Admissibility of colour and brightness deviations in television pictures

As a result of the defocussing of the beam towards the edge of the cathode ray tube of a colour T.V. monitor, the spot no longer lands on the relevant phosphor, which causes colour deviation at the edges of the T.V. screen. This colour-shift is sometimes called colour vignetting, because of some resemblance with the normal brightness vignetting which manifests itself in many imaging systems. The colour and brightness deviations appear to be clearest when large monochromatic fields are displayed. For such fields we determined the just admissible colour deviation and the just admissible brightness deviation on the basis of a perceptual admissibility criterion. Use was made of an optical projection technique in which the T.V. screen was simulated.