At present, there are many popular science articles about mobile phone screens, but many of them are misinformation. Some wrong articles and wrong statements are so widespread that correct information cannot be popularized. For example, many people still believe in the jokes about the low-grade TFT screen and the poor display effect of Sony's flagship computer TFT. After reading this article, I believe you can have a basic understanding of the mobile phone screen. When you choose a mobile phone, you will know what is the best choice to choose.

This article is from: Ainongji Digital Editing Alliance Member - contributed by maomaobear

1、 Principle of LCD

The LCD screen consists of a backlight, which used to be a fluorescent tube, but now it is mostly a LED light source, that is, a light-emitting diode. A light guide plate is required to evenly distribute the light into a plane because the light tube is one or several and the user requires to see a plane. You can imagine it as a shining wall.

Then there is the liquid crystal layer. The liquid crystal molecule has a feature that it will move when it is powered on. When it moves, it blocks the light of the light wall behind, so that there is light and dark. When the light and dark dots are put together, images or text can be displayed. It is similar to the spelling of the Olympic Games, such as the word "and" at the opening ceremony of the Olympic Games.

The voltage you apply to the liquid crystal is different, and the flipping amplitude is different, and the amount of light blocked is also different, so there is light and darkness. The so-called gray scale has two voltages, only black and white, and there are four types, black, black, white and white.

The so-called number of gray levels is the number of applied voltages. Now it is generally an 8-bit screen, which is to apply the voltage of the 8th power of 2 to deflect the liquid crystal molecules into 256 states. 256 kinds of black, white and gray are displayed. The more digits, the more kinds of gray can be displayed between black and white. The more natural the transition.

The students behind said, what's good about the black and white screen? It should be colored. Well, this is the role of the next layer of color filter

Color filter refers to the small color blocks (red, blue and green) that you see when you look at the screen with a magnifying glass (some LCD screens for TV have developed to four colors)

Black, white and gray become red, black and pure red with different shades after passing through the red filter. The 8-bit color screen thus gets 256 kinds of red with different shades. Green and blue are the same.

If you put red, green and blue together and the brightness is the same, you will not see the three colors, but the white mixed by the three colors. That is, pure white.

Red brightness is 0, green and blue are the strongest. What you see is yellow. There are 256 colors respectively. The combination of 256 colors of red, blue and green is 1677216 colors

That is, 16.7 million colors, 24 bit colors (multiplied by three 2s to the eighth power), true colors. Similarly, the human eye's ability to distinguish colors is not very strong, and 1677216 colors are enough for the human eye. So it's called true color.

2、 LCD Limitations and OLEDs

It can be seen from the principle of liquid crystal display that the light emitted by the liquid crystal is actually emitted by the rear lamp. There are two problems

1. There is a limit for liquid crystal molecules to block the light. They can't block everything left. The so-called pure black is actually gray because there is light that can pass through.

Those who have seen the gsmarena website's evaluation know that they test the contrast of the mobile phone screen by turning on 50% brightness and 100% brightness respectively.

Why? If you look at the brightness, you will know the intensity of black light. The higher the brightness, the more light will be exposed, so for a long time, LCD cannot display pure black.

It is impossible to display pure black without infinite contrast. The contrast is limited, so the color is not bright. So many designers still use old Delion.

2. The color area depends on the level of the lamp.

The color that can be distinguished by the human eye belongs to the spectral range of visible light from a scientific point of view, which is quite large. The display device can only display a part of it. For the sake of standards, there are sRGB, NTSC, NTSC, which are old standards. Generally, about 70% of CRT displays and LCD displays. For the sake of energy conservation, 60% of the light tubes are weak in laptops, which is good. Mobile phones The lamp tube is weaker, generally less than 50%. However, with the rapid development of smart phones, most mobile phones can realize about 72% of the NTSC color gamut after 2011.

Later, people had some experience in material development. CRT produced a wide color gamut phosphor, up to 95%, which is a Mitsubishi special for design. The tabletop LCD has also improved the material of the lamp, and there are more than 90% products.

On mobile phones, Sharp once made it to about 100%, most of which are still very weak, including the early iPhone. Samsung's OLED is very strong, reaching or even exceeding 100%.

LED is not a new technology. It is very old. The word "O" of LED is an organic abbreviation. The history of the research is Kodak Laboratories. I won't say more about it.

The advantage of this device is that it can emit light on its own. It doesn't need a lamp. It can be powered on and can control the intensity. It can also be very small. Being able to do very little is the key.

Because active lighting can control the intensity, as can incandescent lamps, it can be precisely controlled, and it can also be very small. At present, only OLED can form the screen.

LED without O, the big screen on the road is all this stuff. But it is too big to be used on the monitor or the mobile phone.

Because of the active light emission, you don't need the light tube. You can turn it off, so you can display pure black. Because of the active light emission, the color area can reach a very high color area without looking at the face of the light tube. Well, the current technology, in addition to laser, is its own, So color can be done very realistically in theory (in fact, because of some factors, it tends to be color biased, which seems absurd logic)

3、 LCD classification

Here we need to correct a long-standing misconception, the concept of TFT screen. TFT is actually an abbreviation, referring to the circuit behind the liquid crystal layer, which controls the liquid crystal layer (OLED is used to control each small light emitting unit). Now all mobile phone screens on the market belong to TFT, and non TFT screens have existed before, but are now obsolete.

Now all mobile phones belong to TFT, which is divided into TFT OLED, TFT LCD, TFT LCD, and liquid crystal molecular arrangement, including TN, VS and IPS. OCB (This kind of product has excellent effect, but has fatal defects. There are few actual products.)

The TN class has poor effect and few visual angles. Then some people say that it is a TFT screen and is opposite to IPS. This is an error. TN is TN and TFT is TFT, not a concept.

VA category includes Fujitsu's MVA, Samsung's PVA and Sharp's CPA

As everyone knows, there is also a modern FFS for IPS, which was later given to BOE.

These technologies were first developed by Japanese manufacturers. Later, during the economic crisis, South Korea made some changes.

In the early days, the difference between these technologies was mainly in the visual angle. TN was very poor, with color scale flip in both horizontal and vertical directions, color bias in VA side view, and 45 degree character scale flip in IPS oblique direction. But generally speaking, it is generally believed that the IPS type color is better, and the display used for EIZO design is IPS type screen. The same is true of mobile phones.

In fact, before Apple, a large number of Japanese mobile phones used IPS screens, such as NEC's N840, but they only knew a little about it.

However, no matter which type, there are two problems existing in ordinary liquid crystals. The color problem can approach the performance of oled by improving the backlight (tricolor led backlight), and the contrast problem cannot be solved. Dynamic contrast is self deception.

4、 What kind of screen is a good screen

Usually these indicators

1. Brightness

2. Contrast (the higher the better, it is better to be infinitely large. The better the contrast, the more bright and gorgeous the color, and the oled looks beautiful, largely due to the contrast)

3. Color area and color accuracy (theoretically, the larger the color area, the closer to reality)

There are two more words here. Because of the large color area, oled should have absolute color advantages. However, most of the pictures we see are optimized for display devices with 72% ntsc color regions, which are used most frequently. Put the picture with 72% ntsc color gamut on the oled with more than 100% ntsc color gamut. If the color management is not well adjusted, it will be distorted.

Is it because Samsung can't adjust the color temperature?

No, it's because the red, blue, and green light-emitting materials of OLEDs have different lifespans. If the color temperature is correct, one of the colors will decay faster, resulting in a reduction in the lifetime of the entire screen, which is not worth the loss.

Therefore, Samsung has built in a "professional photo" mode in its latest products. In this mode, the color is accurate, but users are not recommended to use it frequently. Only used when it is necessary to look at the photos accurately with color. Otherwise, the life of the screen will be affected.

4. Response time

5. Number of hair colors (as explained earlier, 8-bit color is generally enough. Some advanced equipment with 10 bit color is just a gimmick, which is not meaningful. In theory, 10 bit color transition is more natural)

6. Resolution

This also needs a few words. The previous principle is very clear. We see that the resolution of 320 * 240 is 76800 points, but actually each point is composed of three RGB points, and there are actually 230400 points. Why is the p arrangement grainy? Because the same resolution of the p arrangement is less than one third of the points, only 153600 points. Therefore, with the same resolution, the fineness of P arrangement will be much worse.

7. Consistency

This is ignored. Some less professional websites will use the light leak problem to explain when evaluating. In fact, it is not comprehensive. Consistency means that under the solid colors of different colors, the brightness of each area of the screen cannot be too different. White cannot be white and gray, red cannot be dark and red cannot be light and black cannot be dark (the light is the so-called light leak), which also greatly affects the actual effect.