Method of camouflaging defective print elements in a printer

• US 7,639,402 B2
• Filed: 11/04/2004
• Issued: 12/29/2009
• Est. Priority Date: 11/05/2003
• Status: Active Grant

• Current Assignee: Océ-Technologies B.V. (Canon Inc.)
• Original Assignee: Océ-Technologies B.V. (Canon Inc.)
• Inventors: Vestjens, Johannes C. G., Faken, Henry
• Primary Examiner(s): LEE, TOMMY D
• Application Number:
  US10/980,322
• Publication Number:
  US 20050105105A1
• Time in Patent Office: 1,881 Days
• Field of Search: 358/3.26, 358/1.7, 358/1.8, 358/3.14, 358/2.99, 358/3.01, 358/3.03, 358/3.13, 348/246, 348/247, 347/5, 347/19
• US Class Current: 358/3.26
• CPC Class Codes: B41J 2/2139 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 Class Codes: B41J 2/505 from an assembly of identical printing elements

Abstract

A printer, a computer program and a method are provided for camouflaging defective print elements in the printer having a printhead with a plurality of print elements. The method includes (a) representing the image information to be printed by a multi-level pixel matrix wherein a grey level of each pixel is indicated by a number, (b) transferring the grey levels of pixels that are assigned to a defective print element, to neighboring pixels in the pixel matrix, and (c) converting the pixel matrix having the transferred grey levels, into a bitmap to be printed.

Claims

1. A method of camouflaging defective print elements in a printer having a printhead with a plurality of print elements and capable of printing a binary pixel image, wherein each pixel of the image is assigned to a print element with which it is to be printed, and image information of a pixel that is assigned to a defective print element is shifted to nearby pixel positions where it can be printed with a non-defective print element, the method comprising the steps of:

a) representing the image information to be printed by a multi-level pixel matrix wherein a grey level of each pixel is indicated by a number;

b) transferring the grey levels of pixels that are assigned to a defective print element, to neighbouring pixels in the pixel matrix; and

c) converting the pixel matrix having the transferred grey levels, into a bitmap to be printed.

2. The method of claim 1, wherein the step (b) comprises:

transferring the grey levels of pixels in a pixel line (i) that is assigned to the defective print element, to pixels in neighbouring pixel lines (i+1, i−

1).

3. The method of claim 1, wherein, for a print mode in which the pixels of a pixel line (i) can be printed with more than one print element, the step (b) comprises:

transferring the grey levels of pixels that are assigned to the defective print element, to neighbouring pixels.

4. The method of claim 3, wherein the step (b) comprises the transfer of pixels that are assigned to the defective print element to neighbouring pixels in the same pixel line (i).

5. The method of claim 1, wherein the step (b) comprises:

distributing the grey level of each pixel that is assigned to a defective print element, onto a plurality of neighbouring pixels in accordance with predetermined weight factors.

6. The method of claim 5, wherein the weight factors are determined depending on the contents of the image information of an image area that includes the pixel assigned to the defective print element, the grey level of which being distributed.

7. The method of claim 1, wherein the step (c) comprises a dithering step.

8. The method of claim 1, wherein the step (c) comprises an error diffusion step.

9. The method of claim 8, wherein the error diffusion step is performed pursuant to a scheme which prevents a pixel, which is assigned to a defective print element, from receiving a bit that needs to be printed.

10. The method of claim 1, wherein the step (b) comprises:

dividing the grey levels of each pixel in a pixel line (i) that is assigned to the defective print element according to a predetermined algorithm to create first and second grey level percentages; and

adding the first and second percentages to grey levels of corresponding pixels in neighbouring pixel lines (i+1, i−

1).

11. The method of claim 10, wherein the first and second percentages are not equal.

12. The method of claim 1, wherein the step (b) comprises:

for each pixel in a pixel line (i) that is assigned to the defective print element, increasing grey levels of corresponding pixels in neighbouring pixel lines (i+1, i−

1) to a predetermined value equal to or less than a maximum grey level value.

13. A printer capable of printing a binary pixel image, the printer comprising:

a printhead having a plurality of print elements configured to print a binary pixel image; and

a processing unit configured to control the printhead, representing an image information of the image to be printed by a multi-level pixel wherein a grey level of each pixel is indicated by a number, to transfer the grey levels of pixels that are assigned to a defective print element, to neighbouring pixels in the pixel matrix, and to convert the pixel matrix having the transferred grey levels, into a bitmap to be printed.

14. The printer of claim 13, wherein the processing unit is configured to transfer the grey levels of pixels in a pixel line (i) that is assigned to the defective print element, to pixels in neighbouring pixel lines (i+1, i−

1).

15. The printer of claim 13, wherein, for a print mode in which the pixels of a pixel line (i) can be printed with more than one print element, the processing unit is configured to transfer the grey levels of pixels that are assigned to the defective print element, to neighbouring pixels.

16. The printer of claim 15, wherein the processing unit is configured to transfer pixels that are assigned to the defective print element to neighbouring pixels in the same pixel line (i).

17. The printer of claim 13, wherein the processing unit is configured to distribute the grey level of each pixel that is assigned to a defective print element, onto a plurality of neighbouring pixels in accordance with predetermined weight factors.

18. The printer of claim 17, wherein the weight factors are determined depending on the contents of the image information of an image area that includes the pixel assigned to the defective print element, the grey level of which being distributed.

19. The printer of claim 13, wherein the processing unit is configured to convert the pixel matrix into the bitmap using a dithering step or an error diffusion step.

20. The printer of claim 19, wherein the processing unit is configured to perform the error diffusion step pursuant to a scheme which prevents a pixel, which is assigned to a defective print element, from receiving a bit that needs to be printed.

21. The printer of claim 13, wherein the processing unit is configured to

divide the grey levels of each pixel in a pixel line (i) that is assigned to the defective print element according to a predetermined algorithm to create first and second grey level percentages;

and

add the first and second percentages to grey levels of corresponding pixels in neighbouring pixel lines (i+1, i−

1).

22. The printer of claim 21, wherein the first and second percentages are not equal.

23. The printer of claim 13, wherein for each pixel in a pixel line (i) that is assigned to the defective print element, the processing unit is configured to increase grey levels of corresponding pixels in neighbouring pixel lines (i+1, i−

1) to a predetermined value equal to or less than a maximum grey level value.

24. A computer program product embodied on at least one computer-readable medium associated with a processing unit of a printer, for camouflaging defective print elements in the printer having a printhead with a plurality of print elements and capable of printing a binary pixel image, wherein each pixel of the image is assigned to a print element with which it is to be printed, and image information of a pixel that is assigned to a defective print element is shifted to nearby pixel positions where it can be printed with a non-defective print element, the computer program product comprising computer-executable instructions for:

a) representing the image information to be printed by a multi-level pixel matrix wherein a grey level of each pixel is indicated by a number;

b) transferring the grey levels of pixels that are assigned to a defective print element, to neighbouring pixels in the pixel matrix; and

c) converting the pixel matrix having the transferred grey levels, into a bitmap to be printed.

25. The computer program product of claim 24, wherein the transferring (b) comprises:

transferring the grey levels of pixels in a pixel line (i) that is assigned to the defective print element, to pixels in neighbouring pixel lines (i+1, i−

1).

26. The computer program product of claim 24, wherein, for a print mode in which the pixels of a pixel line (i) can be printed with more than one print element, the transferring (b) comprises:

transferring the grey levels of pixels tat are assigned to the defective print element, to neighbouring pixels.

27. The computer program product of claim 26, wherein the transferring (b) comprises the transfer of pixels that are assigned to the defective print element to neighbouring pixels in the same pixel line (i).

28. The computer program product of claim 24, wherein the transferring (b) comprises:

distributing the grey level of each pixel that is assigned to a defective print element, onto a plurality of neighbouring pixels in accordance with predetermined weight factors.

29. The computer program product of claim 28, wherein the weight factors are determined depending on the contents of the image information of an image area that includes the pixel assigned to the defective print element, the grey level of which being distributed.

30. The computer program product of claim 24, wherein the converting (c) comprises a dithering step or an error diffusion step.

31. The computer program product of claim 30, wherein the error diffusion step is performed pursuant to a scheme which prevents a pixel, which is assigned to a defective print element, from receiving a bit that needs to be printed.

32. The computer program product of claim 24, wherein the step (b) comprises:

dividing the grey levels of each pixel in a pixel line (i) that is assigned to the defective print element according to a predetermined algorithm to create first and second grey level percentages; and

adding the first and second percentages to grey levels of corresponding pixels in neighbouring pixel lines (i+1, i−

1).

33. The computer program product of claim 32, wherein the first and second percentages are not equal.

34. The computer program product of claim 24, wherein the step (b) comprises:

for each pixel in a pixel line (i) that is assigned to the defective print element, increasing grey levels of corresponding pixels in neighbouring pixel lines (i+1, i−

1) to a predetermined value equal to or less than a maximum grey level value.