The Nature and Evaluation of the Sharpness of Photographic Images

The ability of a photographic material to produce pictures having good definition is commonly referred to as its sharpness, which is a subjective concept. The objective quantity 〈G
²
x
〉
Av
. DS is shown to be a physical measurement which correlates with sharpness judgments. 〈G
²
x
〉
Av
is the mean of the square of the density gradients, ×D/×x, across an abrupt boundary between a light and a dark area in the developed image and DS is the density difference between these areas. 〈G
²
x
〉
Av
is evaluated only for those values greater than 0.005 in density per micron which represents the threshold gradient. It is shown that, contrary to the generally accepted belief, resolving power does not correlate well with sharpness judgments and in some cases is even misleading.