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Nowadays stretched lcd display allows train stations, buses, metro and other transport facilities to communicate effectively with travellers.

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What exactly is 4K/1080P/Retina?

When purchasing commercial display, will often hear such professional words: retina resolution, 4K screen, PPI, 1080P, and so on, what are they means? What are the differences and connections between them? Let's start with the resolution.

Let's start with the resolution.


Resolution generally refers to the ability of measurement or display system to distinguish details. In the field of commercial display, resolution usually refers to the number of pixels in the horizontal and vertical directions of the screen, which is usually expressed by their product. For example, the resolution of iphone xs Max is 2688 × 1242.

So, how to describe the resolution more accurately? One way is to look at the product of the level and the number of vertical pixels. However, in this way, you will find that the obtained value is too large to be counted, and different screen sizes will also affect the perception of resolution. Therefore, engineers introduced PPI(Pixels Per Inch), that is, Pixels Per Inch, to measure pixel density.


PPI is called Pixels Per Inch, It can be understood that if the ppi of the screen is higher, its pixels per inch is higher, so it is clearer. In many cases, we cannot simply use pixels to measure the clarity of the screen, because the sizes of screens are different, but using ppi can erase the screen size factor, directly compare the definition of the screen.

Theoretically, PPI can be calculated according to the size of the screen and the pixels of the screen. Both the screen size and ppi are calculated by diagonal lines.

The calculation formula is:

Of which:

  • dp is a diagonal pixel
  • wp is a wide-side pixel.
  • hp is a high-side pixel
  • di is a diagonal inch, is the size of the screen inch.

For example, 65-inch 4K screen commercial display has a resolution of 3840*2160, so its PPI is:

Let’s compare the iPhone XS Max with a resolution of 2688 × 1242 and a screen size of 6.5 inches, so the PPI is 458ppi. Does this comparison find that the definition of commercial display is much worse than that of mobile phone!

Now that we have PPI, we can easily compare the clarity between different screens through it!

After talking about PPI, we can introduce the next topic.


Many marked with 4K,1080P and Retina screens in the commercial display market. What is the relationship between them?

4K means that the screen has approximately 4000 pixel points in the horizontal direction, which usually means the resolution is 4K * 2K, for example, about 3840*2160.

The resolution of 1080p is usually 1920*1080, also known as Full HD. 1080p means that the screen has 1080 pixel points in the vertical direction. Of course, according to the name of 4K, we can also call 1080p 2K.

The relationship between 4K and 1080p(2K) is simple. One 4K screen is equivalent to 4 1080p splicing, as shown in the following figure:

Retina Resolution

Retina resolution comes from Apple and is used to represent ultra-high resolution screens. The reason why it is called retinal resolution is that under this kind of pixel, human eyes can no longer distinguish individual pixels.

Retina formula:

Of which:

  • PPI is the unit pixel value described above
  • d is the distance between the naked eye and the screen, in inches
  • alpha is a human eye angle, take 1 ‘= (1/60)°
Best Viewing Distance

What is the best viewing distance for a commercial display? We can calculate according to the above theory.

Now we can use the Retina formula to calculate the optimal viewing distance of Retina level according to the screen unit pixel PPI.

For example:

What is the Retina viewing distance of a 65-inch 4K screen Commercial display?

First, calculate the PPI of 65-inch 4K screen commercial display as 67.8.

Bring in formula:

d = 50 inches, about 1.27 meters. It means the naked eye can no longer distinguish the single pixel of 65-inch 4K screen commercial display!

SHININGLTD © DIGITAL SIGNAGE* Shining International Co., Ltd.(Shiningltd.) was established in 2004. It is a high-tech enterprise specialized in R&D, design, production and sales of Digital signage.

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