Method for estimating white point shift for auto white balance

Abstract

A method of estimating shift of white balance point. According to characteristics of a photograph sensing apparatus, a white-point plane of a YIQ color coordinate is determined. The white-point plane has a normal direction pointing one of the axis of the YIQ color coordinate. The white-point plane is thus perpendicular to such axis with a one-dimensional one-spot value. Consequently, a YIQ image data described by the YIQ color coordinate is obtained. The same rotation operation is performed to rotate the YIQ image data to obtain a one-dimensional image value. The one-dimensional image value is compared to the one-dimensional white-point value to obtain a differential value, so as to estimate the white-point shift. In the above method, the axis of the YIQ color coordinate includes the Y-axis after rotation.

1 . A method of estimating white point shift, comprising: 
 determining a white-point plane in a color coordinate according to an image sensing device, wherein the white-point plane has a normal direction inclined from a plane of the color coordinate by a first angle, and the normal direction is inclined from an Y-axis of the color coordinate by a second angle;    performing a rotation operation on the color coordinate according to the first and second angles to align the normal direction with the Y-axis, so as to obtain a Y-axis white point value;    obtaining an image data in the rotated color coordinate;    performing the rotation operation on the image data according to the first and second angles to transform the image data into the rotated color coordinate to obtain a Y-axis image value; and    obtaining a difference between the Y-axis white point value and the Y-axis image value to estimate the white point shift.    
   
   
       2 . The method according to  claim 1 , wherein the step of performing a rotation operation on the color coordinate further comprises displace the Y-axis thereof.  
   
   
       3 . The method according to  claim 1 , where the step of obtaining the difference further comprises determining a weighting value according to the difference and a calibration mode.  
   
   
       4 . The method according to  claim 1 , further comprising transforming an image in the RGB color coordinate into the image data in the color coordinate.  
   
   
       5 . The method according to  claim 1 , further comprising transforming an image in the YCM color coordinate into the image data in the color coordinate.  
   
   
       6 . A method of estimating white point shift, comprising: 
 selecting a first color coordinate in which a plurality of white points are located on a single plane;    rotating the first color coordinate until the plane of white points is perpendicular to one selected axis of the first color coordinate, such that the white points have a substantially identical coordinate value of the selected axis;    obtaining a coordinate value of the selected axis of a color point to be calibrated; and    obtaining the white point shift by a difference between the coordinate values of the white points and the color point of the selected axis.    
   
   
       7 . The method according to  claim 6 , wherein the first color coordinate includes a YIQ color coordinate or a YUV color coordinate.  
   
   
       8 . The method according to  claim 6 , wherein the step of obtaining a coordinate value of the selected axis of a color point to be calibrated further comprising: 
 obtaining an image including a plurality of color points in the first color coordinate; and    rotation the first color coordinate until a plane of the color points is perpendicular to the selected axis.    
   
   
       9 . The method according to  claim 8 , wherein the step of obtaining an image further comprises: 
 obtaining an image in a second color coordinate different from the first color coordinate; and    transforming the image from the second color coordinate to the first color coordinate.    
   
   
       10 . A method for estimating white point shift, comprising: 
 determining a white-point plane in a color coordinate according to characteristic of an image sensing device, the white-point plane having a normal direction;    performing a rotation operation to make the normal direction of the white-point plane perpendicular to one axis axis of the color coordinate, such that the white-point plane is perpendicular to the coordinate with a one-dimensional white-point value;    obtaining an image data in the color coordinate;    performing the rotation operation to rotate the image data to obtain a one-dimensional image value; and    calculating a difference between the one-dimensional white-point value and the one-dimensional image value to estimate the white point shift.    
   
   
       11 . The method according to  claim 10 , further comprising transforming an image of an RGB color coordinate into a YIQ/YUV image data.