Techniques for reducing color artifacts in digital images

• US 8,724,895 B2
• Filed: 07/23/2007
• Issued: 05/13/2014
• Est. Priority Date: 07/23/2007
• Status: Active Grant

• Current Assignee: NVIDIA Corporation
• Original Assignee: NVIDIA Corporation
• Inventors: Lin, Shang-Hung, Tjandrasuwita, Ignatius
• Primary Examiner(s): SHAH, UTPAL D
• Application Number:
  US11/781,766
• Publication Number:
  US 20090027525A1
• Time in Patent Office: 2,486 Days
• Field of Search: 382/167, 382/275, 382/300, 348/272
• US Class Current: 382/167
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 3/4015 Image demosaicing, e.g. colour filter arrays [CFA] or Bayer patterns
• CPC Class Codes: G06T 5/005 Retouching; Inpainting; Scratch removal detecting, correction, reducing or removing defects, e.g. non-responsive pixels of solid state image sensors H04N25/68, scratch removal for cinematographic films scanned by electronic image sensor H04N5/253
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/77 Retouching; Inpainting; Scratch removal
• CPC Class Codes: H04N 1/648 Transmitting or storing the primary (additive or subtractive) colour signals; Compression thereof H04N1/642 - H04N1/646 take precedence
• 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 technique for reducing artifacts in a digital image, in accordance with one embodiment, includes receiving a stream of raw filter pixel data representing the image. The raw filter pixel data is interpolating to produce red, green-on-red row, green-on-blue row and blue pixel data for each pixel. An artifact in one or more given pixels is reduced as a function of a difference between the green-on-red row and green-on-blue row pixel data of each of the given pixels to generate adjusted interpolated pixel data.

Claims

1. A method of demosaicing digital image data comprising:

receiving raw pixel data for a given image;

low pass filtering the raw pixel data using a first demosiac kernel size to determine first level interpolated pixel data for each pixel;

low pass filtering the raw pixel data using a second demosiac kernel size to determine second level interpolated pixel data for each pixel;

determining if an artifact is present for each pixel from the first level interpolated pixel data;

if the artifact is not present at a given pixel, setting adjusted interpolated pixel data for the given pixel equal to the first level interpolated pixel data for the given pixel;

if the artifact is present at the given pixel, setting the adjusted interpolated pixel data for the given pixel equal to a blend of the first level interpolated pixel data and the second level interpolated pixel data for the given pixel; and

storing the adjusted interpolated pixel data in a computing device readable medium.

2. The method according to claim 1, wherein the raw pixel data comprises Bayer pixel data.

3. The method according to claim 2, wherein:

the first level interpolated pixel data for each pixel comprise a red (R) color value, a green-on-red row (Gr) color value, green-on-blue row (Gb) color value and a blue (B) color value; and

the second level interpolated pixel data for each pixel comprise a red (R) color value, a green-on-red row (Gr) color value, a green-on-blue row (Gb) color value and a blue (B) color value.

4. The method according to claim 3, wherein the demosaic kernel size of the second level is larger than the demosaic kernel size of the first level.

5. The method according to claim 4, wherein determining if a color artifact is present comprises determining the absolute difference between the green-on-red row (Gr) color value and green-on-blue row (Gb) color value in the first level interpolated pixel data.

6. The method according to claim 5, wherein a color artifact is present if the green-on-red row (Gr) color value is substantially different from the green-on-blue row (Gb) color value.

7. The method according to claim 6, wherein the blending ratio between the first and second level interpolated pixel data is a function of the difference between the green-on-red row (Gr) color value and green-on-blue row (Gb) color value.

8. One or more non-transitory computing device readable media containing a plurality of instructions which when executed cause a computing device to implement a method comprising:

receiving a stream of Bayer filter pixel data for a given image;

interpolating red, green-on-red row, green-on-blue row and blue pixel data from the Bayer filter pixel data for each pixel of the given image for two different kernel sizes;

reducing an artifact in one or more given pixels as a function of a difference between the green-on-red row and green-on-blue row pixel data of each of the given pixels of the two different kernel sizes to generate adjusted interpolated pixel data equal to interpolated pixel data of one of the kernel sizes if the artifact is not present and equal to a blend of the interpolated pixel data for the two different kernel sizes if the artifact is present; and

storing the adjusted interpolated pixel data.

9. The one or more non-transitory computing device readable media containing a plurality of instruction which when executed cause a computing device to implement the method according to claim 8, wherein interpolating red, green-on-red row, green-on-blue row and blue pixel data further comprises:

determining a horizontal first level low pass filter value for each pixel utilizing a first kernel size;

determining a horizontal second level low pass filter value for each pixel utilizing a second kernel size;

determining a vertical first level low pass filter value for each pixel utilizing the first kernel size;

determining a vertical second level low pass filter value for each pixel utilizing the second kernel size;

determining first level interpolated pixel data for each pixel from the horizontal first level low pass filter value and the vertical first level low pass filter value;

determining second level interpolated pixel data for each pixel from the horizontal second level low pass filter value and the vertical second level low pass filter value;

converting a color space of the first level interpolated pixel data to separate chroma and luma components; and

converting the color space of the second level interpolated pixel data to separate the chroma and luma components.

10. The one or more non-transitory computing device readable media containing a plurality of instruction which when executed cause a computing device to implement the method according to claim 9, wherein:

determining the horizontal first level low pass filter value for each given pixel comprises averaging the pixels for each corresponding set of adjacent pixels of the first kernel size; and

determining the horizontal second level low pass filter value for each given pixel comprises averaging the pixels for each corresponding set of adjacent pixels of the second kernel size.

11. The one or more non-transitory computing device readable media containing a plurality of instruction which when executed cause a computing device to implement the method according to claim 9, wherein:

determining the vertical first level low pass filter value for each given pixel comprise regressive filtering the pixels for each corresponding set of adjacent pixels of the first kernel size; and

determining the vertical second level low pass filter value for each given pixel comprises regressive filtering the pixels for each corresponding set of adjacent pixels of the second kernel size.

12. The one or more non-transitory computing device readable media containing a plurality of instruction which when executed cause a computing device to implement the method according to claim 9, wherein reducing the artifact in one or more given pixels further comprises:

reducing the chroma component of the first level interpolated pixel data as the function of a difference between the green-on-red row and green-on-blue row chroma components of the pixel data of each of the given pixels to generate adjusted interpolated pixel data.

13. The one or more non-transitory computing device readable media containing a plurality of instruction which when executed cause a computing device to implement the method according to claim 12, further comprising adjusting a weighting of the chroma blending to generate the adjusted interpolated pixel data utilizing a coring parameter.

14. The one or more non-transitory computing device readable media containing a plurality of instruction which when executed cause a computing device to implement the method according to claim 12, further comprising:

adjusting the weightings of a chroma blending to generate the adjusted interpolated pixel data utilizing a weightings parameter.

15. The one or more non-transitory computing device readable media containing a plurality of instruction which when executed cause a computing device to implement the method according to claim 10, wherein:

the kernel size of the first level is a power of two; and

the kernel size of the second level is a power of two and greater then the kernel size of the first level.

16. One or more non-transitory computing device readable media containing a plurality of instructions which when executed cause a computing device to implement a method comprising:

receiving Bayer pixel data for a given image;

low pass filtering the Bayer pixel data using a first kernel size to determine first level interpolated pixel data;

low pass filtering the Bayer pixel data using a second kernel size to determine second level interpolated pixel data;

setting an adjusted interpolated pixel data equal to the first level interpolated pixel data for a given pixel, if a difference between chroma components in the first level interpolated pixel data is below a specified level;

setting the adjusted interpolated pixel data to a blend of the first level interpolated pixel data and the second level interpolated pixel data for a given pixel, if the difference between chroma components in the first level interpolated pixel data is above the specified level and a difference between chroma components in the second level interpolated pixel data is below the specified level; and

outputting the adjusted interpolated pixel data.

17. The one or more non-transitory computing device readable media containing a plurality of instruction which when executed cause a computing device to implement the method according to claim 16, further comprising:

low pass filtering the Bayer pixel data using a third kernel size to determine third level interpolated pixel data; and

setting the adjusted interpolated pixel data to a blend of the second level interpolated pixel data and the third level interpolated pixel data for a given pixel, if the difference between chroma components in the first level interpolated pixel data is above the specified level and a difference between chroma components in the second level interpolated pixel data is below the specified level.

18. The one or more non-transitory computing device readable media containing a plurality of instruction which when executed cause a computing device to implement the method according to claim 17, wherein:

a blending ratio between the first and second level interpolated pixel data is a function of the difference between a green-on-red row (Gr) color value and a green-on-blue row (Gb) chroma value of the first level interpolated pixel data; and

a blending ratio between the second and third level interpolated pixel data is a function of a difference between the green-on-red row (Gr) color value and green-on-blue row (Gb) chroma value of the second level interpolated pixel data.

19. The one or more non-transitory computing device readable media containing a plurality of instruction which when executed cause a computing device to implement the method according to claim 16, further comprising:

generating additional levels of chroma components by low pass filtering the Bayer pixel data using increasingly larger kernel sizes until a difference between the green-on-red row (Gr) color value and green-on-blue row (Gb) chroma value of a given level is below the specified level; and

generating the chroma component of the adjusted interpolated pixel data by blending the chroma component from the given level with one or more previous levels of the interpolated pixel data.