The present invention provides a method for controlling an interpolation direction of a pixel needing to be interpolated between a first row and a second row within an image. The image has a plurality of pixels arranged in a matrix format. The method includes calculating a plurality of first horizontal pixel value differences between pixels positioned in the first row and a plurality of second horizontal pixel value differences between pixels positioned in the second row. The method further includes comparing the plurality of first horizontal pixel value differences with a first threshold and the plurality of second horizontal pixel value differences with a second threshold to control whether the interpolation direction is orthogonal to the first row and the second row.