Apparatus and method for controlling gain of color signal

• US 8,120,670 B2
• Filed: 11/21/2008
• Issued: 02/21/2012
• Est. Priority Date: 07/17/2008
• Status: Expired due to Fees

• Current Assignee: Samsung Electro-Mechanics Co., Ltd. (Samsung Group)
• Original Assignee: Samsung Electro-Mechanics Co., Ltd. (Samsung Group)
• Inventors: Kwon, Tae Hyeon, Choi, Won Tae, Kim, Tae Eung
• Primary Examiner(s): Tran, Sinh
• Assistant Examiner(s): Peterson, Christopher K
• Application Number:
  US12/276,138
• Publication Number:
  US 20100013952A1
• Time in Patent Office: 1,187 Days
• Field of Search: 3482231-2251, 382/162, 382/167
• US Class Current: 348/225.1
• CPC Class Codes: H04N 23/88 for colour balance, e.g. white-balance circuits or colour temperature control

Abstract

An apparatus for controlling gain of color signal includes an auto white balance algorithm applying unit determining a white estimation region from an input image, and calculating a first color signal gain for correcting an average color signal level of pixels of the white estimation region to white, a pixel determining unit determining a form of each pixel according to brightness and color using the color signal level of the each pixel of the input image, and a color signal gain determining unit determining a color signal gain to be applied to the each pixel according to the form of the each pixel of the input image as any one of the first color signal gain, a second color signal gain determined by the color signal level of the each pixel for correcting the each pixel to white and a unit gain.

Claims

1. An apparatus for controlling gain of color signal, comprising:

an auto white balance algorithm applying unit determining a white estimation region from an input image, and calculating a first color signal gain for correcting an average color signal level of pixels of the white estimation region to white;

a pixel determining unit determining a form of each pixel according to brightness and color using the color signal level of the each pixel of the input image; and

a color signal gain determining unit determining a color signal gain to be applied to the each pixel according to the form of the each pixel of the input image as any one of the first color signal gain, a second color signal gain determined by the color signal level of the each pixel for correcting the each pixel to white and a unit gain.

2. The apparatus of claim 1, wherein the auto white balance algorithm applying unit comprises:

a color space converter converting a color space of the input image from an RGB color space to a YCbCr color space;

a white region detector detecting a region capable of estimating an existence of a distorted white pixel on Cb-Cr coordinates of the converted color space;

an average value calculator integrating Y, Cb and Cr values of pixels of the region detected by the white region detector to calculate an average value of the Y, Cb and Cr values; and

an auto white balance gain calculator calculating the first color signal gain for moving the Y, Cb and Cr average values calculated by the average value calculator to the origin of the Cb-Cr coordinates.

3. The apparatus of claim 1, wherein the pixel determining unit determines a corresponding pixel as a first form when a G signal level of a pixel of the input image is greater than a preset first threshold for determining a high brightness pixel, R and B signal levels are greater than a second threshold that is preset for determining a high brightness pixel and is less than the first threshold, and the R and B signal levels are greater than the G signal level;

the pixel determining unit determines a corresponding pixel as a second form when the G signal level of the pixel of the input image is greater than the first threshold, the R and B signal levels are greater than the second threshold, the R and B signal levels are less than the G signal level, and the R and B signal levels are greater than the first threshold;

the pixel determining unit determines a corresponding pixel as a third form when the G signal level of the pixel of the input image is greater than the first threshold, the R and B signal levels are greater than the second threshold, the G signal level is greater than or equal to the R and B signal levels, and the R and B signal levels are less than the first threshold;

the pixel determining unit determines a corresponding pixel as a fourth form when the G signal level of the pixel of the input image is greater than the first threshold, the R and B signal levels are greater than the second threshold, and any one of the R and B signal levels is greater than the G signal level; and

the pixel determining unit determines a corresponding pixel as a fifth form when the G signal level of the pixel of the input image is less than the first threshold, or the R and B signal levels are less than the second threshold.

4. The apparatus of claim 3, wherein the color signal gain determining unit determines a color signal gain of the pixel determined in the first form as the unit gain.

5. The apparatus of claim 3, wherein the color signal gain determining unit determines a color signal gain of the pixel determined in the second form as the second color signal gain.

6. The apparatus of claim 3, wherein when a pixel is determined in the third form;

the color signal gain determining unit determines a color signal gain of a corresponding pixel as the first color signal gain, when a level difference between the R and B signal levels is greater than a preset third threshold;

the color signal gain determining unit compares a multiplication result of an R signal level of a corresponding pixel and an R signal gain of the first color signal gain with a G signal level of a corresponding pixel, when the level difference between the R and B signal levels is less than the third threshold;

the color signal gain determining unit determines an R signal gain of a corresponding pixel as an R signal gain of the second color signal gain, when the G signal level is less than the multiplication result of the R signal level of the corresponding pixel and the R signal gain of the first color signal gain;

the color signal gain determining unit determines an R signal gain of a corresponding pixel as the R signal gain of the first color signal gain and compares a multiplication result of a B signal level of a corresponding pixel and a B signal gain of the first color signal gain with a G signal level of a corresponding pixel, when the G signal level is greater than the multiplication result of the R signal level of the corresponding pixel and the R signal gain of the first color signal gain;

the color signal gain determining unit determines a B signal gain of a corresponding pixel as the B signal gain of the second color signal gain when the G signal level is less than the multiplication result of the B signal level of the corresponding pixel and the B signal gain of the first color signal gain; and

the color signal gain determining unit determines a B signal gain of a corresponding pixel as the B signal gain of the first color signal gain when the G signal level is greater than the multiplication result of the B signal level of the corresponding pixel and the B signal gain of the first color signal gain.

7. The apparatus of claim 3, wherein when a pixel is determined in the fourth form;

the color signal gain determining unit determines a color signal gain of a corresponding pixel as the first color signal gain, when a level difference between the R and B signal levels is greater than a preset fourth threshold; and

the color signal gain determining unit determines a color signal gain of a corresponding pixel as the unit gain, when the level difference between the R and B signal levels is less than the preset fourth threshold.

8. The apparatus of claim 3, wherein the color signal gain determining unit determines a color signal gain of the pixel determined in the fifth form as the first color signal gain.

9. The apparatus of claim 1, wherein the first color signal gain is determined by the following equation (1),

R_gain—

_AWB=G_avg/R_avg

B<sub>gain—

AWB</sub>=G_avg/B_avg 

 

(1)

where R<sub>gain—

AWB</sub> represents an R signal gain of the first color signal gain, B<sub>gain—

AWB</sub> represents a B signal gain of the first color signal gain, G_avg represents an average of the G signal levels of pixels in the white estimation region, R_avg represents an average of the R signal levels of the pixels in the white estimation region, and B_avg represents an average of the B signal levels of the pixels in the white estimation region.

10. The apparatus of claim 1, wherein the second color signal gain is determined by the following equation (2),

R_gain—

_in=G_in/R_in

B<sub>gain—

in</sub>=G_in/B_in 

 

(2)

where R<sub>gain—

in</sub> represents an R signal gain of the second color signal gain, B<sub>gain—

in</sub> represents a B signal gain of the second color signal gain, G_in represents a G signal level of each pixel, R_in represents an R signal level of each pixel, and B_in represents a B signal level of each pixel.

11. A method for controlling gain of color signal, the method comprising:

determining a white estimation region from an input image, and calculating a first color signal gain for correcting an average color signal level of pixels of the white estimation region to white;

determining a form of each pixel according to brightness and color using the color signal level of the each pixel of the input image; and

determining a color signal gain to be applied to the each pixel according to the form of the each pixel of the input image as any one of the first color signal gain, a second color signal gain determined by the color signal level of the each pixel for correcting the each pixel to white and a unit gain.

12. The method of claim 11, wherein the determining of the white estimation region comprises:

converting a color space of the input image from an RGB color space to a YCbCr color space;

detecting a region capable of estimating an existence of a distorted white pixel on Cb-Cr coordinates of the converted color space;

integrating Y, Cb and Cr values of pixels of the region detected by the white region detector to calculate an average value of the Y, Cb and Cr values; and

calculating the first color signal gain for moving the Y, Cb and Cr average values calculated by the average value calculator to the origin of the Cb-Cr coordinates.

13. The method of claim 11, wherein the determining of the form comprises:

comparing a G signal level of a pixel of the input image with a preset first threshold for determining a high brightness pixel;

comparing R and B signal levels of a corresponding pixel with a second threshold that is preset for determining a high brightness pixel with is less than the first threshold, when the G signal level is greater than the first threshold as a result of the comparison;

determining a corresponding pixel as a first form, when the R and B signal levels are greater than the second threshold and the G signal level of the corresponding pixel is greater than the G signal level as a result of the comparison;

determining a corresponding pixel as a second form, when the R and B signal levels are greater than the second threshold, the G signal level of the corresponding pixel is less than the G signal level, and the R and B signal levels are greater than the first threshold as a result of the comparison;

determining a corresponding pixel as a third form, when the R and B signal levels are greater than the second threshold, the G signal level of the corresponding pixel is greater than or equal to the R and B signal levels, and the R and B signal levels are less than the first threshold as a result of the comparison;

determining a corresponding pixel as a fourth form, when the R and B signal levels are greater than the second threshold, and any one of the R and B signal levels is greater than the G signal level; and

determining a corresponding pixel as a fifth form, when the G signal level is less than the first threshold, and the R and B signal levels are less than the second threshold as a result of the comparison.

14. The method of claim 13, wherein the color signal gain of the pixel determined in the first form is determined as the unit gain.

15. The method of claim 13, wherein the color signal gain of the pixel determined in the second form is determined as the second color signal gain.

16. The method of claim 13, wherein when a pixel is determined in the third form, the determining of the color signal gain comprises:

comparing a level difference between the R and B signal levels with a preset third threshold;

determining a color signal gain of a corresponding pixel as the first color signal gain, when the level difference between the R and B signal levels is greater than the third threshold as a result of the comparison;

comparing a multiplication result of an R signal level of a corresponding pixel and an R signal gain of the first color signal gain with a G signal level of a corresponding pixel, when the level difference between the R and B signal levels is less than the third threshold as a result of the comparison;

determining an R signal gain of a corresponding pixel as an R signal gain of the second color signal gain, when the G signal level is less than the multiplication result of the R signal level of the corresponding pixel and the R signal gain of the first color signal gain as a result of the comparison;

determining an R signal gain of a corresponding pixel as an R signal gain of the first color signal gain, when the G signal level is greater than the multiplication result of the R signal level of the corresponding pixel and the R signal gain of the first color signal gain as a result of the comparison;

comparing the multiplication result of the B signal level of the corresponding pixel and the B signal gain of the first color signal gain with the G signal level of the corresponding pixel, when the level difference between the R and B signal levels is less than the third threshold as a result of the comparison;

determining a B signal gain of a corresponding pixel as a B signal gain of the second color signal gain when the G signal level is less than the multiplication result of the B signal level of the corresponding pixel and the B signal gain of the first color signal gain as a result of the comparison; and

determining a B signal gain of a corresponding pixel as a B signal gain of the first color signal gain when the G signal level is greater than the multiplication result of the B signal level of the corresponding pixel and the B signal gain of the first color signal gain as a result of the comparison.

17. The method of claim 13, wherein when a pixel is determined in the fourth form, the determining of the color signal gain comprises:

comparing a level difference between the R and B signal levels is greater than a preset fourth threshold;

determining a color signal gain of a corresponding pixel as the first color signal gain, when the level difference between the R and B signal levels is greater than a preset fourth threshold as a result of the comparison; and

determining the color signal gain of the corresponding pixel as the unit gain, when the level difference between the R and B signal levels is less than the preset fourth threshold as a result of the comparison.

18. The method of claim 13, wherein the color signal gain of the pixel determined in the fifth form is determined as the first color signal gain.

19. The method of claim 11, wherein the first color signal gain is determined by the following equation (1),

R_gain—

_AWB=G_avg/R_avg

B<sub>gain—

AWB</sub>=G_avg/B_avg 

 

(2)

where R<sub>gain—

AWB</sub> represents an R signal gain of the first color signal gain, B<sub>gain—

AWB</sub> represents a B signal gain of the first color signal gain, G_avg represents an average of the G signal levels of pixels in the white estimation region, R_avg represents an average of the R signal levels of the pixels in the white estimation region, and B_avg represents an average of the B signal levels of the pixels in the white estimation region.

20. The method of claim 11, wherein the second color signal gain is determined by the following equation (2),

R_gain—

_in=G_in/R_in

B<sub>gain—

in</sub>=G_in/B_in 

 

(2)

where R<sub>gain—

in</sub> represents an R signal gain of the second color signal gain, B<sub>gain—

in</sub> represents a B signal gain of the second color signal gain, G_in represents a G signal level of each pixel, R_in represents an R signal level of each pixel, and B_in represents a B signal level of each pixel.