1. A method of constructing a tone scale curve so that equal log exposure differences in an x-ray image of an object produce substantially equal brightness differences in a displayed image so that objects of interest, such as tumors, can be better distinguished at all densities, comprising the steps of: a) selecting a brightness versus log exposure relationship; b) developing a luminance versus brightness curve based substantially on the equation ##EQU12## where: B is the perceived brightness; n is in the range of 0.5&lt;n&lt;1.0; L.sub.o =12.6.times.(0.2.times.L.sub..omega.).sup.0.63 +1.083.times.10.sup.-5 ; L is the luminance in cd/m.sup.2 ; L.sub..omega. is the luminance of the minimum density area of the x-ray film; and c) using a density versus luminance curve and thereby producing the tone scale curve in which density is a function of log exposure, such that equal log exposure differences in an x-ray image of an object produce substantially equal brightness differences in the displayed image.