Missing color data of a specified pixel of a Bayer pattern is reconstructed with a plurality of interpolation algorithms. A vertical color data difference index Cv and a horizontal color data difference index Ch are first measured according to color data of a first group of pixels included in a pixel array, wherein the first group of pixels include a plurality of pixels vertically adjacent to the specified pixel, a plurality of pixels horizontally adjacent to the specified pixel, and at least one other pixel non-vertical and non-horizontal to the specified pixel. Then, one of a plurality of preset interpolation algorithms is selected according to a comparing result of the vertical color data difference index Cv and horizontal color data difference index Ch, and executed to obtain a reconstructed color data of the specified pixel.