Which technology is better: AMOLED or IPS? Detailed screen guide.

Two things prompted me to create this article: numerous speculations by marketers and specialized journalists on the topic of screens; and a bunch of exactly the same comment threads under smartphone reviews with exactly the same discussions about which matrices are better. Usually, the hottest happens under reviews of Chinese phones with OLED screens. I'm tired of fighting windmills, talking to each reader individually, in this article I decided to dot all i's and dispel numerous myths about modern screens, looking ahead, I'll say that the emphasis will be on the confrontation between IPS and AMOLED matrices. Most likely, most of you will not see anything new in what is written, you will not receive sacred knowledge here, as well as a breakdown of the covers. I will talk about obvious things that neither bloggers nor journalists want to talk about. The guide is designed for adequate thinking people, convinced fanatics can go about their business.

Definition of the term “screen”

Before getting to the point, it is necessary to define the term screen and clarify its functional purpose. Wikipedia tells us that a screen or display is an electronic device designed to display information visually. If you try to give a less concise and more modern definition of the screen in terms of functionality and with an emphasis on consumer properties, it will turn out something like this: a screen is a device whose task is to display all kinds of content and user interface of operating systems and applications as accurately and in detail as possible. what the authors intended. Physical resolution is responsible for “as detailed as possible”, otherwise: the number of smallest screen elements (picture’s elements) or simply pixels (pixels), the higher the resolution, the better, ideally it should be infinitely large. Parameters such as color accuracy and contrast, or the ratio of the lightest and darkest point on the screen, are responsible for “as accurately as possible”. Secondary parameters that do not directly affect either the accuracy or the detail of the display of information, but affect the consumer properties of the screen, include: maximum brightness, image distortion when the gaze deviates from the perpendicular, reflection coefficient, image refresh rate, response time, energy efficiency and some others. . Standing apart is such a parameter as color gamut - the most important parameter for professional monitors and practically meaningless for devices intended for content consumption. But it is the color gamut in recent years that has been the subject of much speculation by manufacturers of mobile gadgets. Let's clear up this murky topic before moving on.

What is color gamut and why is it the subject of much speculation

You need to start with the fact that any image is encoded when captured and stored in the memory of a photo or video camera. Artificially generated pictures and clips, as well as parts of the graphical user interface of operating systems and applications, are coded in a similar way initially. In both cases, color information is represented using a color model, a special mathematical tool for describing color using numbers or, to be precise, coordinates. The most common is the three-dimensional RGB model, in which each color is described by a set of three coordinates responsible for one of the colors: red, green and blue, the displayed hue depends on the ratio of the brightness of each of the components. Modern screens are capable of displaying only a part of the spectrum of colors and shades visible to a person, color gamut literally means how big this “part” is. Due to this limitation, a person is forced to create standards for the representation of the color spectrum, starting from the capabilities of existing screens. So in 1996, to unify the use of the RGB model in monitors and printing, HP and Microsoft developed the sRGB standard, which used the primary colors described by the BT.709 standard common at that time on television and gamma correction designed for cathode ray tube monitors. It is important to understand that such unification allows, albeit with some reservations, to guarantee that the content creator and consumer will see approximately the same thing on their screens. Subsequently, the sRGB standard has become widespread in all areas of content production, including the creation of Internet sites. Of course, there are other standards for representing the color spectrum, such as Adobe RGB, which has a much wider color gamut, but today the vast majority of content is encoded in accordance with sRGB.

What happens if sRGB content is viewed on a screen with a wider color gamut without adaptation? The sRGB space coordinates will be transferred to the screen's color space coordinate system, causing colors to appear more saturated than they really are, in some cases the hues are distorted so much that orange becomes red, lime green, and blue blue. Conversely, if content with a wider color gamut is viewed on an sRGB screen, coordinate shifting will cause the colors to appear less saturated than they should be.

We all know that the screens of most modern flagship smartphones have an extended color gamut relative to sRGB, how does this affect their consumer properties? If it is a smartphone or tablet on android, then there are three options. At best, the shell settings will contain preset color profiles, among which there is one that brings the space to the sRGB standard, MIUI or Samsung's shell can serve as an example. But, even in this case, the application of profiles "on the fly" is impossible, and the user will have to choose between the extended color gamut and the correct color rendering. The second option is when the system does not have built-in profiles, but you can activate the sRGB mode in the developer settings, for example, this can be done on Google Pixel and OnePlus 3T smartphones. Unfortunately, the graphical interface of the operating system becomes faded when the sRGB mode is activated, as it is encoded in accordance with the color gamut of their screens. In the third worst case, the user will not find any profiles in the system and, accordingly, will not receive any choice, he will only have to enjoy oversaturated colors. But in personal computers on Windows and MacOS, there is no such problem, since both systems not only support color profiles, but can also convert colors from one space to another on the fly, that is, regardless of what content and on what screen will be displayed, the user, with some reservations, will see the colors as the author intended them. A similar color profile management system exists in iOS. Manufacturers, whether for the sake of beautiful numbers on the specifications page, or just for the sake of it, continue to install IPS and OLED screens with extended color gamut in flagship models, despite the fact that there is no need for this, since 99% of the content complies with the sRGB standard and the situation is unlikely to change radically in the near future. There are simply no tasks that such screens can perform in devices designed for content consumption. All this would make at least some sense if Google added color profile management to Android, as Apple did, but at least in 2017 we will not see this. The irony lies in the fact that the problem was created from scratch, and no one is in a hurry to solve it.

Liquid crystal screen: principle of operation; Advantages and disadvantages

Twenty years ago, cathode ray tube screens were installed in most monitors and televisions, they were soon replaced by liquid crystal screens or LCD (liquid crystal display), which over time received several branches of development and today there are three technologies for the production of liquid crystal matrices screens: TN, MVA and IPS, the latter, due to a successful combination of advantages and disadvantages, has become dominant in the mobile technology segment. The principle of operation of the LCD is simple, depending on the manufacturing technology, some details may vary, but a typical matrix includes a backlight and six other layers. First behind the lamp is a vertical filter that polarizes the light accordingly. It is followed by two layers of electrodes with a layer of liquid crystals located between them, the voltage applied to the electrodes orients the crystals and they refract light in such a way that it passes or does not pass through the next layer - a horizontal polarizing filter. The last color filter is red, green or blue. Liquid crystal screens are lighter, more compact and more energy efficient than their predecessors, but they also have a number of serious drawbacks, in particular, low contrast and black depth, limited color gamut even in potential, which depends on the imperfection of backlight lamps. In addition, brightness and contrast performance may deteriorate if you look at the screen not at a right angle.

OLED Screen: Advantages, Disadvantages, PWM, Pentile

Relatively recently, LCD has a serious competitor - these are screens with an active matrix on organic light-emitting diodes or AMOLED. Such screens are fundamentally different from LCDs in that the light source in them is not a backlight, but each subpixel separately, which gives AMOLED many advantages over liquid crystal screens, the main of which are: almost infinite contrast; lower power consumption when displaying images with a predominance of dark tones; potentially wider color gamut; and smaller dimensions. The first AMOLED screens, in addition to the advantages, also had significant disadvantages, including: inaccurate color reproduction; fast burnout of LEDs; high power consumption when displaying images with a predominance of light tones; flickering due to pulse width modulation; and most importantly, the high cost of production. Over time, most of the shortcomings were able to overcome or minimize them, except for PWM, which to this day is the Achilles' heel of technology. Pulse Width Modulation or PWM is one way to adjust the brightness of LEDs, the side effect of which is to flicker the screen at a certain frequency. Most people are not susceptible to this kind of flicker, but PWM can cause eye fatigue and even headaches for some users. It is important to note that the flickering effect is completely absent at brightness values ​​close to the maximum and begins to appear at a brightness level of 80% and below.

It is impossible to get past the topic with the organization of subpixels in OLED screens, the fact is that most AMOLED matrices have subpixels arranged according to the RGBG scheme, when a pixel does not consist of three subpixels like a typical LCD screen, but of four: red, blue and two green, such a scheme is also called Pentile. The manufacturer (Samsung) considers the physical resolution of such screens by the number of green subpixels, red and blue subpixels in the matrix to be exactly half as much. Obviously, at least three full-fledged subpixels are needed to obtain a hue. Thus, the effective resolution of such screens is not equal to the nominal resolution specified in the official specification. For example, for a QHD screen, the nominal resolution is 2560 * 1440 pixels, the resolution based on the number of red and blue subpixels will be approximately 1811 * 1018:

The effective resolution of such a matrix, taking into account the tricky interpolation algorithms embedded in the screen controller, is somewhere between 1811 * 1018 and 2560 * 1440, we can assume that it corresponds to FullHD resolution in RGB matrices. It may very well be that for such a match, Samsung has been choosing QHD resolution for its flagship smartphones for many years in a row.

A detailed comparison of IPS and AMOLED on the example of iPhone 7 and Galaxy S8 smartphone screens

Now, after we have learned all about the characteristics of screens and the features of different types of matrices, we can move on to the main question: which technology is better? I am sure that it is correct to try to answer this question by comparing the best AMOLED and IPS matrices available today, namely the screens of Samsung Galaxy S8 and Apple iPhone 7 smartphones. Since I have not yet acquired test equipment, I will analyze the test results taken from an authoritative resource. Let's start with resolution, Galaxy S8 screen is 2960*1440 pixels, guaranteed effective resolution is 2094*1018, guaranteed effective pixel density is 403 per inch. The iPhone 7 Plus has a nominal effective resolution less: 1920 * 1080, and an effective pixel density of 401 per inch. The advantage in favor of the screen from the Korean vendor is obvious. The resolution of both screens is enough for everyday use and not enough for comfortable use with virtual reality helmets. Moving on to accuracy, the contrast ratio of the Galaxy S8 is almost infinite. The iPhone 7 has a declared contrast ratio of 1400:1, the actual one is slightly higher - 1700:1, this contrast ratio is more than enough for comfortable viewing of content. It turns out that in this parameter, the screen of the Galaxy S8 was ahead. As for color accuracy, both smartphones showed virtually the same results, color errors in the Galaxy S8 and iPhone 7 can be safely neglected. You can see the most important secondary characteristics in my opinion below:

As for the color gamut, the iPhone 7 is ahead here, since it can display the colors of the DCI-P3 space or 126% of the sRGB field, while the user does not need to sacrifice color reproduction, the content is displayed based on the color profile embedded in it. The Galaxy S8 screen has an even wider color gamut - approximately 142% of the sRGB field, but does not have a color profile management, driving the user into a corner, that is, in the Main mode, which corresponds to 100% of the sRGB field.

So what's the bottom line? If we consider screen technologies in isolation from the final product, then AMOLED today surpasses IPS in almost everything, although it still has problems with PWM and high power consumption. Without any doubt, the future belongs to matrices on organic light-emitting diodes. Unfortunately, due to the limitations of Android, their potential has not yet been fully exploited. When comparing ready-made solutions in the face of the Galaxy S8 and iPhone 7, the latter's slight superiority is obvious due to honest DCI-P3 and other reference parameters. I want to warn you against projecting the results of the above comparison onto absolutely all IPS and AMOLED screens. There are a lot of good, average and bad matrices on the market, and in each case you need to deal with it separately. This will help us with online publications focused on technical detail and reliability, such publications I would include the already mentioned, anandtech.com and some other sites from Russian-language sites - ixbt.com.

Perhaps you should not take the consumer properties of screens too seriously, because the factor of subjective perception is almost always superimposed on objective information. For example, in Southeast Asia there are a lot of people who like unnatural oversaturated colors, in our country there are also quite a few such people. On the other hand, broadcasting information poured into the ears by marketers in numerous discussions under reviews on YouTube is at least strange. In the end, I’ll be Cap and give a couple of banal tips: don’t stop thinking and be critical of any information received from brand representatives and the media, be able to analyze data and check facts, or just read resources and watch bloggers you can trust.