Methods and apparatus for calibrating a digital color imaging device that uses multi-hue colorants
View Patent ↗Methods and apparatus are provided for calibrating a digital color imaging device to a printing press by determining a total colorant limit, per-channel colorant limits, and channel linearization tables using colorimetric and/or spectrophotometric techniques. In addition, for digital color imaging devices that use multi-hue colorants, methods and apparatus are provided for determining distribution functions for the multi-hue colorants as a function of input values.
1. A method for calibrating a digital color imaging device to a printing press by determining a plurality of distribution functions for a plurality of multi-hue colorants, the method comprising:
printing a test pattern comprising a plurality of patches, each patch comprising a plurality of colorimetric values;
measuring a plurality of colorimetric values for each patch including at least a first shade of a colorant and at least one additional shade of said colorant;
calculating a first tonal response of said range of hues of said colorant from said measured colorimetric values;
calculating at least one additional tonal response of said at least one additional range of hues of said colorant from said measured colorimetric values;
calculating a tonal response of said printing press;
calculating a first distribution over a first range of input values;
calculating a second distribution over a second range of input values;
creating a table of tonal responses including said first range of input values and said second range of input value; and
calculating a normal distribution including the full range of input values.
2. The method of claim 1 , wherein said tonal response of said printing press is from 0 to 100%.
3. The method of claim 1 , wherein said first range of input values is from 0% to a lower limit.
4. The method of claim 1 , wherein said second range of input values is from a lower limit to 100%.
5. The method of claim 1 , wherein said normal distribution is from a lower limit to 100%.
6. The method of claim 1 , wherein said step of measuring a plurality of colorimetric values is performed by a spectrophotometer.
7. The method of claim 1 , wherein said step of measuring a plurality of colorimetric values is performed by a spectrocolorimeter.
8. The method of claim 1 , wherein said test patches comprise scales of light-hued colorant only, scales of normal-hued colorant only, and combinations of light-hued and normal-hued colorant.
9. The method of claim 1 , wherein said colorant comprises cyan.
10. The method of claim 9 , wherein said tonal response value for cyan is calculated using the following equation:
Tonal
Value
=
(
1
-
X
i
X
W
)
(
1
-
X
100
X
W
)
wherein X i is an X-value for said patch, X w is a X-value of a white paper, and X 100 is an X-value of solid cyan.
11. The method of claim 1 , wherein said colorant comprises magenta.
12. The method of claim 11 , wherein said tonal response for magenta is calculated using the following equation:
Tonal
Value
=
(
1
-
Y
i
Y
W
)
(
1
-
Y
100
Y
W
)
wherein Y i is a Y-value for said patch, Y w is a Y-value of a white paper, and Y 100 is a Y-value of solid magenta.
13. The method of claim 1 , wherein said colorant comprises yellow.
14. The method of claim 13 , wherein said tonal response for yellow is calculated using the following equation:
Tonal
Value
=
(
1
-
Z
i
Z
W
)
(
1
-
Z
100
Z
W
)
wherein Z i is a Z-value for said patch, Z w is a Z-value of a white paper, and Z 100 is a Z-value of solid yellow.
15. The method of claim 1 , wherein said colorant comprises black.
16. The method of claim 15 , wherein said tonal response for black is calculated using the following equation:
Tonal
Value
=
(
1
-
Y
i
Y
W
)
(
1
-
Y
100
Y
W
)
wherein Y i is a Y-value for said patch, Y w is a Y-value of a white paper, and Y 100 is a Y-value of solid black.
17. A system for calibrating a digital color imaging device to a printing press by determining a plurality of distribution functions for a plurality of multi-hue colorants comprising:
a color output device for printing a test pattern comprising a plurality of patches, each patch comprising a plurality of colorimetric values;
a measurement device for measuring a plurality of colorimetric values for each patch including at least a first shade of a colorant and at least one additional shade of said colorant;
a processor for calculating a first tonal response of said range of hues of said colorant from said measured colorimetric values and for calculating at least one additional tonal response of said at least one additional range of hues of said colorant from said measured colorimetric values;
a processor for calculating a tonal response of said printing press from 0 to 100%;
a processor for calculating a first light distribution from 0% to a lower limit;
a processor for calculating a second light distribution from a lower limit to 100%;
a processor for creating a table of light-normal tonal responses from a lower limit to 100%; and
a processor for calculating a normal distribution.
18. The system of claim 17 , wherein said measurement device is a spectrophotometer.
19. The system of claim 17 , wherein said measurement device is a spectrocolorimeter.
20. The system of claim 17 , wherein said colorants comprise magenta, yellow, cyan, and black.