The higher the resolution, the higher the definition?

Display clarity

For the text and pictures displayed on the computer, normally, the higher the monitor resolution, the higher the resolution, but sometimes we can’t recognize the difference after switching some super high resolutions. Why?

In simple terms, the display clarity is determined by physical factors and vision factors . The physical factor is the display resolution of the device, and the difference in vision will affect your visual experience.

The higher the display resolution, the better?

Since the human eye has a certain limit to its resolution, the appropriate resolution and viewing distance are the best. (I will talk about it later)

First understand some basic concepts.

• Screen size : Refers to the diagonal length of the screen, in inches.
• screen resolution : refers to the maximum number of physical pixels that can be displayed in width and height.
• device pixel (also called physical pixel) : Refers to the smallest physical unit that the device can control the display, refers to the dots on the display, the unit is pt, the physical pixel device is fixed after leaving the factory.
• DIP (Device Independent Pixels) : Device Independent Pixels are also called logical pixels, which are used in applications, and then the underlying graphics system converts them into physical pixels suitable for specific devices.
• dot pitch : the distance between pixels, dot pitch and screen size determine the resolution.
• PPI (Pixels Per Inch) : screen pixel density, the number of pixels per inch (1 inch = 2.54 cm).
• DPI (Dots per inch) : Dots per inch, a printing industry term, is the same as PPI for computer screens.

What does 1080p, 2k, 4k stand for

screen resolution of is expressed by multiplying the number of pixels per row by the number of pixels per column, such as: 1024×768. A simple understanding of 1080p, 2k, 4k is:

720p and 1080p indicate how many rows of pixels there are in the vertical direction.

2k, 4k, 8k indicate how many columns of pixels there are in the horizontal direction.

physical factor that determines the display resolution pixel density more accurately. For example, in the same screen size, the higher the resolution described pixel density larger, the higher the sharpness of the display.

pixel density , use the number of diagonal pixels divided by the screen size, \( w \), \( h \) (pixels). \( l \) Screen size (in inches).

$$ ppi=\frac{\sqrt{w^{2}+h^{2}}}{l} $$

What is the limit of the human eye to distinguish pixels?

Because the text and pictures on the monitor are composed of a bunch of pixel arrangements, as long as our eyes cannot clearly distinguish the pixel gap, the text and pictures presented are silky smooth.

When what conditions are met, the pixel gap can not be detected?

In the iPhone4 when released in 2010, Jobs said, when you hold the phone away 10-12 inches when pixel density of 326 is our naked eye can distinguish pixel limit.

That is, to meet pixel density to 326ppi view the screen from 10-12 inches, imperceptible to the human eye pixel gap.

Let's analyze what is the limit of the human eye's resolution?

First understand the principle of visual imaging of the eye. The reflected light of the real object pupil , and then the retina will transmit the imaging information to the cranial nerves, and then our brain will form the corresponding image.

According to the principle of optical geometry, when light passes through the pupil, it will be diffracted due to the wave characteristics, and the light cannot be concentrated into an infinitely small focus, but only a spot with a certain energy distribution will be formed.

The central bright spot bounded by the first dark ring is called Airy (airy disk).

Therefore, every luminous object point will form an Airy disk in the retina after passing through the pupil. For two points that are very close, the Airy disk will be too close after imaging to be able to distinguish.

How to distinguish two points?

We often Rayleigh criterion as standard: the two light source intensity, etc., the actual distance between two points (referred spatial resolution of ) is equal to the radius of the Airy disk, i.e., a Airy When the center of the spot coincides with the edge of another Airy spot, they can just be distinguished. The angle at this time is called the minimum resolution angle .

Airy disk radius estimation formula, \( θ \) angular resolution, \( λ \) is the wavelength, \( d \) is the diameter of the light hole (the eye is the pupil or iris).

$$ sin\theta\approx 1.22 \frac{λ}{d} $$

When \( θ \) is very small, \(sin θ ≈ θ \), \(θ=r/s \), so the actual distance between two points \( s \) is equal to:

Below we estimate the limit angle resolution of the .

Human eyes with normal vision are 555nm , which belong to the green region of the optical spectrum.

The diameter of the iris of an average person is about 5 mm. According to the Rayleigh criterion, the limit angle resolution of the human eye is:

$$ \theta \approx sin\theta = 1.220\frac{\lambda}{d} = 1.220\frac{555\times 10^{-9}}{5\times 10^{-3}} = 0.000135(rad) $$

Radian (rad): The central angle subtended by 1/360 of the circle is called 1 degree angle, which is recorded as 1°, 1 degree = 60 minutes (1° = 60′), and 1 minute is equal to 60 seconds (1′=60) "). The unit system for measuring angles in degrees is called the angle system.

However, according to research, most people’s eyes have an angular resolution limit of 0.0005 rad. Under very ideal conditions, it can reach 0.0002 rad.

So what conditions need to be met by the human eye to distinguish the pixels on the screen?

Display size \( l \) inches, screen resolution \( w \), \( h \) (pixel); when the human eye reaches the limit resolution, the distance between the eye and the screen \( d \) is required to satisfy the relationship :

$$ d\cdot sin\theta \geq \frac{l\cdot2.54}{\sqrt{w^{2}+h^{2}}} $$

Let's estimate the distance of eye resolution of iphone4 according to the above formula.

model	Resolution	Pixel density (PPI)	Normal vision	Extreme vision	Ultimate vision
iphone4	960x640	329.65	15.41cm	38.53cm	57.00cm
iphone13	2532x1170	457.25	11.10cm	27.77cm	41.14cm

vision resolution limit that Jobs said that year, the distance of the mobile phone is 10-12 inches, 25.40cm-30.48cm after conversion.
It can be concluded that the limits he mentioned do cover most of us.