White balance method in multi-exposure imaging system

1. A white-balance method for use in a multi-exposure imaging system having an image capturing unit, the method comprising:

utilizing the image capturing unit to simultaneously capture a first image and a second image of a scene with a first exposure value and a second exposure value, respectively, wherein the second exposure value is lower than the first exposure value, and the first exposure value and the second exposure value comprise individual exposure time and exposure gain;

calibrating the second exposure value, so that an average brightness value of pixels in the second image is equal to a specific ratio of a maximum sensing value of the image capturing unit;

performing light source detection on the second image to obtain light source information and a light source color ratio corresponding to the light source information, wherein the light source color ratio of red, green, and blue colors is a:b:c; and

performing a color gain process on the first image according to the light source color ratio to generate an output image, wherein red, green, and blue colors of each pixel in the output image in the color gain process are respectively defined by the following formulas:

R

′

=

p

×

R

+

(

1

-

p

)

×

b

a

⁢

R

;

G

′

=

p

×

G

+

(

1

-

p

)

×

b

b

⁢

G

;

B

′

=

p

×

B

+

(

1

-

p

)

×

b

c

⁢

B

;

where R, G, and B denote pixel values of red, green, and blue colors in the first image; R′, G′ and B′ denote pixel values of red, green, and blue colors in the output image; and p denotes a weighting factor between 0 and 1.

2. The method as claimed in claim 1 , further comprising:

determining pixels having a specific ratio of brightest pixels in the second image as the light source information.

3. A multi-exposure imaging system, comprising:

an image capturing unit, comprising a plurality of image sensors for simultaneously capturing a first image and a second image of a scene with a first exposure value and a second exposure value, respectively, wherein the second exposure value is smaller than the first exposure value, and the first exposure value and the second exposure value comprise individual exposure time and exposure gain; and

a processor, for performing light source detection on the second image to obtain light source information and a light source color ratio corresponding to the light source information, and performing a color gain process on the first image according to the light source color ratio to generate an output image, wherein the light source color ratio of red, green, and blue colors is a:b:c,

wherein the processor further calibrates the second exposure value, so that an average brightness value of pixels in the second image is equal to a specific ratio of a maximum sensing value of the image capturing unit,

wherein red, green, and blue colors of each pixel in the output image in the color gain process are respectively defined by the following formulas:

R

′

=

p

×

R

+

(

1

-

p

)

×

b

a

⁢

R

;

G

′

=

p

×

G

+

(

1

-

p

)

×

b

b

⁢

G

;

B

′

=

p

×

B

+

(

1

-

p

)

×

b

c

⁢

B

;

where R, G, and B denote pixel values of red, green, and blue colors in the first image; R′, G′ and B′ denote pixel values of red, green, and blue colors in the output image; and p denotes a weighting factor between 0 and 1.

4. The multi-exposure imaging system as claimed in claim 3 , wherein the processor further determines pixels having a specific ratio of brightest pixels in the second image as the light source information.

5. A white-balance method for use in a multi-exposure imaging system having an image capturing unit, the method comprising:

utilizing the image capturing unit to simultaneously capture a first image and a second image of a scene with a first exposure value and a second exposure value, respectively, wherein the second exposure value is lower than the first exposure value, and the first exposure value and the second exposure value comprise individual exposure time and exposure gain;

calibrating the second exposure value, so that an average brightness value of pixels in the second image is equal to a specific ratio of a maximum sensing value of the image capturing unit;

performing light source detection on the second image to obtain light source information and a light source color ratio corresponding to the light source information, wherein the light source color ratio of red, green, and blue colors is a:b:c;

performing an image combination process on the first image and the second image to obtain a third image; and

performing a color gain process on the third image according to the light source color ratio to generate an output image,

wherein red, green, and blue colors of each pixel in the output image in the color gain process are respectively defined by the following formulas:

R

′

=

p

×

R

+

(

1

-

p

)

×

b

a

⁢

R

;

G

′

=

p

×

G

+

(

1

-

p

)

×

b

b

⁢

G

;

B

′

=

p

×

B

+

(

1

-

p

)

×

b

c

⁢

B

;

where R, G, and B denote pixel values of red, green, and blue colors in the third image; R′, G′ and B′ denote pixel values of red, green, and blue colors in the output image; and p denotes a weighting factor between 0 and 1.

6. The method as claimed in claim 5 , further comprising:

calibrating the second exposure value, so that pixel values of the second image are larger than a noise value of the image capturing unit.

7. The method as claimed in claim 5 , further comprising:

calibrating the second exposure value, so that pixel values of the second image are smaller than or equal to a maximum sensing value of the image capturing unit.

8. The method as claimed in claim 5 , further comprising:

calculating a ratio of the first exposure value and the second exposure value; and

multiplying pixels values of the second image by the ratio to obtain the third image.