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Anna Leonova, James S. McLellan, Stephen A. Burns; Do optical phase reversals affect perception of natural scenes?. Journal of Vision 2004;4(11):62. doi: 10.1167/4.11.62.
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© ARVO (1962-2015); The Authors (2016-present)
It is known that spurious resolution (phase reversals) produced by the optics of the eye can have a devastating effect on letter identification in visual acuity tests. Here we investigate the perceptual effect when viewing more complex visual stimuli. The purpose of this work was to investigate computationally the effect of phase reversals on perception of natural scenes.
We used black and white images of natural scenes convolved with 1) a point spread function (PSF) of a real human eye, or 2), a defocused PSF, or 3) a Gaussian filter approximating a shape of the point spread function from conditions 1 and 2. The important difference between the conditions is the presence of the phase reversals in the optically blurred image and their absence in the image convolved with a Gaussian. The amount of blur in the image varied depending on the value of the defocus term (0<c4<2.5). Calculations were also generated using radial sinusoids to confirm the expected effects on the cutoff frequencies and phase shift.
Our results showed that images convolved with a real PSF were not more distorted compared with those convolved with a Gaussian filter. Although phase reversals were strikingly present in letter ‘E’ images and radial sinusoids convolved with the same filters, they could not be detected in the natural scenes. Because natural scenes have complex spectra, approximating a 1/f frequency falloff, and also a complex phase spectra, there are multiple clues at a number of frequencies to most features. Thus, while phase reversals mainly occurred at higher spatial frequencies, these are not critical for general perception of natural images.
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