Displays: myths and reality, present and future

Welcome to our blog. Today we want to continue the publication of interesting translation materials related to the development of mobile gadgets. This time it will be about the most noticeable and, for most users, the most important element - 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 those or other parameters mean. And even holding smartphones and tablets, we tend to compare them with other models, not so much trusting our impressions as reading characteristics. But do we not mislead ourselves? Let's understand, and at the same time we will consider modern technologies for the manufacture of displays and try to predict their further development.

Display diagonal

It would seem that the simplest characteristic by which you can estimate the size of the display. Yes, it is, but it alone 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. With different aspect ratios, displays with a diagonal of the same size will have a different area. For example, a 10-inch display with an aspect ratio of 4: 3 is 12% larger in area than the same, but with a 16: 9 ratio.
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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, visible to the human eye, and it directly depends on the distance to the display. Well, and from that, how much good sight at the specific user. Therefore, ppi should be considered paired 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 approximately 25 cm. People with a vision of 1 can no longer distinguish individual pixels on the iPhone 4 with 326 ppi from such a distance. Moreover, ambient lighting reduces the visual sharpness of the image, because reflected light reduces contrast. Therefore, a further race to increase ppi in mobile device displays has already lost all practical significance.

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, photographs of photos on displays of the same size, but with the resolutions FullHD (1920x1080) and HD (1280x720), will be subjectively 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 significant 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 fairly sharp eyes, 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 it is not. For accurate color reproduction in photos, videos and other content, it is enough that the display has the standard color gamut used to create this content - sRGB / Rec.709. This standard is used in almost all digital cameras, 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 in the original bulk content.

A display with a wider 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 more dim, wider - too saturated and too flashy. Therefore, a subjectively narrower color gamut is better. Most LCD-displays have coverage already sRGB (55-65% of the total range), and most OLED-displays - wider (up to 130%).

In the specifications of many monitors and mobile devices indicated that they display 16 million colors. In fact, it has long become a standard. However, the number of colors and color gamut - not the same thing. In this case we are talking about the number of possible combinations of the color brightness of the red, green and blue subpixels. Each subpixel has 256 brightness levels, which results in 256x256x256 = 16.7 million possible combinations. But this is not a synonym for "color" in terms 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 stated possibility.

Viewing angles

According to manufacturers, many displays have a viewing angle of more than 170 degrees. Recall that the maximum possible angle is 180. Many people think that this parameter says 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 wrong. In fact, 170 degrees is a sector within which the image contrast ratio drops to 10. This is about 1% (one percent) of the contrast ratio when viewed at a 90 degree angle.

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

Contrast ratio

This parameter characterizes the quality of the display of dark content, black or close to that. The contrast ratio is especially important for watching videos in low or absent ambient light. For other cases, this parameter is secondary. Mobile displays should have a contrast ratio of at least 500, good TVs should be at least 1500. Video cameras should have plasma panels with at least 4000.

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

Today, the best LCD displays have a ratio of about 2000, while for OLED this parameter ranges from 50,000 and almost to infinity.

Response time

Another bloated option. With the rapid movement of the object on the display, behind it can sometimes form a blurry trail. 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 put a lot of effort to make the response time less than this value. But many marketers are also engaged in this, so today in the specifications there are massive numbers such as 8, 4 and even 1 millisecond. However, the real response time for most displays is much longer than 30 milliseconds.

Perspectives

2014 promises to be very generous with success in the development of various technologies for the manufacture of displays. Let's look at the main directions of development in this area.

• Quantum dots (Quantum Dots).


This is an incredible increase in the characteristics of LCD-displays due to the unique application of quantum physics. Quantum Dots embedded in the matrix illumination generate very saturated primary colors (red, green, blue), at the level of OLED technology. Also increases the brightness of the image and energy efficiency. Unlike traditional white LEDs (which use 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 allow to achieve high color accuracy. This will save us from the uneven color gamut and errors of the "white point" that are present in most modern displays. Probably, in the next five years, the technology of Quantum Dots will allow breathing new life into the LCD. In 2013, the first commercial products using quantum dot displays from several manufacturers appeared . This year, more manufacturers will apply this technology, but not the fact that many will advertise this circumstance. For now, they will keep an eye on 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, which promises a significant improvement in image quality due to a sharp decrease in parasitic 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, the curvature even slightly reduces the trapezoidal distortion of the image on large displays. In most cases, curved displays are built on OLED technology, but there are several examples of LCD. 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. Recently, LG has demonstrated a 18-inch flexible OLED-display on a nylon substrate, with a resolution of 1200x810. It can be rolled 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 this year to expect the appearance of the first products with full-fledged flexible displays (attached to the device with only one side, like a flag to the flagpole). Probably, the pioneers will be smart watches, but in 2015 already.

• Displays with a wide color gamut. As we have already mentioned, until recently, LCD displays actually displayed only 55-65% of the standard sRGB / Rec.709 color gamut. This is due to the fact that expanding the displayed coverage reduces the brightness and energy efficiency. However, thanks to Quantum Dots, this phenomenon can be conquered. Now high-quality LCD displays display more than 85% of standard coverage, and the best samples are selected to 100%. Against this background, iPad mini with a Retina display and Microsoft Surface 2 launched in 2013 look particularly sluggish with their 63%. On the contrary, OLED-displays due to their color range, 30% higher than the standard, significantly distort the colors of the original image. But, for example, Samsung in some of its devices has introduced an 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 substantially exceeding the standard one. The fact is that external lighting worsens the color reproduction 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 precisely adjust the color rendition of a specific display to compensate for the influence of ambient light. By the way, according to this parameter, the best samples of smartphones, tablets and televisions are already comparable with professional studio monitors.

• High resolution displays and ppi. Users have always eagerly switched to higher resolution devices. However, we have already mentioned 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 the increase in resolution compared to 1920x1080, you will have to watch TV (provided that you have vision 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 will have to sit two times closer than recommended for comfortable viewing. Otherwise, you hardly notice the difference in resolution between 4K HDTV.

However, the resolution and ppi displays of both TVs and mobile devices will grow. In 2013, several smartphones with 5-6-inch displays with a resolution of 1920x1080 and ppi from 400 to 468 were released. Due to the development of technology and increased competition, a smartphone with a resolution of QuadHD (2560x1440) and 538 ppi has already appeared. The increase in these two parameters, though little effect on the sharpness of the image, but gives 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 permits observed in the camp of the tablets.

Conclusion

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