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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 many more details in the image. Therefore, the experience would be much more realistic. But is this true?
Nowadays we want the human being to be mechanized and the machine to be humanized. That is why it is not surprising that the market proposes trans-humanist products that go beyond our natural capabilities. One of these fatuous pretensions is that the human eye is capable of discerning tiny objects.
The ancient Greeks had Lyceus, mythological hero who, according to the poet Pindar, was “the man who had the eyes with the greatest acuity of all who lived on earth.”
It could be that the name comes from the Greek lynx (lynx), an animal that was believed to have a greater visual acuity. So, if we are not Linceo, the first thing to ask yourself is: What is normal visual acuity of a human eye?
Visual acuity is the ability of the eye 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 it is to the observer.
In this way we would say, for example, that Juan sees an ant of 2 cm if it 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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Let’s see it with an example:
The Moon has an equatorial radius of 1,737 km and is at a distance from Earth of about 406,400 km at its peak (closest point in the orbit).
If we form a right triangle whose legs are those two distances, we have that the angle that forms the distance between the Earth and the Moon with the hypotenuse is that whose tangent is twice the quotient between the radius of the Moon and its distance.
This calculation results in 29.39 arc minutes. Similar to what happens with the time measurements of a clock, 60 arc minutes are one degree and 60 arc seconds, one arc minute.
In this case it is said that the moon subtends 29,39 arcminutes. 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 supermoon. That is why we see in more detail the full Moon in its perigee than in its apogee.
Cones, canes and pixels
The visual acuity of an eye is limited by the density of photosensitive cells – rods and sticks, the pixels of our eye – of our retina and the so-called diffraction limit – the action of an aperture makes light from a point source not converge on a single point-.
These two limits, one anatomical and one physical, establish a first maximum value of visual acuity around 48 seconds of arc. Any object whose angular size is smaller than that 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 conversion of luminous signal into electrical and neuronal processing.
On the other, the optics of the eye is not perfect: the so-called optical aberrations degrade the formation of images.
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Some studies place the real threshold in a minute and a half of arc. An intermediate value is the one used in optics. When we go to an optician to measure our visual acuity they ask us to observe what is called a Snellen test.
This assumes that an eye without refractive errors (myopia, hyperopia or astigmatism) or other pathologies should see a letter that subtends an angular size of a minute of arc.
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 its number. As we have seen, neither its size in microns. The important thing is the angular size that each of these pixels projects on our retina.
Therefore, it is advisable to estimate the distance to which the television would be placed, find out the actual pixel size of the screen and 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 take full advantage of the resolution of the screen.
Suppose that the pixel size of the TV screen is 0.25 mm. In this case, assuming a visual acuity of one minute of arc, we would only take full advantage of 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 teles are called TeleLynx.
Only Linceo, with his lynx eyesight, could appreciate them.