Online grey balance with dynamic highlight and shadow controls
Tone reduction curves are utilized to map an input value to an output value. A tone reduction curve is normally produced by an algorithm that fits a curve to a series of knots. Knots can be determined from calibration data. Printing a calibration patch pattern yields a target patch pattern. The desired reflectances of the calibration patches and the measured reflectances of target patches can be used as calibration data. The series of knots can also include a highlight knot and a shadow knots so that the tone reduction curve functions better in the highlight and shadow regions.
1 . A method comprising:
producing a target patch pattern by printing a calibration patch pattern on a substrate wherein said calibration patch pattern comprises at least two calibration patches that are developable and have at least two desired reflectances;
measuring said target patch pattern to obtain at least two target reflectances; and
determining a target highlight value from calibration data comprising an input highlight value, said at least two target reflectances and said at least two desired reflectances, thereby obtaining a target highlight value in a less developable region.
2 . The method of claim 1 further comprising using said target highlight value and said calibration data to produce a tone reproduction curve.
3 . The method of claim 1 wherein said at least two calibration patches comprise at least two calibration patches printed with black.
4 . The method of claim 1 wherein said at least two calibration patches comprise at least two calibration patches printed with at least one primary color.
5 . The method of claim 1 wherein said target highlight value is determined by linear extrapolation.
6 . The method of claim 1 wherein said at least two calibration patches are three developable calibration patches.
7 . A method comprising:
obtaining calibration data comprising at least one target saturation and at least one maximum desired saturation;
using said calibration data to produce a tone reproduction curve, thereby setting said tone reproduction curve for use in printing saturated areas.
8 . The method of claim 7 wherein one of said at least one target saturation is a primary color's maximum possible saturation.
9 . The method of claim 7 wherein one of said at least one target saturation is black's maximum possible saturation.
10 . The method of claim 7 wherein said at least one target saturation is a user selected saturation.
11 . The method of claim 10 further comprising producing a target patch by printing a calibration patch based on said user selected saturation, measuring a target reflectance of said target patch, and wherein said calibration data further comprises said target reflectance.
12 . A system comprising:
a storage device adapted to store a calibration patch pattern comprising at least two calibration patches;
a marking engine that marks a substrate based on said calibration patch pattern to produce a target patch pattern;
a color measuring device that obtains at least two target reflectances from said target patch pattern;
a processor that determines at least one target highlight value and at least one tone reproduction curve from calibration data comprising an input highlight value and said at least two target reflectances;
a second storage device adapted to store said at least one tone reproduction curve.
13 . The system of claim 12 wherein said calibration data further comprises at least one target saturation and at least one maximum desired saturation.
14 . The system of claim 13 wherein said at least one target saturation comprises at least one primary color's maximum possible saturation.
15 . The system of claim 13 wherein one of said at least one target saturation is black's maximum possible saturation.
16 . The system of claim 13 wherein said at least one target saturation comprises at least one user selected saturation.
17 . The system of claim 16 wherein at least one of said at least one calibration patch is based on said at least one user selected saturation and wherein said calibration data further comprises said at least one maximum desired saturation and said at least one user selected saturation.
18 . The system of claim 12 wherein said processor uses linear extrapolation to produce said at least one target highlight value.
19 . The system of claim 12 wherein said at least two calibration patches comprise at least two calibration patches printed with black.
20 . The system of claim 12 wherein said at least two calibration patches comprise at least two calibration patches printed with at least one primary color.