Method of detecting clipped image pixels

• US 7,327,504 B2
• Filed: 12/06/2002
• Issued: 02/05/2008
• Est. Priority Date: 12/06/2002
• Status: Active Grant

• Current Assignee: Monument Peak Ventures, LLC (Dominion Harbor Enterprises, LLC)
• Original Assignee: Eastman Kodak Company
• Inventors: Gallagher, Andrew C.
• Primary Examiner(s): NGUYEN, MADELEINE ANH VINH
• Application Number:
  US10/313,612
• Publication Number:
  US 20040109072A1
• Time in Patent Office: 1,887 Days
• Field of Search: 358/1.9, 358/518, 358/520, 358/521, 358/522, 358/530, 358/539, 382/162, 382/167, 382/270, 382/274, 382/172, 348/246, 348/247, 348/223.1, 348/231.9
• US Class Current: 358/518
• CPC Class Codes: H04N 9/646 for image enhancement, e.g. vertical detail restoration, cross-colour elimination, contour correction, chrominance trapping filters

Abstract

A method is described for detecting the clipped pixels of a digital color image. The method includes the steps of: (a) producing a uniformity map from the digital color image, where the uniformity map indicates locations within the digital color image that are substantially uniform; (b) providing a threshold value; and (c) using the uniformity map, the threshold value, and the digital color image to produce a map indicating the location of clipped pixels within the digital color image.

Claims

1. An improved method for detecting clipped pixels of a digital color image, comprising the steps of:

(a) producing a uniformity map from the digital color image, said uniformity map indicating locations within the digital color image that are substantially uniform;

(b) providing a threshold value; and

(c) using the uniformity map, the threshold value, and the digital color image to produce a map indicating the location of clipped pixels within the digital color image.

2. The method as claimed in claim 1 wherein the map indicating the location of clipped pixels is applied to a filter to produce an enhanced map.

3. The method as claimed in claim 1 further comprising the steps of applying the map indicating the location of clipped pixels to a map analyzer to produce one or more correction parameters based on a characteristic of the clipped pixels;

and applying the correction parameters to an image transform to enhance the digital color image in accordance with the correction parameters.

4. The method as claimed in claim 3 wherein the characteristic is that the clipped pixels are highlight pixels and the image transform is a scene balance algorithm or an exposure determination algorithm.

5. The method as claimed in claim 3 wherein the characteristic is that the clipped pixels are highlight pixels and the image transform performs a tone scale adjustment of the digital color image.

6. The method as claimed in claim 3 wherein the digital color image comprises a plurality of color channels and the map analyzer employs a histogram-based process to operate on image pixels of the digital color image that are clipped in two or more of the channels.

7. The method as claimed in claim 3 wherein the correction parameter relates to the percentage of pixels that are clipped and is used by the image transform to pro-rate the effect of the image transform on the digital color image.

8. An improved method for detecting clipped pixels of a digital color image, comprising the steps of:

(a) producing a uniformity map from the digital color image, said uniformity map indicating regions within the digital color image that are substantially uniform, and furthermore indicating locations within the digital color image where the variation of pixel values within a local region is below a first threshold;

(b) providing a second threshold value; and

(c) using the uniformity map, the second threshold value, and the digital color image to produce a map indicating the location of clipped pixels within the digital color image.

9. The method as claimed in claim 8 wherein the map indicating the location of clipped pixels is applied to a filter to produce an enhanced map.

10. The method claimed in claim 8, wherein the uniformity map indicates locations within the digital color image where the pixel values are identical.

11. The method claimed in claim 8, wherein the second threshold is applied to pixels within a substantially uniform region that are below the first threshold.

12. The method as claimed in claim 8 further comprising the steps of applying the map indicating the location of clipped pixels to a map analyzer to produce one or more correction parameters based on a characteristic of the clipped pixels;

and applying the correction parameters to an image transform to enhance the digital color image in accordance with the correction parameters.

13. The method as claimed in claim 12 wherein the characteristic is that the clipped pixels are highlight pixels and the image transform is a scene balance algorithm or an exposure determination algorithm.

14. The method as claimed in claim 12 wherein the characteristic is that the clipped pixels are highlight pixels and the image transform performs a tone scale adjustment of the digital color image.

15. The method as claimed in claim 12 wherein the digital color image comprises a plurality of color channels and the map analyzer employs a histogram-based process to operate on image pixels of the digital color image that are clipped in two or more of the channels.

16. The method as claimed in claim 12 wherein the correction parameter relates to the percentage of pixels that are clipped and is used by the image transform to pro-rate the effect of the image transform on the digital color image.