Pictorial digital image processing incorporating adjustments to compensate for dynamic range differences

• US 20030179924A1
• Filed: 02/21/2003
• Published: 09/25/2003
• Est. Priority Date: 03/24/1997
• Status: Active Grant

• Current Assignee: RPX Corporation
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Holm, Jack M.
• Granted Patent: US 6,628,823 B1
• Time in Patent Office: Days
• US Class Current: 382/162
• CPC Class Codes: H04N 1/4072 dependent on the contents of the original
• CPC Class Codes: H04N 1/6027 Correction or control of colour gradation or colour contrast H04N1/6058 takes precedence
• CPC Class Codes: H04N 1/603 controlled by characteristics of the picture signal generator or the picture reproducer
• CPC Class Codes: H04N 1/6088 by viewing conditions, i.e. conditions at picture output
• CPC Class Codes: H04N 23/88 for colour balance, e.g. white-balance circuits or colour temperature control
• CPC Class Codes: H04N 9/64 Circuits for processing colour signals H04N9/77 takes precedence; camera processing pipelines for processing colour signals H04N23/84
• CPC Class Codes: H04N 9/69 for modifying the colour signals by gamma correction controlling camera response for colour signals H04N23/83

Abstract

Image-dependent tone and color reproduction processing of digital images is accomplished by creating a spatially blurred and sub-sampled version of the original image, and applying knowledge of the capture device physical characteristics to obtain statistics related to the scene or original captured. The statistics are used for image-dependent linearization of the captured image data based on an OECF model, and in conjunction with information about the output medium, to calculate image-specific preferred tone reproduction curves based on a preferred reproduction model. The image data can then be processed for reproduction on output media with different density ranges and color gamuts. All the processing described can be accomplished automatically, but the access to accurate scene information afforded by the image-dependent linearization, and to the perceptually intuitive parameters controlling the calculation of the preferred reproduction curves, also allows for simple, intuitive manual adjustment.

Claims

1. A method of pictorial digital image processing of an original image comprising the steps of:

collecting statistics of an original image;

obtaining density capabilities of an output device to be used for producing a reproduction;

determining both an original pictorial dynamic range from the statistics of the original image and a reproduction pictorial dynamic range from the density capabilities of the output device;

constructing a tone reproduction curve relating the statistics of the original image to the visual density capabilities of the output device, based on a comparison between the original pictorial dynamic range and the reproduction pictorial dynamic range; and

transforming the original image into color space values, using the tone reproduction curve, for producing the reproduction with the output device.

2. The method of claim 1 in which the original image is comprised of initial color space values of a scene captured by a capture device.

3. The method of claim 1 in which the original image is comprised of initial color space values of a focal plane image captured by a capture device.

4. The method of claim 1 in which the original image is comprised of capture device values.

5. The method of claim 1 in which the original image is comprised of initial color space values of an original captured by a capture device.

6. The method of claim 5 in which the original is one of a print, a negative, and a transparency.

7. The method of claim 1 including a further step of obtaining information about characteristics of a capture device arranged for acquiring the original image.

8. The method of claim 7 in which the capture device characteristics are obtained from information in an image file.

9. The method of claim 1 in which the step of collecting statistics of the original image includes first creating a scaled image from the original image and then collecting statistics of the scaled image.

10. The method of claim 9 in which the scaled image is a spatially blurred and sub-sampled image.

11. The method of claim 1 in which the step of collecting statistics of the original image includes first applying a transform to the original image and then collecting statistics of the transformed image.

12. The method of claim 11 in which the transform is a conversion to a luminance image.

13. The method of claim 11 in which the transform is based on physical characteristics of a capture device arranged for acquiring the original image.

14. The method of claim 13 in which the transform compensates for non-linearities of the capture device.

15. The method of claim 13 in which the capture device values are transformed into an intermediate color space.

16. The method of claim 5 in which information concerning processing used to create the original image in initial color space values is ascertained by one of the steps of:

(a) extracting information from an image file and (b) assuming a preferred reproduction based on a preferred reproduction model.

17. The method of claim 16 in which the processing used to create the original image is undone to produce estimated color space values of a scene captured by the capture device.

18. The method of claim 16 in which the processing used to create the original image is undone to produce estimated color space values of a focal plane image captured by the capture device.

19. The method of claim 1 in which the step of collecting statistics of the original image includes estimating a key of the original image.

20. The method of claim 9 in which the step of determining the original pictorial dynamic range includes determining the original pictorial dynamic range from the statistics collected from the scaled version of the original image.

21. The method of claim 20 in which the step of constructing the tone reproduction curve relates the original pictorial dynamic range from the scaled version to the reproduction pictorial dynamic range.

22. The method of claim 1 in which the density capabilities of the output device are assumed to be those of a standard output device.

23. The method of claim 1 in which the density capabilities of the output device are specified using some metric other than density.

24. The method of claim 23 in which the density capabilities of the output device are specified using one of reflectance values, transmittance values, and luminance factors.

25. The method of claim 1 in which the step of determining the original pictorial dynamic range includes adjusting the dynamic range obtained from the statistics of the original image to obtain a different original pictorial dynamic range.

26. The method of claim 25 in which the adjustment is determined by a preferred reproduction model.

27. The method of claim 25 in which the adjustment is user controlled.

28. The method of claim 1 in which the step of determining the reproduction pictorial dynamic range includes adjusting an output medium dynamic range obtained from the density capabilities to obtain a different reproduction pictorial dynamic range.

29. The method of claim 28 in which the adjustment is determined by a preferred reproduction model.

30. The method of claim 28 in which the adjustment is user controlled.

31. The method of claim 1 in which the step of constructing the tone reproduction curve includes applying an S-shaped flex adjustment to the tone reproduction curve based on a difference between the original pictorial dynamic range and the reproduction pictorial dynamic range.

32. The method of claim 31 including a further step of providing for user control of the flex adjustment to regulate contrast of the reproduction.

33. The method of claim 1 in which the step of constructing a tone reproduction curve includes applying a shift adjustment to the tone reproduction curve based on the statistics from the original image.

34. The method of claim 33 including a further step of providing for user control of the shift adjustment to regulate brightness of the reproduction.

35. The method of claim 1 in which the step of constructing the tone reproduction curve is in part based on an estimate of a key of the original image.

36. The method of claim 1 in which the tone reproduction curve is incorporated into a lookup table.

37. The method of claim 36 including a further step of providing for user control by manipulating the lookup table incorporating the tone reproduction curve.

38. The method of claim 1 in which the tone reproduction curve is at least in part defined by mathematical relationships relating the statistics of the original image and the density capabilities of the output device.

39. The method of claim 38 in which the tone reproduction curve is further defined by a lookup table.

40. The method of claim 38 including a further step of providing for user control by altering parameters of the mathematical relationships describing the tone reproduction curve.

41. The method of claim 1 including a further step of obtaining information about viewing conditions under which the reproduction is intended to be viewed.

42. The method of claim 41 in which the viewing condition information is used to adjust the reproduction pictorial dynamic range.

43. The method of claim 41 in which the viewing condition information is used to adjust the tone reproduction curve.

44. The method of claim 1 in which the step of transforming the original image includes applying the tone reproduction curve to a luminance channel.

45. The method of claim 1 in which the step of transforming the original image includes applying the tone reproduction curve to color channels.

46. The method of claim 1 including a further step of obtaining a transform for the output device and the step of transforming the original image data includes applying both the tone reproduction curve and the transform for the output device.

47. The method of claim 46 in which the transform for the output device is a transform from the color space values produced by applying the tone reproduction curve to values appropriate for producing the reproduction on the output device.

48. The method of claim 46 in which the transform for the output device includes at least one of:

a lookup table of one or more dimensions and mathematical relationships specifying the transform.

49. The method of claim 46 in which the tone reproduction curve and transform for the output device are combined into a single transform and applied to produce the reproduction.