Abstract :
A new method of assessing the performance of a picture reproducing system is described. The effect of the simultaneous variation of the four parameters¿brightness, contrast, resolution, and viewing distance¿was explored. Measurements were made under conditions of best picture reproduction, with the system maintained at this level of adaptation. Various photographic and television systems were examined. The work involved a similar investigation of the behaviour of the ¿average observer.¿ The experimental results show useful correlation with system performance, and lead to a possible explanation of the interaction of the three limits¿resolving power, brightness characteristic, and signal/noise (graininess). The measurements need to be extended to lower values of contrast to confirm these ideas. A fundamental performance factor, Qe, related to signal/noise limitations, is proposed, measured in terms of the number of quanta per picture element per picture required for a signal/noise ratio of unity. Non-linear transfer characteristics are shown to have advantages at the low brightness end. An extension of the ¿C.I.E. Observer¿ to cover the variables explored in the experiments is desirable, with the object of replacing the human observer with electronic measuring apparatus. It is shown that both the ratio viewing distance/picture height and the viewing distance must be specified before system comparisons can be made. The results support the importance of low contrast test objects. 35-mm motion pictures appear to provide about half the resolving power of the eye over the range of brightness and contrast explored, and a tentative estimate shows that this can be equalled by a properly engineered 600-line television system using spot wobbling. Band saving techniques are considered, e.g. restriction of definition at low brightness and contrast.
