Producing correction data for printer
View Patent ↗Correction data is produced for density errors in prints produced using a printer. While printing a test image, the periods of rotation of one or more rotatable imaging members arranged along a receiver feed path in the printer are measured using respective period sensors. The printed test image is measured along a selected measurement direction and a reproduction error signal representing deviation from aim density is determined. For each period sensor, the autocorrelation of the reproduction error signal for the corresponding period is determined. If the determined autocorrelation exceeds a selected threshold, the reproduction error signal is decomposed at the corresponding period to extract the variation from the measured component. The remaining error signal is separated by frequency terms. The variations from the data at measured periods and the remaining error signal are used to produce a correction signal.
1. A method of producing correction data for a printer, comprising:
arranging a plurality of rotatable imaging members along a receiver feed path in the printer;
arranging one or more period sensors in operative arrangement with respective rotatable imaging members, the period sensors sensing a period and a phase of the respective rotatable imaging members;
printing a test image using the rotatable imaging members and simultaneously using the period sensors to record the respective periods and phases of the corresponding rotatable imaging members, the test image defining an aim density pattern;
measuring the printed test image along a selected measurement direction, determining a reproduced density pattern from the measurements, and determining a reproduction error signal using the aim density pattern and the reproduced density pattern;
a member-variation-determining step of, for each period sensor, determining a respective autocorrelation of the reproduction error signal for the corresponding period and, if the determined autocorrelation exceeds a selected threshold, decomposing the reproduction error signal at the corresponding period to determine a respective member-variation signal and removing the determined respective member-variation signal from the reproduction error signal to produce an adjusted reproduction error signal and a respective adjusted member variation signal;
a remaining-variation-determining step of, after the member-variation-determining step, separating the adjusted reproduction error signal into one or more remaining-variation signals, each having a respective significance;
a modifying step of, if the significance of any of the remaining-variation signals exceeds a selected threshold, modifying the adjusted reproduction error signal by removing that remaining-variation signal from the adjusted reproduction error signal and producing a respective adjusted remaining-variation signal;
repeating the remaining-variation-determining and modifying steps until no remaining-variation signal has significance exceeding the selected threshold; and
a correction step of automatically producing a correction signal using the adjusted member-variation signals and the adjusted remaining-variation signals using a processor, wherein the correction signal varies with the determined phases of the rotatable imaging members having autocorrelations that exceed the selected threshold;
using the correction signal to print image data using the printer, thereby compensating for banding artifacts.
2. The method according to claim 1 , further including:
repeating the measuring through correction steps for a plurality of selected detection angles to produce respective correction signals;
selecting two or more of the respective correction signals; and
repeating the applying step using each of the selected respective correction signals in turn to produce the corrected image data.
3. The method according to claim 2 , wherein each of the respective correction signals has a respective amplitude and one or more respective characteristic frequencies, and the selecting step includes selecting a particular one of the respective correction signals if:
the amplitude of the particular correction signal exceeds a selected amplitude threshold; or
a beat term between one of the characteristic frequencies of the particular correction signal and one of the characteristic frequencies of a selected correction signal different from the particular correction signal has an amplitude exceeding the selected amplitude threshold.
4. The method according to claim 2 , further including receiving through an input interface an indication of one or more of the selected detection angles.
5. The method according to claim 2 , wherein the detection angles include 0° and 90°.
6. The method according to claim 2 , wherein the detection angles include 45°.
7. The method according to claim 1 , further comprising automatically identifying an artifact signature from the member-variation signals, adjusted member-variation signals, remaining-variation signals, or adjusted remaining-variation signals using the processor, and reporting the identified artifact signature using an output interface.
8. The method according to claim 1 , wherein the remaining-variation-determining step includes decomposing the adjusted reproduction error signal using a discrete cosine transform to provide the remaining-variation signals.
9. The method according to claim 1 , wherein each remaining-variation signal has a respective stored probability of occurrence, and the remaining-variation-determining step includes selecting remaining-variation signals in an order based on their respective probabilities of occurrence and adjusting the respective probability of occurrence of each remaining-variation signal using the determined significance of that remaining-variation signal.
10. The method according to claim 9 , further including receiving an update to one of the respective probabilities of occurrence through an input interface and storing the updated probability.
11. The method according to claim 9 , further including reporting one or more of the respective probabilities of occurrence through an output interface.
12. The method according to claim 1 , wherein the remaining-variation-determining step includes transforming the adjusted reproduction error signal from the time domain to the frequency domain.
13. The method according to claim 1 , wherein the printer is an electrophotographic printer.
14. The method according to claim 1 , further including reporting one or more of the remaining-variation signals through an output interface.
15. The method according to claim 1 , further including changing the frequency of one of the rotational members and printing a second test target, wherein the measuring step includes measuring both test targets and the subsequent steps include analyzing measurements for both test targets, and the correction step further includes comparing the member-variation signals, adjusted member-variation signals, remaining-variation signals, or adjusted remaining-variation signals to determine for which signals to produce the correction data.