1. A method of estimating white point shift, comprising: determining a white-point plane in a YIQ color coordinate according to an image sensing device, wherein the white-point plane has a normal direction inclined from either a YQ plane or a YI plane of the YIQ color coordinate by a first angle, and the normal direction is inclined from an Y-axis of the YIQ color coordinate by a second angle; performing a rotation operation on the YIQ 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 a YIQ image data in the rotated YIQ color coordinate; performing the rotation operation on the YIQ image data according to the first and second angles to transform the YIQ image data into the rotated YIQ 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.