The
ability of a scanning system to resolve vertical details in a scene depends
upon the number of scanning lines used per frame. This is generally referred to
as the scan ratio of a television system. The realistic limit is the number of
lines is set by the resolving capacity of the human eye, viz, about one minute
of visual angle. For comfortable viewing, an angle of about 10 to 15º can be
taken as the optimum visual angle, hence the best viewing distance for watching
television is about 4 to 8 times the height of the picture, i.e. a visual angle
of about 10º as shown in figure 1 below.
ability of a scanning system to resolve vertical details in a scene depends
upon the number of scanning lines used per frame. This is generally referred to
as the scan ratio of a television system. The realistic limit is the number of
lines is set by the resolving capacity of the human eye, viz, about one minute
of visual angle. For comfortable viewing, an angle of about 10 to 15º can be
taken as the optimum visual angle, hence the best viewing distance for watching
television is about 4 to 8 times the height of the picture, i.e. a visual angle
of about 10º as shown in figure 1 below.
The
maximum numbers of alternate dark and white elementary horizontal lines which
can be resolved by the eye are thus 600 for a 10º visual angle, or 900 for a
15º visual angle. There has been a large
difference of opinion about what constitute a sufficient number of lines because
of the subjective assessment method involved. This has been made further
difficult to assess because of the effects of the finite size of the scanning
beam spot.
maximum numbers of alternate dark and white elementary horizontal lines which
can be resolved by the eye are thus 600 for a 10º visual angle, or 900 for a
15º visual angle. There has been a large
difference of opinion about what constitute a sufficient number of lines because
of the subjective assessment method involved. This has been made further
difficult to assess because of the effects of the finite size of the scanning
beam spot.
