Dynamic range of human visual system is one to billion. This expanded range provides a good capability for human visual system discriminate color, spatial and temporal changes in different luminous conditions. One of the psychophysical methods for evaluation of visual system function is contrast sensitivity. The contrast sensitivity function not only is used in visual system evaluation but also for image processing. The contrast sensitivity is “minimum luminance differences that is necessary for edge detection“. Three mechanisms 1- pupil size changes 2- ascending nerve activation changes and 3- photo pigment level in retina can affect the contrast sensitivity function.
E. Jafarzadehpur, S.M.P. Firoozabadi, B. Hashemi, S.M.M. Shushtarian, A. Kazemnezhad, "Achromatic Induction of Contrast Threshold in Spatial Frequency Modulation" in Proc. IS&T CGIV 2004 Second European Conf. on Colour in Graphics, Imaging, and Vision, 2004, pp 74 - 76, https://doi.org/10.2352/CGIV.2004.2.1.art00016