Apparatus, medium, and method with automatic white balance control

• US 20060290957A1
• Filed: 02/17/2006
• Published: 12/28/2006
• Est. Priority Date: 02/18/2005
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Sung-su, Lee, Ho-young, Park, Du-Sik, Kim, Chang-yeong
• Granted Patent: US 7,791,649 B2
• Time in Patent Office: Days
• US Class Current: 358/1.9
• CPC Class Codes: H04N 1/4072 dependent on the contents of the original
• CPC Class Codes: H04N 1/608 within the L, C1, C2 colour signals

Abstract

An automatic white balance control image apparatus, medium, and method. The automatic white balance control imaging apparatus may include a color space conversion unit converting the input image data into color space data having a chromatic component, a gray region extraction unit extracting a gray region for the input image data based on gray regions for light sources, the gray regions being detected based on plural light sources and a predetermined color checker, a detection unit extracting initial light source information using a color gamut average value and a color gamut center value, and adjusting the initial light source information in order for a chromatic component introduced into the extracted gray region to be excluded, a gain control unit calculating gains to scale the input image data based on the adjusted initial light source information, and controlling a white balance by applying the calculated gains to the input image data.

Claims

1. An apparatus with automatic white balance control, comprising:

a color space conversion unit to convert input image data captured by an image sensor into color space data having a chromatic component;

a gray region extraction unit to extract a gray region for the input image data based on gray regions for light sources related to the input image data, the gray regions being identified based on plural light sources and a predetermined color checker;

a detection unit to extract initial light source information by using a color gamut average value and a color gamut center value of the input image data, and adjust the initial light source information to exclude a chromatic component introduced into the extracted gray region by using a determined existence of a luminance difference between a gray component and the chromatic component; and

a gain control unit to calculate gains to be applied to scale the input image data based on the adjusted initial light source information, and control a white balance of the input image data by applying the calculated gains to the input image data.

2. The apparatus of claim 1, further comprising a signal-processing unit for signal-processing and displaying the white-balanced input image.

3. The apparatus of claim 1, further comprising a charge coupled device (CCD), with the CCD being the image sensor and providing the input image data.

4. The apparatus of claim 1, wherein the color space is either a color space having a luminance (Y) axis, an R/R+G+B axis, and a B/R+G+B axis or a color space having a luminance (Y) axis, an R/G axis, and a B/G axis.

5. The apparatus of claim 1, wherein the gray region extraction unit detects a white point for each light source based on an average value of gray patch data obtained by using the plural light sources, detects a certain range about a respective white point for each light source as a respective gray region of each light source, and extracts a region including all the gray regions for the plural light sources as the gray region of the input image.

6. The apparatus of claim 1, wherein the detection unit comprises:

a light source information extraction unit to calculate a weighted average value on which the color gamut average value is reflected, based on the color gamut average value and color gamut center value of the input image, and extract the initial light source information based on the weighted average value; and

an adjustment unit to divide the gray region into a first region of low luminance and a second region of high luminance by using the determined existence of the luminance difference between the gray component and the chromatic component, and adjust the initial light source information based on an average value of the first region and an average value of the second region.

7. The apparatus of claim 6, wherein the light source information extraction unit vertically maps the weighted average value onto a center axis connecting white points of the plural light sources, corrects the weighted average value mapped onto the center axis based on movement enabling errors to be minimized when mapping a weighted average value of each light source onto a white point for each light source, and extracts the corrected weighted average value as the initial light source information.

8. The apparatus of claim 6, wherein weighted average values are calculated according to:

r_weighted=(α

×

r_ave+β

×

r_gm)/(α

+β

)
b_weighted=(α

×

b_ave+β

×

b_gm)/(α

+β

),

where, r_weighted denotes an R/R+G+B value of the weighted average value, b_weighted denotes a B/R+G+B value of the weighted average value, α and

β

denote constants, respectively, r_ave denotes an R/R+G+B value of the color gamut average value, and b_ave denotes a B/R+G+B value of the color gamut average value.

9. The apparatus of claim 6, wherein the adjustment unit divides the gray region into the first region and the second region based on a threshold luminance value determined by using an average value of maximum and minimum values in the gray region and an average value of the gray region, and adjusts the initial light source information by using the average value of the first region and the average value of the second region.

10. The apparatus of claim 9, wherein the threshold luminance value is calculated according to:

Y_threshold=(α

×

Y_region+β

×

Y_ave)/(α

+β

),

where, Y_threshold denotes the threshold luminance value, Y_region denotes an average value of the average values of the first and second regions, Y_ave denotes the average value of the gray region, and α and

β

are an arbitrary constants.

11. The apparatus of claim 9, wherein the adjustment unit selectively detects, as the adjusted light source information, either the average value of the first region or the average value of the second region located according to a shortest distance to the initial light source information.

12. The apparatus of claim 11, wherein the adjusted light source information is calculated according to:

r_wht=r_down, b_wht=b_down if Dist_up>

Dist_down
r_wht=r_up, b_wht=b_up if Dist_up<

Dist_down,

where, r_wht and b_wht denote R/R+G+B and B/R+G+B values of the adjusted light source information, respectively, r_down and b_down denote R/R+G+B and B/R+G+B values of the average value of the first region, and r_up and b_up denote R/R+G+B and B/R+G+B values of an color gamut average value of the second region, respectively, and Dist_up and Dist_down denote a distance from the initial light source information to the average value of the second region and a distance from the initial light source information to the average value of the first region, respectively.

13. The apparatus of claim 1, wherein the gains are calculated according to:

$\begin{array}{cc}{R}_{\mathrm{gain}}=\underset{\mathrm{scaling}}{f}\times <br><br>\frac{g_{\mathrm{wht}}}{r_{\mathrm{wht}}}<br><br><br><br>B_{\mathrm{gain}}=f_{\mathrm{scaling}}\times <br><br>\frac{g_{\mathrm{wht}}}{b_{\mathrm{wht}}},& \mathrm{Equation}<br><br>\text{\hspace{1em}<br><br>}<br><br>6\end{array}$

where, R_gain and B_gain denote gains to be applied to a red color R and a blue color B, respectively, f_scaling denotes a scaling factor for scaling the input image, and r_wht and b_wht denote R/R+G+B and B/R+G+B values of the adjusted light source information, respectively.

14. The apparatus as claimed in claim 13, wherein the gain control unit controls the white balance for the input image by multiplying the red color R of the input image by a reciprocal number of the scaling factor and the calculated gain of the red color R and multiplying the blue color B of the input image by the reciprocal number of the scaling factor and the calculated gain of the blue color B.

15. An automatic white balance control method, comprising:

converting input image data captured by an image sensor into color space data having a chromatic component;

extracting a gray region for the input image data based on gray regions of light sources, the gray regions being identified based on plural light sources related to the input image data and a predetermined color checker;

extracting initial light source information by using a color gamut average value and a color gamut center value of the input image data, and extracting final light source information by adjusting the initial light source information to exclude a chromatic component introduced into the extracted gray region by using a determined existence of a luminance difference between a gray component and the chromatic component; and

calculating gains to be applied to scale the input image data based on the adjusted final light source information, and controlling a white balance of the input image data by applying the calculated gains to the input image data.

16. The method of claim 15, further comprising signal-processing and displaying the white-balanced input image.

17. The method of claim 15, further comprising providing the input image data from a charge coupled device (CCD) as the image sensor.

18. The method of claim 15, wherein the color space is either a color space having a luminance (Y) axis, an R/R+G+B axis, and a B/R+G+B axis or a color space having a luminance (Y) axis, an R/G axis, and a B/G axis.

19. The method of claim 15, wherein the extracting of the gray region comprises:

detecting a white point for each light source based on an average value of gray patch data obtained by using plural light sources; and

extracting, as the gray region of the input image, a region including all respective gray regions for the plural light sources by detecting a certain respective range about a white point of each respective light source as a respective gray region of each light source.

20. The method of claim 15, wherein the extracting of the final light source information comprises:

calculating a weighted average value on which the color gamut average value is reflected, based on the color gamut average value and color gamut center value of the input image data, and extracting the initial light source information based on the weighted average value; and

dividing the gray region into a first region of low luminance and a second region of high luminance by using the determined existence of the luminance difference between the gray component and the chromatic component, and adjusting the initial light source information based on average values of the first region and an average value of the second region.

21. The method of claim 20, wherein the extracting of the light source information further comprises vertically mapping the weighted average value onto a center axis connecting white points of the plural light sources, correcting the weighted average value mapped onto the center axis based on movement enabling errors to be minimized when mapping a weighted average value of each light source onto a white point for each light source, and extracting the corrected weighted average value as the initial light source information.

22. The method of claim 20, wherein the weighted average values are calculated according to:

r_weighted=(α

×

r_ave+β

×

r_gm)/(α

+β

)
b_weighted=(α

×

b_ave+β

×

b_gm)/(α

+β

),

where, r_weighted denotes an R/R+G+B value of the weighted average value, and b_weighted denotes a B/R+G+B value of the weighted average value, α and

β

denote constants, respectively, r_ave denotes an R/R+G+B value of the color gamut average value, and b_ave denotes a B/R+G+B value of the color gamut average value.

23. The method of claim 20, wherein the adjusting of the initial light source information comprises dividing the gray region into the first region and the second region based on a threshold luminance value decided by using an average value of maximum and minimum values in the gray region and an average value of the gray region, and adjusting the initial light source information by using the average value of the first region and the average value of the second region.

24. The method of claim 23, wherein the threshold luminance value is calculated according to:

Y_threshold=(α

×

Y_region+β

×

Y_ave)/(α

+β

),

where, Y_threshold denotes the threshold luminance value, Y_region denotes an average value of the average values of the first and second regions, Y_ave denotes the average value of the gray region, and α and

β

denote arbitrary constants.

25. The method of claim 23, wherein the adjusting of the initial light source information comprises detecting as the adjusted light source information either the average value of the first region or the average value of the second region located in a shortest distance to the initial light source information.

26. The method of claim 25, wherein the adjusted light source information is calculated according to:

r_wht=r_down, b_wht=b_down if Dist_up>

Dist_down
r_wht=r_up, b_wht=b_up if Dist_up<

Dist_down

where, r_wht and b_wht denote R/R+G+B and B/R+G+B values of the adjusted light source information, respectively, r_down and b_down denote R/R+G+B and B/R+G+B values of the average value of the first region, and r_up and b_up denote R/R+G+B and B/R+G+B values of an color gamut average value of the second region, respectively, and Dist_up and Dist_down denote a distance from the initial light source information to the average value of the second region and a distance from the initial light source information to the average value of the first region, respectively.

27. The method of claim 15, wherein the gains are calculated according to:

$\begin{array}{cc}{R}_{\mathrm{gain}}=\underset{\mathrm{scaling}}{f}\times <br><br>\frac{g_{\mathrm{wht}}}{r_{\mathrm{wht}}}<br><br><br><br>B_{\mathrm{gain}}=f_{\mathrm{scaling}}\times <br><br>\frac{g_{\mathrm{wht}}}{b_{\mathrm{wht}}},& \mathrm{Equation}<br><br>\text{\hspace{1em}<br><br>}<br><br>6\end{array}$

where, R_gain and B_gain denote gains to be applied to a red color R and a blue color B, respectively, f_scaling denotes a scaling factor for scaling the input image, and r_wht and b_wht denote R/R+G+B and B/R+G+B values of the adjusted light source information, respectively.

28. The method of claim 15, wherein the controlling of the white balance comprises controlling the white balance for the input image by multiplying the red color R of the input image by a reciprocal number of the scaling factor and the calculated gain of the red color R and multiplying the blue color B of the input image by the reciprocal number of the scaling factor and the calculated gain of the blue color B.

29. At least one medium comprising computer readable code to implement the method of claim 15.