Distance between image and a viewer’s eyes. In television, the distance is usually measured in picture heights. In film it is sometimes measured in picture widths. As a viewer gets closer to a television set from a long distance, the amount of detail perceptible on the screen continually increases until, at a certain point, it falls off rapidly. At that point, scanning line or triad visibility is interfering with the viewer’s ability to see all of the detail in the picture, sort of not being able to see the forest for the trees. The finer the triad or scanning structure, the closer to the screen this point can be (in picture heights). Therefore, high-definition screens allow either closer viewing for the same size screen or larger screens for the same physical viewing distance (not in picture heights).

When the effects of scanning lines and triads are reduced, other artifacts (such as temporal alias of panning called strobing) may become more obvious.

From far enough away, it is impossible to tell high-definition resolution from NTSC resolution.