Pubblicato il

🗓️ 30 giugno 2015

TV Monitors HD, 4K: The Viewing Distance

How to calculate viewing distance?

A general certainty can be summarized in a simple theorem:

The higher the resolution, the shorter the viewing distance can be. The greater the distance, the lower the resolution can be.

This rule gives us an immediate general idea of the situation to help us choose a display based on our viewing distance. But the most important thing to understand is: how do we calculate the correct viewing distance to fully benefit from all the details that our display allows us to see? This calculation is less straightforward.

Calculate Viewing Distance Part 1: Resolution

To address these issues, in another in-depth article, I examined how HD and 4K TV and Monitor resolution works. I showed how and how much screen resolution actually affects the viewing quality of audiovisual content, particularly movies and video games, showing a couple of “interactive” examples. Finally, I analyzed an often underestimated factor: how human eye resolution works, how it can be calculated (or rather, estimated) and how it affects viewing quality relative to distance.

We need to use all this knowledge to calculate the correct viewing distance and get the most out of our displays.

The optimal viewing distance

To simplify the work, I created a TV and Monitor viewing distance calculator, which provides the minimum, maximum, and “recommended” distance to maintain in relation to the display’s diagonal and screen resolution. The recommended distance (“Visual acuity” in the calculator) should not be considered absolute and can vary from person to person as it is derived from a visual acuity¹ of 20/20².

Visual acuity (or visus) is one of the main visual abilities of the visual system and is defined as the eye’s ability to resolve and perceive details of an object depending on the sharpness of the image projected onto the retina. Higher visual acuity corresponds to a greater ability to perceive details at long distances. When acuity is lower, viewing distance decreases and it’s necessary to get closer to the screen to perceive all the benefits of high resolution.

Moving too far away from a high-resolution display causes a progressive and inevitable decrease in detail that ends up partially or totally nullifying the benefits of 4K Monitors and TVs. On the other hand, getting too close to a light source can strain your eyes.

According to research conducted by SMPTE, viewing an Ultra HD television at too close a distance causes side effects in some subjects similar to those who suffer from motion sickness³, particularly in subjects with lower visual acuity. Motion sickness is usually characterized by symptoms such as nausea, vomiting, dizziness, paleness, and cold sweats.

Differences between Full HD and 4K

In the example below, you can observe the same image at different resolutions with a subject gradually approaching the viewer. When the distance from the observed object is very marked, Full HD and 4K images appear perfectly identical to the human eye.

4K resolution (UHD or 2160p) is recommended for closer viewing distances, or for panels, TVs, and monitors much larger than the average we were used to. For example, Sony recommends positioning yourself at 1.1 meters as the ideal distance and 1.5 meters as the maximum distance for a 55” 4K TV. THX⁴ also recommends positioning at similar distances.

At over 2 meters distance, you need at least a 70-inch screen to observe significant differences compared to a Full HD panel, but an 80/100-inch is preferable. If instead you want to buy a 40 or 50-inch display, it’s advisable to position yourself at a distance between 1 meter and 1.5 meters from the screen. All this without taking into consideration the difficulties due to imperfect panel calibration or non-ideal ambient lighting and backlighting conditions.

But with a calibrated panel, favorable ambient lighting (no external lighting disturbing the display) and high-level panel contrast, with little or no backlighting (OLED), the perceptible details in 4K or 2160p are exceptional and allow for an unprecedented viewing experience, even if perhaps not as evident as what happened with the transition from SD to HD content.

Another factor to consider is that when watching a TV with a resolution higher than the input source, the TV or player spreads the image to adapt it to the higher resolution through a conversion process called upscaling, which always leads to a loss of quality, with more or less optimal results depending on the quality of the algorithms and processing processors used. In particular, you notice muddied colors and grainy images. A completely different discussion should be made about the reverse process, downscaling: projecting a high-resolution source onto a panel with lower resolution, which in some cases can actually improve image quality⁵.

For gamers, 4K is a difficult goal. Impossible to achieve with current consoles and extremely onerous for a PC Gamer. For enthusiast gamers who want to leave Full HD behind without spending too much, a 1440p (QHD) monitor is almost always the most balanced solution and still allows for an excellent quality jump. But don’t forget: panel quality is fundamental, it must have high contrast (OLED) and be paired with non-invasive external light sources that don’t disturb its light emissions.

Calculate Viewing Distance Part 1: Resolution