Retina E-Paper Reaches Human-Eye Resolution (WO₃)

Display sizes have steadily shrunk while resolutions have soared, bringing screens ever closer to our eyes.

In the early days, televisions and projectors were designed for shared distant viewing. This resulted in them being large, heavy, and fixed, forcing users to adjust to the screen.

That was until the rise of personal computers, which put screens right within our arms’ reach. Soon, displays became personal, which led to a shift from shared to individual interaction.

Then came the smartphone revolution, bringing screens even closer to our eyes. We could carry our screens with us everywhere, and interactions became more intimate.

Now, in the latest stage of this evolution, displays have moved onto our very bodies. Wearables such as smartwatches, fitness bands, AR glasses, and VR headsets sit mere millimetres from the eye, turning screens into extensions of ourselves.

Ongoing research is moving into retinal projection, near-eye displays, and neural interfaces to effectively merge display and perception, where the display becomes part of our visual system itself.

At each step of this process, physical distance has been reduced and immersion increased. But as display tech continues to advance, we are now faced with the limits of display size and resolution. 

Human Eye Resolution Limits (PPD) That Define Display Progress

Swipe to scroll →

While scientists, engineers, and designers are focused on improving the resolution of mobile, augmented reality, and virtual reality displays, the question is whether they are actually delivering noticeable benefits.

The thing is, while innovators and manufacturers can keep increasing the resolution of their display tech by adding more pixels, the human eye has a limit. 

The limit is referred to as the retinal resolution or eye-limiting resolution, which has nothing to do with our retina itself but our brain. The good thing is that this limit is higher than what we originally thought, i.e., the 60 pixels per degree (PPD) based on the Snellen chart.

To determine the maximum resolution limit of displays, a recent study¹ sought to identify the limit of retinal resolution. What they have found is that adding more pixels to a display makes it less efficient, more costly, and power-intensive.

The study aims to determine the ultimate resolution at which an image appears sharp to our eyes with no perceivable blur. For this, the researchers ran an experiment involving 19 participants who were shown patterns on a sliding display (for continuous control of the resolution) with fine gradations, in shades of gray and color. To measure PPD, the researchers moved the screen closer to and farther from the participants.

The researchers found that when the pixel resolution exceeds the observer’s visual limit, the observer is unable to reliably distinguish between fine-line patterns and a plain gray image. So, once observers reach their resolution limit, they simply can’t distinguish between two images, which means adding more pixels or details doesn’t matter because the human eye just can’t see it.

As per the study’s measurements, the human eye can resolve details at 94 pixels per degree for achromatic (black-and-white) images viewed straight on, but this drops for chromatic images. It was 89 for red and green patterns, and even lower, 53 PPD, for yellow and violet. The researchers also reported observing a bigger drop in the resolution limit for colored patterns than for black-white patterns.

“Our eyes are essentially sensors that aren’t all that great, but our brain processes that data into what it thinks we should be seeing.”

– Rafał Mantiuk, Co-author of the study and also a professor of Graphics and Displays at Cambridge

Why Shrinking Emissive Pixels Breaks at Ultra-High PPI

Pushing pixel density beyond what our eyes can distinguish comes at a cost. As pixel sizes continue to shrink in emissive displays, the uniformity and intensity of their emission degrade, brightness is reduced, and colour cross-talk and fabrication complexity increase, making it challenging to achieve very high-resolution imaging.

Commercial phone panels today use pixels roughly ~60 µm across (≈450 PPI). According to the Nature study, that’s on the order of a few thousand times larger than what an ultimate eye-matched display would theoretically need—hence the push to entirely new pixel architectures rather than just shrinking emitters. At this scale, the naked eye struggles to perceive the emitted light, particularly in bright outdoor environments.

As for the smallest colorful micro-LED display, its smaller pixel size makes it challenging to achieve retinal-level resolution across an expansive field of view. When pixels are smaller than 1 micrometer (μm), they perform poorly. At such small scales, uniformity and colour cross-talk also present technical hurdles, limiting the use of conventional emissive display tech to create the ultimate VR display.

But then there’s electronic paper, which makes use of ambient light and can maintain high optical contrast no matter the size of the pixel.

Electronic paper, E-paper, or intelligent paper, is a display device that reflects ambient light to mimic the appearance of ink on paper, instead of emitting its own light, as flat-panel displays do, which requires additional energy. This is what makes E-paper or E-ink comfortable to read. It can also provide a wider viewing angle than most light-emitting displays.

Moreover, E-paper can retain static images even without power. Its ability to display content without continuous refreshing makes it highly energy-efficient.

This is made possible by millions of tiny capsules filled with a clear fluid containing ultra-small, colored particles with different electric charges. Electrodes are placed above and below the thin capsule film, and depending on the applied electric field, the particles move to either the top or the bottom of the capsule, giving the display surface its specific color.

But E-paper has its own limitations. They cannot achieve high resolution due to the size restrictions of their capsules. 

So, researchers from the University of Gothenburg, Chalmers University of Technology, and Uppsala University came together to present a new E-paper tech, dubbed retina E-paper, that can achieve ultra-high resolutions.

Their retina E-paper has surpassed 25,000 pixels per inch (PPI), which researchers note exceeds the theoretical human visual limit of 60 pixels per degree across a 120° field of view on an 8 mm screen. 

This new E-paper features electrochromic WO3 metapixels that transition from insulator to metal upon electrochemical reduction, enabling dynamic modulation of refractive index and optical absorption and allowing precise control over reflectance and contrast at the nanoscale. 

Leveraging this effect, the metapixels can achieve densities close to the visual resolution limit when the display size matches the pupil’s diameter. The new technology, as per the study, demonstrates strong optical contrast, low energy consumption, reflectance as high as 80%, video capability above 25 Hz, and support for anaglyph 3D display, which highlights its potential as a next-generation solution for immersive virtual reality systems.

Retina E-Paper: WO₃ Metapixels Deliver Human-Resolution

Published in Nature, the study, “Video‐rate tunable colour electronic paper with human resolution,“² detailed the new technology, featuring the smallest pixels in a screen with the highest resolution the human eye can perceive. 

The pixels reproduce colors using nanoparticles whose dimensions and arrangement both control just how light is scattered. The optical properties of nanoparticles can also be electrically modulated. 

With this breakthrough, the technology promises to help create virtual worlds that look just like the real world.

According to the study’s lead author, Kunli Xiong, who is an Associate Senior Lecturer and Assistant Professor at the Department of Materials Science and Engineering at Uppsala University, Sweden:

“The technology that we have developed can provide new ways to interact with information and the world around us. It could expand creative possibilities, improve remote collaboration, and even accelerate scientific research.”

What the new E-paper has done is overcome the size problem.

The size and number of pixels determine the resolution and the realism of the on-screen display. However, pixels cannot be made too small without affecting their performance. As a result, experiences in today’s AR and VR are limited, since the screens are small and positioned close to the eyes.

Each pixel in the Retina E-paper measures just 560 nanometers. The overall screen area, meanwhile, is comparable to the size of a human pupil, offering a resolution that exceeds 25,000 PPI.

“This means that each pixel roughly corresponds to a single photoreceptor in the eye, i.e., the nerve cells in the retina that convert light into biological signals. Humans cannot perceive a higher resolution than this.”

– Andreas Dahlin, Professor at the Department of Chemistry and Chemical Engineering at Chalmers

The new type of reflective screen, which can be placed extremely close to the eye, is passive. This means it doesn’t have its own light source. Instead, the colors of the pixels appear only when ambient light strikes small structures on their surface.

Interestingly, the plumage of many small birds, such as hummingbirds and starlings, follows this principle: it displays color only when light hits them at specific angles.

Now, the new type of E-paper has overcome the physical and optical limits of traditional display technologies through nanoscale optical engineering, enabling it to maintain clarity and color accuracy at extreme pixel densities.

The tiny pixels of retina E-paper contain particles of tungsten oxide (WO3), a chemical compound of oxygen and the transition metal tungsten. It is visible-light responsive and exhibits multiple crystal phases. The material has potential applications as a key functional material for photoelectrodes, catalysis, electrochromic devices, and chemical sensors.

The researchers patterned WO3 nanodisks onto a reflective substrate of aluminum and platinum, with each of these nanodisks acting like an optical ‘metapixel,’ thus generating color through Mie scattering and interference.

By adjusting the size and relative positions of WO3 particles, the team was able to control how light of different colors is diffused and reflected. This creates pixels in red, blue, and green colors, which can be used to generate other colors.

To turn them black, particles can be switched off by applying a weak voltage.

With electrochromic WO₃ maintaining its color state without requiring continuous power, the display consumes only about 1.7 mW/cm² during video playback and 0.5 mW/cm² for static images.

Meanwhile, the use of a 1.0 M LiClO4 electrolyte, one of the more common lithium salts used in Li-ion batteries, combined with a lateral electrode gap of 500 nm, enables the tech to achieve rapid ion movement, allowing color changes in just 40 milliseconds. This speed is fast enough for smooth video playback at over 25 Hz.

“This is a major step forward in the development of screens that can be shrunk to a miniature size while improving quality and reducing energy consumption. The technology needs to be fine-tuned further, but we believe that retina E-paper will play a major role in its field and will eventually have an impact on us all.”

– Giovanni Volpe, Professor at the Department of Physics at the University of Gothenburg

To showcase the performance of their retina E-paper, the team of researchers created an image of ‘The Kiss’, the famous artwork by Gustav Klimt, on a surface measuring 1.4 × 1.9 millimetres. This surface is 1/4000th of a standard smartphone. 

They also reproduced a 3D anaglyph butterfly, demonstrating stereoscopic depth and fine-art color fidelity.

With over 80% of information conveyed through visual signals, the new E-paper marks a technological advancement with the potential to change how we interact with information.

In the realm of AR applications, retina E-paper’s inherent compatibility with the environment enables natural visual integration, substantial battery downsizing. It opens up the possibility of fully self-powered displays when combined with solar cells.

Despite its high potential, the technology needs to be refined further, with the study outlining future steps: optimizing colour gamut and operational stability and lifetime, lowering the operating voltage, and exploring alternative electrolytes to extend durability and reduce energy consumption.

The team will also be integrating ultra-high-resolution thin-film transistor (TFT) arrays for independent pixel control, enabling large-area displays. “Looking ahead, we anticipate significant advancements in this field and firmly believe that the evolution of the retina E-paper will ultimately influence everyone,” noted the study.

Investing in Advanced Display Tech

The tech giant Apple Inc. (AAPL +1.49%) has long been involved in display R&D, focusing on a human-eye-matched retina resolution. 

Retina display is a series of LCD and OLED displays by Apple with a higher pixel density than Apple’s traditional displays. These displays debuted in initial iPhone versions and later in the 3rd-generation iPad, where each screen was replaced by four smaller pixels. Today, the Retina display can be found in most Apple products.

The minimum pixel density of Apple’s Retina displays isn’t fixed; it varies with the viewing distance.

The company also invests heavily in AR glasses and next-gen low-power displays. In 2023, it launched the Apple Vision Pro, the first wearable headset, offering a mixed reality experience. According to a recent report by Bloomberg, Apple has paused a planned overhaul of the headset. 

While a lighter, more affordable version of Vision Pro may not come anytime soon, Apple is now focusing on developing smart glasses to rival Meta Platforms’ (META -5.3%) products. The company aims to launch smart glasses in a couple of years, with a model featuring a display on the lens expected to be released sometime around 2028.

Apple’s key products are iPhone, iPad, Mac, Apple Watch, and AirPods, while its software platforms include iOS, macOS, iPadOS, watchOS, visionOS, and tvOS. Meanwhile, its services include AppleCare, advertising, cloud services, digital content, and payment services.

Last week, Apple announced its financial results for its fiscal 2025 Q4, which ended September 27, 2025, and beat analyst expectations. The company reported an 8% YoY increase in revenue to $102.5 billion. This includes $49.03 billion in iPhone revenue, $8.73 billion in Mac revenue, $6.95 billion in iPad revenue, $9.01 billion in Other Products revenue, and $28.75 billion in Services revenue.

During this period, the company reported diluted earnings per share of $1.85, up 13% YoY.

“Thanks to our very high levels of customer satisfaction and loyalty, our installed base of active devices also reached a new all-time high across all product categories and geographic segments.”

– Apple CFO Kevan Parekh

Apple CEO Tim Cook, meanwhile, stated that the company will be releasing an updated version of its virtual assistant and chatbot, Siri, next year. He also noted upcoming partnerships, such as the one with OpenAI to integrate ChatGPT into Apple Intelligence.

“Our intention is to integrate with more people over time.”

– Tim Cook

According to recent reports, Apple is planning to pay about $1 billion a year for a 1.2 trillion-parameter AI model developed by Google to support Siri’s overhaul.

When it comes to Apple’s $4 trillion market cap, its stock is currently trading just above $269, up 7.87% YTD. It has an EPS (TTM) of 7.43 and a P/E (TTM) of 36.37. Apple recently declared a cash dividend of $0.26 per share.

Conclusion

Display technology is advancing with one goal in mind: achieving seamless integration between human vision and the digital world. To accomplish this, scientists and engineers have been shrinking the boundary between perception and projection.

The recent research into retina E-paper represents a big achievement in this regard, achieving human-eye-level resolution using ambient light alone by combining the energy efficiency of reflective displays with the precision of nanoscale optical control. This breakthrough opens up new pathways for sustainable, high-fidelity visual systems, and as the researchers refine color range, stability, and scalability, retina E-paper could become the foundation for the next generation of immersive, energy-efficient display technologies.

References

<sup>1. Ashraf, M., Chapiro, A. & Mantiuk, R.K. Resolution limit of the eye — how many pixels can we see? Nature Communications 16, 9086 (2025). https://doi.org/10.1038/s41467-025-64679-2
2. Santosa, A. S., Chang, Y-W., Dahlin, A. B., Österlund, L., Volpe, G. & Xiong, K. Video-rate tunable colour electronic paper with human resolution. Nature 646, 1089–1095 (2025). https://doi.org/10.1038/s41586-025-09642-3</sup>