Screenless conversion of continuous tone images with alterable dot spacing patterns

• US 5,764,810 A
• Filed: 12/20/1995
• Issued: 06/09/1998
• Est. Priority Date: 12/20/1995
• Status: Expired due to Fees

• Current Assignee: Cirrex Corp. (Cirrex Systems, LLC)
• Original Assignee: RR Donnelley & Sons Company
• Inventors: Xie, Zhenhua
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): LEE, CHEUKFAN
• Application Number:
  US08/575,909
• Time in Patent Office: 902 Days
• Field of Search: 358/455, 358/456, 358/458, 358/466, 358/465, 358/457, 358/454, 358/447, 358/298, 358/534, 358/533, 358/535, 358/462, 358/464, 382/252, 382/275, 382/270, 382/263, 382/260, 395/109, 395/106, 395/104
• US Class Current: 358/3.05
• CPC Class Codes: H04N 1/4051 producing a dispersed dots halftone pattern, the dots having substantially the same size different sizes H04N1/4057

Abstract

A system, which converts a continuous tone value undergoing conversion to an output value, generates first and second errors and an output. The first error is based upon (i) the continuous tone value undergoing conversion, (ii) output values corresponding to previously converted continuous tone values, output values predicted for continuous tone values yet to be converted, and an output value having an assumed first level for the continuous cone value undergoing conversion, and (iii) a matrix value based upon the continuous tone value undergoing conversion. The second error is based upon (i) the continuous tone value undergoing conversion, (ii) the output values corresponding to the previously converted continuous tone values, the output values predicted for the continuous tone values yet to be converted, and an output value having an assumed second level for the continuous tone value undergoing conversion, and (iii) the matrix value based upon the continuous tone value undergoing conversion. The continuous tone value undergoing conversion is set to an output value having the first level if the first error is less than the second error and to an output value having the second level if the first error is greater than the second error. Parts (ii) and (iii), in each instance, are conversely related so that the matrix value has greater influence at lower end continuous tone values and less influence at higher end continuous tone values.

Claims

1. A method of converting continuous tone values to output values comprising the following steps:

a) applying a first filter to a continuous tone value if the continuous tone value has a magnitude greater than a criterion;

b) applying a second filter to the continuous tone value if the continuous tone value has a magnitude smaller than the criterion, wherein the first and second filters are different; and

c) setting the continuous tone value to an output value depending upon the results from steps a) and b);

wherein step a) comprises the steps of generating, if the continuous tone value has a magnitude grcater than the criterion, a first error based upon a difference between the continuous tone value and a value derived by applying the first filter to an assumed output value of zero for the continuous tone value, and a second error based upon a difference between the continuous tone value and a value derived by applying the first filter to an assumed output value of one for the continuous tone value, wherein step b) comprises the steps of generating, if the continuous tone value has a magnitude smaller than the criterion, a third error based upon a difference between the continuous tone value and a value derived from the second filter dependent upon the continuous tone value, and a fourth error based upon a difference between the continuous tone value and a value derived from the second filter dependent upon the continuous tone value, and wherein step c) comprises the steps of setting the continuous tone value to an output value of zero if the first error is less than the second error, setting the continuous tone value to an output value of one if the first error is oreater than the second error, setting the continuous tone value to an output value of zero if the third error is less than the fourth error, and setting the continuous tone value to an output value to an output value of one if the third error is greater than the fourth error, as appropriate.

2. The method of claim 1 wherein the second filter comprises a plurality of values having suppressed low frequency components.

3. The method of claim 2 further comprising the steps of diffusing the first error if the continuous tone value is set to an output value of zero, of diffusing the second error if the continuous tone value is set to an output value of one, of diffusing the third error if the continuous tone value is set to an output value of zero, and of diffusing the fourth error if the continuous tone value is set to an output value of one, as appropriate.

4. A method of converting continuous tone values to output values comprising the following steps:

a) applying a first filter to a continuous tone value if the continuous tone value has a magnitude greater than a criterion;

b) applying a second filter to the continuous tone value if the continuous tone value has a magnitude smaller than the criterion, wherein the first and second filters are different; and

c) setting the continuous tone value to an output value depending upon the results from steps a) and b);

Wherein step a) comprises the steps of generating a first error based upon a difference between (I) the continuous tone value, (ii) a value derived from the second filter dependent upon the continuous tone value, and (iii) a value derived by applying the first filter to an assumed output value of zero for the continuous tone value, and generating a second error based upon a difference between (I) the continuous tone value, (ii) a value derived from the second filter dependent upon the continuous tone value, and (iii) a value derived by applying the first filter to an assumed output value of one for the continuous tone value, and wherein step c) comprises the steps of setting the continuous tone value to an output value of zero if the first error is less than the second error, and setting the continuous tone value to an output value of one if the first error is greater than the second error.

5. The method of claim 4 wherein all parts (ii) above are multiplied by 1-γ

, wherein all parts (iii) above are multiplied by γ

, wherein γ

is given by the expression ##EQU5## wherein C_i,j is a corresponding continuous tone value, and wherein α and

Cut are constants.

6. The method of claim 4 wherein the second filter comprises a plurality of values having suppressed low frequency components.

7. The method of claim 6 further comprising the steps of diffusing the first error if the continuous tone value is set to an output value of zero, and of diffusing the second error if the continuous tone value is set to an out-put value of one.

8. A method of converting continuous tone values to output values for rendering in the same reproduction comprising the following steps:

a) converting a group of continuous tone values to a first group of output values if the continuous tone values of the group of continuous tone values are greater than a predetermined level, wherein the output values of the first group of output values, when rendered, produces dots in a substantially random pattern; and

b) converting the group of continuous tone values to a second group of output values if the continuous tone values of the group of continuous tone values are less than the predetermined level, wherein the output values of the second group of output values, when rendered, produces dots in a substantially even pattern;

wherein the steps a) and b) comprises the following steps;

generating first errors based upon first, second, and third parts, wherein the first part is based upon the continuous tone values of the group of continuous tone values, wherein the second part is based upon (I) previously converted continuous tone values neighboring corresponding continuous tone values of the group of continuous tone values, (ii) yet to be converted continuous tone values neighboring corresponding continuous tone values of the group continuous tone values, and (iii) output values having an assumed first level for the corresponding continuous tone values of the group of continuous tone values, and wherein the third part is based upon values selected from a filter dependent upon corresponding continuous tone values of the group of continuous tone values;

generating second errors based upon the first part, the third part, and a fourth part, wherein the fourth part is based upon (I) previously converted continuous tone values neighboring corresponding continuous tone values of the group of continuous tone values, (ii) yet to converted continuous tone values neighboring corresponding continuous tone values of the group of continuous tone values, and (iii) output values having an assumed second level for the corresponding continuous tone values of the group of continuous tone values;

setting those continuous tone values of the group of continuous tone values to output values having the first level if corresponding ones of the first errors are less than corresponding ones of the second errors and setting those continuous tone values of the group of continuous tone values to output values having the second level if corresponding ones of the first errors are greater than corresponding ones of the second errors.

9. The method of claim 8 wherein the third parts are multiplied by 1-γ

, wherein the second and fourth parts are multiplied by γ

, wherein γ

is given by the expression ##EQU6## wherein C_i,j is a corresponding continuous tone value, wherein α and

Cut are constants, and wherein step c) is dependent upon Cut.

10. The method of claim 8 wherein the filter comprises a plurality of values having suppressed low frequency components.

11. The method of claim 10 further comprising the steps of diffusing the first errors if the corresponding continuous tone values are set to output values having the first level, and of diffusing the second errors if the corresponding continuous tone values are set to the output values hating the second level.

12. The method of claim 8 wherein steps a) and b) are dependent upon first and second filters.

13. The method of claim 12 wherein the first filter is applied primarily in step a) and wherein the second filter is applied primarily in step b).

14. The method of claim 13 wherein the second filter is comprised of filter values which are selected from the second filter based upon corresponding continuous tone values.

15. The method of claim 14 wherein the second filter comprises a plurality of values having suppressed low frequency components.

16. A system for converting an input value undergoing conversion to an output value, the system comprising:

first error generating means for generating a first error for the input value undergoing conversion, wherein the first error is based upon first and second parts, wherein the second part is based upon an output value having an assumed first level for the input value undergoing conversion, and wherein the first and second parts are conversely related;

second error generating means for generating a second error for the input value undergoing conversion, wherein the second error is based upon the first part and a third part, wherein the third part is based upon an output value having an assumed second level for the input value undergoing conversion, and wherein the first and third parts are conversely related; and

,

output value setting means for setting the input value undergoing conversion to an output value having the first level if the first error is less than the second error and to an output value having the second level if the first error is greater than the second error.

17. The system of claim 16 wherein the first error generating means generates the first error based upon the input value undergoing conversion, the first part, and the second part, wherein the second part is based upon (i) a selected number of output values corresponding to input values previously converted, (ii) output values predicted for a selected number of input values yet to be converted, and (iii) an output value having an assumed first level for the input value undergoing conversion, and wherein the second error generating means generates the second error based upon the input value undergoing conversion, the first part, and the third part, wherein the third part is based upon (i) the selected number of output values corresponding to input values previously converted, (ii) the output values predicted for the selected number of input values yet to be converted, and (iii) an output value having an assumed second level for the input value undergoing conversion.

18. The system of claim 17 wherein the first part is a value based upon the input value undergoing conversion.

19. The system of claim 18 wherein the value based upon the input value undergoing conversion is a matrix value which is selected from a matrix dependent upon the input value undergoing conversion.

20. The system of claim 19 wherein the matrix is arranged to affect the output value to which the input value is converted only when the input value undergoing conversion is within a predetermined range of input values.

21. The system of claim 20 wherein the first part is multiplied by 1-γ

, wherein the second and third parts are multiplied by γ

, wherein γ

is given by the expression ##EQU7## wherein C_i,j is the input value undergoing conversion, and wherein α and

Cut are constants.

22. The system of claim 16 wherein the first part is multiplied by 1-γ

, wherein the second and third parts are multiplied by γ

.

23. The system of claim 22 wherein the first part is a value based upon the input value undergoing conversion.

24. The system of claim 23 wherein the value based upon the input value undergoing conversion is a matrix value which is selected from a matrix dependent upon the input value undergoing conversion.

25. The system of claim 24 wherein the matrix is arranged to affect the output value to which the input value is converted only when the input value undergoing conversion is within a predetermined range of input values.

26. The system of claim 25 wherein γ

is given by the expression ##EQU8## wherein C_i,j is the input value undergoing conversion, and wherein α and

Cut are constants.

27. The system of claim 16 wherein the first part is a value based upon the input value undergoing conversion.

28. The system of claim 27 wherein the value based upon the input value undergoing conversion is a matrix value which is selected from a matrix dependent upon the input value undergoing conversion.

29. The system of claim 28 wherein the matrix is arranged to affect the output value to which the input value is converted only when the input value undergoing conversion is within a predetermined range of input values.

30. The system of claim 16 further comprising error diffusing means for diffusing the first error if the input value undergoing conversion is set to the output value having the first level and for diffusing the second error if the input value undergoing conversion is set to the output value having the second level.

31. A system for converting an input value undergoing conversion to an output value, the system comprising:

first error generating means for generating a first error for the input value undergoing conversion, wherein the first error is based upon first and second parts, wherein the first part is based upon a filter, wherein the second part is based upon an output value having an assumed first level for the input value undergoing conversion, and wherein the first and second parts are conversely related;

second error generating means for generating a second error for the input value undergoing conversion, wherein the second error is based upon third and fourth parts, wherein the third part is based upon the filter, wherein the fourth part is based upon an output value having an assumed second level for the input value undergoing conversion, and wherein the third and fourth parts are conversely related; and

,

output value setting means for setting the input value undergoing conversion to an output value having the first level if the first error is less than the second error and to an output value having the second level if the first error is greater than the second error.

32. The system of claim 31 wherein the first error generating means generates the first error based upon the input value undergoing conversion, the first part, and the second part, wherein the second part is based upon (i) a selected number of output values corresponding to input values previously converted, (ii) output values predicted for a selected number of input values yet to be converted, and (iii) an output value having an assumed first level for the input value undergoing conversion, and wherein the second error generating means generates the second error based upon the input value undergoing conversion, the third part, and the fourth part, wherein the fourth part is based upon (i) the selected number of output values corresponding to input values previously converted, (ii) the output values predicted for the selected number of input values yet to be converted, and (iii) an output value having an assumed second level for the input value undergoing conversion.

33. The system of claim 32 wherein the first and third parts are a value based upon the input value undergoing conversion.

34. The system of claim 33 wherein the value based upon the input value undergoing conversion is a filter value which is selected from the filter dependent upon the input value undergoing conversion.

35. The system of claim 34 wherein the filter is arranged to affect the output value to which the input value undergoing conversion is converted only when the input value undergoing conversion is within a predetermined range of input values.

36. The system of claim 35 wherein the filter comprises a plurality of values having suppressed low frequency components.

37. The system of claim 36 wherein the first and third parts are multiplied by 1-γ

, wherein the second and fourth parts are multiplied by γ

, wherein γ

is given by the expression ##EQU9## wherein C_i,j is the input value undergoing conversion, and wherein α and

Cut are constants.

38. The system of claim 31 wherein the first and third parts are multiplied by 1-γ

, and wherein the second and fourth parts are multiplied by γ

.

39. The system of claim 38 wherein the first and third parts are a value based upon the input value undergoing conversion.

40. The system of claim 39 wherein the value based upon the input value undergoing conversion is a filter value which is selected from the filter dependent upon the input value undergoing conversion.

41. The system of claim 40 wherein the filter is arranged to affect the output value to which the input value undergoing conversion is converted only when the input value undergoing conversion is within a predetermined range of input values.

42. The system of claim 41 wherein the filter comprises a plurality of values having suppressed low frequency components.

43. The system of claim 42 wherein γ

is given by the expression ##EQU10## wherein C_i,j is the input value undergoing conversion, and wherein α and

Cut are constants.

44. The system of claim 31 wherein the first and third parts are a value based upon the input value undergoing conversion.

45. The system of claim 44 wherein the value based upon the input value undergoing conversion is a filter value which is selected from the filter dependent upon the input value undergoing conversion.

46. The system of claim 45 wherein the filter is arranged to affect the output value to which the input value undergoing conversion is converted only when the input value undergoing conversion is within a predetermined range of input values.

47. The system of claim 46 wherein the filter comprises a plurality of values having suppressed low frequency components.

48. The system of claim 31 further comprising error diffusing means for diffusing the first error if the input value undergoing conversion is set to the output value having the first level and for diffusing the second error if the input value undergoing conversion is set to the output value having the second level.

49. The system of claim 31 wherein the filter comprises a plurality of values having suppressed low frequency components.

50. A screenless conversion method for converting continuous tone values to output values representing dots to be rendered by a marking device, wherein the continuous tone values range between values of M and N, and wherein the screenless conversion method comprises the following steps:

a) determining first errors corresponding to the continuous tone values so that the first errors produce generally evenly distributed dots for continuous tones values between about M and about Cut and so that the first errors produce generally randomly distributed dots for continuous tones values between about Cut and about N, wherein Cut is a value between M and N, and wherein the first errors are based upon an output value having an assumed first level for the continuous tone values;

b) determining second errors corresponding to the continuous tone values so that the second errors produce generally evenly distributed dots for continuous tones values between about M and about Cut and so that the second errors produce generally randomly distributed dots for continuous tones values between about Cut and about N, wherein the second errors are based upon an output value having an assumed second level for the continuous tone values;

c) setting those continuous tone values whose corresponding first errors are less than their corresponding second errors to output values having the first level; and

,

d) setting those continuous tone values whose corresponding first errors are greater than their corresponding second errors to output values having the second level.

51. The screenless conversion method of claim 50 wherein step a) comprises the step of generating each of the first errors based upon a corresponding continuous tone value, a corresponding first part, and a corresponding second part, wherein the corresponding second part is based upon (i) a selected number of output values corresponding to previously converted continuous tone values, (ii) output values predicted for a selected number of continuous tone values yet to be converted, and (iii) an output value having the assumed first level for the continuous tone value, and wherein step b) comprises the step of generating each of the second errors based upon a corresponding continuous tone value, the corresponding first part, and a corresponding third part, wherein the corresponding third part is based upon (i) the selected number of output values corresponding to previously converted continuous tone values, (ii) the output values predicted for the selected number of continuous tone values yet to be converted, and (iii) an output value having the assumed second level for the continuous tone value.

52. The screenless conversion method of claim 51 wherein the corresponding first part is multiplied by 1-γ

, wherein the corresponding second and third parts are multiplied by γ

, wherein γ

is given by the expression ##EQU11## wherein C_i,j is a continuous tone value, and wherein α and

Cut are constants.

53. The screenless conversion method of claim 52 wherein the corresponding first part is a value based upon a corresponding continuous tone value.

54. The screenless conversion method of claim 53 wherein the value based upon a corresponding continuous tone value is a filter value which is selected from a filter dependent upon the corresponding continuous tone value.

55. The screenless conversion method of claim 54 wherein the filter is arranged to affect the output values to which corresponding continuous tone values are converted only when the corresponding continuous tone values have magnitudes between about M and about Cut.

56. The screenless conversion method of claim 55 wherein the filter comprises a plurality of values having suppressed low frequency components.

57. The screenless conversion method of claim 50 wherein the corresponding first part is multiplied by 1-γ

, and wherein the corresponding second and third parts are multiplied by γ

.

58. The screenless conversion method of claim 57 wherein the corresponding first part is a value based upon a corresponding continuous tone value.

59. The screenless conversion method of claim 58 wherein the value based upon a corresponding continuous tone value is a filter value which is selected from a filter dependent upon the corresponding continuous tone value.

60. The screenless conversion method of claim 59 wherein the filter is arranged to affect the output values to which corresponding continuous tone values are converted only when the corresponding continuous tone values have magnitudes between about M and about Cut.

61. The screenless conversion method of claim 60 wherein the filter comprises a plurality of values having suppressed low frequency components.

62. The screenless conversion method of claim 61 wherein γ

is given by the expression ##EQU12## wherein C_i,j is a continuous tone value, and wherein α and

Cut are constants.

63. The screenless conversion method of claim 50 wherein the corresponding first part is a value based upon a corresponding continuous tone value.

64. The screenless conversion method of claim 63 wherein the value based upon a corresponding continuous tone value is a filter value which selected from a filter dependent upon the corresponding continuous tone value.

65. The screenless conversion method of claim 64 wherein the filter is arranged to affect the output values to which corresponding continuous tone values are converted only when the corresponding continuous tone value have magnitudes between about M and about Cut.

66. The screenless conversion method of claim 65 wherein the filter comprises a plurality of values having suppressed low frequency components.

67. The screenless conversion method of claim 50 further comprising error diffusing means for diffusing the first errors when corresponding continuous tone values are set to output values having the first level and for diffusing the second errors when corresponding continuous tone values are set to the output values having the second level.

68. A system for converting one input value of a series of input values to an output value wherein previous input values have been converted to previous output values and subsequent input values are to be converted to output values, the system comprising:

first error generating means for generating a first error for the one input value, wherein the first error is based upon (i) the one input value, (ii) a selected number of previous output values, output values predicted for a selected number of subsequent input values, and an output value having an assumed first level for the one input value, and (iii) an output value having an assumed second level for the one input value; and

,

second error generating means for generating a second error for the one input value, wherein. the second error is based upon (i) the one input value, (iv) the selected number of previous output values, the output values predicted for the selected number of subsequent input values, and an output value having an assumed third level for the one input value, and (iii) the output value having the assumed second level for the one input value; and

,

output value setting means for setting the one input value to an output value having the first level if the first error is less than the second error and to an output value having the third level if the first error is greater than the second error.

69. The system of claim 68 wherein part (iii) is multiplied by 1-γ

, wherein parts (ii) and (iv) are multiplied by γ

, wherein γ

is given by the expression ##EQU13## wherein C_i,j is the one input value, and wherein α and

Cut are constants.

70. The system of claim 69 wherein the output value having the assumed second level is selected from a matrix based upon the one input value.

71. The system of claim 70 wherein the output value having the assumed second level is arranged to affect the output value to which the one input value is converted when the one input value is within a predetermined range of input values.

72. The system of claim 71 wherein the matrix comprises a plurality of values having suppressed low frequency components.

73. The system of claim 68 wherein the output value having the assumed second level is a value based upon the one input value.

74. The system of claim 73 wherein the value based upon the one input value is a matrix value selected from a matrix based upon the one input value.

75. The system of claim 74 wherein the output value having the assumed second level is arranged to affect the output value to which the one input value is converted when the one input value is within a predetermined range of input values.

76. The system of claim 75 wherein the matrix comprises a plurality of values having suppressed low frequency components.

77. The system of claim 68 further comprising error diffusing means for diffusing the first error if the one input value is set to the output value having the first level and for diffusing the second error if the one input value is set to the output value having the third level.