#pixels-per-inch

Traditionally, CES 2020 has demonstrated the main modern trends in improving TVs. Of course, the demonstration of 8K models from the leaders of this segment became one of the main events of this year. In addition, companies have demonstrated a huge number of innovative solutions in terms of design, color rendering, new features, audio playback, etc. For example, Samsung showed a very unconventional 43-inch 4K Sero Vertical TV, perfectly adapted for content from a smartphone.

The screen of this TV easily rotates 90 degrees. TCL announced the innovative Vidrian Mini LED on glass technology, which was the next generation of Mini-LEDs backlight.

In the case of its implementation, the color accuracy of LCD TVs can almost come close to the level of OLED technology.

8K resolution

But increasing the resolution remains one of the main directions of improving the image quality. As known, this aspect causes quite heated discussions among experts. First, many recall the relatively recent history of 3D technology. At the first stage, it won a huge number of fans among consumers and many experts quite reasonably predicted excellent prospects. Of course, the manufacturers adequately responded to demand, significantly improving and cheapening this technology in its models. Unfortunately, the high cost of producing 3D content has become an insurmountable obstacle to its further development. As a result, almost all companies abandoned 3D support in their TVs. Therefore, today experts quite reasonably express doubts regarding the prospects for the production of native 8K content. As known, today it's practically absent. Therefore, just in case, companies are actively improving 8K AI upscaling technology.

At a minimum, 8K TVs will provide better quality playback of lower resolution content. Secondly, many experts doubt the advisability of increasing the resolution in terms of the physiological characteristics of our vision. Indeed, visual acuity has a maximum limit.

Accordingly, at some stage, a further increase in resolution becomes meaningless. But the results of some recent studies open up new prospects for this trend.

Resolution vs PPI

As known, screen resolution is defined as the number of pixels per unit area. For these reasons, ppi (pixels per inch) most correctly characterizes the screen.

Today many smartphone manufacturers often indicate this value in specs as one of the main parameters of the screen. Basically, its value affects the image detail. Unfortunately, TVs manufacturers initially replaced it with the marketing concept of “screen resolution”. Today, companies use the terms HD Ready (720p), Full HD (1080p), 4K Ultra HD (2160p), or 8K Ultra HD (4320p). Accordingly, these abbreviations correspond to 1366 x 768 or 1280 x 720, 1920 x 1080, 3840 x 2160, or 7680 x 4320 pixels.

Maybe companies were trying to replace the not very clear "ppi" with simpler names. Indeed, today HD, UHD, 4K or 8K are more understandable for most consumers. In addition, it's very convenient from a marketing point of view, providing companies with additional opportunities for maneuver due to uncertainty. Obviously, the image clarity on the screen, in addition to the number of pixels, directly depends on the size of the screen and pixels. Therefore, the visualization of the difference between UHD and 4K resolutions begins to appear on screens from 55 inches and above.

Of course, companies are well aware that image quality does not depend on ambitious abbreviations, but on real ppi. Therefore, they increase the actual number of pixels (resolution) while increasing the diagonal of their models. But manufacturers can rarely resist the marketing temptation to write 4K Ultra HD on the box, instead of the more informative ppi.

Pixels Per Inch

The pixel density is calculated using a fairly simple formula: PPI = / d, where a and b - the number of pixels horizontally and vertically (resolution), d - inches of the screen. But today, the Internet offers many simple and convenient online calculators. For example, the ppi for the 49-inch LG 49UJ630V with a resolution of 3840 x 2160 is 89.91. Of course, this value is not very informative for most consumers. But there are quite a few recommended schemes for choosing a TV viewing distance in terms of optimal image clarity.

According to it, LG 49UJ630V provides a high image clarity at a distance of 1 meter or more. The situation with smartphones is significantly different. On the one hand, the screen size of a modern model usually does not exceed 7 inches. Accordingly, the size of its pixel is also significantly smaller compared to TV. But the distance between the eye and the screen rarely exceeds 12 inches. Therefore, high detail requires significantly more ppi compared to TVs. For example, many modern smartphones already provide 400 ppi and higher. According to many ophthalmologists, 600 ppi is close to the limit of perception for our vision. Accordingly, a further increase in resolution does not make much sense. Moreover, it increases the energy consumption of the screen matrix, significantly reducing the battery life of the smartphone. But many companies continue to increase it. Today, the absolute record belongs to the Sony Xperia Z5 with 806 ppi.

Similar to TV, this value corresponds to 4K. Of course, this trend is mainly due to marketing considerations.

Conclusions

According to statistics, a modern person uses a PC or smartphone for up to 10 hours a day. Of course, this mode significantly increases the load on the eyes. Therefore, this aspect excites many people. Usually, a person blinks about eighteen times per minute. This frequency provides constant hydration with tear fluid. But while working on any display, a person on average blinks only 2-3 times per minute. Accordingly, hydration is reduced by almost 10 times. As a result, the eyes begin to watery. Myopia due to eye fatigue, can be true or false. False myopia due to spasms of the eye muscles reduces the clarity of image perception. But these sensations quickly disappear even after a short rest. Unfortunately, the constant tension of the eye muscles provokes the occurrence of true myopia, in which the shape of the eyeball is slightly elongated.

In this case, the person is forced to constantly use glasses. But choosing a model with optimal screen can minimize these risks. Of course, camera, smartphone performance, smartphone storage, operating system, price, etc remain the main criteria when choosing a model. But screen with optimal PPI (pixels-per-inch), brightness and backlight technology will reduce eye strain.

PPI

In terms of ophthalmology, eye fatigue is inversely proportional to image clarity. In other words, the eye strains as much as possible when viewing a blurred image. As known, PPI is the ratio of resolution (in pixels) to diagonal size (in inches) and directly affects the image clarity. Therefore, a small screen with high resolution requires much less eye strain compared to a large screen at low resolution. In fact, at low resolution the eye is constantly forced to adjust the sharpness, which leads to fatigue of the eye muscles. Today the Internet offers an abundance of online calculators that automatically calculate the PPI of any smartphone based on its diagonal and screen resolution.

For example, the PPI of a 4.3-inch HD (720 × 1280) screen reaches 342, and the PPI of a 4.7-inch HD display does not exceed 312. Accordingly, the first model will be more comfortable for the eyes. Modern models with a 6-inch Full HD (1080p) screen provide 350 ppi and higher. 8-inch models already require Quad HD (2560 x 1440) resolution to provide this pixel density. Large 12-inch models use 4K Ultra HD (3840 x 2160) screens to provide the required PPI. Sony Xperia Z5 Premium was the first to use an Ultra HD display on a 5.5-inch screen, providing a pixel density of 806 ppi.

Of course, this model is the most comfortable for the eyes. But overall, 300 ppi and higher is considered a good value. According to many experts, the person ceases to perceive the visual difference at a pixel density of 300-350 ppi and higher. Therefore, many companies limit their models to these values. But in terms of ophthalmology, this consideration seems controversial.

Brightness and backlight technology

As known, the human eye is poorly adapted to the perception of direct bright light. Therefore, many use sunglasses. But the screens of a smartphone and other digital gadgets are forced to use bright backlight for contrasting perception of images in bright external lighting. On the other hand, it will be redundant in low light conditions. Of course, the smartphone model does not affect vision in this case. Today, even budget smartphones have a brightness control, providing optimal settings depending on the surrounding lighting. But the screen brightness also depends on its type. For example, LCD screens use continuous backlight technology. Therefore, the bright light from the backlight LEDs constantly affect the eyes. As known, all OLED displays, including AMOLED, Super AMOLED, Super AMOLED Plus, P-OLED and Dynamic AMOLED, use their own radiation from organic diodes and do not have a backlight. As a result, the eye perceives light only from active pixels on the screen. At the same time, all other screen pixels are completely black. Of course, such a screen has a minimal effect on the eyes. But many users consider the higher brightness of the LCD vs AMOLED a plus.

Unfortunately, screen flicker due to PWM in OLED screen increases eye strain.

Conclusion

Thus, OLED models with high PPI minimize eye strain. But today only expensive models have large screens with high PPI. Mid-budget models provide no more than 300 ppi for 5-inch screens. In addition, the relatively low brightness of OLED screens reduces the saturation of colors. For these reasons, Retina displays from Apple with pixel densities of 300 ppi or higher have very good prospects.