Method and apparatus for calibrating spot color

1. A method for calibrating a spot color, comprising:

determining a target value for the spot color; and

calibrating a printing device in an enumeration cycling manner, so that a spot color measurement value of a color block output by the printing device approximates the target value, wherein the calibrating further comprises:

1) setting the target value as a spot color standard value;

2) setting a plurality of spot color values centered at the spot color standard value, the spot color standard value and the plurality of spot color values constituting a set of spot color enumeration values;

3) printing, by the printing device, a color target chart by using the spot color enumeration values;

4) measuring each color block on the color target chart to obtain a spot color measurement value of the each color block;

5) determining a chromatic aberration between the spot color standard value and each obtained spot color measurement value;

6) determining the spot color enumeration value of the color block corresponding to the spot color measurement value having a minimum chromatic aberration;

7) setting the determined spot color enumeration value which is corrected by a set amplitude as a new spot color standard value;

8) repeating steps 2 to 7 until a minimal value of the chromatic aberrations begins to rebound, then stopping the repeating and determining the spot color enumeration value of the color block corresponding to the spot color measurement value having a minimum chromatic aberration as a final print value.

2. The method of claim 1 , wherein the determining a target value for the spot color further comprises:

measuring a spot color block on a color card to obtain a color value as the target value for the spot color.

3. The method of claim 1 , wherein the printing device has a color space of Lab, and the step of setting a plurality of spot color values centered at the spot color standard value further comprises:

setting step sizes of Lab as:

L step i =( L step 0 , . . . ,L step m-1 )

a step i =( a step 0 , . . . ,a step z-1 )

b step i =( b step 0 , . . . ,b step k-1 )

where m, z, k are numbers of step sizes of Lab respectively;

wherein m*z*k spot color values are obtained by using spot color standard values L std , a std , b std as center and using L step i , a step i , b step i as step size.

4. The method of claim 3 , further comprising:

determining values of m, a, k based on chromatic aberrations ΔL, Δa, Δb between Lstd, a std , b std and spot color target values L target , a target , b target ,

wherein m, z, k are ranked according to their values so as to correspond to a rank of ΔL, Δa, and Δb.

5. The method of claim 3 , wherein the step of determining a chromatic aberration between the spot color standard value and each obtained spot color measurement value is carried out by rule of:

Δ

⁢

⁢

E

i

=

Δ

⁢

⁢

L

i

2

+

Δ

⁢

⁢

a

i

2

+

Δ

⁢

⁢

b

i

2

i

∈

[

0

,

n

-

1

]

Δ

⁢

⁢

L

i

=

L

measurement

⁢

⁢

i

-

L

target

i

∈

[

0

,

n

-

1

]

Δ

⁢

⁢

a

i

=

a

measurement

⁢

⁢

i

-

a

target

i

∈

[

0

,

n

-

1

]

Δ

⁢

⁢

b

i

=

b

measurement

⁢

⁢

i

-

b

target

i

∈

[

0

,

n

-

1

]

where L measure i , a measure i , b measure i are measured chromaticity values of n color blocks, respectively.

6. The method of claim 5 , wherein the step of setting the determined spot color enumeration value which is corrected by a set amplitude as a new spot color standard value is carried out by rule of:

L

std

=

L

enumeration

-

(

L

measurement

-

L

target

)

*

rat

rat

∈

[

0

,

1

]

a

std

=

a

enumeration

-

(

a

measurement

-

a

target

)

*

rat

rat

∈

[

0

,

1

]

b

std

=

b

enumeration

-

(

b

measurement

-

b

target

)

*

rat

rat

∈

[

0

,

1

]

where L measure , a measure , b measure represent the spot color measurement values corresponding to the minimum chromatic aberration, and rat is a set correction factor.

7. An apparatus for printing a spot color, comprising:

a target module configured to determine a target value for the spot color; and

a calibration module which comprises:

a standard value module configured for setting the target value as a spot color standard value;

a enumeration value module configured for setting a plurality of spot color values centered at the spot color standard value, the spot color standard value and the plurality of spot color values constituting a set of spot color enumeration values;

a color target module configured for enabling a printing device to print a color target chart by using the spot color enumeration values;

a measurement module configured for measuring each color block on the color target chart to obtain a spot color measurement value of the each color block;

a chromatic aberration module configured for determining a chromatic aberration between the spot color standard value and the each spot color measurement value;

a determination module configured for determining a spot color enumeration value of the color block corresponding to the spot color measurement value having a minimum chromatic aberration;

a correction module configured for setting the determined spot color enumeration value which is corrected by a set amplitude as a new spot color standard value; and

a control module configured to control the enumeration module, the color target module, the measurement module, the chromatic aberration module, the determination module and the correction module to repeat their respective functioning until a minimal value of the chromatic aberrations begins to rebound, and then determine the spot color enumeration value of the color block corresponding to the spot color measurement value having a minimum chromatic aberration as a final print value.

8. The apparatus of claim 7 , wherein the calibration module is configured to calibrate the printing device in an enumeration cycling manner, so that a spot color measurement value of a color block output by the printing device approximates the target value.

9. The apparatus of claim 7 , wherein the printing device has a color space of Lab, and the setting the plurality of spot color values centered at the spot color standard value further comprises:

setting step sizes of Lab as:

L step i =( L step 0 , . . . ,L step m-1 )

a step i =( a step 0 , . . . ,a step z-1 )

b step i =( b step 0 , . . . ,b step k-1 )

where m, z, k are numbers of step sizes of Lab respectively;

m*z*k spot color values are obtained by using spot color standard values L std , a std , b std as center and using L step i , a step i , b step i as step size.

10. The apparatus of claim 9 , wherein:

values of m, a, k are determine based on chromatic aberrations ΔL, Δa, Δb between Lstd, a std , b std and spot color target values L target , a target , b target ,

wherein m, z, k are ranked according to their values so as to correspond to a rank of ΔL, Δa, and Δb.

11. The apparatus of claim 9 , wherein the calibration module is configured to calibrate the printing device in an enumeration cycling manner, so that a spot color measurement value of a color block output by the printing device approximates the target value.

12. The apparatus of claim 11 , wherein:

values of m, a, k are determined based on chromatic aberrations ΔL, Δa, Δb between Lstd, a std , b std and spot color target values L target , a target , b target ,

wherein m, z, k are ranked according to their values so as to correspond to a rank of ΔL, Δa, and Δb.

13. The apparatus of claim 11 , wherein the step of determining a chromatic aberration between the spot color standard value and each obtained spot color measurement value is carried out by rule of:

Δ

⁢

⁢

E

i

=

Δ

⁢

⁢

L

i

2

+

Δ

⁢

⁢

a

i

2

+

Δ

⁢

⁢

b

i

2

i

∈

[

0

,

n

-

1

]

Δ

⁢

⁢

L

i

=

L

measurement

⁢

⁢

i

-

L

target

i

∈

[

0

,

n

-

1

]

Δ

⁢

⁢

a

i

=

a

measurement

⁢

⁢

i

-

a

target

i

∈

[

0

,

n

-

1

]

Δ

⁢

⁢

b

i

=

b

measurement

⁢

⁢

i

-

b

target

i

∈

[

0

,

n

-

1

]

where L measure i , a measure i , b measure i are measured chromaticity values of n color blocks, respectively.

14. The apparatus of claim 9 , wherein the step of determining a chromatic aberration between the spot color standard value and each obtained spot color measurement value is carried out by rule of:

Δ

⁢

⁢

E

i

=

Δ

⁢

⁢

L

i

2

+

Δ

⁢

⁢

a

i

2

+

Δ

⁢

⁢

b

i

2

i

∈

[

0

,

n

-

1

]

Δ

⁢

⁢

L

i

=

L

measurement

⁢

⁢

i

-

L

target

i

∈

[

0

,

n

-

1

]

Δ

⁢

⁢

a

i

=

a

measurement

⁢

⁢

i

-

a

target

i

∈

[

0

,

n

-

1

]

Δ

⁢

⁢

b

i

=

b

measurement

⁢

⁢

i

-

b

target

i

∈

[

0

,

n

-

1

]

where L measure i , a measure i , b measure i are measured chromaticity values of n color blocks, respectively.

15. The apparatus of claim 14 , wherein the step of setting the determined spot color enumeration value which is corrected by a set amplitude as a new spot color standard value is carried out by rule of:

L

std

=

L

enumeration

-

(

L

measurement

-

L

target

)

*

rat

rat

∈

[

0

,

1

]

a

std

=

a

enumeration

-

(

a

measurement

-

a

target

)

*

rat

rat

∈

[

0

,

1

]

b

std

=

b

enumeration

-

(

b

measurement

-

b

target

)

*

rat

rat

∈

[

0

,

1

]

where L measure , a measure , b measure represent the spot color measurement values corresponding to the minimum chromatic aberration, and rat is a set correction factor.