Images are filtered by the various stages of visual processing and undergo a perceptual transformation. To begin to quantify this process, the appearance of sinewave gratings, images with a sinusoidal luminance profile, was studied. The most salient features of these images is that at high contrast they do not in general appear sinusoidal. A logarithmic transform, based on Fechner's law, is suggested as a first approximation to the perceptual transform in the luminance domain, and shown to characterize the apparent luminance profiles of sinewave gratings. Furthermore, the sinusoidal image profile can be pre-processed (inverse transformed) to create a new image which, when viewed, reverses to a large extent the perceptual distortions discussed above. This `corrected' image would appear as if the combined effects of the perceptual transform had not acted, making the now non-sinusoidal profile conform much more closely to our symmetrical expectations of a sinusoidal appearance. The principle of inversion used here is suggested as a general way of testing the validity of some human vision models proposed to achieve better image processing algorithms based on visual perception.
© (1994) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Adar Pelah, "Inverting the perceptual transform", Proc. SPIE 2179, Human Vision, Visual Processing, and Digital Display V, (1 May 1994); doi: 10.1117/12.172659; https://doi.org/10.1117/12.172659

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