Szukana fraza: [Abstract = "In this paper we describe a general mathematical framework that allows extensions of these models by various means while preserving their mathematical properties. We propose a parametric extension of LTIP models and discuss its similarities with the human visual system. The usability of the proposed extension model is verified for an application of contrast based auto\-focus in extreme lighting conditions. The closing property of the named models facilitates superior behavior when compared with state\-of\-the\-art methods."]