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