1. An image processing apparatus in which output pixel values are generated with respect to pixels of an input image selected in accordance with an image feature direction in the input image, the apparatus comprising: means for comparing blocks of pixels of the input image, the blocks being disposed with respect to a pixel position under test so that a correlation between the blocks indicate an image feature direction applicable to the pixel position; and means for detecting the image feature direction applicable to the pixel position under test as a direction corresponding to a block comparison performed by the means for comparing for corresponding blocks having the highest correlation based on a monotonicity criteria, such that a test block comprising the pixel position under test exhibits a generally monotonic variation in a pixel property along a horizontal direction.