Two 5-graduated counter current gray scales are arranged on a gray background (D=0.83), the gray scales being graduated logarithmically. Related to the densities of the gray scales: gamma= 0.45. Related to the remission values (brightness): gamma = 2.2, that being exactly the reciprocal value of gamma = 0.45.

The signal of the background is in the middle of the 3 ^rd?and the 4^th?step. The output of an optimally gamma-corrected camera yields two 5-graduated counter current linear step signals. The contrast range of the gray scales is 40: 1.

The values of the 5-graduated gray scale are as follows:

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The density values are based on a density of BaO4S=0. A field of black velvet is located between the gray scales. The density of this field is D > 2.4 (reflectance < 0.5 %).