Replacing a defective colorant

• US 8,576,450 B2
• Filed: 06/23/2011
• Issued: 11/05/2013
• Est. Priority Date: 06/23/2011
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Shepherd, Matthew A, Verzwyvelt, Vanessa
• Primary Examiner(s): TRAN, DUNG D
• Application Number:
  US13/167,072
• Publication Number:
  US 20120327478A1
• Time in Patent Office: 866 Days
• Field of Search: None
• US Class Current: 358/3.06
• CPC Class Codes: H04N 1/405 Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
• CPC Class Codes: H04N 1/60 Colour correction or control H04N1/54 takes precedence
• CPC Class Codes: H04N 1/62 Retouching, i.e. modification of isolated colours only or in isolated picture areas only

Abstract

A system and methods for modifying the values of halftoned image pixels to replace a defective colorant with at least one non-defective colorant.

Claims

1. A method of forming an image using a plurality of device-dependent colorants, comprising:

receiving at least one raster of halftoned image pixels each having a discrete value for each of the colorants;

for a raster associated with a defective colorant, modifying the values of the pixels to replace the defective colorant with an added amount of at least one non-defective colorant, the added amount for each individual pixel determined at least in part from a local density of the defective colorant at the corresponding pixel, the added amount having a predetermined non-linear relationship to the local density.

2. The method of claim 1, wherein the modifying includes sequentially modifying the values of each of the pixels, comprising:

converting the value of each pixel that has a non-zero value for the defective colorant to a count for at least one of the non-defective colorants that is added to a total count for that non-defective colorant; and

re-halftoning the total counts for the non-defective colorants to generate the new one of the N discrete values for the pixels.

3. The method of claim 1, wherein the local density of the defective colorant at a given pixel corresponds to a distance of the given pixel from a last prior pixel in the raster that had a non-zero value for the defective colorant prior to modification.

4. The method of claim 1, wherein the amount of the at least one non-defective colorant that replaces the defective colorant for a given pixel has a non-integer relationship to the value of the defective colorant associated with the given pixel.

5. The method of claim 1, wherein the received raster has a grain structure, and wherein the modified raster retains the grain structure.

21. The method of claim 1, wherein the discrete value is selected from a first set of integer values, the first set smaller than a second set of integer values for non-halftoned image pixels.

22. The method of claim 21, wherein the first set of integer values comprises sixteen values or fewer.

6. A printing system for printing color image data using a plurality of colorants, comprising:

a plurality of print elements each configured to emit drops of one of the colorants to print halftoned pixels of a raster of the data, each pixel having a drop value for each of the colorants;

a detector to identify a defective one of the print elements;

a color replacer to modify the drop values of the pixels to replace the colorant of the defective print element with an added amount of colorant from at least one non-defective print element, the added amount determined for each individual pixel at least in part from a local density at the individual pixel of the colorant of the defective print element, the added amount having a predetermined non-linear relationship to the local density.

7. The printing system of claim 6, wherein the color replacer comprises:

a drop-to-count converter to convert the drop value of each pixel that has a non-zero value for the colorant of the defective print element to a count for at least one of the colorants of the non-defective print elements, and to add the count to a total count for that colorant; and

a forward-only error-diffusion halftoner to halftone the total counts for the colorants of the non-defective print elements to generate the modified drop values for each pixel.

8. The printing system of claim 7, wherein the drop-to-count converter comprises:

a cross-color converter that converts a drop of a particular one of the colorants to a number of counts of at least one other one of the colorants based on a distance from a last replaced pixel, where the distance is a representation of the local density of the particular colorant.

9. The printing system of claim 6, wherein the raster has a grain structure, and wherein the raster retains the grain structure after modification of the drop values of the pixels by the color replacer.

10. A method of forming an image using a plurality of device-dependent colorants, comprising:

transforming a raster of halftoned image pixels each having one of N discrete values for each of the colorants to a human-vision-equivalent raster that replaces a defective one of the colorants by, for each pixel,

converting the value for each non-defective colorant to a count, and adding the count to a total count for that non-defective colorant,

converting the value for the defective colorant to a second count for at least one of the non-defective colorants, and adding the second count to the total count for that non-defective colorant, and

re-halftoning the total counts of the non-defective colorants to generate a new value for the pixel.

11. The method of claim 10, wherein the second count is determined based on a local density of the defective colorant at a location of the pixel.

12. The method of claim 11, wherein the local density has a predetermined non-linear relationship to the count.

13. The method of claim 11, wherein the local density of the defective colorant corresponds to a distance of the pixel from a closest prior pixel in the raster for which the value of the defective colorant was previously converted.

14. The method of claim 11, wherein the second count has a non-integer relationship to the value for the defective colorant of the pixel.

15. The method of claim 10, wherein the new pixel value has one of the N discrete values for each of the non-defective colorants and a value of zero for the defective colorant.

16. The method of claim 10, wherein the set of locations in the raster of the transformed pixels having a non-zero value for at least one of the colorants is substantially the same as the set of locations in the raster of pixels having a non-zero value for at least one of the colorants prior to the transforming.

17. The method of claim 11, wherein the converting to a second count is not performed if the pixel value for the defective colorant is zero.

18. The method of claim 10, wherein the raster has a grain structure prior to the transforming, and wherein the transformed raster retains the grain structure.

19. The method of claim 10, wherein the re-halftoning is forward-only error diffusion.

20. The method of claim 10, wherein the image is formed using a printer and

wherein each value represents a number of drops of the colorant to print the pixel, further comprising:

printing each pixel of the transformed raster on the printer by emitting the number of drops corresponding to the new value of each of the non-defective colorants of that pixel onto a print medium at a location corresponding to that pixel.