a) Apparent image resolution. High sharpness may be the result of high resolution, or it might be an optical illusion caused by image enhancement or by visible edges in a display, such as the vertical stripes of an aperture grille CRT (e.g., Trinitron). Visible scanning lines can actually increase perceived sharpness. This may be one reason why, in some subjective ATV tests, some viewers have expressed a preference for NTSC pictures over ATV. b) Sharpness is the casual, subjective evaluation of detail clarity in an image. It is often assumed that sharpness and resolution are directly related, in that images possessed of greater sharpness are assumed to have greater resolution. An increase in subjective sharpness is usually reported when objects are more clearly delineated from each other and from background having hard, sharply-defined edges. A major contribution to subjective sharpness is this high contrast at edge transitions, as is emphasized by both edge enhancement and aperture correction, for example. In many practical systems, increasing the contrast at edge transitions is often accompanied by a reduction in fine detail, and under these conditions, sharpness and resolution may describe opposite characteristics.