Imaging system and method

• US 6,462,835 B1
• Filed: 07/15/1999
• Issued: 10/08/2002
• Est. Priority Date: 07/15/1998
• Status: Expired due to Fees

• Current Assignee: Eastman Kodak Company
• Original Assignee: Kodak Polychrome Graphics Company Limited (Eastman Kodak Company)
• Inventors: Peterson, Mark A., Loushin, Robert S.
• Primary Examiner(s): Grant, II, Jerome
• Application Number:
  US09/353,997
• Time in Patent Office: 1,181 Days
• Field of Search: 358/518, 382/162, 382/167, 758/1.9, 758/506, 758/487
• US Class Current: 358/1.9
• CPC Class Codes: G06T 11/001 Texturing; Colouring; Generation of texture or colour inpainting G06T5/77
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 5/40 using histogram techniques
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: H04N 1/6027 Correction or control of colour gradation or colour contrast H04N1/6058 takes precedence
• CPC Class Codes: H04N 1/6094 depending on characteristics of the input medium, e.g. film type, newspaper

Abstract

A system and method for correction and reconstruction of digital color images make use of one or more of a set of algorithms for color calibration and correction, and reconstruction. An algorithm for optimized bit depth reduction also can be used to match the response curve of the scanner to that of the scanned media, thereby improving signal-to-noise ratio and decreasing artifacts such as pixelization, which can result from sampling the tone curve too coarsely. In a photographic film application, in particular, a color calibration and correction algorithm enables correction of the image for variations in hue from film type to film type, over-exposure or under-exposure, exposure-induced hue shifts, hue shifts caused by lighting effects, processing related hue shifts, and other variables in film processing, while preserving overall hue of the subject matter in the originally photographed image. An image reconstruction algorithm allows creation of look-up tables (LUTs) that create a visually pleasing version of the image when applied to the original data.

Claims

1. A method for correcting a digital color image scanned from film, the method comprising:

producing average color value data for the scanned color image;

performing exposure correction of the image using the average color value data and exposure calibration data;

performing chromatic correction of the image using a subject failure suppression boundary following the exposure correction;

generating image correction data representative of the exposure correction and the chromatic correction; and

applying the image correction data to the image to produce a corrected color image.

2. The method of claim 1, further comprising:

producing the average color value data by;

producing histogram information representative of a distribution of RGB color values within the scanned color image, and

determining average RGB color values within the image based on the histogram information;

converting the average RGB color values to HSL coordinate values; and

performing the exposure correction of the image using the HSL coordinate values and the exposure calibration data.

3. The method of claim 2, further comprising selecting the exposure calibration data based on the HSL coordinate values and a type of the film from which the color image was scanned.

4. The method of claim 3, further comprising selecting the exposure calibration data by:

selecting a set of the exposure calibration data corresponding to the type of film from which the color image was scanned;

determining whether the image was over-exposed, under-exposed, or normally exposed by comparing the HSL coordinate values to reference values; and

selecting a subset of the exposure calibration data based on whether the image was over-exposed, under-exposed, or normally exposed.

5. The method of claim 4, further comprising performing the exposure correction by:

adjusting the HSL lightness values for the image relative to HSL lightness values specified by the exposure calibration data; and

adjusting HSL color values for the image relative to HSL color values specified by the exposure calibration data.

6. The method of claim 2, wherein the exposure calibration data includes multiple sets of exposure calibration data, each of the sets corresponding to a type of film from which the image was scanned and an exposure level of the image.

7. The method of claim 2, further comprising scanning the image such that each of the RGB color values has a color resolution of n bits, and reducing the color resolution of the RGB color values to m bits following the application of the image correction data to the image to produce the corrected color image.

8. A system for correcting a digital color image scanned from film, the system comprising:

means for producing average color value data for the scanned color image;

means for performing exposure correction of the image using the average color value data and exposure calibration data;

means for performing chromatic correction of the image using a subject failure suppression boundary following the exposure correction;

means for generating image correction data representative of the exposure correction and the chromatic correction; and

means for applying the image correction data to the image to produce a corrected color image.

9. The system of claim 8, wherein the means for producing the average color value data produces histogram information representative of a distribution of RGB color values within the scanned color image, and determines average RGB color values within the image based on the histogram information, the system further comprising means for converting the average RGB color values to HSL coordinate values, wherein the means for performing exposure correction of the image uses the HSL coordinate values and the exposure calibration data.

10. The system of claim 9, further comprising means for selecting the exposure calibration data based on the HSL coordinate values and a type of the film from which the color image was scanned.

11. The system of claim 10, wherein the means for selecting the exposure calibration data further includes:

means for selecting a set of the exposure calibration data corresponding to the type of film from which the color image was scanned;

means for determining whether the image was over-exposed, under-exposed, or normally exposed by comparing the HSL coordinate values to reference values; and

means for selecting a subset of the exposure calibration data based on whether the image was over-exposed, under-exposed, or normally exposed.

12. The system of claim 11, wherein the means for performing the exposure correction further includes:

means for adjusting the HSL lightness values for the image relative to HSL lightness values specified by the exposure calibration data; and

means for adjusting HSL color values for the image relative to HSL color values specified by the exposure calibration data.

13. The system of claim 9, wherein the exposure calibration data includes multiple sets of exposure calibration data, each of the sets corresponding to a type of film from which the image was scanned and an exposure level of the image.

14. The system of claim 9, further comprising means for scanning the image such that each of the RGB color values has a color resolution of n bits, and means for reducing the color resolution of the RGB color values to m bits following the application of the image correction data to the image to produce the corrected color image.

15. A method for reconstructing a digital color image scanned from film, the method comprising:

producing average RGB color value data for the scanned color image;

performing exposure correction of the image using the average color value data and exposure calibration data;

performing chromatic correction of the image using a subject failure suppression boundary following the exposure correction;

generating image correction data representative of the exposure correction and the chromatic correction;

generating reconstruction lookup tables (LUTs) based on the color correction data and the average color value data, each of the reconstruction LUTs representing a curve for reconstruction of one of the RGB color channels for the image; and

applying each of the reconstruction LUTs independently for the respective RGB color channels to produce a reconstructed color image.

16. The method of claim 15, further comprising:

producing the average RGB color value data by;

histogram information representative of a distribution of RGB color values within the scanned color image, and

determining average RGB color values within the image based on the histogram information;

converting the average RGB color values to HSL coordinate values; and

performing the exposure correction of the image using the HSL coordinate values and the exposure calibration data.

17. The method of claim 16, wherein each of the reconstruction LUTs is a preliminary reconstruction LUT, and applying the reconstruction LUTs includes:

adjusting each of the preliminary reconstruction LUTs by gamma correction based on the minima, maxima, and midpoint of the reconstruction curve;

applying a shaping function to each of the adjusted preliminary reconstruction LUTs to thereby generate respective final reconstruction LUTs; and

applying the final reconstruction LUTs to produce a reconstructed color image.

18. The method of claim 16, wherein each of the reconstruction LUT is a preliminary reconstruction LUT, and applying the reconstruction LUTs includes:

selecting a target color value;

adjusting each of the preliminary reconstruction LUTs to map the average RGB color value to the target color value and thereby generate respective final reconstruction LUTs; and

applying the final reconstruction LUTs to produce a reconstructed color image.

19. The method of claim 16, further comprising selecting the exposure calibration data based on the HSL coordinate values and a type of the film from which the color image was scanned.

20. The method of claim 19, further comprising selecting the exposure calibration data by:

selecting a set of the exposure calibration data corresponding to the type of film from which the color image was scanned;

determining whether the image was over-exposed, under-exposed, or normally exposed by comparing the HSL coordinate values to reference values; and

selecting a subset of the exposure calibration data based on whether the image was over-exposed, under-exposed, or normally exposed.

21. The method of claim 20, further comprising performing the exposure correction by:

adjusting the HSL lightness values for the image relative to HSL lightness values specified by the exposure calibration data; and

adjusting HSL color values for the image relative to HSL color values specified by the exposure calibration data.

22. The method of claim 16, wherein the exposure calibration data includes multiple sets of exposure calibration data, each of the sets corresponding to a type of film from which the image was scanned and an exposure level of the image.

23. The method of claim 16, further comprising scanning the image such that each of the RGB color values has a color resolution of n bits, and reducing the color resolution of the RGB color values to m bits following the application of the image correction data to the image to produce the corrected color image.

24. A system for reconstructing a digital color image scanned from film, the system comprising:

means for producing average RGB color value data for the scanned color image;

means for performing exposure correction of the image using the average color value data and exposure calibration data;

means for performing chromatic correction of the image using a subject failure suppression boundary following the exposure correction;

means for generating image correction data representative of the exposure correction and the chromatic correction;

means for generating reconstruction lookup tables (LUTs) based on the color correction data and the average color value data, each of the reconstruction lookup tables representing a curve for reconstruction of one of the RGB color channels for the image; and

means for applying each of the reconstruction LUTs independently for the respective RGB color channels to produce a reconstructed color image.

25. The system of claim 24, wherein the means for producing the average color value data produces histogram information representative of a distribution of RGB color values within the scanned color image, and determines average RGB color values within the image based on the histogram information, the system further comprising means for converting the average RGB color values to HSL coordinate values, wherein the means for performing the exposure correction of the image uses the HSL coordinate values and the exposure calibration data.

26. The system of claim 25, wherein each of the reconstruction LUTs is a preliminary reconstruction LUT, and the means for applying the reconstruction LUTs includes:

means for adjusting each of the preliminary reconstruction LUTs by gamma correction based on the minima, maxima, and midpoint of the reconstruction curve;

means for applying a shaping function to each of the adjusted preliminary reconstruction LUTs to thereby generate respective final reconstruction LUTs; and

means for applying the final reconstruction LUTs to produce a reconstructed color image.

27. The system of claim 25, wherein each of the reconstruction LUTs is a preliminary reconstruction LUT, and the means for applying the reconstruction LUTs includes:

means for selecting a target color value;

means for adjusting each of the preliminary reconstruction LUTs to map the average RGB color value to the target color value and thereby generate respective final reconstruction LUTs; and

means for applying the final reconstruction LUTs to produce a reconstructed color image.

28. The system of claim 25, further comprising means for selecting the exposure calibration data based on the HSL coordinate values and a type of the film from which the color image was scanned.

29. The system of claim 25, wherein the means for selecting the exposure calibration data includes:

means for selecting a set of the exposure calibration data corresponding to the type of film from which the color image was scanned;

means for determining whether the image was over-exposed, under-exposed, or normally exposed by comparing the HSL coordinate values to reference values; and

means for selecting a subset of the exposure calibration data based on whether the image was over-exposed, under-exposed, or normally exposed.

30. The system of claim 29, wherein the means for performing the exposure correction includes:

means for adjusting the HSL lightness values for the image relative to HSL lightness values specified by the exposure calibration data; and

means for adjusting HSL color values for the image relative to HSL color values specified by the exposure calibration data.

31. The system of claim 25, wherein the exposure calibration data includes multiple sets of exposure calibration data, each of the sets corresponding to a type of film from which the image was scanned and an exposure level of the image.

32. The system of claim 25, further comprising means for scanning the image such that each of the RGB color values has a color resolution of n bits, and means for reducing the color resolution of the RGB color values to m bits following the application of the image correction data to the image to produce the corrected color image.

33. A method for correcting a digital color image scanned from film, the method comprising:

producing average color value data for the scanned color image;

performing exposure correction of the image using the average color value data and exposure calibration data;

performing chromatic correction of the image using a subject failure suppression boundary following the exposure correction;

generating image correction data representative of the exposure correction and the chromatic correction; and

applying the image correction data to the image to produce a corrected color image.

34. A system for correcting a digital color image scanned from film, the system comprising:

means for producing average color value data for the scanned color image;

means for performing exposure correction of the image using the average color value data and exposure calibration data;

means for performing chromatic correction of the image using a subject failure suppression boundary following the exposure correction;

means for generating image correction data representative of the exposure correction and the chromatic correction; and

means for applying the image correction data to the image to produce a corrected color image.