Can the human eye enjoy a 4K TV?


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4K TVs promise to offer a much better visual experience than previous technologies.

This is argued by the size of the pixels, the minimum unit that forms a digital image. It is said that if its size is smaller, the eye is able to perceive much more detail in the image. So the experience would be much more realistic. But is this true?

Today we want the human being to be mechanized and the machine to be humanized. This is why it is not surprising that the market proposes transhuman products that go beyond our natural capabilities. One of these pretensions is that the human eye is able to discern tiny objects.

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The ancient Greeks had Lyceus, mythological hero who, according to the poet Pindar, was "the man who had eyes with the keenest eagerness of all who lived on earth."

It may be that the name comes from the Greek lynx (lynx), an animal believed to have greater visual acuity. So if we are not Lynch, the first thing to ask is: AssoneIs the normal visual acuity of a human eye?

Visual acuity is the eye's ability to distinguish small objects, a concept that can be quantified. It depends not only on the size of the observed object, but also on the distance that it is to the observer.

Thus we would say, for example, that Juan sees a 2 cm ant if he is less than 1 meter away. One way to save language and simplify this dependence on distance is to use angular sizes.

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Image subtitle

What is the normal visual acuity of a human eye?

Let's see this with an example:

The Moon has an equatorial radius of 1,737 km and is at an Earth distance of about 406,400 km at its peak (the closest point of the orbit).

If we form a rectangle triangle whose legs are these two distances, we have that the angle that forms the distance between the Earth and the Moon with the hypotenuse is one whose tangent is twice the quotient between the ray of the Moon and its distance.

This calculation results in 29.39 arc minutes. Similar to the time measurements of a clock, 60 minutes of arc are one degree and 60 seconds of arc, one minute of arc.

In this case, the moon is said to subtend 29.39 arc minutes. When the satellite approaches our planet (perigee) it decreases its distance to 356,000 km, in which case the angular size increases to 33.55 arc minutes.

This difference of 4.15 arcminutes explains phenomena such as the super moon. This is why we see the full moon in its perigee more fully than it is in its heyday.

Cones, sticks and pixels

The visual acuity of an eye is limited by the density of photosensitive cells – rods and rods, the pixels of our eye – of our retina and the so-called diffraction boundary – the action of an aperture illuminates from a point source converge in a single Score.

These two limits, one anatomical and the other physical, establish a first maximum value of visual acuity around the 48 arc seconds. Any object whose angular size is smaller than this could not be distinguished.

However, there are other factors that further limit visual acuity. On the one hand, the vision is not only optical, there is also a process of converting luminous signal into electrical and neuronal processing.

On the other hand, the optics of the eye is not perfect: the calls optical aberrations they degrade imaging.

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Image subtitle

4K TVs promise to offer a much better visual experience than previous technologies.

Some studies put the real threshold in a minute and a half arc. An intermediate value is that used in optics. When we go to an ophthalmologist to measure our visual acuity, they ask us to observe what is called the Snellen test.

This presupposes that an eye without refractive errors (myopia, hyperopia or astigmatism) or other pathologies should see a letter subtending an angular size of a minute of arc.

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A TV only suitable for lynx

When we talk about 4K, 8K or any other device made up of pixels, the important parameter is not their number. As we have seen, nor its size in microns. The important thing is angular size which each of these pixels projects into our retina.

Therefore, it is advisable to estimate the distance at which the television would be placed, to find out the actual pixel size of the screen and to obtain the angular size that this forms in our retina.

If this number is below the given values, we can conclude that our eyes would not get the most out of it the screen resolution.

Suppose the TV screen pixel size is 0.25 mm. In this case, assuming a visual acuity of one minute of arc, we would only use the resolution of the device, placing it at a distance of less than 860 mm.

So, going back to the Greeks, I suggest, let me make a joke, that some telephones are called TeleLynx.

Only Lynx, with his lynx vision, could appreciate them.

* Sergio Barbero Briones is a specialist in optics at the Optical Institute of the Superior Council for Scientific Research.Icts (IO – CSIC), from Espaat

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