[Signal-to-noise ratio or the number of perceptible grey tones in the x-ray picture. II: Information content and viewing conditions].

The information obtainable from a radiograph depends on the viewing conditions under which the radiograph is viewed. All the viewing conditions can be defined in terms of scattered light. The amount of information taken from a radiograph with S = 1000 (S = speed class) and perfect conditions is the same as that from a radiography with S = 100 viewed under poor conditions.

[Signal to noise ratio or the number of perceptible gray tones in the x-ray picture. I. The dependence on the system sensitivity S (DIN 6867)].

It is shown that the number of contrasts which can be differentiated on a radiograph depends on the detail size, the noise, and the viewing conditions. The minimum signal-to-noise ratio (SNR) for a perception approach is equivalently described by the SGA value. This testing method was first developed by De Belder and Bollen to examine the visibility of low contrast details.

[The mean optical density in x-ray pictures: measurement methodology, results and parameters].

A simple testing method for defining the average density or the integral density of x-ray images is described. In a semiquantitative way the physicians in radiological offices can measure the proper integral density. The amount of scattered x-rays influences the integral density significantly.