Radiometric procedure for linearising computer-interfaced display systems

Procedures for the adjustment of computer-interfaced display devices have been based on a subjective approach, generally relying on the visual examination of digital test patterns. The lack of an objective adjustment procedure means that the best image quality may not always be achieved. This paper describes how a simple home-made radiometer can be used to make screen luminance as well as density measurements on transparency film. The measurements are first used to determine the brightness and contrast settings for the display which enable the film to be used in the linear range of its optical densities. The display device characteristics, showing how luminance varies with grey level, are then determined. Using this information a simple display-linearising mapping can be produced to ensure that screen luminance (and hence film density) is a linear function of display grey-level value. Film-density measurements are also used to investigate the luminance and hence phosphor uniformity characteristics of the screen. The linearisation of the display device is an essential step in optimising the quality of recorded images. The measurements described are reproducible and sufficiently simple to provide the basis for a reliable quality-control procedure for the periodic assessment of the performance and settings of the display device.