Method and apparatus for controlling a spot function for digital halftoning
View Patent ↗A digital halftoning technique for controlling a spot function is disclosed. A method for generating a spot for use in halftoning according to the present invention includes defining a spot function that combines two functions selected to provide a predetermined spot shape for use in a halftone cell and scaling the spot function using a scaling function that varies according to a value of a first and second spot function ordinate. Asymmetric modulation of spot functions is used to control the touching of adjacent spots, and to change the shape of the spots with the gray region.
1. A method for generating a spot for use in halftoning, comprising:
defining a spot function that combines two functions selected to provide asymmetrically changing of the shape of a spot for use in a halftone cell;
scaling the spot function according to grayscale levels using a parameterized spot radius scaling function that varies according to a value of a first and second spot function ordinate and an asymmetric shape changing scaling function based on a gray level for the spot, and
printing using the scaled spot function;
wherein the spot function is described by:
f
(
x
,
y
)
=
1
2
(
cos
(
π
x
/
p
x
)
+
1
S
(
p
,
r
)
cos
(
π
y
/
p
y
)
)
where x and y are the first and second spot function ordinates, p x scales ordinate x, p y scales ordinate y, p is a spot shape parameter for controlling the shape of the spot, S(p,r) is a scaling function, and r is the radius of the spot.
2. The method of claim 1 , wherein the two functions allow non-separable changes in spot shape.
3. The method of claim 1 , wherein the scaling function, S(p,r), is described by:
S
(
p
,
r
)
=
1
+
1
p
m
2
π
exp
(
-
(
r
/
2
-
1
/
2
)
2
2
p
2
)
,
where p m sets a maximum ellipticity of the spot.
4. A printing system, comprising:
a control unit for receiving a print file and processing the print file for printing;
a print head for conveying a print job according to the print file; and
a device for generating a spot for use in halftoning wherein the halftoning reproduces an image defined by the print file using the print head, the device defines a spot function that combines two functions selected to provide asymmetrically changing of the shape of a spot for use in a halftone cell and scales the spot function according to grayscale level using a parameterized spot radius scaling function that varies according to a value of a first and second spot function ordinate and an asymmetric shape changing scaling function based on a gray level for the spot,
wherein the spot function used by the device is described by:
f
(
x
,
y
)
=
1
2
(
cos
(
π
x
/
p
x
)
+
1
S
(
p
,
r
)
cos
(
π
y
/
p
y
)
)
where x and y are the first and second spot function ordinates, p x scales ordinate x, p y scales ordinate y, p is a spot shape parameter for controlling the shape of the spot, S(p,r) is a scaling function, and r is the radius of the spot.
5. The printing system of claim 4 , wherein the two functions allow non-separable changes in spot shape.
6. The printing system of claim 4 , wherein the scaling function, S(p,r), is described by:
S
(
p
,
r
)
=
1
+
1
p
m
2
π
exp
(
-
(
r
/
2
-
1
/
2
)
2
2
p
2
)
,
where p m sets a maximum ellipticity of the spot.
7. The printing system of claim 4 , wherein the device is a hardware card disposed between the control unit and the print head.
8. The printing system of claim 4 , wherein the device is a hardware card disposed within the control unit.
9. A program storage medium readable by a computer, the medium tangibly embodying one or more programs of instructions executable by the computer to perform halftoning an image by:
defining a spot function that combines two functions selected to provide asymmetrically changing of the shape of a spot for use in a halftone cell;
scaling the spot function according to grayscale level using a parameterized spot radius scaling function that varies according to a value of a first and second spot function ordinate and an asymmetric shape changing scaling function based on a gray level for the spot, and
printing using the scaled spot function;
wherein the spot function is described by:
f
(
x
,
y
)
=
1
2
(
cos
(
π
x
/
p
x
)
+
1
S
(
p
,
r
)
cos
(
π
y
/
p
y
)
)
where x and y are the first and second spot function ordinates, p x scales ordinate x, p y scales ordinate y, p is a spot shape parameter for controlling the shape of the spot, S(p,r) is a scaling function, and r is the radius of the spot.
10. The program storage medium of claim 9 , wherein the two functions allow non-separable changes in spot shape.
11. The program storage medium of claim 9 , wherein the scaling function, S(p,r), is described by:
S
(
p
,
r
)
=
1
+
1
p
m
2
π
exp
(
-
(
r
/
2
-
1
/
2
)
2
2
p
2
)
,
where p m sets a maximum ellipticity of the spot.
12. A printing system, comprising:
means for receiving a print file and processing the print file for printing;
means for conveying a print job according to the print file; and
means for generating a spot for use in halftoning wherein the halftoning reproduces an image defined by the print file using the print head, the means for generating a spot defines a spot function that combines two functions selected to provide asymmetrically changing of the shape of a spot for use in a halftone cell and scales the spot function according to grayscale level using a parameterized spot radius scaling function that varies according to a value of a first and second spot function ordinate and an asymmetric shape changing scaling function based on a gray level for the spot,
wherein the spot function is described by:
f
(
x
,
y
)
=
1
2
(
cos
(
π
x
/
p
x
)
+
1
S
(
p
,
r
)
cos
(
π
y
/
p
y
)
)
where x and y are the first and second spot function ordinates, p x scales ordinate x, p y scales ordinate y, p is a spot shape parameter for controlling the shape of the spot, S(p,r) is a scaling function, and r is the radius of the spot.