Calculation method for the correction of white balance
A calculation method for calculating a white balance correction value is disclosed. When an image capture device utilizes an auxiliary light to capture an image, the weightings of the image color impacted by the color temperature of each light source are obtained by the brightness-rate which is provided by the environment light and the flash, and then the weightings of the color temperatures of the two light sources are balanced to obtain a white balance correction value. At last, the white balance correction value is applied to correct the white balance of the image.
1. A calculation method for calculating a white balance correction value for use in an image capture device that stores a color temperature of a default auxiliary light CT 2 and a relationship table of a pulse width P and a default brightness R, comprising:
(A) under the same scene, capturing a first image and a second image having an auxiliary light, wherein a brightness of the auxiliary light is supplied with a first pulse width;
(B) obtaining an environment color temperature CT 1 and a first environment brightness Y 1 from the first image;
(C) obtaining a second environment brightness Y 2 from the second image;
(D) subtracting the first environment brightness Y 1 from the second environment brightness Y 2 to obtain a first flash brightness F 1 ;
(E) supplying the brightness of the auxiliary light with a second pulse width P 2 to obtain a third image;
(F) obtaining a first default flash brightness R 1 and a second default flash brightness R 2 by looking up the relationship table of the pulse width P and the default brightness R and calculating the second flash brightness F 2 by a second flash brightness formula, wherein
F
2
=
R
2
R
1
×
F
1
;
and
(G) calculating a white balance correction value WB by a white balance correction value formula, wherein
WB
=
CT
1
×
Y
1
+
CT
2
×
F
2
Y
1
+
F
2
.
2. The calculation method of claim 1 , wherein the environment color temperature CT 1 and the first environment brightness Y 1 are obtained from the RGB of pixels within a specific area of the first image.
3. The calculation method of claim 1 , wherein the auxiliary light is a flash or an AF auxiliary light.
4. The calculation method of claim 1 , wherein the RGB of the color temperature of the default auxiliary light CT 2 are (R CT2 , G CT2 , B CT2 ).
5. The calculation method of claim 1 , wherein the RGB of the environment color temperature CT 1 are (R CT1 , G CT1 , B CT1 ).
6. The calculation method of claim 1 , wherein the color temperature of the default auxiliary light CT 2 is obtained by the image capture device performing an image capture operation to a gray card in a darkroom and driving an auxiliary light device to generate the auxiliary light to compensate for the brightness of the environment and capturing the image and performing an average calculation for a summation of the RGB value of each pixel within the specific area of the image to generate the default auxiliary light CT 2 .
7. The calculation method of claim 2 , wherein the specific area comprises partial or entire areas of the first image.
8. The calculation method of claim 1 , wherein the environment color temperature CT 1 is obtained by a calculating result of averaging a summation of the RGB value of each pixel within the specific area of the first image.
9. The calculation method of claim 4 , wherein the first environment brightness Y 1 is represented by the RGB value of the G CT1 value of the environment color temperature CT 1 .
10. The calculation method of claim 1 , wherein the first default flash brightness R 1 and the second default flash brightness R 2 are respectively obtained by looking up the relationship table of the pulse width P and the default brightness R using the first pulse width P 1 and the second pulse width P 2 .
11. The calculation method of claim 1 , wherein the second flash brightness F 2 is the brightness of the auxiliary light supplied during capturing the third image.
12. The calculation method of claim 1 , wherein the white balance correction value WB further comprises the white balance correction value of a red color WB R , the white balance correction value of a green color WB G and the white balance correction value of a blue color WB B .
13. The calculation method of claim 12 , wherein the white balance correction value formula further comprises:
a white balance correction value formula of the red color:
WB
R
=
R
CT
1
×
Y
1
+
R
CT
2
×
F
2
Y
1
+
F
2
;
a white balance correction value formula of the green color:
WB
G
=
G
CT
1
×
Y
1
+
G
CT
2
×
F
2
Y
1
+
F
2
;
and
a white balance correction value formula of the blue color:
WB
B
=
B
CT
1
×
Y
1
+
B
CT
2
×
F
2
Y
1
+
F
2
.
14. The calculation method of claim 1 , wherein the first environment brightness Y 1 is represented by RGB value of the G CT1 value of the environment color temperature CT 1 .