ;
b) when a xy ≦(L−1) and S a <(m×n), proceeding the following operations:
traversing each value in a preset initial halftone one-bit amplitude-modulation screen threshold matrix T until t ru =S a , where t ru represents a value of an element in r th line and u th row in T;
setting g j =C in i th line of G, where j=u×m+r;
increasing the threshold cumulative value C: C=C+1;
increasing the cumulative array S a : S a =S a +1;
correcting a=L−1 if it is not satisfied with a condition of a xy ≦(L−1) and S a <(m×n);
c) setting I=I+1;
d) repeating the steps (a) to (c) until C>M, and then ending the operations.
4. The method according to claim 3 , wherein the initial halftone one-bit amplitude-modulation screen threshold matrix T is preset as
[
t
11
,
t
12
,
t
13
,
…
t
1
m
t
21
,
t
22
,
t
23
,
…
t
2
m
⋮
t
xy
⋮
t
n
1
,
t
n
2
,
t
n
3
,
…
t
nm
]
where t xy ∈[1,m×n] and t xy in the matrix T meets element anisotropy for each two; and
the permutation matrix A i is preset to
[
Line
0
:
a
01
,
a
02
,
a
03
,
…
a
0
U
0
,
Line
1
:
a
11
,
a
12
,
a
13
,
…
a
1
(
U
1
-
L
+
1
)
,
⋮
Line
i
:
a
i
1
,
a
i
2
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a
i
3
,
…
a
xy
,
…
a
iU
i
,
⋮
Line
L
-
3
:
a
(
L
-
3
)
1
,
a
(
L
-
3
)
2
,
a
(
L
-
3
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3
,
a
(
L
-
3
)
4
,
Line
L
-
2
:
a
(
L
-
2
)
1
,
a
(
L
-
2
)
2
,
a
(
L
-
3
)
3
,
a
(
L
-
3
)
4
,
Line
L
-
1
:
a
(
L
-
1
)
1
]
wherein
1) a i1 =a i2 =a i3 = . . . =a iU i =i
2) the number of elements in each line decreases from line 0 to line L−1, and (U i−1 −U i )−(U i −U i+1 )=1.
5. An apparatus for generating multi-bit depth halftone amplitude-modulation dots, comprising:
a scanning module configured to scan an input image to obtain a value of a current pixel P xy , wherein x represents a lateral position index of the current pixel, and y represents a vertical position index of the current pixel;
a generating module configured to obtain g i from a preset multi-bit depth threshold matrix G by starting with i=0, if P xy <g j , then the generating module is further configured to set a screening output gray level gradation value of a printer as Out=L−1−i; and
a repeating module configured to increase i and to invoke the generating module;
wherein L represents number of a frequency-modulation screen gradation, L=2 e , e represents a bit depth value of the printer, i is an integer and i∈[0,L−1], h is an index number of an element g arranged sequentially in G and h is provided to h=(y % n)×m+(x % m)+i×m×n, and g j is an element value of the i th line and j th row in G.
6. The apparatus according to claim 5 , wherein the multi-bit depth threshold matrix G is preset as
[
Line
1
:
g
1
,
g
2
,
g
3
,
…
g
n
×
m
Line
2
:
g
n
×
m
+
1
,
g
n
×
m
+
2
,
g
n
×
m
+
3
…
g
2
×
(
n
×
m
)
⋮
Line
i
:
…
g
j
Line
i
-
1
:
g
(
L
-
2
)
×
(
n
×
m
)
+
1
,
g
(
L
-
2
)
×
(
n
×
m
)
+
2
…
g
(
L
-
1
)
×
(
n
×
m
)
]
,
where m represents a width of the matrix, and n represents a height of the matrix.
7. The apparatus according to claim 6 , wherein the presetting step of the multi-bit depth threshold matrix G comprises:
1) setting initial parameters comprising:
a) M=(L−1)×n×m, where M represents the maximum of G;
b) setting (L−1) cumulative arrays S i and initializing S i to S i =0; meanwhile, setting an index I of the cumulative arrays and an initial value of the index I is 0;
c) setting a cumulative threshold as C and the initial value of the threshold C is 1;
2) transferring logic are given as follows:
a) setting a=a xy , where x=I % m, if x>U i , x=U i , y=I(L−1); and when I %(n×m)=0, i=i+1, % represents a modulo operation, a xy represents a value of an element in x th line and y th row in a permutation matrix A i , U i represents the number of elements in i th line in the matrix A i ;
b) when a xy ≦(L−1) and S a <(m×n), proceeding the following operations:
traversing each value in a preset initial halftone one-bit amplitude-modulation screen threshold matrix T until t ru =S a , where t ru represents a value of an element in r th line and u th row in T;
setting g j =C in the i th line of G, where j=u×m+r;
increasing the threshold cumulative value C: C=C+1;
increasing the cumulative array S a : S a =S a +1;
correcting a=L−1, if it is not satisfied with the condition of a xy ≦(L−1) and S a <(m×n);
c) setting I=I+1;
d) repeating the steps (a) to (c) until C>M, and then ending the operations.
8. The apparatus according to claim 7 , wherein the initial halftone one-bit amplitude-modulation screen threshold matrix T is preset as
[
t
11
,
t
12
,
t
13
,
…
t
1
m
t
21
,
t
22
,
t
23
,
…
t
2
m
⋮
t
xy
⋮
t
n
1
,
t
n
2
,
t
n
3
,
…
t
nm
]
where t xy ∈[1,m×n] and t xy in the matrix meets element anisotropy for each two; and
the permutation matrix A i is preset to
[
Line
0
:
a
01
,
a
02
,
a
03
,
…
a
0
U
0
,
Line
1
:
a
11
,
a
12
,
a
13
,
…
a
1
(
U
1
-
L
+
1
)
,
⋮
Line
i
:
a
i
1
,
a
i
2
,
a
i
3
,
…
a
xy
,
…
a
iU
i
,
⋮
Line
L
-
3
:
a
(
L
-
3
)
1
,
a
(
L
-
3
)
2
,
a
(
L
-
3
)
3
,
a
(
L
-
3
)
4
,
Line
L
-
2
:
a
(
L
-
2
)
1
,
a
(
L
-
2
)
2
,
a
(
L
-
3
)
3
,
a
(
L
-
3
)
4
,
Line
L
-
1
:
a
(
L
-
1
)
1
]
wherein
1) a i1 =a i2 =a i3 = . . . =a iU i =i
2) the number of elements in each line decreases from line 0 to line L−1, and (U i−1 −U i )−(U i −U i+1 )=1.