Defective inkjet compensation using halftone screen permutations

Patent metadata

Field	Value
Publication number	US-2025313024-A1
Application number	US-202418627952-A
Country	US
Kind code	A1
Filing date	Apr 5, 2024
Priority date	Apr 5, 2024
Publication date	Oct 9, 2025
Grant date	—

Abstract

A method for compensating for defective ink jets includes, for an original halftone screen including cells arranged in columns and rows, each cell comprising a threshold value, identifying a first column in the original halftone screen corresponding to a defective inkjet in a marking device. A permuted halftone screen is generated from the original halftone screen with a protocol which includes, for each row in the original halftone screen, providing for swapping a threshold value of a cell in the identified first column with threshold values in cells of neighboring columns, such that the first column assumes the largest threshold value of: the threshold value in the identified first column, a threshold value in a first of the neighboring columns, and a threshold value in a second of the neighboring columns. The permuted screen is stored for halftoning an input image to be printed by the marking device.

First claim

What is claimed is:

1 . A method for compensating for defective ink jets comprising:
for an original halftone screen including cells arranged in columns and rows, each cell comprising a threshold value, identifying a first column in the original halftone screen corresponding to a defective inkjet in a marking device; generating a permuted halftone screen from the original halftone screen with a protocol which includes:
(a) for each row in the original halftone screen, providing for swapping a threshold value of a cell in the identified first column with threshold values in cells of neighboring columns, such that the first column assumes the largest threshold value of: the threshold value in the identified first column, a threshold value in a first of the neighboring columns, and a threshold value in a second of the neighboring columns; and
storing the permuted screen for halftoning an input image to be printed by the marking device.

2 . The method of claim 1 , wherein in (a), where the threshold values in the cells of the first and second neighboring columns are both larger than the threshold value of the cell in the identified first column, the protocol includes swapping the threshold value of the cell in the identified first column with a smaller one of the threshold values in the cells of the first and second of the neighboring columns, followed by swapping the threshold value currently in the cell in the identified first column with the threshold value in the other of the first and second neighboring columns.

3 . The method of claim 1 , wherein the protocol further includes:
(b) circularizing the threshold values in the first column in a first direction; (c) after step (b), repeating step (a); (d) circularizing the threshold values in the first column in a second direction, opposite to the first direction.

4 . The method of claim 3 , wherein the protocol further includes:
(e) circularizing the threshold values in the first column in the second direction; (f) after step (e), repeating step (a); and (h) circularizing the threshold values in the first column in the first direction.

5 . The method of claim 1 , wherein the protocol includes at least two iterations, wherein in a first of the iterations, the neighboring columns are each spaced from the first column by one cell, and in a second of the iterations, the neighboring columns are each spaced from the first column by more than one cell.

6 . The method of claim 5 , wherein in the second of the iterations, the neighboring columns are each spaced from the first column by two cells.

7 . The method of claim 6 , wherein in a third of the iterations, the neighboring columns are each spaced from the first column by three cells.

8 . The method of claim 1 , wherein the original screen comprises a first row of sub-screens, the method comprising performing the protocol for each of the sub-screens in the first row that include a first column corresponding to a respective defective inkjet in the marking device and assembling the permuted sub-screens to form the permuted screen.

9 . The method of claim 8 , wherein the original screen comprises a plurality of rows of sub-screens, the method comprises repeating the permuted sub-screens to form a plurality of rows of the permuted screen.

10 . The method of claim 1 , wherein the marking device comprises a plurality of printheads, a first of the printheads ejecting a first ink through respective inkjets and a second of the printheads ejecting a second ink through respective inkjets, the method including generating a first permuted halftone screen from the original halftone screen with the protocol to compensate for defective ink jets in the first printhead and generating a second permuted halftone screen from the original halftone screen or from another halftone screen with the protocol to compensate for defective ink jets in the second printhead.

11 . The method of claim 1 , wherein step (a) is performed with a processor including hardware.

12 . The method of claim 1 , further comprising detecting the defective inkjets, the detecting including rendering a halftone test pattern with the marking device to generate a printed image and evaluating the printed image.

13 . The method of claim 1 , wherein the identifying of the first column in the original halftone screen corresponding to a defective inkjet includes accessing a data structure which lists pixels in the original halftone screen corresponding to the defective inkjet.

14 . The method of claim 1 , further comprising halftoning an input image with the permuted screen to generate a halftone image and printing an output image with the marking device, using the halftone image.

15 . A computer program product comprising a non-transitory recording medium storing instructions, which when executed on a computer, causes the computer to perform the method of claim 1 .

16 . A printing system comprising instructions for performing the method of claim 1 and an ink jet marking device which receives a halftone image generated with the permuted halftone screen.

17 . A printing system comprising:
a marking device comprising inkjets; and a controller, in communication with the marking device, the controller storing instructions which:
for an original halftone screen including cells arranged in columns and rows, each cell comprising a threshold value, identify a first column in the original halftone screen corresponding to a defective inkjet in the marking device;
generate a permuted halftone screen from the original halftone screen with a protocol which includes, for each row in the original halftone screen, providing for swapping a threshold value of a cell in the identified first column with threshold values in cells of neighboring columns, such that the first column assumes the largest threshold value of: the threshold value in the identified first column, a threshold value in a first of the neighboring columns, and a threshold value in a second of the neighboring columns; and
store the permuted screen for halftoning an input image to be printed by the marking device.

18 . The printing system of claim 17 , wherein the marking device comprises a plurality of printheads, each of the printheads ejecting a respective ink from inkjets and wherein the instructions include, for each of the printheads, generating a respective permuted screen with the protocol.

19 . A method for compensating for defective ink jets of a marking device when printing an image comprising:
providing a permuted halftone screen which has been generated from an original halftone screen, the original screen comprising an array of threshold values, with a protocol which includes swapping ones of the threshold values, each corresponding to a defective inkjet, with neighboring threshold values that are larger; and halftoning an input image using the permuted screen, wherein the halftoning comprises comparing contone values of the input image with threshold values in the permuted screen to generate a halftone image.

20 . The method of claim 19 , further comprising:
providing an original screen comprising an array of threshold values; and with the protocol, swapping ones of the threshold values, each corresponding to a defective inkjet, with neighboring threshold values that are larger.

Assignees

• Xerox Corp

Inventors

• Schweid Stuart A
• Taylor Douglas R

Classifications

• B41J2/2142

  Detection of malfunctioning nozzles (generating single droplets or particles on demand by pressure, e.g. electromechanical transducers B41J2/045, B41J2/05; jet deflection sensors B41J2/125; for cleaning purposes B41J2/16579) · CPC title

• B41J2/2146

  for line print heads · CPC title

• B41J2/2139

  Compensation for malfunctioning nozzles creating dot place or dot size errors (generating single droplets or particles on demand by pressure, e.g. electromechanical transducers B41J2/045) · CPC title

• B41J2029/3935

  by means of printed test patterns · CPC title

• B41J29/393

  Devices for controlling or analysing the entire machine {; Controlling or analysing mechanical parameters involving printing of test patterns} · CPC title