The natural statistics of blur

Abstract

Blur from defocus can be both useful and detrimental for visual perception: It can be useful as a source of depth information and detrimental because it degrades image quality. We examined these aspects of blur by measuring the natural statistics of defocus blur across the visual field. Participants wore an eye-and-scene tracker that measured gaze direction, pupil diameter, and scene distances as they performed everyday tasks. We found that blur magnitude increases with increasing eccentricity. There is a vertical gradient in the distances that generate defocus blur: Blur below the fovea is generally due to scene points nearer than fixation; blur above the fovea is mostly due to points farther than fixation. There is no systematic horizontal gradient. Large blurs are generally caused by points farther rather than nearer than fixation. Consistent with the statistics, participants in a perceptual experiment perceived vertical blur gradients as slanted top-back whereas horizontal gradients were perceived equally as left-back and right-back. The tendency for people to see sharp as near and blurred as far is also consistent with the observed statistics. We calculated how many observations will be perceived as unsharp and found that perceptible blur is rare. Finally, we found that eye shape in ground-dwelling animals conforms to that required to put likely distances in best focus.

Dioptric defocus maps across the visual field for different indoor environments

“…In line with Sprague et al [14], the current results suggest that stronger blurring is more likely to occur when fixation is located on near objects, compared with the situation when fixation is on distal objects. The same authors also concluded that defocus of more than ± 0.5 diopters is highly unexpected.…”

“…However, the theoretical approach presented in [13] accounted neither for temporal variations of the scene nor for temporal summation. An experimental approach was implemented by Sprague and colleagues [14], who presented the first procedure to map out the defocus blur from scenes into the eye. The method relied on the disparities detected by stereo cameras but was limited to the central 10° around the fovea and did not include peripheral positions assumed to be important for emmetropisation (20°-40°) [15].…”

Asymmetries in visual acuity around the visual field

“…This hypothesis is based on two main findings: (1) Horizontal disparity is absent from the HM but varies along the VM: stimuli presented above the fixation point have uncrossed disparity and perceived as further away from fixation, whereas stimuli below fixation have crossed disparity and appear closer to fixation. This pattern has been shown both behaviorally in humans (Helmholtz, 1925;Hibbard & Bouzit, 2005;Sprague et al, 2016;Sprague et al, 2015) and neurophysiologically in monkeys (Sprague et al, 2015). 2Blur caused by disparity increases and covers more area as stimulus eccentricity increases (Sprague et al, 2016).…”

“…This pattern has been shown both behaviorally in humans (Helmholtz, 1925;Hibbard & Bouzit, 2005;Sprague et al, 2016;Sprague et al, 2015) and neurophysiologically in monkeys (Sprague et al, 2015). 2Blur caused by disparity increases and covers more area as stimulus eccentricity increases (Sprague et al, 2016). Given that these two factors increase with eccentricity, horizontal disparity could be a contributing source to the HVA and VMA and affect their extent.…”

Accurate Image‐Based Estimates of Focus Error in the Human Eye and in a Smartphone Camera

“…The human visual system and most cameras have arrays of sensors that are differentially sensitive to long-, medium-, and short-wavelength light. In human vision, the sensitivities of the long-(L), medium-(M), and short-(S) wavelength cones peak at 570, 530, and 445 nm, respectively 13 In the human eye, the change in chromatic defocus between the peak sensitivities of the L and S cones is approximately 1 diopter (D). 1 In many cameras, the sensitivity of the red, green, and blue sensors peak at 590, 530, and 460 nm.…”