Image forming apparatus, image forming method and image forming program

• US 7,431,413 B2
• Filed: 08/24/2005
• Issued: 10/07/2008
• Est. Priority Date: 08/27/2004
• Status: Active Grant

• Current Assignee: Konica Minolta Holdings Incorporated (Konica Minolta Inc.)
• Original Assignee: Konica Minolta Holdings Incorporated (Konica Minolta Inc.)
• Inventors: Mizutani, Toshiyuki, Hiramoto, Kenichirou
• Primary Examiner(s): Nguyen; Lamson D.
• Application Number:
  US11/210,547
• Publication Number:
  US 20060044339A1
• Time in Patent Office: 1,140 Days
• Field of Search: 347/15, 347/41, 347/43, 347/12, 347/19, 358/1.2, 358/1.9, 358/3.23, 358/524, 358/3.01, 358/3.03, 358/3.05
• US Class Current: 347/15
• CPC Class Codes: H04N 1/40087 Multi-toning, i.e. converting a continuous-tone signal for reproduction with more than two discrete brightnesses or optical densities, e.g. dots of grey and black inks on white paper

Abstract

An image forming apparatus, for forming an image by using distribution of plural types of dots, including: a first section, for making comparison between a pixel value of a target pixel and a value in a dither matrix stored in advance, and determining, whether a dot having the highest density be formed at a position corresponding to the pixel; a second section for determining whether a second type dot having lower density be formed at the position where the dot having the highest density is determined not to be formed; and a section for instructing, based on results of determination by the first and second sections, whether a dot should be formed at the position, wherein the dither matrix comprises values, each being not less than a predetermined value smaller than the maximum pixel value of the input image.

Claims

1. An image forming apparatus, for forming an image by using distribution of two or more types of dots, each type of dots having a density per unit area different from a density per unit area of other type of dots, the image forming apparatus comprising:

a first dot formation determining section, for making comparison between a pixel value of a target pixel in an input image and a value in a dither matrix stored in advance, and for determining, based on a result of the comparison, whether or not a dot, of a first type of dots having the highest density per unit area out of the two or more types of dots, should be formed at a position corresponding to the target pixel;

a second dot formation determining section for determining whether or not a dot, of a second type of dots whose density per unit area is lower than that of the first type of dots, should be formed at the position where the first dot formation determining section has determined that the dot of the first type of dots should not be formed, wherein the second dot formation determining section makes a second comparison between the pixel value of the target pixel and a value obtained by subtracting from each value of the dither matrix a fixed value in response to the density per unit area of the second type of dots, and based on a result of the second comparison, the second dot formation determining section determines whether or not any one of the dots of the second type of dots should be formed at the position where the first dot formation determining section determined that a dot should not be formed; and

a dot formation instructing section for instructing, based on results of determination by the first and second dot formation determining sections, whether or not a dot should be formed at the position corresponding to the target pixel;

wherein the dither matrix comprises values, each of the values being equal to or greater than a predetermined value, which is greater than 0 and smaller than the maximum value taken by the pixel value of the input image.

2. The image forming apparatus of claim 1, wherein the second type of dots comprises a plurality of types of dots, each of the plurality of types of dots having a different density per unit area with each other, and the second dot formation determining section determines whether or not a dot of any one of the plurality of types of dots should be formed, in such an order that a type of dots having the higher density per unit area is the earlier.

3. The image forming apparatus of claim 1, wherein the dither matrix is a Bayer type matrix.

4. The image forming apparatus of claim 1, wherein the dither matrix is a blue noise mask type matrix.

5. The image forming apparatus of claim 1, wherein the predetermined value in the dither matrix is changed in response to printing resolution.

6. The image forming apparatus of claim 1, wherein the predetermined value in the dither matrix is changed in response to a recording mode.

7. The image forming apparatus of claim 1, wherein the predetermined value in the dither matrix is changed in response to a type of the recording medium.

8. An image forming apparatus, for forming an image by using distribution of two or more types of dots, each type of dots having a density per unit area different from a density per unit area of other type of dots, the image forming apparatus comprising:

a first dot formation determining section, for making comparison between a pixel value of a target pixel in an input image and a value in a dither matrix stored in advance, and for determining, based on a result of the comparison, whether or not a dot, of a first type of dots having the highest density per unit area out of the two or more types of dots, should be formed at a position corresponding to the target pixel;

a second dot formation determining section for determining whether or not a dot, of a second type of dots whose density per unit area is lower than that of the first type of dots, should be formed at the position where the first dot formation determining section has determined that the dot of the first type of dots should not be formed; and

a dot formation instructing section for instructing, based on results of determination by the first and second dot formation determining sections, whether or not a dot should be formed at the position corresponding to the target pixel;

wherein the dither matrix comprises values, each of the values being equal to or greater than a predetermined value, which is greater than 0 and smaller than the maximum value taken by the pixel value of the input image,

wherein the two or more types of dots having different densities per unit area have a resultant value corresponding to each of the density per unit area, and the image forming apparatus further comprising;

an error calculation section for calculating an error between the resultant value and a corrected pixel value obtained by correcting the input pixel value using a neighboring error diffused from a pixel having been processed; and

an error diffusion section for assigning a weight to the error calculated by the error calculation section, and diffusing the error weighted to neighboring unprocessed pixels;

wherein the second dot formation determining section determines whether or not a dot of at least one type of the second type dots should be formed, based on a result of comparison between the corrected pixel value and a second predetermined.

9. The image forming apparatus of claim 8, wherein the second type of dots comprises a plurality of types of dots, each of the plurality of types of dots having a different density per unit area with each other, and the second dot formation determining section determines whether or not a dot of any one of the plurality of types of dots should be formed, in such an order that a type of dots having the higher density per unit area is the earlier.

10. The image forming apparatus of claim 8, wherein the dither matrix is a Bayer type matrix.

11. The image forming apparatus of claim 8, wherein the dither matrix is a blue noise mask type matrix.

12. The image forming apparatus of claim 8, wherein the predetermined value in the dither matrix is changed in response to printing resolution.

13. The image forming apparatus of claim 8, wherein the predetermined value in the dither matrix is changed in response to a recording mode.

14. The image forming apparatus of claim 8, wherein the predetermined value in the dither matrix is changed in response to a type of the recording medium.

15. An image forming method, for forming an image by using distribution of two or more types of dots, each type of dots having a density per unit area different from a density per unit area of other type of dots, the image forming method comprising:

a first dot formation determining step, for making comparison between a pixel value of a target pixel in an input image and a value in a dither matrix stored in advance, and for determining, based on a result of the comparison, whether or not a dot, of a first type of dots having the highest density per unit area out of the two or more types of dots, should be formed at a position corresponding to the target pixel;

a second dot formation determining step for determining whether or not a dot, of a second type of dots whose density per unit area is lower than that of the first type of dots, should be formed at the position where the first dot formation determining step has determined that the dot of the first type of dots should not be formed, wherein the second dot formation determining step makes a second comparison between the pixel value of the target pixel and a value obtained by subtracting from each value of the dither matrix a fixed value in response to the density per unit area of the second type of dots, and based on a result of the second comparison, the second dot formation determining step determines whether or not any one of the dots of the second type of dots should be formed at the position where the first dot formation determining step determined that a dot should not be formed; and

a dot formation instructing step for instructing, based on results of determination by the first and second dot formation determining steps, whether or not a dot should be formed at the position corresponding to the target pixel;

wherein the dither matrix comprises values, each of the values being equal to or greater than a predetermined value, which is greater than 0 and smaller than the maximum value taken by the pixel value of the input image.

16. The image forming method of claim 15, wherein the second type of dots comprises a plurality of types of dots, each of the plurality of types of dots having a different density per unit area with each other, and the second dot formation determining step determines whether or not a dot of any one of the plurality of types of dots should be formed, in such an order that a type of dots having the higher density per unit area is the earlier.

17. The image forming method of claim 15, wherein the dither matrix is a Bayer type matrix.

18. The image forming method of claim 15, wherein the dither matrix is a blue noise mask type matrix.

19. The image forming method of claim 15, wherein the predetermined value in the dither matrix is changed in response to printing resolution.

20. The image forming method of claim 15, wherein the predetermined value in the dither matrix is changed in response to a recording mode.

21. The image forming method of claim 15, wherein the predetermined value in the dither matrix is changed in response to a type of the recording medium.

22. An image forming method, for forming an image by using distribution of two or more types of dots, each type of dots having a density per unit area different from a density per unit area of other type of dots, the image forming method comprising:

a first dot formation determining step, for making comparison between a pixel value of a target pixel in an input image and a value in a dither matrix stored in advance, and for determining, based on a result of the comparison, whether or not a dot, of a first type of dots having the highest density per unit area out of the two or more types of dots, should be formed at a position corresponding to the target pixel;

a second dot formation determining step for determining whether or not a dot, of a second type of dots whose density per unit area is lower than that of the first type of dots, should be formed at the position where the first dot formation determining step has determined that the dot of the first type of dots should not be formed; and

a dot formation instructing step for instructing, based on results of determination by the first and second dot formation determining steps, whether or not a dot should be formed at the position corresponding to the target pixel;

wherein the dither matrix comprises values, each of the values being equal to or greater than a predetermined value, which is greater than 0 and smaller than the maximum value taken by the pixel value of the input image,

wherein the two or more types of dots having different densities per unit area have a resultant value corresponding to each of the density per unit area, and the image forming method further comprising;

an error calculating step for calculating an error between the resultant value and a corrected pixel value obtained by correcting the input pixel value using a neighboring error diffused from a pixel having been processed; and

an error diffusing step for assigning a weight to the error calculated by the error calculating step, and diffusing the error weighted to neighboring unprocessed pixels;

wherein the second dot formation determining step determines whether or not a dot of at least one type of the second type dots should be formed, based on a result of comparison between the corrected pixel value and a second predetermined.

23. The image forming method of claim 22, wherein the second type of dots comprises a plurality of types of dots, each of the plurality of types of dots having a different density per unit area with each other, and the second dot formation determining step determines whether or not a dot of any one of the plurality of types of:

dots should be formed, in such an order that a type of dots having the higher density per unit area is the earlier.

24. The image forming method of claim 22, wherein the dither matrix is a Bayer type matrix.

25. The image forming method of claim 22, wherein the dither matrix is a blue noise mask type matrix.

26. The image forming method of claim 22, wherein the predetermined value in the dither matrix is changed in response to printing resolution.

27. The image forming method of claim 22, wherein the predetermined value in the dither matrix is changed in response to a recording mode.

28. The image forming method of claim 22, wherein the predetermined value in the dither matrix is changed in response to a type of the recording medium.

29. One or more computer-readable media having computer-readable instructions thereon which, when executed by a computer, cause the computer to execute an image forming program to make an image forming apparatus realize functions, for forming an image by using distribution of two or more types of dots, each type of dots having a density per unit area different from a density per unit area of other type of dots, the functions comprising:

a first dot formation determining function, for making comparison between a pixel value of a target pixel in an input image and a value in a dither matrix stored in advance, and for determining, based on a result of the comparison, whether or not a dot, of a first type of dots having the highest density per unit area out of the two or more types of dots, should be formed at a position corresponding to the target pixel;

a second dot formation determining function for determining whether or not a dot, of a second type of dots whose density per unit area is lower than that of the first type of dots, should be formed, wherein the second dot formation determining function makes a second comparison between the pixel value of the target pixel and a value obtained by subtracting from each value of the dither matrix a fixed value in response to the density per unit area of the second type of dots, and based on a result of the second comparison, the second dot formation determining section determines whether or not any one of the dots of the second type of dots should be formed at the position where the first dot formation determining section determined that a dot should not be formed at the position where the first dot formation determining function has determined that the dot of the first type of dots should not be formed; and

a dot formation instructing function for instructing, based on results of determination by the first and second dot formation determining functions, whether or not a dot should be formed at the position corresponding to the target pixel;

wherein the dither matrix comprises values, each of the values being equal to or greater than a predetermined value, which is greater than 0 and smaller than the maximum value taken by the pixel value of the input image.

30. The image forming program of claim 29, wherein the second type of dots comprises a plurality of types of dots, each of the plurality of types of dots having a different density per unit area with each other, and the second dot formation determining function determines whether or not a dot of any one of the plurality of types of dots should be formed, in such an order that a type of dots having the higher density per unit area is the earlier.

31. One or more computer-readable media having computer-readable instructions thereon which, when executed by a computer, cause the computer to execute an image forming program to make an image forming apparatus realize functions, for forming an image by using distribution of two or more types of dots, each type of dots having a density per unit area different from a density per units area of other type of dots, the functions comprising:

a first dot formation determining function, for making comparison between a pixel value of a target pixel in an input image and a value in a dither matrix stored in advance, and for determining, based on a result of the comparison, whether or not a dot, of a first type of dots having the highest density per unit area out of the two or more types of dots, should be formed at a position corresponding to the target pixel;

a second dot formation determining function for determining whether or not a dot, of a second type of dots whose density per unit area is lower than that of the first type of dots, should be formed at the position where the first dot formation determining function has determined that the dot of the first type of dots should not be formed; and

a dot formation instructing function for instructing, based on results of determination by the first and second dot formation determining functions, whether or not a dot should be formed at the position corresponding to the target pixel;

wherein the dither matrix comprises values, each of the values being equal to or greater than a predetermined value, which is greater than 0 and smaller than the maximum value taken by the pixel value of the input image,

wherein two or more types of dots having different densities per unit area have a resultant value corresponding to each of the density per unit area, and the functions further comprising;

an error calculating function for calculating an error between the resultant value and a corrected pixel value obtained by correcting the input pixel value using a neighboring error diffused from a pixel having been processed; and

an error diffusing function for assigning a weight to the error calculated by the error calculating function, and diffusing the error weighted to neighboring unprocessed pixels;

wherein the second dot formation determining function determines whether or not a dot of at least one type of the second type dots should be formed, based on a result of comparison between the corrected pixel value and a second predetermined.