System and method for asymmetrically demosaicing raw data images using color discontinuity equalization

• US 20020167602A1
• Filed: 03/20/2001
• Published: 11/14/2002
• Est. Priority Date: 03/20/2001
• Status: Abandoned Application

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Nguyen, Truong-Thao
• Application Number:
  US09/813,750
• Publication Number:
  US 20020167602A1
• Time in Patent Office: Days
• US Class Current: 348/280
• CPC Class Codes: G06T 2200/12 involving antialiasing
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 3/4007 based on interpolation, e.g. bilinear interpolation image demosaicing G06T3/4015; edge-driven or edge-based scaling G06T3/403
• CPC Class Codes: G06T 3/4015 Image demosaicing, e.g. colour filter arrays [CFA] or Bayer patterns
• CPC Class Codes: G06T 3/403 Edge-driven scaling; Edge-based scaling
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: G06T 5/73 Deblurring; Sharpening
• CPC Class Codes: H04N 2209/046 Colour interpolation to calculate the missing colour values
• CPC Class Codes: H04N 23/843 Demosaicing, e.g. interpolating colour pixel values
• CPC Class Codes: H04N 25/134 based on three different wavelength filter elements

Abstract

A system and method for demosaicing raw data (“mosaiced”) images utilizes an asymmetric interpolation scheme to equalize color discontinuities in the resulting demosaiced images using discontinuities of a selected color component of the mosaiced images. Discontinuities of the selected color component are assumed to be equal to discontinuities of the other remaining color components. Thus, color discontinuity equalization is achieved by equating the discontinuities of the remaining color components with the discontinuities of the selected color component. The asymmetric interpolation scheme allows the system and method to reduce color aliasing and non-colored “zippering” artifacts along feature edges of the resulting demosaiced images, as well as colored artifacts.

Claims

1. A method of demosaicing a mosaiced image to derive a demosaiced image comprising:

independently interpolating first color values of said mosaiced image to derive first interpolated values of said demosaiced image; and

interpolating second color values of said mosaiced image to derive second interpolated values of said demosaiced image, including substantially equalizing a discontinuity of said second interpolated values with a corresponding discontinuity of said first interpolated values.

2. The method of claim 1 wherein said step of independently interpolating said first color values includes adaptively interpolating said first color values using an interpolation technique selected from at least a first interpolation technique and a second interpolation technique.

3. The method of claim 2 wherein said step of adaptively interpolating said first color values includes determining variations in said first and second color values along at least a first direction and a second direction to select said interpolation technique.

4. The method of claim 1 wherein said step of interpolating said second color values includes computing color discontinuity equalization values using interpolated first color values and averaged first color values, said color discontinuity equalization values being used to substantially equalize said discontinuity of said second interpolated values with said corresponding discontinuity of said first interpolated values.

5. The method of claim 4 wherein said step of computing said color discontinuity equalization values includes subtracting said averaged first color values from said interpolated first color values to derive said color discontinuity equalization values.

6. The method of claim 4 wherein said step of computing said color discontinuity equalization values includes adaptively interpolating said first color values of said mosaiced image using an interpolation technique selected from at least a first interpolation technique and a second interpolation technique to derive said averaged first color values.

7. The method of claim 4 wherein said step of computing said color discontinuity equalization values includes:

sub-sampling said interpolated first color values with respect to pixel locations of said mosaiced image that correspond to said second color values of said mosaiced image to derive sub-sampled values; and

averaging said sub-sampled values to generate said averaged first color values.

8. The method of claim 4 wherein said step of interpolating said second color values includes:

averaging said second color values of said mosaiced image to derived averaged second color values; and

summing said color discontinuity equalization values and said averaged second color values to derive said second interpolated values.

9. The method of claim 1 wherein said step of substantially equalizing said discontinuity of said second interpolated values includes compensating for a subsequent color correction process by introducing one or more compensating constants.

10. A system for demosaicing a mosaiced image to derive a demosaiced image comprising:

first interpolating means for independently interpolating first color values of said mosaiced image to derive first interpolated values of said demosaiced image;

second interpolating means for interpolating second color values of said mosaiced image to derive second interpolated values of said demosaiced image; and

equalization means for substantially equalizing a discontinuity of said second interpolated values with a corresponding discontinuity of said first interpolated values.

11. The system of claim 10 wherein said first interpolation means includes an adaptive interpolator that is configured to adaptively interpolate said first color values using an interpolation technique selected from at least a first interpolation technique and a second interpolation technique.

12. The system of claim 11 wherein said adaptive interpolator includes a gradient direction detector that is configured to determine variations in said first and second color values along at least a first direction and a second direction to select said interpolation technique.

13. The system of claim 10 wherein said equalization means is configured to compute color discontinuity equalization values using interpolated first color values and averaged first color values, said color discontinuity equalization values being used by said equalization means to substantially equalize said discontinuity of said second interpolated values with said corresponding discontinuity of said first interpolated values.

14. The system of claim 13 wherein said equalization means is configured to subtract said averaged first color values from said interpolated first color values to derive said color discontinuity equalization values.

15. The system of claim 13 wherein said equalization means includes an adaptive interpolator that is configured to adaptively interpolate said first color values using an interpolation technique selected from at least a first interpolation technique and a second interpolation technique.

16. The system of claim 13 wherein said equalization means includes:

a sub-sampling unit that is configured to sub-sample said interpolated first color values with respect to pixel locations of said mosaiced image that correspond to said second color values of said mosaiced image to derive sub-sampled values; and

an averaging unit that is configured to average said sub-sampled values to generate said averaged first color values.

17. The system of claim 13 wherein said second interpolating means includes:

an averaging unit that is configured to average said second color values of said mosaiced image to derived averaged second color values; and

means for summing said color discontinuity equalization values and said averaged second color values to derive said second interpolated values.

19. The method of claim 18 wherein said step of independently interpolating said first intensity values includes adaptively interpolating said first intensity values using an interpolation technique selected from at least a horizontal interpolation technique and a vertical interpolation technique.

20. The method of claim 18 wherein said step of interpolating said second and third intensity values includes computing said color discontinuity equalization values using interpolated first intensity values and averaged first intensity values.

21. The method of claim 20 wherein said step of computing said color discontinuity equalization values includes subtracting said averaged first intensity values from said interpolated first intensity values to derive said color discontinuity equalization values.

22. The method of claim 20 wherein said step of computing said color discontinuity equalization values includes adaptively interpolating said first intensity values of said mosaiced image using an interpolation technique selected from at least a horizontal interpolation technique and a vertical interpolation technique to derive said interpolated first intensity values.

23. The method of claim 20 wherein said step of computing said color discontinuity equalization values includes:

sub-sampling said interpolated first intensity values with respect to pixel locations of said mosaiced image that correspond to said second intensity values of said mosaiced image to derive second sub-sampled values;

sub-sampling said interpolated first intensity values with respect to pixel locations of said mosaiced image that correspond to said third intensity values of said mosaiced image to derive third sub-sampled values; and

averaging said second and third sub-sampled values to generate said averaged first intensity values.

24. The method of claim 20 wherein said step of interpolating said second and third intensity values includes:

averaging said second and third intensity values of said mosaiced image to derived averaged second and third intensity values;

summing said color discontinuity equalization values and said averaged second intensity values to derive said second interpolated values; and

summing said color discontinuity equalization values and said averaged third intensity values to derive said third interpolated values

18. A method of demosaicing a mosaiced image to derive a demosaiced image comprising:

independently interpolating first intensity values of said mosaiced image to derive first interpolated values of said demosaiced image; and

interpolating second and third intensity values of said mosaiced image to derive second interpolated values and third interpolated values, including equalizing discontinuities of said second and third interpolated values with corresponding discontinuities of said first interpolated values.