1. 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 would indicate an image feature direction applicable to that 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 for blocks having the highest correlation amongst blocks having block contents meeting one or more predetermined criteria.