With the rapid advancement of display technology in recent years, there has been an increase in the availability and adoption of ultra-high definition (UHD) displays like 4K and 8K. This has led many to wonder – can the human eye actually tell the difference between 4K and 8K resolution?
What is 4K and 8K resolution?
4K resolution refers to displays with around 4000 pixels horizontally, resulting in a total resolution of 3840 x 2160 pixels. This is exactly twice the horizontal and vertical resolution of 1080p displays (1920 x 1080).
8K resolution takes it even further with approximately 8000 pixels horizontally, for a total resolution of 7680 x 4320 pixels. This is four times the pixel count of 1080p and twice that of 4K.
As seen in the table above, 4K has 4 times as many pixels as 1080p, while 8K has 16 times as many pixels!
Visual Acuity Limitations of the Human Eye
The ability of the human eye to resolve fine details is limited by the density of photoreceptor cells on the retina, specifically the cone cells that are responsible for central and color vision. These cells are concentrated in an area of the retina called the fovea centralis.
The angular resolution of cone cells in the fovea is around 0.4 to 1.0 arcminutes per line pair. This means under ideal conditions, the average human eye can distinguish two lines separated by 0.4 to 1.0 arcminute.
For a display viewed at typical distances, this equates to being able to resolve around 60 pixels per degree of visual angle. So at a viewing distance of 1 meter, the average eye can resolve about 60 pixels per degree over a display width of around 52 degrees – working out to about 3,120 distinguishable pixels horizontally.
Of course, visual acuity can vary substantially between individuals. Younger people with good vision can resolve closer to 70-80 pixels per degree or more. The maximum theoretical acuity of the human eye is around 0.3 arcminutes, or 90 pixels per degree – equating to around 4,680 distinguishable pixels at 1 meter.
4K vs 8K at Typical Viewing Distances
Given that visual acuity of the average human eye is limited to around 60 pixels per degree, we can calculate the viewing distances required to fully distinguish a 4K and 8K display:
|Minimum Viewing Distance
|1080p (1920 x 1080)
|52 ppd at 1m
|4K (3840 x 2160)
|105 ppd at 1m
|8K (7680 x 4320)
|210 ppd at 1m
As we can see, the full benefit of 4K resolution becomes clearly apparent when viewing from 0.75m or closer. Getting close to an 85″ 4K TV allows the enhanced detail to be seen.
For 8K, the full resolution generally exceeds visual acuity when further than 38cm from an 85″ display. Most viewers sit further away than this, so will not be able to distinguish the additional detail in native 8K content.
Real World Viewing Conditions
The values above consider ideal conditions with perfect vision. In the real world, there are many other factors that can limit resolved detail:
- Imperfect vision – many people naturally can’t resolve 60 ppd
- Viewing distance – most people sit further than 38cm from large displays
- Display size – higher resolutions benefit smaller displays
- Eye movement – eyes continuously scan, unable to fixate on fine details
- Contrast ratio – insufficient contrast masks finer distinctions
- Reflections and glare – light scattering reduces apparent sharpness
- Motion blur – detail lost with movement on screen
- Compression artifacts – encoding can discard subtle detail
Considering these factors, the difference between 4K and 8K is unlikely to be noticeable except under controlled conditions with very large displays.
4K vs 8K Viewing Tests
Various studies have put 4K and 8K screens to the test to see whether there is a perceptible difference:
- NHK (Japan) – Viewers unable to distinguish 8K from 4K at typical viewing distances on an 85″ display
- Rundfunk (Germany) – Very close viewing distances required to see advantage of 8K over 4K
- Intel – Estimated less than 2% of population could appreciate 8K resolution
- Forbes – Viewers needed to be closer than 1.5m on 85″ TV to distinguish 8K
While results can depend on factors like the display quality and content, most tests show that 8K resolution exceeds normal visual acuity.
Enhanced Perception Through Increased Immersion
Some researchers suggest increased immersion could improve ability to perceive details in 8K images. By filling more of the visual field, the eye’s focal range is optimized to resolve finer detail. Increased immersion can be achieved by:
- Larger displays – filling more peripheral vision
- Curved/surround displays – increasing sense of immersion
- Head-mounted displays – display dominates entire field of view
With greater immersion, subtle details and added realism in 8K content may become more apparent and impactful.
Other Benefits of 8K
While visual acuity limitations mean the full resolution of 8K may not always be perceived, there can still be benefits to 8K displays:
- Higher screen size flexibility – An 8K screen can display a 4K signal with improved sharpness due to the higher density of pixels.
- Improved aliasing – The higher pixel density reduces jagged edges (aliasing artifacts).
- Higher bit-depth – Increased data rate allows greater color depth and smoother gradients.
- Future-proofing – Allows displaying future 8K content without downscaling.
The extremely high resolution of 8K exceeds normal 20/20 visual acuity. While the full benefit of 8K will only be realized under very constrained and ideal viewing conditions, advances in display technologies continue to push the limits of human perception.
However, for real world conditions there appears to be limited perceptual difference between 4K and 8K for most viewers. Current 4K resolution already offers a tangible improvement in detail over 1080p HD.
Nonetheless, wider adoption of 8K displays can bring other advantages. The jury is still out whether 8K delivers a true visually distinguishable jump in resolution, but it remains an important benchmark for innovation in display technology.