User interfaces of critical systems, such as air traffic control displays, use graphical objects to code for an ever increasing amount of information. This evolution brings forth concerns about the detection and identification of the displayed objects, in particular for small size objects. First, graphic properties of the interface should include some knowledge about the interplay between colour, shape and size interactions, and the visual perception. Second, the redesign of any interactive system should take into account the particularities of the evolving software and hardware display technology (pixel size and structure, for example) in order to preserve crucial aspects of the initial visual display. The two experiments described in this paper are aiming towards building a more systematic knowledge of graphic properties interactions per se, and their changes as a function of display technologies. More precisely, we examined the effect of the object size, shape and luminosity, as well as its contrast with the background. Results show that object perception is dependent upon its size, its contrast with the background and the overall luminosity of the background. Furthermore, for small size objects, interactions between pixel luminosities and pixel arrangement greatly influence their perception by the human eye.