Image processor, image forming apparatus, method of processing image

• US 20060077466A1
• Filed: 09/13/2005
• Published: 04/13/2006
• Est. Priority Date: 10/07/2004
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Ishii, Hiroshi, Morimoto, Etsuo
• Granted Patent: US 7,760,400 B2
• Time in Patent Office: Days
• US Class Current: 358/3.30
• CPC Class Codes: H04N 1/4052 by error diffusion, i.e. transferring the binarising error to neighbouring dot decisions

Abstract

In an image processor, a data corrector corrects input image data, a determining unit determines an output tone value of a target pixel from the corrected image data and threshold, and a calculator calculates a difference between the output tone value and the corrected image data as an error value. The threshold is set in such manner that a rate of change of the mean error of the error values with respect to a change in the input tone value is within a predetermined range.

Claims

1. An image processor comprising:

a input data corrector that corrects image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

an output tone value determining unit that determines an output tone data of the target pixel based on corrected image data, and a threshold corresponding to a position of the target pixel; and

an error value calculator that calculates a difference between the output tone data and the corrected image data as an error value, wherein

the output tone value determining unit sets the threshold in such a manner that a rate of change of a mean error value obtained from error values calculated by the error value calculator with respect to a change in the input tone value falls within a predetermined range.

2. The image processor according to claim 1, wherein the output tone value determining unit sets the threshold in such a manner that the mean error value is substantially zero regardless of the input tone value.

3. The image processor according to claim 1, wherein the output tone value determining unit sets the threshold by combining the weight and the threshold so that the rate of change of the mean error value is within the predetermined range with respect to a change in the input tone value.

4. The image processor according to claim 3, wherein in a steady state in which an image having a certain input tone value is input, the output tone value determining unit sets the threshold by combining the weight and the threshold so that the rate of change of the mean error value in respective steady states in which images having input tone values slightly different from each other are input is within a predetermined range.

5. An image processor comprising:

an input data corrector that corrects image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

an output tone value determining unit that determines an output tone data of the target pixel based on corrected image data, and a threshold corresponding to a position of the target pixel; and

an error value calculator that calculates a difference between the output tone data and the corrected image data as an error value, wherein

the output tone value determining unit sets the threshold in such a manner that a mean error value obtained from error values calculated by the error value calculator falls within a predetermined range regardless of the input tone value.

6. The image processor according to claim 5, wherein the output tone value determining unit sets the threshold in such a manner that the mean error value is substantially zero regardless of the input tone value.

7. The image processor according to claim 6, wherein the output tone value determining unit sets the threshold by combining the weight and the threshold so that the mean error value is substantially zero regardless of the input tone value.

8. The image processor according to claim 7, wherein the output tone value determining unit sets the threshold by combining the weight and the threshold so that the mean error value is substantially zero in a steady state in which an image having a certain input tone value is input.

9. The image processor according to claim 5, wherein the output tone value determining unit sets the threshold by combining the weight and the threshold so that the mean error value falls within the predetermined range regardless of the input tone value.

10. The image processor according to claim 9, wherein the output tone value determining unit sets the threshold by combining the weight and the threshold so that the mean error value falls within the predetermined range in a steady state in which an image having a certain input tone value is input.

11. An image processor comprising:

an input data corrector that corrects image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

an output tone value determining unit that determines an output tone data of the target pixel based on corrected image data, and a threshold corresponding to a position of the target pixel; and

an error value calculator that calculates a difference between the output tone data and the corrected image data as an error value, wherein

the output tone value determining unit sets the threshold in such a manner that a mean error value obtained from error values calculated by the error value calculator with respect to a change in the input tone value is substantially any one of a monotonous decrease and a monotonous increase with respect to the input tone value.

12. The image processor according to claim 11, wherein the output tone value determining unit sets the threshold by combining the weight and the threshold so that the mean error value with respect to the change in the input tone value is substantially any one of the monotonous decrease and the monotonous increase with respect to the input tone value.

13. The image processor according to claim 12, wherein in a steady state in which an image having a certain input tone value is input, the output tone value determining unit sets the threshold by combining the weight and the threshold so that the mean error value is substantially any one of the monotonous decrease and the monotonous increase with respect to the input tone value.

15. The image processor according to claim 13, wherein the output tone value determining unit sets the threshold from neighborhood of a median, including the median, in the obtained threshold range.

14. An image processor comprising:

an input data corrector that corrects image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

an output tone value determining unit that determines an output tone data of the target pixel based on corrected image data, and a threshold corresponding to a position of the target pixel; and

an error value calculator that calculates a difference between the output tone data and the corrected image data as an error value, wherein

the output tone value determining unit sets the threshold from a threshold range determined by obtaining respective corrected image data corresponding to a plurality of output dot patterns output as output tone values in a steady state, to determine the threshold range for defining the obtained respective corrected image data.

16. The image processor according to claim 14, wherein the output tone value determining unit sets the threshold from the threshold range for outputting the predetermined output dot patterns in the maximum number, as different output dot patterns in the steady state.

17. The image processor according to claim 16, wherein the output tone value determining unit sets the threshold from a neighborhood of a median, including the median, in the threshold range for outputting the predetermined output dot patterns in the maximum number, as different output dot patterns in the steady state, as the predetermined threshold.

18. The image processor according to claim 14, wherein the output tone value determining unit sets the threshold from the threshold range, when a mean error value is specified respectively with respect to the predetermined output dot patterns.

19. The image processor according to claim 14, wherein the output tone value determining unit sets the threshold by excluding an output dot pattern having a small mean output tone value in neighborhood of a pixel having the output tone value in the predetermined range, from the predetermined output dot patterns, when the setting is such that as the pixel value becomes larger, the density becomes higher.

20. The image processor according to claim 19, wherein the output tone value determining unit set the threshold from the range of small output tone values, excluding the lowest density from the predetermined range.

21. The image processor according to claim 19, wherein the output tone value determining unit sets the threshold by changing the predetermined range corresponding to the output tone value in the neighborhood.

22. The image processor according to claim 19, wherein the output tone value determining unit sets the threshold by assuming that neighboring pixels are adjacent to the target pixel.

23. The image processor according to claim 19, wherein the output tone value determining unit sets the threshold by assuming that neighboring pixels are neighboring pixels of the target pixel in the horizontal scanning direction.

24. The image processor according to claim 19, wherein the output tone value determining unit includes a phase controller that controls a phase of the pixels.

25. The image processor according to claim 24, wherein the phase controller determines a phase of the target pixel based on values of pixels that are adjascent to the target pixel in the horizontal scanning direction.

26. The image processor according to claim 14, wherein the output tone value determining unit sets the threshold by excluding an output dot pattern in which there is no pixel having a large output tone value in neighborhood of a pixel having the output tone value in the predetermined range, from the predetermined output dot patterns, when the setting is such that as the pixel value becomes larger, the density becomes higher.

27. The image processor according to claim 14, wherein the output tone value determining unit sets the threshold by excluding an output dot pattern having a large mean output tone value in neighborhood of a pixel having the output tone value in the predetermined range, from the predetermined output dot patterns.

28. The image processor according to claim 27, wherein the output tone value determining unit sets the threshold from the range of large output tone values, excluding the highest density from the predetermined range.

29. The image processor according to claim 14, wherein the output tone value determining unit sets the threshold by excluding an output dot pattern in which there is no pixel having a small output tone value in neighborhood of a pixel having the output tone value in the predetermined range, from the predetermined output dot patterns.

30. An image processor comprising an output tone value determining unit that outputs any one of N (N>

2) output tone values based on comparison of an input tone value of a target pixel and a threshold corresponding to the target pixel position, wherein

the output tone value determining unit determines the output tone value set so as to exclude a tone value in a predetermined range, with respect to a predetermined pixel position.

31. The image processor according to claim 30, wherein the output tone value determining unit determines the output tone value, by using the tone value in the predetermined range to be excluded, which is set based on-the number of dots to be formed prior to the predetermined pixel position in the neighborhood of the predetermined pixel position.

32. The image processor according to claim 30, wherein the output tone value determining unit determines the output tone value, by using the tone value in the predetermined range to be excluded, which is set to a tone value corresponding to a relatively low density, when number of dots to be formed prior to the predetermined pixel position in the neighborhood of the predetermined pixel position is small.

33. The image processor according to claim 32, wherein the output tone value determining unit determines the output tone value, by using the tone value in the predetermined range to be excluded, which is set to a tone value corresponding to a dotting output.

34. The image processor according to claim 30, wherein the output tone value determining unit determines the output tone value, by using the tone value in the predetermined range to be excluded, which is set to a tone value corresponding to a relatively high density, when the number of dots to be formed prior to the predetermined pixel position in the neighborhood of the predetermined pixel position is large.

35. The image processor according to claim 34, wherein the output tone value determining unit determines the output tone value, by using the tone value in the predetermined range to be excluded, for which a tone value other than the tone value for outputting the highest density is set.

36. The image processor according to claim 34, wherein the output tone value determining unit determines the output tone value, by using the predetermined pixel position, for which a pixel position to be dotted in a relatively large number prior to the neighborhood thereof is set.

37. The image processor according to claim 30, wherein the output tone value determining unit determines the output tone value, by using the predetermined pixel position, for which a pixel position to be dotted in a relatively small number prior to the neighborhood thereof is set.

38. The image processor according to claim 30, wherein the output tone value determining unit determines the output tone value, by using the predetermined pixel position, for which a position to be dotted prior to the back and front pixels in the horizontal scanning direction is set.

39. The image processor according to claim 30, wherein the output tone value determining unit determines the output tone value, by using the predetermined pixel position, for which a position to be dotted later than the back and front pixels in the horizontal scanning direction is set.

40. The image processor according to claim 30, wherein the output tone value determining unit determines the output tone value, by using a dither threshold for obtaining a dotted output as the threshold.

41. The image processor according to claim 30, further comprising a phase controller that controls a phase of the output tone value determined by the output tone value determining unit.

42. The image processor according to claim 41, wherein the phase controller controls a phase of an output tone value of the target pixel, based on tone values of pixels that are adjascent to the target pixel in the horizontal scanning direction.

43. An image processor comprising:

an input data corrector that corrects image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

an output tone value determining unit that outputs any one of N (N>

2) output tone values based on comparison of corrected image data of the target pixel and a threshold corresponding to the target pixel; and

an error value calculator that calculates a difference between the output tone value and the corrected image data as an error value, wherein

the output tone value determining unit determines the output tone value set so as to exclude a tone value in a predetermined range, with respect to a predetermined pixel position.

44. The image processor according to claim 43, wherein the output tone value determining unit determines output tone value by using the tone value in the predetermined range to be excluded, which is set based on number of dots to be formed prior to the predetermined pixel position in the neighborhood of the predetermined pixel position.

45. The image processor according to claim 43, wherein the output tone value determining unit determines the output tone value, by using the tone value in the predetermined range to be excluded, which is set to a tone value corresponding to a relatively low density, when number of dots to be formed prior to the predetermined pixel position in the neighborhood of the predetermined pixel position is small.

46. The image processor according to claim 45, wherein the output tone value determining unit determines the output tone value, by using a tone value in the predetermined range to be excluded, which is set to a tone value corresponding to a dotting output.

47. The image processor according to claim 43, wherein the output tone value determining unit determines the output tone value, by using the tone value in the predetermined range to be excluded, which is set to a tone value corresponding to a relatively high density, when the number of dots to be formed prior to the predetermined pixel position in the neighborhood of the predetermined pixel position is large.

48. The image processor according to claim 47, wherein the output tone value determining unit determines the output tone value, by using the tone value in the predetermined range to be excluded, for which a tone value other than the tone value for outputting the highest density is set.

49. The image processor according to claim 47, wherein the output tone value determining unit determines the output tone value, by using the predetermined pixel position, for which a pixel position to be dotted in a relatively large number prior to the neighborhood thereof is set.

50. The image processor according to claim 43, wherein the output tone value determining unit determines the output tone value, by using the predetermined pixel position, for which a pixel position to be dotted in a relatively small number prior to the neighborhood thereof is set.

51. The image processor according to claim 43, wherein the output tone value determining unit determines the output tone value, by using the predetermined pixel position, for which a position to be dotted prior to the back and front pixels in the horizontal scanning direction is set.

52. The image processor according to claim 43, wherein the output tone value determining unit determines the output tone value, by using the predetermined pixel position, for which a position to be dotted later than the back and front pixels in the horizontal scanning direction is set.

53. The image processor according to claim 43, wherein the output tone value determining unit determines the output tone value, by using a dither threshold for obtaining a dotted output as the threshold.

54. The image processor according to claim 43, further comprising a phase controller that controls a phase of the output tone value determined by the output tone value determining unit.

55. The image processor according to claim 54, wherein the phase controller controls a phase of a pixel at the target pixel position, based on tone values of pixels that are adjascent to to the target pixel in the horizontal scanning direction.

56. An image forming apparatus comprising:

a data converter configured to receive image data and to convert image data of each of a plurality of pixels to a tone value;

an image processor that processes the tone values thereby obtaining output image data; and

an image output device that outputs an image based on the output image data, wherein

the image processor comprises includes

an input data corrector that corrects image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

an output tone value determining unit that determines an output tone data of the target pixel based on corrected image data, and a threshold corresponding to a position of the target pixel; and

an error value calculator that calculates a difference between the output tone data and the corrected image data as an error value, wherein

the output tone value determining unit sets the threshold in such a manner that a rate of change of a mean error value obtained from error values calculated by the error value calculator with respect to a change in the input tone value falls within a predetermined range.

57. An image forming apparatus comprising:

a data converter configured to receive image data and to convert image data of each of a plurality of pixels to a tone value;

an image processor that processes the tone values thereby obtaining output image data; and

an image output device that outputs an image based on the output image data, wherein

the image processor comprises includes

an input data corrector that corrects image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

an output tone value determining unit that determines an output tone data of the target pixel based on corrected image data, and a threshold corresponding to a position of the target pixel; and

an error value calculator that calculates a difference between the output tone data and the corrected image data as an error value, wherein

the output tone value determining unit sets the threshold in such a manner that a mean error value obtained from error values calculated by the error value calculator falls within a predetermined range regardless of the input tone value.

58. An image forming apparatus comprising:

a data converter configured to receive image data and to convert image data of each of a plurality of pixels to a tone value;

an image processor that processes the tone values thereby obtaining output image data; and

an image output device that outputs an image based on the output image data, wherein

the image processor comprises includes

an input data corrector that corrects image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

an output tone value determining unit that determines an output tone data of the target pixel based on corrected image data, and a threshold corresponding to a position of the target pixel; and

an error value calculator that calculates a difference between the output tone data and the corrected image data as an error value, wherein

the output tone value determining unit sets the threshold in such a manner that a mean error value obtained from error values calculated by the error value calculator with respect to a change in the input tone value is substantially any one of a monotonous decrease and a monotonous increase with respect to the input tone value.

59. An image forming apparatus comprising:

a data converter configured to receive image data and to convert image data of each of a plurality of pixels to a tone value;

an image processor that processes the tone values thereby obtaining output image data; and

an image output device that outputs an image based on the output image data, wherein

the image processor comprises an output tone value determining unit that outputs any one of N (N>

2) output tone values based on comparison of an input tone value of a target pixel and a threshold corresponding to the target pixel position, and

the output tone value determining unit determines the output tone value set so as to exclude a tone value in a predetermined range, with respect to a predetermined pixel position.

60. A method of image processing comprising:

correcting image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

determining an output tone data of the target pixel based on corrected image data, and a threshold corresponding to a position of the target pixel; and

calculating a difference between the output tone data and the corrected image data as an error value, wherein

the determining includes setting the threshold in such a manner that a rate of change of a mean error value obtained from error values calculated at the calculating with respect to a change in the input tone value falls within a predetermined range.

61. The method according to claim 60, wherein the determining includes setting the threshold in such a manner that the mean error value is substantially zero regardless of the input tone value.

62. The method according to claim 60, wherein the determining includes setting the threshold by combining the weight and the threshold so that the rate of change of the mean error value is within the predetermined range with respect to a change in the input tone value.

63. The method according to claim 62, wherein in a steady state in which an image having a certain input tone value is input, the determining includes setting the threshold by combining the weight and the threshold so that the rate of change of the mean error value in respective steady states in which images having input tone values slightly different from each other are input is within a predetermined range.

64. A method of image processing comprising:

correcting image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

determining an output tone data of the target pixel based on corrected image data, and a threshold corresponding to a position of the target pixel; and

calculating a difference between the output tone data and the corrected image data as an error value, wherein

the determining includes setting the threshold in such a manner that a mean error value obtained from error values calculated at the calculating falls within a predetermined range regardless of the input tone value.

65. The method according to claim 64, wherein the determining includes setting the threshold in such a manner that the mean error value is substantially zero regardless of the input tone value.

66. The method according to claim 64, wherein the determining includes setting the threshold by combining the weight and the threshold so that the mean error value is substantially zero regardless of the input tone value.

67. The method according to claim 66, wherein the determining includes setting the threshold by combining the weight and the threshold so that the mean error value is substantially zero in a steady state in which an image having a certain input tone value is input.

68. The method according to claim 64, wherein the determining includes setting the threshold by combining the weight and the threshold so that the mean error value falls within the predetermined range regardless of the input tone value.

69. The method according to claim 68, wherein the determining includes setting the threshold by combining the weight and the threshold so that the mean error value falls within the predetermined range in a steady state in which an image having a certain input tone value is input.

70. A method of image processing comprising:

correcting image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

determining an output tone data of the target pixel based on corrected image data, and a threshold corresponding to a position of the target pixel; and

calculating a difference between the output tone data and the corrected image data as an error value, wherein the determining includes setting the threshold in such a manner that a mean error value obtained from error values calculated at the calculating with respect to a change in the input tone value is substantially any one of a monotonous decrease and a monotonous increase with respect to the input tone value.

71. The method according to claim 70, wherein the determining includes setting the threshold by combining the weight and the threshold so that the mean error value with respect to the change in the input tone value is substantially any one of the monotonous decrease and the monotonous increase with respect to the input tone value.

72. The method according to claim 71, wherein in a steady state in which an image having a certain input tone value is input, the determining includes setting the threshold by combining the weight and the threshold so that the mean error value is substantially any one of the monotonous decrease and the monotonous increase with respect to the input tone value.

73. The method according to claim 72, wherein the determining includes setting sets the threshold from the threshold range for outputting the predetermined output dot patterns in the maximum number, as different output dot patterns in the steady state.

76. The method according to claim 73, wherein the determining includes setting the threshold from a neighborhood of a median, including the median, in the threshold range for outputting the predetermined output dot patterns in the maximum number, as different output dot patterns in the steady state, as the predetermined threshold.

74. A method of image processing comprising:

correcting image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

determining an output tone data of the target pixel based on corrected image data, and a threshold corresponding to a position of the target pixel; and

calculating a difference between the output tone data and the corrected image data as an error value, wherein

the determining includes setting the threshold from a threshold range determined by obtaining respective corrected image data corresponding to a plurality of output dot patterns output as output tone values in a steady state, to determine the threshold range for defining the obtained respective corrected image data.

75. The method according to claim 74, wherein the determining includes setting the threshold from neighborhood of a median, including the median, in the obtained threshold range.

77. The method according to claim 74, wherein the determining includes setting the threshold from the threshold range, when a mean error value is specified respectively with respect to the predetermined output dot patterns.

78. The method according to claim 74, wherein the determining includes setting the threshold by excluding an output dot pattern having a small mean output tone value in neighborhood of a pixel having the output tone value in the predetermined range, from the predetermined output dot patterns, when the setting is such that as the pixel value becomes larger, the density becomes higher.

79. The method according to claim 78, wherein the determining includes setting the threshold from the range of small output tone values, excluding the lowest density from the predetermined range.

80. The method according to claim 78, wherein the determining includes setting the threshold by changing the predetermined range corresponding to the output tone value in the neighborhood.

81. The method according to claim 78, wherein the determining includes setting the threshold by assuming that neighboring pixels are adjacent to the target pixel.

82. The method according to claim 78, wherein the determining includes setting the threshold by assuming that neighboring pixels are neighboring pixels of the target pixel in the horizontal scanning direction.

83. The method according to claim 74, wherein the determining includes setting the threshold by excluding an output dot pattern in which there is no pixel having a large output tone value in neighborhood of a pixel having the output tone value in the predetermined range, from the predetermined output dot patterns, when the setting is such that as the pixel value becomes larger, the density becomes higher.

84. The method according to claim 74, wherein the determining includes setting the threshold by excluding an output dot pattern having a large mean output tone value in neighborhood of a pixel having the output tone value in the predetermined range, from the predetermined output dot patterns.

85. The method according to claim 84, wherein the determining includes setting the threshold from the range of large output tone values, excluding the highest density from the predetermined range.

86. The method according to claim 74, wherein the determining includes setting the threshold by excluding an output dot pattern in which there is no pixel having a small output tone value in neighborhood of a pixel having the output tone value in the predetermined range, from the predetermined output dot patterns.

87. The method according to claim 74, wherein the determining includes controlling a phase of the pixels.

88. The method according to claim 74, wherein the controlling includes determining a phase of the target pixel based on values of pixels that are adjascent to the target pixel in the horizontal scanning direction.

89. A method of image processing comprising outputting any one of N (N>

2) output tone values based on comparison of an input tone value of a target pixel and a threshold corresponding to the target pixel position, wherein

the outputting includes determining the output tone value set so as to exclude a tone value in a predetermined range, with respect to a predetermined pixel position.

90. The method according to claim 89, wherein the outputting includes determining the output tone value, by using the tone value in the predetermined range to be excluded, which is set based on the number of dots to be formed prior to the predetermined pixel position in the neighborhood of the predetermined pixel position.

91. The method according to claim 89, wherein the outputting includes determining the output tone value, by using the tone value in the predetermined range to be excluded, which is set to a tone value corresponding to a relatively low density, when number of dots to be formed prior to the predetermined pixel position in the neighborhood of the predetermined pixel position is small.

92. The method according to claim 91, wherein the outputting includes determining the output tone value, by using the tone value in the predetermined range to be excluded, which is set to a tone value corresponding to a dotting output.

93. The method according to claim 89, wherein the outputting includes determining the output tone value, by using the tone value in the predetermined range to be excluded, which is set to a tone value corresponding to a relatively high density, when the number of dots to be formed prior to the predetermined pixel position in the neighborhood of the predetermined pixel position is large.

94. The method according to claim 93, wherein the outputting includes determining the output tone value, by using the tone value in the predetermined range to be excluded, for which a tone value other than the tone value for outputting the highest density is set.

95. The method according to claim 93, wherein the outputting includes determining the output tone value, by using the predetermined pixel position, for which a pixel position to be dotted in a relatively large number prior to the neighborhood thereof is set.

96. The method according to claim 89, wherein the outputting includes determining the output tone value, by using the predetermined pixel position, for which a pixel position to be dotted in a relatively small number prior to the neighborhood thereof is set.

97. The method according to claim 89, wherein the outputting includes determining the output tone value, by using the predetermined pixel position, for which a position to be dotted prior to the back and front pixels in the horizontal scanning direction is set.

98. The method according to claim 89, wherein the outputting includes determining the output tone value, by using the predetermined pixel position, for which a position to be dotted later than the back and front pixels in the horizontal scanning direction is set.

99. The method according to claim 89, wherein the outputting includes determining the output tone value by using a dither threshold for obtaining a dotted output as the threshold.

100. The method according to claim 89, further comprising controlling a phase of the output tone value determined at the outputting.

101. The method according to claim 100, wherein the controlling includes controlling a phase of an output tone value of the target pixel based on tone values of pixels that are adjascent to to the target pixel in the horizontal scanning direction.

102. A method of image processing comprising:

correcting image data of a target pixel by giving a weight to error values in the neighborhood of the target pixel and adding weighted error values to a tone value of the target pixel;

outputting any one of N (N>

2) output tone values based on comparison of corrected image data of the target pixel and a threshold corresponding to the target pixel; and

calculating a difference between the output tone value and the corrected image data as an error value, wherein

the outputting includes determining the output tone value set so as to exclude a tone value in a predetermined range, with respect to a predetermined pixel position.

103. The method according to claim 102, wherein the outputting includes determining output tone value by using the tone value in the predetermined range to be excluded, which is set based on number of dots to be formed prior to the predetermined pixel position in the neighborhood of the predetermined pixel position.

104. The method according to claim 102, wherein the outputting includes determining the output tone value, by using the tone value in the predetermined range to be excluded, which is set to a tone value corresponding to a relatively low density, when number of dots to be formed prior to the predetermined pixel position in the neighborhood of the predetermined pixel position is small.

105. The method according to claim 104, wherein the outputting includes determining the output tone value, by using a tone value in the predetermined range to be excluded, which is set to a tone value corresponding to a dotting output.

106. The method according to claim 102, wherein the outputting includes determining the output tone value, by using the tone value in the predetermined range to be excluded, which is set to a tone value corresponding to a relatively high density, when the number of dots to be formed prior to the predetermined pixel position in the neighborhood of the predetermined pixel position is large.

107. The method according to claim 106, wherein the outputting includes determining the output tone value, by using the tone value in the predetermined range to be excluded, for which a tone value other than the tone value for outputting the highest density is set.

108. The method according to claim 106, wherein the outputting includes determining the output tone value, by using the predetermined pixel position, for which a pixel position to be dotted in a relatively large number prior to the neighborhood thereof is set.

109. The method according to claim 102, wherein the outputting includes determining the output tone value, by using the predetermined pixel position, for which a pixel position to be dotted in a relatively small number prior to the neighborhood thereof is set.

110. The method according to claim 102, wherein the outputting includes determining the output tone value, by using the predetermined pixel position, for which a position to be dotted prior to the back and front pixels in the horizontal scanning direction is set.

111. The method according to claim 102, wherein the outputting includes determining the output tone value, by using the predetermined pixel position, for which a position to be dotted later than the back and front pixels in the horizontal scanning direction is set.

112. The method according to claim 102, wherein the outputting includes determining the output tone value, by using a dither threshold for obtaining a dotted output as the threshold.

113. The method according to claim 102, further comprising controlling a phase of an output tone value determined at the determining.

114. The method according to claim 113, wherein the controlling includes controlling a phase of an output tone value of the target pixel based on tone values of pixels that are adjascent to to the target pixel in the horizontal scanning direction.