Enhancing the tonal characteristics of digital images

• US 20030235342A1
• Filed: 06/24/2002
• Published: 12/25/2003
• Est. Priority Date: 06/24/2002
• Status: Active Grant

• Current Assignee: Monument Peak Ventures, LLC (Dominion Harbor Enterprises, LLC)
• Original Assignee: Eastman Kodak Company
• Inventors: Gindele, Edward B.
• Granted Patent: US 7,113,649 B2
• Time in Patent Office: Days
• US Class Current: 382/260
• CPC Class Codes: H04N 1/4074 using histograms

Abstract

A method of producing a tone scale function which can operate on a source digital image to improve tonal characteristics, includes generating the tone scale function having a highlight tone scale segment and a shadow tone scale segment defined relative to a reference point on the tone scale function, and that is adapted to operate on the source digital image to improve its tonal characteristics by: using a first function with a monotonically decreasing slope characteristic to produce the highlight tone scale segment that includes points that are equal to or greater than the reference point; and using a second function with a monotonically increasing slope characteristic to produce the shadow tone scale segment that includes points that are equal to or less than the reference point.

Claims

1. A method of producing a tone scale function which can operate on a source digital image to improve tonal characteristics, comprising the steps of:

generating the tone scale function having a highlight tone scale segment and a shadow tone scale segment defined relative to a reference point on the tone scale function, and that is adapted to operate on the source digital image to improve its tonal characteristics by;

i) using a first function with a monotonically decreasing slope characteristic to produce the highlight tone scale segment that includes points that are equal to or greater than the reference point; and

ii) using a second function with a monotonically increasing slope characteristic to produce the shadow tone scale segment that includes points that are equal to or less than the reference point.

2. The method of claim 1 using the tone scale function and the source digital image to generate an enhanced digital image.

3. The method of claim 2 using a sigmoid shaped rendering function independent of the source digital image and the enhanced digital image to generate a rendered digital image.

4. The method of claim 1 wherein the first function is manually controlled with at least one highlight control parameter and the second function is manually controlled with at least one shadow control parameter.

5. The method of claim 1 wherein an exponential function is used in the first and second functions.

6. The method of claim 1 wherein the slopes of the highlight and shadow tone scale segments are each equal at the reference point.

7. The method of claim 1 wherein the slopes of the highlight and shadow tone scale segments are unequal at the reference point.

8. The method of claim 1 further including the step of using the pixels of the source digital image to produce the first and second functions.

9. The method of claim 1 further including the step of using the pixels of the source digital image to produce a histogram and producing the first and second functions based on such histogram.

10. The method of claim 9 wherein the highlight tone scale segment maps a fixed percentile of the histogram to a predetermined output value relating to a white paper density and the shadow tone scale segment maps a fixed percentile of the histogram to a predetermined output value relating to a black paper density.

11. The method of claim 1 wherein the source digital image is in a luminance-chrominance representation.

12. The method of claim 1 wherein the source digital image includes pixels having at least three different colors.

13. The method of claim 1 wherein the pixels of the source digital image have a logarithmic relationship to original scene intensities.

14. The method of claim 2 further including using a spatial filter in applying the tone scale function to the source digital image.

15. The method of claim 1 wherein step c) furthers includes combining the first function with a linear function to produce the highlight tone scale segment wherein the contribution of the linear function to the highlight tone scale segment is selected by at least one controllable parameter.

16. The method of claim 1 wherein step c) furthers includes combining the second function with a linear function to produce the shadow tone scale segment wherein the contribution of the linear function to the shadow tone scale segment is selected by at least one controllable parameter.

17. The method of claim 1 wherein step c) furthers includes combining the first function with a third function that has a monotonically decreasing slope characteristic to produce the highlight tone scale segment wherein the contribution of the third function to the highlight tone scale segment is selected by at least one controllable parameter.

18. The method of claim 1 wherein step d) furthers includes combining the second function with a third function that has a monotonically increasing slope characteristic to produce the shadow tone scale segment wherein the contribution of the third function to the shadow tone scale segment is selected by at least one controllable parameter.

19. The method of claim 1 wherein step c) furthers includes combining the first function with a third function that has a monotonically decreasing slope characteristic and a fourth linear function to produce the highlight tone scale segment wherein the contribution of the fourth linear function to the highlight tone scale segment is selected by at least one controllable parameter.

20. The method of claim 1 wherein step d) furthers includes combining the second function with a third function that has a monotonically increasing slope characteristic and a fourth linear function to produce the shadow tone scale segment wherein the contribution of the fourth linear function to the shadow tone scale segment is selected by at least one controllable parameter.

55. A computer storage product having at least one computer storage medium having instructions stored therein causing one or more computers to perform the method of claim 1.

21. A method of producing a tone scale function which can operate on a source digital image to improve tonal characteristics, comprising the steps of:

a) receiving a source digital image including a plurality of pixels; and

b) generating the tone scale function having a highlight tone scale segment and a shadow tone scale segment defined relative to a reference point on the tone scale function, and that is adapted to operate on the source digital image to improve its tonal characteristics, including;

i) providing a first function based upon information in the pixels of the source digital image and using such first function with a monotonically decreasing slope characteristic to produce the highlight tone scale segment that includes points that are equal to or greater than the reference point; and

ii) providing a second function based upon information in the pixels of the source digital image and using such second function with a monotonically increasing slope characteristic to produce the shadow tone scale segment that includes points that are equal to or less than the reference point.

22. The method of claim 21 using the tone scale function and the source digital image to generate an enhanced digital image.

23. The method of claim 22 using a sigmoid shaped rendering function independent of the source digital image and the enhanced digital image to generate a rendered digital image.

24. The method of claim 21 wherein an exponential function is used in the first and second functions.

25. The method of claim 21 wherein the slopes of the highlight and shadow tone scale segments are each equal at the reference point.

26. The method of claim 21 wherein the slopes of the highlight and shadow tone scale segments are unequal at the reference point.

27. The method of claim 21 further including the step of using the pixels of the source digital image to produce a histogram and producing the first and second functions based on such histogram.

28. The method of claim 27 wherein the highlight tone scale segment maps a fixed percentile of the histogram to a predetermined output value relating to a white paper density and the shadow tone scale segment maps a fixed percentile of the histogram to a predetermined output value relating to a black paper density.

29. The method of claim 21 wherein the source digital image is in a luminance-chrominance representation.

30. The method of claim 21 wherein the source digital image includes pixels having at least three different colors.

31. The method of claim 21 wherein the pixels of the source digital image have a logarithmic relationship to original scene intensities.

32. The method of claim 21 further including using a spatial filter in applying the tone scale function to the source digital image.

33. The method of claim 21 wherein step c) furthers includes combining the first function with a linear function to produce the highlight tone scale segment wherein the contribution of the linear function to the highlight tone scale segment is selected by at least one controllable parameter.

34. The method of claim 21 wherein step c) furthers includes combining the second function with a linear function to produce the shadow tone scale segment wherein the contribution of the linear function to the shadow tone scale segment is selected by at least one controllable parameter.

35. The method of claim 21 wherein step c) furthers includes combining the first function with a third function that has a monotonically decreasing slope characteristic to produce the highlight tone scale segment wherein the contribution of the third function to the highlight tone scale segment is selected by at least one controllable parameter.

36. The method of claim 21 further including combining the second function with a third function that has a monotonically increasing slope characteristic to produce the shadow tone scale segment wherein the contribution of the third function to the shadow tone scale segment is selected by at least one controllable parameter.

37. The method of claim 21 wherein step c) furthers includes combining the first function with a third function that has a monotonically decreasing slope characteristic and a fourth linear function to produce the highlight tone scale segment wherein the contribution of the fourth linear function to the highlight tone scale segment is selected by at least one controllable parameter.

38. The method of claim 21 further including combining the second function with a third function that has a monotonically increasing slope characteristic and a fourth linear function to produce the shadow tone scale segment wherein the contribution of the fourth linear function to the shadow tone scale segment is selected by at least one controllable parameter.

56. A computer storage product having at least one computer storage medium having instructions stored therein causing one or more computers to perform the method of claim 21.

39. A method of producing a tone scale function which can operate on a source digital image to improve tonal characteristics, comprising the steps of:

generating a tone scale function having a highlight tone scale segment and a shadow tone scale segment defined relative to a reference point on the tone scale function, and that is adapted to operate on the source digital image to improve its tonal characteristics, wherein;

i) the highlight and shadow tone scale segments are defined by different non-linear mathematical functions; and

ii) the shape of the highlight tone scale segment can be controlled independently of the shape of the shadow tone scale segment.

40. The method of claim 39 using the tone scale function and the source digital image to generate an enhanced digital image.

41. The method of claim 40 using a sigmoid shaped rendering function independent of the source digital image and the enhanced digital image to generate a rendered digital image.

42. The method of claim 39 wherein the highlight tone scale and shadow tone scale segments are defined by different sigmoid shaped functions.

43. The method of claim 39 wherein the highlight tone scale segment is manually controlled with at least one highlight control parameter and the shadow tone scale segment is manually controlled with at least one shadow control parameter.

44. The method of claim 39 wherein an exponential function is used in the highlight and shadow tone scale segments.

45. The method of claim 39 wherein the slopes of the highlight and shadow tone scale segments are each equal at the reference point.

46. The method of claim 39 wherein the slopes of the highlight and shadow tone scale segments are unequal at the reference point.

47. The method of claim 39 further including the step of using the pixels of the source digital image to produce the highlight and shadow tone scale segments.

48. The method of claim 39 further including the step of using the pixels of the source digital image to produce a histogram and producing the highlight and shadow tone scale segments based on such histogram.

49. The method of claim 48 wherein the highlight tone scale segment maps a fixed percentile of the histogram to a predetermined output value relating to a white paper density and the shadow tone scale segment maps a fixed percentile of the histogram to a predetermined output value relating to a black paper density.

50. The method of claim 39 wherein the source digital image is in a luminance-chrominance representation.

51. The method of claim 39 wherein the source digital image includes pixels having at least three different colors.

52. The method of claim 39 wherein the pixels of the source digital image have a logarithmic relationship to original scene intensities.

53. The method of claim 40 further including using a spatial filter in applying the tone scale function to the source digital image.

57. A computer storage product having at least one computer storage medium having instructions stored therein causing one or more computers to perform the method of claim 39.

54. A method of producing a tone scale function which can operate on a source digital image to improve tonal characteristics, comprising the steps of:

generating the tone scale function having a highlight tone scale segment and a shadow tone scale segment defined relative to a reference point on the tone scale function, and that is adapted to operate on the source digital image to improve its tonal characteristics wherein;

i) the highlight tone scale segment includes points that are equal to or greater than the reference point and has a monotonically decreasing slope characteristic; and

ii) the shadow tone scale segment includes points that are equal to or less than the reference point and has a monotonically increasing slope characteristic.

58. A computer storage product having at least one computer storage medium having instructions stored therein causing one or more computers to perform the method of claim 54.

59. A method for producing an enhanced digital image from a source digital image employing a tone scale function which operates on the source digital image to improve tonal characteristics, comprising:

a) generating a tone scale function having a highlight tone scale segment and a shadow tone scale segment defined relative to a reference point on the tone scale function, and that is adapted to operate on the source digital image to improve its tonal characteristics;

b) automatically generating the highlight tone scale segment that includes points that are equal to or greater than the reference point and has a monotonically decreasing slope characteristic;

c) automatically generating the shadow tone scale segment that includes points that are equal to or less than the reference point and has a monotonically increasing slope characteristic;

d) using the tone scale function and the source digital image to generate a first enhanced digital image;

e) receiving user input selections and using the user input selections and the tone scale function to generate a modified tone scale function; and

f) using the modified tone scale function and the source digital image to generate a second enhanced digital image.

60. A system for producing an enhanced digital image from a source digital image employing a tone scale function which operates on the source digital image to improve tonal characteristics, comprising:

a) means for receiving a source digital image including a plurality of pixels;

b) means for generating a tone scale function having a highlight tone scale segment and a shadow tone scale segment defined relative to a reference point on the tone scale function, and that is adapted to operate on the source digital image to improve its tonal characteristics;

c) means for automatically generating the highlight tone scale segment that includes points that are equal to or greater than the reference point and has a monotonically decreasing slope characteristic;

d) means for automatically generating the shadow tone scale segment that includes points that are equal to or less than the reference point and has a monotonically increasing slope characteristic;

e) means responsive to the tone scale function and the source digital image for generating a first enhanced digital image;

f) means for receiving user input selections that can be used to generate a modified tone scale function; and

g) means for using the modified tone scale function and the source digital image to generate a second enhanced digital image.