Fixed pattern noise (FPN) is a well studied phenomenon in pixels of micrometer dimensions designed for typical cameras. This noise refers to the non-uniform response of a pixel array to uniform intensity scenes, due to mismatch between devices used in these pixels and leads to contrast loss in the imaging system[1]. Using pictures captured by an uncorrected logarithmic camera, having a response function similar to that of human eye, this work argues that photoreceptors in natural visual systems may have different responses to uniform intensities, in a way similar to that of artificial imaging systems, leading to FPN in these systems, and the visual system corrects for these non-uniformities either algorithmically or systematically. Further, either high amount of FPN or the failure of the visual system to correct for these non-uniformities may be one of the causes of contrast loss in conditions like amblyopia. Conclusions of unrelated physiological studies will also be used to point towards non-uniform visual systems [2].

[1] B.Choubey, S.Aoyama, S.Otim, D.Jospeh and S.Collins, "An electronic calibration scheme for logarithmic CMOS pixels, ISCAS, 2004, Vancouver

[2] H.Hofer, B.Singer, D.R.Williams "Different sensations from cones with the same photopigment" Journal of Vision, 5(5), 2005, pp 444-454