White balance method

• US 7,495,696 B2
• Filed: 04/11/2005
• Issued: 02/24/2009
• Est. Priority Date: 01/27/2005
• Status: Expired due to Fees

• Current Assignee: Arima Computer (Texas) Corporation (Arima Communications Corporation)
• Original Assignee: Arima Computer (Texas) Corporation (Arima Communications Corporation)
• Inventors: Hsueh, Albert, Chikane, Varsha, Fuh, Chiou-Shann
• Primary Examiner(s): Vu; Ngoc-Yen T
• Assistant Examiner(s): FOSSELMAN, JOEL W
• Application Number:
  US11/104,076
• Publication Number:
  US 20060164521A1
• Time in Patent Office: 1,415 Days
• Field of Search: 348/223.1, 358/516, 358/518, 358/522, 382/162, 382/163, 382/167, 382/168
• US Class Current: 348/223.1
• CPC Class Codes: H04N 23/88 for colour balance, e.g. white-balance circuits or colour temperature control

Abstract

A white balance method for an image formed by a digital still camera is provided. The white balance method comprises steps of: removing a color cast over a white object of the image; detecting a reference white point from the image by extracting an a pixel information of the white object; and adjusting a white balance of the white object by determining a scale factor based on the color cast and the pixel information.

Claims

1. A white balance method for an image formed by a digital still camera, comprising steps of:

(a) removing a color cast over a white object of said image,

wherein the step (a) includes sub-steps of;

storing an original image data I_org (R_org, G_org, B_org) of said image;

performing a histogram equalization for said original image data I_org; and

converting said original image data I_org from an RGB color space to a YC_rC_b color space so as to obtain a histogram-equalized image data I_Hist (Y_Hist, C_rHist, C_bHist);

(b) detecting a reference white point from said image by extracting a pixel information of said white object,

wherein the step (b) includes sub-steps of;

determining all candidate white pixels from said histogram-equalized image data I_Hist with an equation (1);

Y_Hist≧

210, and

−

3≦

C_rHist, C_bHist≦

+3 

 

(1);

obtaining a relatively brightest pixel (Y_Hist^bright, C_rHist^bright, C_bHist^bright) from said candidate white pixels, wherein said relatively brightest pixel has a relatively maximum Y_Hist value and has C_rHist and C_bHist values being relatively closest to zero;

calculating an average pixel (Y_Hist^avg, C_rHist^avg, C_bHist^avg) of said candidate white pixels;

determining all reference white pixels from said RGB color space if corresponding pixels thereof from said histogram-equalized image data I_Hist satisfy equation (2);

Y₁≦

Y_Hist≦

Y_u

C_r1≦

C_{r Hist}≦

C_ru

C_b1≦

C_{b Hist}≦

C_bu 

 

(2),

wherein Y_l and Y_u are a relatively maximum value and a relatively minimum value of said Y_Hist^bright and said Y_Hist^avg respectively, C_rl and C_cu are a relatively maximum value and a relatively minimum value of said C_rHist^bright and said C_rHist^avg respectively, and C_bl and C_bu are a relatively maximum value and a relatively minimum value of said C_bHist^bright and said C_bHist^avg respectively; and

calculating an average W(R_w,G_w,B_w) of said reference white pixels as said pixel information; and

(c) adjusting a white balance of said white object by determining a scale factor based on said color cast and said pixel information.

2. The white balance method according to claim 1, wherein said step (c) further comprises steps of:

calculating a first scale factor (R_scale, G_scale, B_scale) from said average W(R_w,G_w,B_w) of said reference white pixels with equations (3) and (4);

R_scale=Y_w/R_w

G_scale=Y_w/G_w

B_scale=Y_w/B_w 

 

(3)

Y_w=0.299*R_w+0.587*G_w+0.114*B_w 

 

(4); and

calculating a second scale factor (R_GWA, G_GWA, B_GWA) with equations (5) and (6);

R_GWA=Y_avg/R_avg

G_GWA=Y_avg/G_avg

B_GWA=Y_avg/B_avg 

 

(5)

Y_avg=0.299*R_avg+0.587*G_avg+0.114*B_avg 

 

(6),

wherein R_avg, G_avg, and B_avg are average color components of said original image data I_org (R_org, G_org, B_org), respectively.

3. The white balance method according to claim 2, further comprising steps of:

determining said color cast as being bluish if B_Hist^avg+3≧

G_Hist^avg and B_Hist^avg>

R_Hist^avg, wherein (R_Hist^avg, G_Hist^avg, B_Hist^avg) is obtained by converting said average pixel (Y_Hist^avg, C_rHist^avg, C_bHist^avg) of said candidate white pixels from said YC_rC_b color space to said RGB color space; and

taking (R_scale, G_scale, B_GWA) as said scale factor.

4. The white balance method according to claim 2, further comprising steps of:

determining said color cast as being reddish if G_Hist^avg+3>

R_Hist^avg>

B_Hist^avg, wherein (R_Hist^avg, G_Hist^avg, B_Hist^avg) is obtained by converting said average pixel (Y_Hist^avg, C_rHist^avg, C_bHist^avg) of said candidate white pixels from said YC_rC_b color space to said RGB color space; and

taking (R_GWA, G_scale, B_scale) as said scale factor.

5. The white balance method according to claim 2, further comprising steps of:

determining said color cast as being greenish if R_Hist^avg>

G_Hist^avg>

B_Hist^avg, wherein (R_Hist^avg, G_Hist^avg, B_Hist^avg) is obtained by converting said average pixel (Y_Hist^avg, C_Hist^avg, C_Hist^avg) of said candidate white pixels from said YC_rC_b color space to said RGB color space; and

taking (R_scale, G_GWA, B_scale) as said scale factor.