Displays: myths and reality, present and future

Welcome to our blog. Today we want to continue publishing interesting translation materials related to the development of mobile gadgets. This time it will be about the most noticeableand, for most users, the most important element is the display. As you all know, displays in their specifications have a number of characteristics by which we judge the possible image quality without seeing it. However, often many users mistakenly understand what these or those parameters mean. And even holding smartphones and tablets in our hands, we tend to compare them with other models not so much trusting our impressions as read characteristics. But are we not thereby misleading ourselves? Let's figure it out, and at the same time consider modern display technology and try to predict their future development.

Display diagonal

It would seem that the simplest characteristic by which you can evaluate the size of the display. Yes, it is, but one is not enough. It is best to rely on the size of the visible area. And it changes much faster than the diagonal, so we often overestimate or underestimate the true size of the display. For different aspect ratios, displays of the same size will have different sizes. For example, a 10-inch display with a 4: 3 aspect ratio is 12% larger in area than the same, but with a 16: 9 aspect ratio.

ppi, pixels per inch

Recently, this is one of the most popular characteristics, but at the same time the most misunderstood. On the one hand, the higher this parameter, the sharper the image gives the display. But much more important is the sharpness, distinguishable by the human eye, and it directly depends on the distance to the display. Well, and on how good a particular user has vision. Therefore, ppi must be considered in conjunction with the viewing distance, only then can the visual sharpness of the display be adequately evaluated. The normal distance at which a smartphone is usually held is about 25 cm. People with a vision of 1 can no longer distinguish between the individual pixels on the iPhone 4 display with its 326 ppi. Moreover, ambient lighting reduces the visual sharpness of the image, because the reflected light reduces the contrast.

Separately, you need to mention viewing photos and videos. Unlike computer graphics and fonts, such content has a much less ordered structure in terms of pixel colors. Therefore, the image of the photograph on the displays of the same size, but with the resolutions FullHD (1920x1080) and HD (1280x720), subjectively will differ little in sharpness. Especially if the image is in JPEG format. In the case of video, the difference will be even smaller, since a noticeable proportion of small details will simply not be perceived due to the short duration of their display on the screen.

Of course, there are a small number of people with rather sharp vision, for whom the difference between displays with different resolutions and ppi is very noticeable. But their share is small.

Color gamut

This parameter characterizes the color range that the display can display. It is believed that the more colors the display shows, the better. But this is not so. For accurate color reproduction in photographs, video and other content, it is enough for the display to have the standard color gamut used to create this content - sRGB / Rec. 709. This standard is used in almost all digital cameras, in digital television, on the Internet, in the production of the vast majority of digital visual content. All colors that go beyond sRGB / Rec. 709 are simply missing from the original mass content.

A display with a wider color gamut will not display colors that are not in the original image, it will simply exaggerate and distort them. A narrower color gamut will make the image fainter, wider - too saturated and too flashy. Therefore, subjectively narrower color gamut is better. Most LCD displays already have sRGB coverage (55-65% of the total range), and most OLED displays are wider (up to 130%).

The specifications of many monitors and mobile devices indicate that they display 16 million colors. In fact, it has long become the standard. However, the number of colors and color gamut are not the same thing. In this case, we are talking about the number of possible combinations of color brightness of red, green and blue subpixels. Each subpixel has 256 brightness levels, which leads to 256x256x256 = 16.7 million possible combinations. But this is not a synonym for “color” from the point of view of our senses. Our eyes simply do not distinguish many combinations. Plus, many displays in fact are not able to display all 16 million combinations, despite the declared possibility.

Viewing angles

According to manufacturers, many displays have a viewing angle of over 170 degrees. Recall that the maximum possible angle is 180. Many people think that this parameter means that brightness, contrast and color accuracy do not change, even if we look at the display at an angle of 5 degrees (180-170 / 2). This is absolutely untrue. In fact, 170 degrees is the sector within which the contrast ratio of the image is reduced to 10. This is about 1% (one percent) of the contrast ratio when viewed at an angle of 90 degrees.

Changing the viewing angle degrades the image quality for almost all existing displays. For example, in the case of LCD displays on IPS matrices, the brightness and contrast ratio are reduced by half when the deviation from the normal is 30 degrees. For TN Film LCDs, this drop is achieved with a 15 degree deviation. The situation is somewhat better with OLED displays: brightness and contrast ratio are reduced by 30% when deviated from the normal by 30 degrees.

Contrast ratio

This parameter characterizes the display quality of dark content, black or close to that. The contrast ratio is especially important when viewing a video in low or no ambient light. For other cases, this parameter is secondary. Mobile displays should have a contrast ratio of at least 500, good TVs at least 1500. For video filmmakers, give plasma panels with a coefficient of at least 4000.

However, advertising often refers to contrast ratios from 20,000 to 1,000,000. If these are not OLED displays that can really show such characteristics, then we are talking about the so-called “dynamic contrast ratio”. Moreover, the word "dynamic" may not be mentioned. In fact, this is a trick of manufacturers: the coefficient is calculated as the difference between the maximum brightness level in one picture and the minimum brightness level in another picture. A “true” contrast ratio should be measured within a single image.

Today, the best LCD displays have a ratio of about 2,000, while OLED has this parameter from 50,000 and almost to infinity.

Response time

Another bloated parameter. When you quickly move an object across the display, a blurry trace may sometimes form behind it. This is due to the fact that liquid crystals do not have time to react quickly enough. Standard video content has a frequency of 60 frames / sec, that is, a frame change occurs every 17 milliseconds. Therefore, manufacturers make a lot of efforts to make the response time less than this value. But a lot of marketers are also involved in this, so today in the specifications there are such numbers as 8, 4 and even 1 millisecond. However, the real response time for most displays is well over 30 milliseconds.

Prospects

2014 promises to be very generous with successes in the development of various display technologies. Let's look at the main directions of development in this area.

• Quantum Dots.


We are talking about an incredible increase in the performance of LCD displays thanks to the unique application of quantum physics. Quantum Dots, embedded in the matrix backlight, generate very saturated primary colors (red, green, blue), at the level of OLED technology. Image brightness and energy efficiency are also enhanced. Unlike traditional white LEDs (which use a yellow phosphor), Quantum Dots directly transform light from blue LEDs into saturated narrow-band primary colors. And as an added bonus: these colors can be very finely tuned during the production process, which will achieve high color accuracy. This will save us from uneven color gamut and white point errors that are present in most modern displays. Probably, in the next five years, the technology of Quantum Dots will breathe new life into the LCD. In 2013, the first commercial products using quantum dot displays fromseveral manufacturers . This year, even more manufacturers will use this technology, but not the fact that many will advertise this fact. So far, they will look closely at the reaction of users.

• Curved displays. Also last year, the first models of smartphones and TVs with curved displays appeared. This is a very popular and promising technology, promising a significant increase in image quality due to a sharp decrease in spurious reflections from the display surface. In turn, this will reduce the brightness of the display and thereby increase its energy efficiency. Please note that the degree of curvature is very small and does not have a noticeable effect on the image. Moreover, curvature even slightly reduces keystone distortion in large displays. In most cases, curved displays are built on OLED technology, but there are a few examples of LCDs. In 2014, one can hardly expect a large number of devices with curved displays due to the low volume of matrix production.

• Flexible displays. Perhaps one of the most popular technologies in the field of wearable electronics. The other day, LG showed off an 18-inch flexible OLED display on a nylon substrate, with a resolution of 1200x810. It can be rolled up into a tube with a diameter of about 2.5 cm. By 2017, the company plans to create a 60-inch flexible display.



It is hardly worth expecting the appearance of the first products with full-fledged flexible displays (attached to the device with only one side, like a flag to a pole) this year. Probably smart watches will be pioneers, but already in 2015.

• Wide color gamut displays. As we already mentioned, until recently, LCD displays actually only represented 55-65% of the standard color gamut of sRGB / Rec. 709. This is due to the fact that with the expansion of the displayed coverage, the brightness and energy efficiency are reduced. However, thanks to Quantum Dots, this phenomenon can be defeated. High-quality LCD displays now display more than 85% of standard coverage, and the best samples are matched to 100%. Against this backdrop, the 2013 iPad mini mini with Retina display and Microsoft Surface 2 look especially sluggish with their 63%. In contrast, OLED displays, due to their color gamut, 30% higher than the standard, significantly distort the color of the original image. But, for example, Samsung in somedevices introduced the advanced color management mode, in which coverage is forcibly reduced to about 100% of the standard. However, there is a sense in displays with a wide coverage that significantly exceeds the standard. The fact is that external lighting affects the color rendering of displays, because very rarely anyone uses them in complete darkness. Therefore, thanks to the color management system, it will be possible in real time to fine-tune the color rendering of a particular display to compensate for the effect of external lighting. By the way, in this parameter the best samples of smartphones, tablets and televisions are already comparable with professional studio monitors.

• High resolution displays and ppi. Users are always willing to switch to higher resolution devices. However, we have already said above that a further increase in resolution and ppi is not advisable from the point of view of a noticeable improvement in image quality. Consider 4K TVs (3840x2160). To notice an increase in resolution compared to 1920x1080, you have to watch TV (provided that you have 1):
o 40-inch (100 cm) from a distance of less than 160 cm
o 50-inch (127 cm) from a distance of less than 200 cm
o 60-inch (152 cm) from a distance of less than 240 cm
o 70-inch (177 cm) from a distance of less than 280 cm
o 80-inch (203 cm) from a distance of less than 320 cm
That is, you have to sit two times closer than recommended for comfortable viewing. Otherwise, you are unlikely to notice a difference in resolution between 4K HDTV.

However, the resolution and ppi displays of both TVs and mobile devices will increase. In 2013, several smartphone models with 5-6-inch displays with a resolution of 1920 × 1080 and ppi from 400 to 468 were released. Due to the development of technology and fiercer competition, a smartphone with a resolution of QuadHD (2560 × 1440) and 538 ppi has already appeared . The increase in these two parameters, although it does not affect the sharpness of the image, has a number of advantages:
o greater compliance with the resolution of digital photos,
o the ability to display FullHD content with 1.6 MP fields, where you can place additional information,
o Effective and easy scaling to different resolution formats to speed up processing and improve image quality.

A similar race of permissions is observed in the camp of tablets.

Conclusion

Most likely, future YotaPhone models will receive the main displays produced by other technologies. Until recently, it seemed that the LCD has practically no chance compared to OLED, but Quantum Dots can dramatically change the alignment. Who knows, maybe in a few years we will offer a YotaPhone with a 4K display and the ability to use in bright sunshine no less comfortably than a second electronic ink display. And how do you see smartphone displays in the 3-5 year term?