Pitch to pitch online gray balance calibration
A printer or other marking engine includes a marking material transfer device, such as a photoreceptor drum or belt, that includes a plurality of pitches. Each pitch receives an individual color of marking material and conveys the marking material to a substrate. The marking engine forms a desired image in a main image area of the substrate using marking material from one or more of the pitches, and produces a target patch pattern for each of the pitches in a margin area located outside the main image area. A measuring device such as a spectrophotometer is used to measure each target patch pattern, and based on the measured values, an individual color calibration is performed for each pitch for use in a subsequent marking operation. The color calibration may include generating or modifying a tone reproduction curve for each pitch based on the measured values. The margin area may be later trimmed off, thereby removing the portion of the substrate on which the target patch pattern is formed.
1. A method of calibrating a marking engine that comprises a marking material transfer device that includes a plurality of pitches, each pitch receiving an individual color of marking material and conveying the marking material to a substrate, the method comprising:
forming a user-controlled or user-selected desired image in a first area of the substrate by transferring marking material from one or more of the pitches of the marking material transfer device to the substrate, each pitch being a separate image forming area of the marking material transfer device, each pitch receiving an individual color of marking material and conveying the marking material to the substrate, the first area being a normal image forming area in which the user-controlled or user-selected image is formed;
producing a target patch pattern for each of the pitches in a second area of the substrate, the second area being a margin area located outside the first area;
measuring each target patch pattern to obtain measured values for each patch in each target patch pattern; and
based on the measured values, performing an individual color calibration for each pitch for use in a subsequent marking operation, and thereby compensating for differences among inherent or acquired characteristics of each pitch.
2. The method of claim 1 , wherein performing the calibration comprises:
determining a separate tone reproduction curve for each pitch based on the measured values; and
applying the tone reproduction curves to their respective pitches.
3. The method of claim 1 , wherein producing a target patch pattern comprises:
producing at least one process gray patch;
producing at least one black-based gray patch; and
producing at least one patch of each primary color used by the marking engine.
4. The method of claim 3 , wherein producing at least one process gray patch includes producing a plurality of process gray patches with an area coverage value in the range of from about 0 to about 100 percent.
5. The method of claim 3 , wherein producing at least one black-based gray patch includes producing a plurality of patches with area coverage values in the range of from about 0 to about 90.
6. The method of claim 3 , wherein producing at least one patch for each primary color used by the printer includes producing patches of each primary color with area coverage values of about 100.
7. The method of claim 1 , wherein measuring includes employing a color sensor to measure L*a*b* values of the patches of each target patch pattern.
8. The method of claim 2 , wherein determining a tone reproduction curve comprises:
obtaining calibration data comprising at least one target saturation and at least one maximum desired saturation;
using the calibration data to produce a tone reproduction curve, thereby setting said tone reproduction curve for use in printing saturated areas.
9. A system comprising:
a marking engine that includes a marking material transfer device that includes a plurality of pitches, each pitch receiving an individual color of marking material and conveying the marking material to a substrate, each pitch being a separate image forming area of the marking material transfer device;
a first storage device adapted to store a target patch pattern for each pitch;
the marking engine marking a user-controlled or user-selected desired image on a first area of a substrate by transferring marking material from one or more of the pitches of the marking material transfer device to the substrate, and producing a target patch pattern for each of the pitches in a second area of the substrate based on the stored target patch pattern, the first area being a normal image forming area in which the user-controlled or user-selected image is formed, the second area being a margin area located outside the first area;
a color measuring device that obtains a target reflectance from each target patch of the target patch pattern;
a processor that determines an individual color calibration value for each pitch, based on the target reflectances, thereby compensating for differences among inherent or acquired characteristics of each pitch; and
a second storage device adapted to store the color calibration value for each pitch of the marking material transfer device for use in a subsequent marking operation.
10. The system of claim 9 , wherein the processor determines at least one tone reproduction curve based on the target reflectances.
11. The system of claim 9 , wherein the marking material transfer device is a photoreceptor.
12. The method of claim 1 , wherein the marking material transfer device is a photoreceptor.