Resolution limit of the eye: how many pixels can we see?

TL;DR

This paper determines the ultimate display-resolution limit of human vision by measuring achromatic and chromatic thresholds across foveal and parafoveal regions using a moving-display rig that provides continuous ppd control. It combines 2IFC psychophysics with a Watson 2018 field-CSF model to fit color-channel-specific thresholds and to map these limits across eccentricity, revealing higher-than-expected resolution (up to 94 ppd achromatic, 89 ppd red-green, 53 ppd yellow-violet) and stronger eccentricity-dependent declines for chromatic channels. By modeling population variability with Gaussian distributions and linking ppd to viewing distance, the work offers practical implications for display design, VR/AR rendering, and video coding, including potential reductions in chroma subsampling for certain channels. The study also demonstrates how foveated filtering informed by these thresholds can reduce data rates without perceptible loss, guiding next-generation display and encoding guidelines.

Abstract

As large engineering efforts go towards improving the resolution of mobile, AR and VR displays, it is important to know the maximum resolution at which further improvements bring no noticeable benefit. This limit is often referred to as the "retinal resolution", although the limiting factor may not necessarily be attributed to the retina. To determine the ultimate resolution at which an image appears sharp to our eyes with no perceivable blur, we created an experimental setup with a sliding display, which allows for continuous control of the resolution. The lack of such control was the main limitation of the previous studies. We measure achromatic (black-white) and chromatic (red-green and yellow-violet) resolution limits for foveal vision, and at two eccentricities (10 and 20 deg). Our results demonstrate that the resolution limit is higher than what was previously believed, reaching 94 pixels-per-degree (ppd) for foveal achromatic vision, 89 ppd for red-green patterns, and 53 ppd for yellow-violet patterns. We also observe a much larger drop in the resolution limit for chromatic patterns (red-green and yellow-violet) than for achromatic. Our results set the north star for display development, with implications for future imaging, rendering and video coding technologies.

Figures (16)

• Figure 1: Spatial sensitivity and resolution limits for various colour directions across the visual field. a. The measured resolution limit in pixels-per-degree (ppd) at each eccentricity across the sample (N=18), with median (open circles), 95% Confidence Intervals (CIs; error bars), and mean (horizontal bars). Numbers next to the violins indicate median ppd values of the observed data. Dashed lines represent the model fit. The edges of the shaded violin plot areas indicate the 95th percentile of thresholds. b. Heatmap showing the cumulative probability density of resolution limits within the observer sample, centred around predictions from the fitted Watson (2018)watson2018field model. c. Ideal display vertical resolution as a function of viewing distance expressed in display height (H). The red horizontal bars indicate the ITU-R BT.2100-2bt2100 recommended viewing distances for various display resolutions: FHD (2K), 4K, and 8K. d. Required pixel-per-inch (ppi) resolution needed as a function of viewing distance (meters). In plots b-d, blue areas indicate that any further increase in pixel resolution would not be perceptible to almost all observers, while yellow areas represent resolutions that will be within the visual perceptual limit of almost all observers. The dotted and dashed lines represent different percentiles of the sample as shown in the legend.
• Figure 2: Eccentricity-dependent filtering that removes invisible details to improve coding performance. The contour lines show the retinal eccentricity positions relative to the gaze position. The filter was applied uniformly across discrete segments of eccentricity to better show the differences. Please zoom the page on the screen such that the red rectangle in the bottom-left corner of the simulated image is approximately the size of a credit card and view the image from 50 cm away. When the gaze is centred on the red backpack in the image, the degradation of high-frequency details in the periphery, will not be noticeable to the human eye.
• Figure 3: Threshold pixel-per-degree (ppd) comparison with other models and datasets from the literature.
• Figure 4: Left: Rendition of the experimental setup. The display can slide on rails towards and away from the observer. The movement is controlled by a motorised camera slider to present stimuli at different pixel-per-degree (ppd) resolutions. The fixation point for the foveal presentation is the black cross in the centre of the screen. For peripheral viewing, an LED on the curved LED mast is lit up corresponding to the retinal eccentricity. The curvature was designed to approximate the distance to the horopter (for the average display position). The photograph of the actual apparatus can be found in the supplementary information Figure \ref{['fig:movable-display']}. Right: Stimuli used in the experiments. From top-to-bottom: achromatic, red-green and yellow-violet square-wave gratings, black-on-white text, and white-on-black text.
• Figure A: Experimental setup. The display can slide on the rails towards and away from the observer. The movement is controlled by a motorized camera slider to show stimulus at different pixel-per-degree (ppd) resolutions. The fixation point for the foveal presentation is the black cross in the centre of the screen. For peripheral viewing, an LED on the curved LED mast is lit up for the corresponding retinal eccentricity.