1. An image de-interlacing method for estimating an interpolation luminance of an interpolated pixel, comprising: selecting a plurality of first and second candidate pixels respectively on upper and lower lines adjacent to the interpolated pixel; calculating a plurality of directional differences, a plurality of weighting values and a plurality of weighted directional differences, each associated with one of the first candidate pixels and one of the second candidate pixels, wherein each of the directional differences is an absolute luminance difference between the associated first and second candidate pixels, each of the weighting values is determined by comparing a first luminance difference vector of a first weighting region with a second luminance difference vector of a second weighting region, the first and second weighting regions respectively residing on the upper and lower lines and comprising the associated first and second candidate pixels, each element of the first and second luminance difference vectors respectively determined according to luminance difference between two pixels associated with the elements in the first and second weighting regions, and each of the weighted directional differences is determined according to the directional difference and the weighting value; selecting a first selected pixel and a second selected pixel respectively from the first and second candidate pixels associated with the smallest weighted directional difference; and obtaining the interpolation luminance according to the first and second selected pixels.