Digital color image pre-processing

• US 20030184659A1
• Filed: 04/02/2002
• Published: 10/02/2003
• Est. Priority Date: 04/02/2002
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Skow, Michael
• Granted Patent: US 7,102,669 B2
• Time in Patent Office: Days
• US Class Current: 348/223.1
• CPC Class Codes: H04N 2209/046 Colour interpolation to calculate the missing colour values
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/843 Demosaicing, e.g. interpolating colour pixel values

Abstract

In one embodiment, the invention involves a method for processing an image. A sensor output is provided. An automatic gain control of the sensor output is performed to generate a first output. An automatic white balance correction to the first output is performed to generate a second output. A gamma correction of the second output is performed to generate a third output. A color interpolation is performed to the third output to generate a fourth output. A low-pass spatial filtration of the fourth output is performed to generate a fifth output. A color saturation and correction of the fifth output is performed to generate a sixth output, and a high-pass spatial filtration of the sixth output is performed to generate an image output.

Claims

1. A method for processing an image, comprising:

providing a sensor output;

performing an automatic gain control of the sensor output to generate a first output;

performing an automatic white balance correction to the first output to generate a second output;

performing a gamma correction of the second output to generate a third output;

performing a color interpolation to the third output to generate a fourth output;

performing a low-pass spatial filtration of the fourth output to generate a fifth output;

performing a color saturation and correction of the fifth output to generate a sixth output; and

performing a high-pass spatial filtration of the sixth output to generate an image output.

2. The method of claim 1, wherein the automatic gain control comprises performing an expansion of a histogram to fill a dynamic range.

3. The method of claim 1, wherein the automatic white balance correction comprises calculating a gray world model ratio of a set of colors in a pattern and applying a multiplier to each color.

4. The method of claim 1, wherein the gamma correction is performed in gray space.

5. The method of claim 1, wherein the color interpolation comprises performing a three-by-three edge enhanced demosaic of a raw Bayer signal to an RGB signal.

6. The method of claim 1, wherein the low-pass spatial filtration comprises performing a low-pass spatial filter on each of a plurality of color planes.

7. The method of claim 1, wherein the color saturation and correction comprises manipulating color ratios of a plurality of color planes within each of a plurality of pixels.

8. The method of claim 1, wherein the high-pass spatial filtration comprises enhancing a spatial edge.

9. An imaging device configured to implement the method of claim 1.

10. An application specific integrated circuit configured to implement the method of claim 1.

33. An imaging device configured to implement the method of claim 1.

34. An application specific integrated circuit configured to implement the method of claim 1.

11. A method for digital processing of an image, comprising:

providing a sensor output;

performing an automatic exposure control of the sensor output to generate a first output and second output;

using the first output to update the sensor output;

performing an automatic gain control of the second output to generate a third output;

performing an automatic white balance correction of the third output to generate a fourth output;

performing color interpolation of the fourth output to generate a fifth output;

performing a low-pass spatial filtration of the fifth output to generate a sixth output;

performing color saturation of the sixth output to generate a seventh output;

performing a high-pass spatial filtration of the seventh output to generate an eighth output;

performing an auto gamma correction of the eighth output to generate a ninth output;

converting the ninth output to an output image.

12. The method of claim 11, wherein the automatic exposure control comprises continuously monitoring a sensor output at a frame rate.

13. The method of claim 11, wherein to update the sensor output comprises feeding back an automatic exposure control signal to a sensor.

14. The method of claim 11, wherein the automatic gain control comprises performing an expansion of a histogram to fill a dynamic range.

15. The method of claim 11, wherein the color interpolation comprises performing a three-by-three edge enhanced demosaic of a raw Bayer signal to an RGB signal.

16. The method of claim 11, wherein the low-pass spatial filtration comprises performing a low-pass spatial filter on each of a plurality of color planes.

17. The method of claim 11, wherein the color saturation comprises manipulating color ratios of a plurality of color planes within each of a plurality of pixels.

18. The method of claim 11, wherein the high-pass spatial filtration comprises enhancing a spatial edge.

19. The method of claim 11, wherein the auto gamma correction comprises automatically selecting a gamma level based on scene illumination data.

20. The method of claim 19, further comprising utilizing the scene illumination data to detect an expected amount of signal-to-noise ratio before applying a fixed gamma table.

21. An imaging device configured to implement the method of claim 11.

22. An application specific integrated circuit configured to implement the method of claim 11.

23. A method for digital processing an image, comprising:

providing a sensor output;

performing a color interpolation of the sensor output to generate a first output;

performing a color correction of the first output to generate a second output;

performing a gamma correction of the second output to generate a third output;

performing a color space conversion of the third output to generate a fourth output and fifth output;

performing an automatic exposure and gain control of the fourth output to generate a sixth output and feeding the sixth output back to the sensor;

performing a high-pass spatial filtration of the fourth output to generate a seventh output;

performing an automatic white balance correction of the fifth output to generate an eighth output and feeding the eighth output back to the sensor;

performing a chromatic median filtration of the fifth output to generate a ninth output; and

combining the seventh output with the ninth output to generate an image output.

24. The method of claim 23, wherein the color interpolation comprises performing a three-by-three edge enhanced demosaic of a raw Bayer signal to an RGB signal.

25. The method of claim 23, wherein the color correction comprises manipulating color ratios of a plurality of color planes within each of a plurality of pixels.

26. The method of claim 23, wherein the automatic exposure and gain control comprises increasing an available signal-to-noise ratio and eliminating digital missing code by performing an automatic gain control function in an analog domain on the fourth output before an analog-to-digital conversion.

27. The method of claim 23, wherein the high-pass spatial filtration comprises enhancing a spatial edge.

28. The method of claim 23, wherein the high-pass spatial filtration comprises performing a high-pass spatial filtration of the fourth output in a luma space.

29. The method of claim 23, wherein the fifth output is a C_rC_b color space conversion output.

30. The method of claim 23, wherein the automatic white balance correction comprises calculating a plurality of gray world model ratios for a plurality of colors in a pattern and applying a multiplier to each of the plurality of colors.

31. The method of claim 23, wherein feeding the sixth output back to the sensor comprises performing a color gain in an analog domain.

32. The method of claim 23, wherein the chromatic median filtration comprises detecting a false color based on a plurality of other values in a local area and replacing the false color with a median.

35. A method of performing a color image processing of an image from a sensor, comprising:

performing automatic exposure control with feedback to the sensor;

performing an automatic gain control with feedback to the sensor; and

performing an automatic white balance control with feedback to the sensor.