Blue sky color detection technique

• US 8,351,724 B2
• Filed: 05/08/2009
• Issued: 01/08/2013
• Est. Priority Date: 05/08/2009
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Xu, Xinyu, Pan, Hao
• Primary Examiner(s): Lu, Tom Y
• Application Number:
  US12/387,864
• Publication Number:
  US 20100284614A1
• Time in Patent Office: 1,341 Days
• Field of Search: None
• US Class Current: 382/254
• CPC Class Codes: G06T 1/00 General purpose image data processing
• CPC Class Codes: H04N 1/58 Edge or detail enhancement; Noise or error suppression, e.g. colour misregistration correction H04N1/62 takes precedence
• CPC Class Codes: H04N 1/62 Retouching, i.e. modification of isolated colours only or in isolated picture areas only
• CPC Class Codes: H04N 1/628 Memory colours, e.g. skin or sky
• CPC Class Codes: H04N 9/643 Hue control means, e.g. flesh tone control

Abstract

An image enhancement technique includes a filter that receives an input image and provides a low-pass filtered image that maintains a substantial number of edges therein. The low pass filtered image is provided a likelihood of being a sky color for each pixel of the low pass filtered image. The low-pass filtered image is filtered based upon a user selection to selectively enhance the sky color. The low-pass filtered image and the filtered low-pass filtered image are blended based upon the user selection based upon the likelihood. The blended image is combined with a high pass filtered input image to provide an enhanced image.

Claims

1. An image enhancement technique comprising the steps of:

(a) receiving an input image and providing a low-pass filtered image that maintains a substantial number of edges therein;

(b) processing said low-pass filtered image to provide respective scores for pixels of said low pass filtered image based on a likelihood map of said image denoting respective likelihoods that pixels of said image are a sky color, said likelihood map constructed by;

(i) dividing a color space of said image into a plurality of areas;

(ii) defining HSV values independently for each of said plurality of areas; and

(iii) using the HSV values of each area to determine said likelihoods;

(c) filtering said low-pass filtered image based upon a user selection to selectively enhance said sky color;

(d) blending said low-pass filtered image and said filtered low-pass filtered image with one another based upon said scores;

(e) combining said blended image with a high pass filtered said input image to provide an enhanced imaged.

2. The image enhancement technique of claim 1 wherein said filter is a spatial filter.

3. The image enhancement technique of claim 2 wherein said filter is a sigma filter.

4. The image enhancement technique of claim 3 wherein said filter is calculated based upon

5. The image enhancement technique of claim 1 wherein said identification is based upon at least one look up table.

6. The image enhancement technique of claim 5 wherein said at least one look up table includes a two dimensional look up table.

7. The image enhancement technique of claim 6 wherein said at least one look up table includes a one dimensional look up table.

8. The image enhancement technique of claim 7 wherein said at least one look up table includes at least two two dimensional look up tables and at least two one dimensional look up tables.

9. The image enhancement technique of claim 1 wherein said identification is based upon a non-RGB color space.

10. The image enhancement technique of claim 9 wherein said non-RGB color space is based upon saturation.

11. The image enhancement technique of claim 10 wherein said non-RGB color space is based upon value.

12. The image enhancement technique of claim 11 wherein said non-RGB color space is based upon hue.

13. The image enhancement technique of claim 1 wherein said identification is based upon adjusting for low luminance blue colors.

14. The image enhancement technique of claim 1 wherein said identification further includes a smoothing filter to smooth said identification.

15. The image enhancement technique of claim 14 wherein said smoothing filter is a non-linear low-pass filter.

16. The image enhancement technique of claim 15 wherein said smoothing filter is an IIR filter.