Image processing apparatus and method

• US 20020176105A1
• Filed: 07/10/2002
• Published: 11/28/2002
• Est. Priority Date: 07/22/1996
• Status: Active Grant

• Current Assignee: Akihiro Matsuya, Takashi Kawai, Takeshi Aoyagi
• Original Assignee: Akihiro Matsuya, Takashi Kawai, Takeshi Aoyagi
• Inventors: Aoyagi, Takeshi, Kawai, Takashi, Matsuya, Akihiro
• Granted Patent: US 7,085,009 B2
• Time in Patent Office: Days
• US Class Current: 358/1.9
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: G06T 5/73 Deblurring; Sharpening
• CPC Class Codes: H04N 1/40012 Conversion of colour to monochrome
• CPC Class Codes: H04N 1/4092 Edge or detail enhancement
• CPC Class Codes: H04N 1/46 Colour picture communication systems
• CPC Class Codes: H04N 1/6072 adapting to different types of images, e.g. characters, graphs, black and white image portions

Abstract

This invention provides an image processing apparatus which simplifies the circuit arrangement required for edge emphasis correction. For this purpose, the apparatus has a first color conversion unit (102) for color-separating input image data into lightness data and chromaticity data, a delay unit (103) for delaying the separated lightness data by N lines, and delaying the chromaticity data by N/2 lines, an image edge amount extraction unit (113) for extracting an image edge portion from the lightness data, a saturation amount extraction unit (114) for extracting the saturation component from the chromaticity data, and an image edge emphasis amount distribution unit (116) for distributing the emphasis amount of the edge portion to an edge emphasis unit (104) so that the distribution ratio for chromaticity correction is higher than that for lightness correction when the saturation component extracted by the saturation extraction unit (114) is large, and the distribution ratio for lightness correction is higher than that for chromaticity correction when the saturation component extracted by the saturation extraction unit (114) is small.

Claims

1. An image processing apparatus for performing sharpness correction on input image data, comprising:

extraction means for extracting lightness data and chromaticity data from the input image data;

edge amount extraction means for extracting an edge amount on the basis of the lightness data;

saturation extraction means for extracting a saturation component on the basis of the chromaticity data;

distribution means for distributing an emphasis amount of an edge portion on the basis of the edge amount extracted by said edge amount extraction means to the lightness data and chromaticity data in correspondence with the saturation component extracted by said saturation extraction means; and

edge emphasis means for correcting the lightness data and chromaticity data using the emphasis amount of the edge portion distributed by said distribution means.

2. The apparatus according to claim 1, wherein the input image data is R, G, and B data, and said apparatus further comprises conversion means for converting the lightness data and chromaticity data emphasized by said edge emphasis means into R, G, and B data.

3. The apparatus according to claim 1, wherein said distribution means sets a higher distribution ratio for chromaticity correction than a distribution ratio for lightness correction when the saturation component is large, and sets a higher distribution ratio for lightness correction than a distribution ratio for chromaticity correction when the saturation component is small.

4. The apparatus according to claim 1, wherein said extraction means converts the input image data into the lightness data and chromaticity data including two components.

5. The apparatus according to claim 1, further comprising achromatic color/chromatic color determination means for determining based on the saturation component extracted by said saturation extraction means if the input image data has a chromatic color or an achromatic color.

6. The apparatus according to claim 1, further comprising delay means for delaying the lightness data by N lines, and delaying the chromaticity data by N/2 lines.

7. The apparatus according to claim 6, wherein said saturation extraction means performs spatial filtering processing of (N/2)+1 lines for the chromaticity data delayed by the N/2 lines by said delay means.

8. The apparatus according to claim 6, wherein said achromatic color/chromatic color determination means performs spatial filtering processing of (N/2)+1 lines for the chromaticity data delayed by the N/2 lines by said delay means.

9. The apparatus according to claim 5, wherein said distribution means changes the distribution ratio of an image edge amount in correspondence with the saturation component extracted by said saturation extraction means and a determination result determined by said achromatic color/chromatic color determination means.

10. The apparatus according to claim 5, wherein said edge emphasis means performs correction for removing chromaticity components for the chromaticity data when said achromatic color/chromatic color determination means determines that an image has an achromatic color.

11. An image processing method for performing sharpness correction for input image data, comprising:

an extraction step of extracting lightness data and chromaticity data from the input image data;

an edge amount extraction step of extracting an edge amount on the basis of the lightness data;

a saturation extraction step of extracting a saturation component on the basis of the chromaticity data;

a distribution step of distributing an emphasis amount of an edge portion on the basis of the edge amount extracted in the edge amount extraction step to the lightness data and chromaticity data in correspondence with the saturation component extracted in the saturation extraction step; and

an edge emphasis step of correcting the lightness data and chromaticity data using the emphasis amount of the edge portion distributed in the distribution step.

12. The method according to claim 11, wherein the input image data is R, G, and B data, and said method further comprises the conversion step of converting the lightness data and chromaticity data emphasized in the edge emphasis step into R, G, and B data.

13. The method according to claim 11, wherein the distribution step includes the step of setting a higher distribution ratio for chromaticity correction than a distribution ratio for lightness correction when the saturation component is large, and setting a higher distribution ratio for lightness correction than a distribution ratio for chromaticity correction when the saturation component is small.

14. The method according to claim 11, wherein the extraction step includes the step of converting the input image data into the lightness data and chromaticity data including two components.

15. The method according to claim 11, further comprising an achromatic color/chromatic color determination step of determining based on the saturation component extracted in the saturation extraction step if the input image data has a chromatic color or an achromatic color.

16. The method according to claim 11, further comprising a delay step of delaying the lightness data by N lines, and delaying the chromaticity data by N/2 lines.

17. The method according to claim 16, wherein the saturation extraction step includes a step of performing spatial filtering processing of (N/2)+1 lines for the chromaticity data delayed by the N/2 lines in the delay step.

18. The method according to claim 16, wherein the achromatic color/chromatic color determination step includes a step of performing spatial filtering processing of (N/2)+1 lines for the chromaticity data delayed by the N/2 lines in the delay step.

19. The method according to claim 16, wherein the distribution step includes a step of changing the distribution ratio of an image edge amount in correspondence with the saturation component extracted in the saturation extraction step and a determination result determined in the achromatic color/chromatic color determination step.

20. The method according to claim 16, wherein the edge emphasis step includes a step of performing correction for removing chromaticity components for the chromaticity data when it is determined in the chromatic color/chromatic color determination step that an image has an achromatic color.

21. An image processing apparatus comprising:

generation means for generating lightness data and chromaticity data;

extraction means for extracting data corresponding to spatial frequency characteristics on the basis of the lightness data; and

control means for controlling the spatial frequency characteristics of the lightness data and chromaticity data on the basis of the data extracted by said extraction means.

22. The apparatus according to claim 21, wherein the data corresponding to the spatial frequency characteristics is data representing an edge amount of an image.

23. The apparatus according to claim 21, wherein said control means controls edge emphasis of the lightness data and chromaticity data.

25. The method according to claim 24, wherein the data corresponding to the spatial frequency characteristics is data representing an edge amount of an image.

26. The method according to claim 24, wherein the control step includes a step of controlling edge emphasis of the lightness data and chromaticity data.

28. The apparatus according to claim 27, wherein said control means controls edge emphasis of the lightness data or chromaticity data.

29. The apparatus according to claim 27, further comprising determination means for performing achromatic color/chromatic color determination on the basis of the saturation component extracted by said second extraction means, and

wherein said control means controls the spatial frequency characteristics on the basis of a determination result of said determination means.

24. An image processing method comprising:

a generation step of generating lightness data and chromaticity data;

an extraction step of extracting data corresponding to spatial frequency characteristics on the basis of the lightness data; and

a control step of controlling the spatial frequency characteristics of the lightness data and chromaticity data on the basis of the data extracted in the extraction step.

27. An image processing apparatus comprising:

generation means for generating lightness data and chromaticity data;

first extraction means for extracting an edge amount on the basis of the lightness data;

second extraction means for extracting a saturation component on the basis of the chromaticity data; and

control means for controlling the spatial frequency characteristics of the lightness data or chromaticity data on the basis of the edge amount and the saturation component extracted by said first and second extraction means.

30. An image processing method comprising:

a generation step of generating lightness data and chromaticity data;

a first extraction step of extracting an edge amount on the basis of the lightness data;

a second extraction step of extracting a saturation component on the basis of the chromaticity data; and

a control step of controlling the spatial frequency characteristics of the lightness data or chromaticity data on the basis of the edge amount and the saturation component extracted in the first and second extraction steps.

31. The method according to claim 30, wherein the control step includes a step of controlling edge emphasis of the lightness data or chromaticity data.

32. The method according to claim 30, further comprising a determination step of performing achromatic color/chromatic color determination on the basis of the saturation component extracted in the second extraction step, and

wherein the control step includes a step of controlling the spatial frequency characteristics on the basis of a determination result in the determination step.

33. An image processing apparatus comprising:

generation means for generating lightness data and chromaticity data;

delay means which can delay the lightness data by N liens and can delay the chromaticity data by N lines;

extraction means for extracting an edge amount using the lightness data delayed by the N lines by said delay means; and

control means for controlling spatial frequency characteristics of the chromaticity data delayed by N/2 lines by said delay means in accordance with the edge amount extracted by said extraction means.

38. The apparatus according to claim 37, wherein said edge decision means decides on the basis of changes in luminance data of the color image data in a two-dimensional region including the pixel of interest if the pixel of interest is located at the edge portion.

39. The apparatus according to claim 37, wherein said first determination means determines on the basis of saturation data obtained based on the color image data if the pixel of interest is a chromatic color pixel or an achromatic color pixel.

40. The apparatus according to claim 39, wherein said first determination means determines based on saturation data of the pixel of interest and pixels around the pixel of interest.

41. The apparatus according to claim 37, wherein said second determination means comprises:

first means for discriminating if the determination result of said first determination means for the pixel of interest indicates a chromatic color or an achromatic color;

second means for, when said first means discriminates a chromatic color, discriminating based on results obtained by said edge decision means for surrounding pixels around the pixel of interest if the surrounding pixels around the pixel of interest are located in the vicinity of an edge of a character line image; and

third means for, when said second means discriminates that the surrounding pixels around the pixel of interest are located in the vicinity of the edge of the character line image, discriminating if the number of achromatic color pixels around the pixel of interest is not less than a predetermined value, and

said second determination means determines that the pixel of interest is an achromatic color pixel when said third means determines that a predetermined number of achromatic color pixels are present in the vicinity of the pixel of interest, and determines that the pixel of interest is a chromatic color pixel when said third means obtains other results.

42. The apparatus according to claim 37, wherein said discrimination means comprises:

first count means for counting the number of chromatic color pixels determined by said second determination means in units of main scanning lines;

accumulation means for, when the number of effective chromatic color pixels counted by said first count means is not less than a predetermined value, accumulating the count value;

second count means for counting the number of successive lines each having the number of effective chromatic color pixels not less than the predetermined value; and

determination means for determining based on the number of effective chromatic color pixels accumulated by said accumulation means and the number of lines counted by said second count means whether or not the input image is a color image.

43. The apparatus according to claim 42, wherein said determination means determines that the input image is a color image when the number of effective chromatic color pixels is not less than a predetermined value or when the number of lines counted by said second count means is a predetermined number of lines.

44. The apparatus according to claim 42, wherein said determination means determines that an image of interest is a color image when an occupation ratio of the number of effective chromatic color pixels is not less than a predetermined value or when the number of lines counted by said second count means is a predetermined number of lines.

45. The apparatus according to claim 37, wherein when said edge decision means decides that the pixel of interest is located in the vicinity of the edge portion of the line image, said second determination means determines that the pixel of interest is an achromatic color pixel.

46. The apparatus according to claim 37, further comprising image forming means for forming an image on a predetermined recording medium on the basis of a discrimination result of said discrimination means.

48. The method according to claim 47, wherein the edge decision step includes the step of deciding on the basis of changes in luminance data of the color image data in a two-dimensional region including the pixel of interest if the pixel of interest is located at the edge portion.

49. The method according to claim 47, wherein the first determination step includes the step of determining on the basis of saturation data obtained based on the color image data if the pixel of interest is a chromatic color pixel or an achromatic color pixel.

50. The method according to claim 49, wherein the first determination step includes a step of determining based on saturation data of the pixel of interest and pixels around the pixel of interest.

51. The method according to claim 47, wherein the second determination step comprises:

a first step of discriminating if the determination result in the first determination step for the pixel of interest indicates a chromatic color or an achromatic color;

a second step of discriminating based on results obtained in the edge decision step for surrounding pixels around the pixel of interest if the surrounding pixels around the pixel of interest are located in the vicinity of an edge of a character line image, when a chromatic color is determined in the first discrimination step; and

a third step of discriminating if the number of achromatic color pixels around the pixel of interest is not less than a predetermined value, when it is determined in the second discrimination step that the surrounding pixels around the pixel of interest are located in the vicinity of the edge of the character line image, and

it is determined in the second discrimination step that the pixel of interest is an achromatic color pixel when it is determined in the third discrimination step that a predetermined number of achromatic color pixels are present in the vicinity of the pixel of interest, and it is determined that the pixel of interest is a chromatic color pixel when other results are obtained in the third discrimination step.

52. The method according to claim 47, wherein the discrimination step comprises:

a first count step of counting the number of chromatic color pixels determined in the second determination step in units of main scanning lines;

an accumulation step of accumulating the count value when the number of effective chromatic color pixels counted in the first count step is not less than a predetermined value;

a second count step of counting the number of successive lines each having the number of effective chromatic color pixels not less than the predetermined value; and

a determination step of determining based on the number of effective chromatic color pixels accumulated in the accumulation step and the number of lines counted in the second count step whether or not the input image is a color image.

53. The method according to claim 52, wherein it is determined in the determination step that the input image is a color image when the number of effective chromatic color pixels is not less than a predetermined value or when the number of lines counted in the second count step is a predetermined number of lines.

54. The method according to claim 52, wherein it is determined in the determination step that an image of interest is a color image when an occupation ratio of the number of effective chromatic color pixels is not less than a predetermined value or when the number of lines counted in the second count step is a predetermined number of lines.

55. The method according to claim 47, wherein when it is decided in the edge decision step that the pixel of interest is located in the vicinity of the edge portion of the line image, it is determined in the second determination step that the pixel of interest is an achromatic color pixel.

56. The method according to claim 47, further comprising an image forming step of forming an image on a predetermined recording medium on the basis of a discrimination result in the discrimination step.

58. The apparatus according to claim 57, wherein said discrimination means includes first decision means for deciding if chromatic color pixels continue in a main scanning direction.

59. The apparatus according to claim 58, wherein said discrimination means further includes second decision means for deciding if the number of portions including continuous chromatic color pixels in the main scanning direction is not less than a predetermined value.

60. The apparatus according to claim 59, wherein said discrimination means further includes third decision means for deciding if not less than a predetermined number of chromatic color lines continue in a sub-scanning direction.

34. An image processing apparatus comprising:

generation means for generating lightness data and chromaticity data; and

correction means for performing correction processing of spatial frequency characteristics on the chromaticity data,

wherein said correction means performs the correction processing so that a hue of an image expressed by the lightness data and chromaticity data is preserved before and after the correction processing.

35. An image processing method comprising:

a generation step of generating lightness data and chromaticity data; and

a correction step of performing correction processing of spatial frequency characteristics for the chromaticity data,

wherein, in the correction step, the correction processing is performed so that a hue of an image expressed by the lightness data and chromaticity data is preserved before and after the correction processing.

36. An image processing apparatus comprising:

reading means for scanning an original and generating image data representing the original;

determination means for determining based on the image data obtained by a first scan of the original by said reading means whether the original is a color original or monochrome original; and

processing means for converting the image data obtained by the first scan of the original by said reading means into lightness data and chromaticity data, and fixing the chromaticity data at a predetermined value in accordance with a determination result of said determination means.

37. An image processing apparatus for determining whether an input image is a color image or monochrome image, comprising:

input means for inputting color image data in units of pixels;

edge decision means for deciding in accordance with the input color image data whether a pixel of interest is located at an edge portion of a line image;

first determination means for determining in accordance with the color image data whether the pixel of interest is a chromatic color pixel or an achromatic color pixel;

second determination means for determining based on a decision result of said edge decision means and a determination result of said first determination means whether the pixel of interest is a chromatic color pixel or an achromatic color pixel; and

discrimination means for discriminating in accordance with a determination result of said second determination means whether the input image is a color image or monochrome image.

47. An image processing method for determining whether an input image is a color image or monochrome image, comprising:

an input step of inputting color image data in units of pixels;

an edge decision step of deciding in accordance with the input color image data whether a pixel of interest is located at an edge portion of a line image;

a first determination step of determining in accordance with the color image data whether the pixel of interest is a chromatic color pixel or an achromatic color pixel;

a second determination step of determining based on a decision result in the edge decision step and a determination result in the first determination step whether the pixel of interest is a chromatic color pixel or an achromatic color pixel; and

a discrimination step of discriminating in accordance with a determination result in the second determination step whether the input image is a color image or monochrome image.

57. An image processing apparatus having a function of discriminating whether an input image is a color image or not, comprising:

determination means for determining whether a pixel of interest is a chromatic color pixel; and

discrimination means for discriminating in accordance with continuity of determination results of said determination means in two-dimensional directions whether the input image is a color image.

61. An image processing method having a function of discriminating whether an input image is a color image or not, comprising:

a determination step of determining whether a pixel of interest is a chromatic color pixel; and

a discrimination step of discriminating in accordance with continuity of determination results in the determination step in two-dimensional directions if the input image is a color image.

62. The method according to claim 61, wherein the discrimination step includes the first decision step of deciding if chromatic color pixels continue in a main scanning direction.

63. The method according to claim 62, wherein the discrimination step further includes a second decision step of deciding if the number of portions including continuous chromatic color pixels in the main scanning direction is not less than a predetermined value.

64. The method according to claim 63, wherein the discrimination step further includes a third decision step of deciding if not less than a predetermined number of chromatic color lines continue in a sub-scanning direction.

65. An image processing apparatus for determining attributes in units of pixels on the basis of color image data in a color space expressed by lightness data and chromaticity data, comprising:

input means for inputting the chromaticity data in units of predetermined areas;

calculation means for calculating a saturation amount on the basis of the input chromaticity data in the predetermined area; and

determination means for determining based on the saturation amount obtained by said calculation means if a pixel of interest is an achromatic color pixel or a chromatic color pixel.

66. The apparatus according to claim 65, further comprising switching means for switching processing for the input color image data on the basis of a result of said determination means.

67. The apparatus according to claim 65, wherein said calculation means calculates a weighted mean value for chromaticity of the pixel of interest on the basis of the input chromaticity data in the predetermined area, and calculates the saturation amount on the basis of the calculated weighted mean value.

68. The apparatus according to claim 65, further comprising:

reading means for reading an original image as color image data; and

conversion means for converting the read color image data into the lightness data and chromaticity data, the lightness and chromaticity data obtained by said conversion means being input by said input means.

70. The apparatus according to claim 69, wherein said first determination means determines whether or not a color of the pixel of interest belongs to a blue/green region.

69. An image-processing apparatus for determining attributes in units of pixels on the basis of color image data in a color space expressed by lightness data and chromaticity data, comprising:

calculation means for calculating a saturation amount on the basis of the chromaticity data;

first determination means for determining based on the chromaticity data whether or not a pixel of interest belongs to a predetermined color region;

threshold value setting means for setting a threshold value on the basis of a determination result of said first determination means; and

second determination means for comparing the saturation amount calculated by said calculation means with the threshold value set by said threshold value setting means to determine if a pixel of interest is an achromatic color pixel or a chromatic color pixel.

71. An image processing apparatus for determining attributes in units of pixels on the basis of color image data in a color space expressed by lightness data and chromaticity data, comprising:

calculation means for calculating a saturation amount on the basis of the chromaticity data;

determination means for determining a degree of lightness of a pixel of interest on the basis of the lightness data;

threshold value setting means for setting a threshold value on the basis of a determination result of said determination means; and

determination means for comparing the saturation amount calculated by said calculation means with the threshold value set by said threshold value setting means to determine if the pixel of interest is an achromatic color pixel or a chromatic color pixel.

72. The apparatus according to claim 71, wherein said determination means determines whether or not the lightness of the pixel of interest belongs to a middle lightness region defined between a predetermined value and another predetermined value.

73. An image processing apparatus for determining attributes in units of pixels on the basis of color image data in a color space expressed by lightness data and chromaticity data, comprising:

first and second achromatic color/chromatic color determination means,

said first achromatic color determination means comprising

calculation means for calculating a saturation amount on the basis of the chromaticity data,

first determination means for determining based on the chromaticity data whether or not a pixel of interest belongs to a predetermined color region,

first threshold value setting means for setting a first threshold value when said first determination means determines that the pixel of interest belongs to the predetermined color region, and

second determination means for determining based on the saturation amount calculated by said calculation means and the first threshold value set by said first threshold value setting means if the pixel of interest is an achromatic color pixel or a chromatic color pixel, and

said second achromatic color/chromatic color determination means comprising,

when said first determination means determines that the pixel of interest does not belong to the predetermined color region,

third determination means for determining a degree of lightness of the pixel of interest on the basis of the lightness data,

second threshold value setting means for setting a threshold value on the basis of a determination result of said second determination means, and

fourth determination means for comparing the saturation amount calculated by said calculation means and the threshold value set by said second threshold value setting means to determine if the pixel of interest is an achromatic color pixel or a chromatic color pixel.

74. The apparatus according to claim 73, wherein said first determination means determines whether or not a color of the pixel of interest belongs to a blue/green region.

75. The apparatus according to claim 74, wherein said third determination means determines whether or not the lightness of the pixel of interest belongs to a middle lightness region defined between a predetermined value and another predetermined value.

76. The apparatus according to claim 74, further comprising:

storage means for storing a determination result of said third or fourth determination means;

average saturation amount calculation means for calculating an average saturation amount at a position of the pixel of interest on the basis of a plurality of chromaticity data of pixels around the pixel of interest;

identification means for identifying based on the calculated average saturation amount if the pixel of interest belongs to an achromatic color region, a chromatic color region, or a middle region between the achromatic and chromatic color regions; and

third achromatic color/chromatic color determination means for, when said identification means identifies that the pixel of interest belongs to the chromatic or achromatic color region, outputting the corresponding identification result, and for, when said identification means identifies that the pixel of interest belongs to the middle region, determining an achromatic color/chromatic color of the pixel of interest on the basis of a plurality of determination results of pixels around the pixel of interest stored in said storage means.

77. The apparatus according to claim 76, further comprising:

average lightness calculation means for calculating an average lightness value at the position of the pixel of interest on the basis of a plurality of lightness data of pixels around the pixel of interest; and

threshold value adjustment means for adjusting, on the basis of the calculated average lightness value, the threshold value used in said identification means to identify if the pixel of interest belongs to the achromatic color, chromatic color, or middle region.

79. The method according to claim 78, further comprising a switching step of switching processing for the input color image data on the basis of a result in the determination step.

80. The method according to claim 78, wherein the calculation step includes a step of calculating a weighted mean value for chromaticity of the pixel of interest on the basis of the input chromaticity data in the predetermined area, and calculating the saturation amount on the basis of the calculated weighted mean value.

81. The method according to claim 78, further comprising:

a reading step of reading an original image as color image data; and

a conversion step of converting the read color image data into the lightness data and chromaticity data, the lightness and chromaticity data obtained in the conversion step being input in the input step.

78. An image processing method for determining attributes in units of pixels on the basis of color image data in a color space expressed by lightness data and chromaticity data, comprising:

an input step of inputting the chromaticity data in units of predetermined areas;

a calculation step of calculating a saturation amount on the basis of the input chromaticity data in the predetermined area; and

a determination step of determining based on the saturation amount obtained in the calculation step if a pixel of interest is an achromatic color pixel or a chromatic color pixel.

82. An image processing method for determining attributes in units of pixels on the basis of color image data in a color space expressed by lightness data and chromaticity data, comprising:

a calculation step of calculating a saturation amount on the basis of the chromaticity data;

a first determination step of determining based on the chromaticity data whether or not a pixel of interest belongs to a predetermined color region;

a threshold value setting step of setting a threshold value on the basis of a determination result in the first determination step; and

a second determination step of comparing the saturation amount calculated in the calculation step with the threshold value set in the threshold value setting step to determine if a pixel of interest is an achromatic color pixel or a chromatic color pixel.

83. The method according to claim 82, wherein the first determination step includes a step of determining whether or not a color of the pixel of interest belongs to a blue/green region.

84. An image processing method for determining attributes in units of pixels on the basis of color image data in a color space expressed by lightness data and chromaticity data, comprising:

a calculation step of calculating a saturation amount on the basis of the chromaticity data;

a determination step of determining a degree of lightness of a pixel of interest on the basis of the lightness data;

a threshold value setting step of setting a threshold value on the basis of a determination result in the determination step; and

a determination step of comparing the saturation amount calculated in the calculation step with the threshold value set in the threshold value setting step to determine if the pixel of interest is an achromatic color pixel or a chromatic color pixel.

85. The method according to claim 84, wherein the determination step includes a step of determining whether or not the lightness of the pixel of interest belongs to a middle lightness region defined between a predetermined value and another predetermined value.

86. An image processing method for determining attributes in units of pixels on the basis of color image data in a color space expressed by lightness data and chromaticity data, comprising:

a first and second achromatic color/chromatic color determination steps,

a first achromatic color determination step comprising

a calculation step of calculating a saturation amount on the basis of the chromaticity data,

a first determination step of determining based on the chromaticity data whether or not a pixel of interest belongs to a predetermined color region,

a first threshold value setting step of setting a first threshold value when it is determined in the first determination step that the pixel of interest belongs to the predetermined color region, and

a second determination step of determining based on the saturation amount calculated in the calculation step and the first threshold value set in the first threshold value setting step if the pixel of interest is an achromatic color pixel or a chromatic color pixel, and

a second achromatic color/chromatic color determination step comprising,

when it is determined in the first determination step that the pixel of interest does not belong to the predetermined color region,

a third determination step of determining a degree of lightness of the pixel of interest on the basis of the lightness data,

a second threshold value setting step of setting a threshold value on the basis of a determination result in the second determination step, and

a fourth determination step of comparing the saturation amount calculated in the calculation step and the threshold value set in the second threshold value setting step to determine if the pixel of interest is an achromatic color pixel or a chromatic color pixel.

87. The method according to claim 86, wherein the first determination step includes a step of determining whether or not a color of the pixel of interest belongs to a blue/green region.

88. The method according to claim 86, wherein the third determination step includes a step of determining whether or not the lightness of the pixel of interest belongs to a middle lightness region defined between a predetermined value and another predetermined value.

89. The method according to claim 86, further comprising:

a storage step of storing a determination result in the third or fourth determination step;

an average saturation amount calculation step of calculating an average saturation amount at a position of the pixel of interest on the basis of a plurality of chromaticity data of pixels around the pixel of interest;

an identification step of identifying based on the calculated average saturation amount if the pixel of interest belongs to an achromatic color region, a chromatic color region, or a middle region between the achromatic and chromatic color regions; and

a third achromatic color/chromatic color determination step of outputting the corresponding identification result when it is identified in the identification step that the pixel of interest belongs to the chromatic or achromatic color region, and determining an achromatic color/chromatic color of the pixel of interest on the basis of a plurality of determination results of pixels around the pixel of interest stored in the storage step when it is identified in the identification step that the pixel of interest belongs to the middle region.

90. The method according to claim 89, further comprising:

an average lightness calculation step of calculating an average lightness value at the position of the pixel of interest on the basis of a plurality of lightness data of pixels around the pixel of interest; and

a threshold value adjustment step of adjusting, on the basis of the calculated average lightness value, the threshold value used in the identification step to identify if the pixel of interest belongs to the achromatic color, chromatic color, or middle region.

91. A storage medium that stores a program code for determining attributes in units of pixels on the basis of color image data in a color space expressed by lightness data and chromaticity data, comprising:

a program code of the input step of inputting the chromaticity data in units of predetermined areas;

a program code of the calculation step of calculating a saturation amount on the basis of the input chromaticity data in the predetermined area; and

a program code of the determination step of determining based on the saturation amount obtained in the calculation step if a pixel of interest is an achromatic color pixel or a chromatic color pixel.

92. The storage medium according to claim 91, further comprising a program code of the switching step of switching processing for the input color image data on the basis of a result in the determination step.

93. The storage medium according to claim 91, wherein the calculation step includes the step of calculating a weighted mean value for chromaticity of the pixel of interest on the basis of the input chromaticity data in the predetermined area, and calculating the saturation amount on the basis of the calculated weighted mean value.

94. The storage medium according to claim 91, further comprising:

a program code of the reading step of reading an original image as color image data; and

a program code of the conversion step of converting the read color image data into the lightness data and chromaticity data, the lightness and chromaticity data obtained in the conversion step being input in the input step.

95. A storage medium that stores a program code for determining attributes in units of pixels on the basis of color image data in a color space expressed by lightness data and chromaticity data, comprising:

a program code of the calculation step of calculating a saturation amount on the basis of the chromaticity data;

a program code of the first determination step of determining based on the chromaticity data whether or not a pixel of interest belongs to a predetermined color region;

a program code of the threshold value setting step of setting a threshold value on the basis of a determination result in the first determination step; and

a program code of the second determination step of comparing the saturation amount calculated in the calculation step with the threshold value set in the threshold value setting step to determine if a pixel of interest is an achromatic color pixel or a chromatic color pixel.

96. The storage medium according to claim 95, wherein the first determination step includes the step of determining whether or not a color of the pixel of interest belongs to a blue/green region.

97. A storage medium that stores a program code for determining attributes in units of pixels on the basis of color image data in a color space expressed by lightness data and chromaticity data, comprising:

a program code of the calculation step of calculating a saturation amount on the basis of the chromaticity data;

a program code of the determination step of determining a degree of lightness of a pixel of interest on the basis of the lightness data;

a program code of the threshold value setting step of setting a threshold value on the basis of a determination result in the determination step; and

a program code of the second determination step of comparing the saturation amount calculated in the calculation step with the threshold value set in the threshold value setting step to determine if the pixel of interest is an achromatic color pixel or a chromatic color pixel.

98. The storage medium according to claim 97, wherein the determination step includes the step of determining whether or not the lightness of the pixel of interest belongs to a middle lightness region defined between a predetermined value and another predetermined value.

99. A storage medium that stores a program code for determining attributes in units of pixels on the basis of color image data in a color space expressed by lightness data and chromaticity data, comprising:

program codes of the first and second achromatic color/chromatic color determination steps,

the first achromatic color determination step comprising

a program code of the calculation step of calculating a saturation amount on the basis of the chromaticity data,

a program code of the first determination step of determining based on the chromaticity data whether or not a pixel of interest belongs to a predetermined color region,

a program code of the first threshold value setting step of setting a first threshold value when it is determined in the first determination step that the pixel of interest belongs to the predetermined color region, and

a program code of the second determination step of determining based on the saturation amount calculated in the calculation step and the first threshold value set in the first threshold value setting step if the pixel of interest is an achromatic color pixel or a chromatic color pixel, and

the second achromatic color/chromatic color determination step comprising,

when it is determined in the first determination step that the pixel of interest does not belong to the predetermined color region,

a program code of the third determination step of determining a degree of lightness of the pixel of interest on the basis of the lightness data,

a program code of the second threshold value setting step of setting a threshold value on the basis of a determination result in the second determination step, and

a program code of the fourth determination step of comparing the saturation amount calculated in the calculation step and the threshold value set in the second threshold value setting step to determine if the pixel of interest is an achromatic color pixel or a chromatic color pixel.

100. The storage medium according to claim 99, wherein the first determination step includes the step of determining whether or not a color of the pixel of interest belongs to a blue/green region.

101. The storage medium according to claim 99, wherein the third determination step includes the step of determining whether or not the lightness of the pixel of interest belongs to a middle lightness region defined between a predetermined value and another predetermined value.

102. The storage medium according to claim 99, further comprising:

a program code of the storage step of storing a determination result in the third or fourth determination step;

a program code of the average saturation amount calculation step of calculating an average saturation amount at a position of the pixel of interest on the basis of a plurality of chromaticity data of pixels around the pixel of interest;

a program code of the identification step of identifying based on the calculated average saturation amount if the pixel of interest belongs to an achromatic color region, a chromatic color region, or a middle region between the achromatic and chromatic color regions; and

a program code of the third achromatic color/chromatic color determination step of outputting the corresponding identification result when it is identified in the identification step that the pixel of interest belongs to the chromatic or achromatic color region, and determining an achromatic color/chromatic color of the pixel of interest on the basis of a plurality of determination results of pixels around the pixel of interest stored in the storage step when it is identified in the identification step that the pixel of interest belongs to the middle region.

103. The storage medium according to claim 102, further comprising:

a program code of the average lightness calculation step of calculating an average lightness value at the position of the pixel of interest on the basis of a plurality of lightness data of pixels around the pixel of interest; and

a program code of the threshold value adjustment step of adjusting, on the basis of the calculated average lightness value, the threshold value used in the identification step to identify if the pixel of interest belongs to the achromatic color, chromatic color, or middle region.