Topic: How to choose a good LCD monitor

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How to choose a good LCD monitor

Monitors are a kind of thing that is compared. After you see a monitor in a store, you cross the street to another store to see another one. When you go home, you have no idea which one is better. The only impression you have is which one has a more attractive design and which one is more expensive. The way to choose should be based on your budget and the specifications you want to buy. Choose a few that you like in advance and put them together for comparison. Resolution . Currently, there are roughly the following resolutions for LCD monitors available on the market : XGA: 1024*768 / SXGA: 1280*1024 / SXGA+: 1400*1050 / UXGA: 1600*1200. There are also some panels with higher resolutions (usually for special purposes), and wide screens of 16:9 or 16:10 that are probably not used in Taiwan. Let's not discuss the resolution of an LCD monitor here. It refers to the number of dots it can display. This is a fixed value and cannot be adjusted. Under the same size, the higher the resolution, the more detailed the picture can be. Suppose you buy an XGA monitor, Then your display card must not be set to other resolutions, such as 800*600, because in this case the computer actually scales an 800*600 screen to 1024*768, and the result is a blurry screen. The correct way is to set the display card to the resolution of the monitor you bought. DVI (Digital Visual Interface) Computers process digital signals, and the signals sent out after processing are also digital signals, but traditional CRT monitors use analog signals. In order to communicate with the CRT, the signals sent to the CRT must be converted to analog before they can be used, so the output of general display cards (D-sub, which is the small slot with 15 pins) sends analog signals. LCD monitors also use digital signals, but in order to be compatible with general display cards, they are designed to receive analog signals sent from the D-sub connector, and then convert this analog signal into a digital signal for processing and display. This creates a problem. Whether it is digital to analog or analog to digital, there will definitely be signal loss, so in order to communicate with the CRT, Due to the stupid reason of compatibility, the LCD monitor has undergone two unnecessary signal losses. As a result, the image you see will be a little blurry, but in fact, the original ability of the LCD can display more clearly. Since LCD monitors have become popular in the past two years, display card manufacturers have also begun to launch display cards that can directly output digital video, that is, there is an additional slot called DVI. If you buy a display card with a DVI slot and then buy an LCD monitor with a DVI slot, the clarity displayed by the LCD monitor is the original design capability of the LCD. Of course, this combination seems to be more expensive now. If you are not very picky about the image quality and just want to use it, you can consider saving this money. Bad pixels (dot defect) The so-called bad pixels refer to the points on the LCD monitor that are constantly bright or dark and cannot be controlled. The cause of bad pixels is a defect caused by various factors during the production of the LCD panel. It may be particles falling into the panel, static electricity damage to the panel, poor process control, etc. There are two types of bad pixels: bright spots and dark spots. Bright spots are points that are constantly bright in any picture. Switch to a black screen and you will find that dark spots are dots that are always dark in any picture. Switch to a white screen and you will find that generally speaking, bright spots are more unacceptable than dark spots, so many monitor manufacturers will guarantee that there will be no bright spots, but it seems that fewer will guarantee that there will be no dark spots. Some panel manufacturers will fix bright spots to dark spots before shipping. In addition, some types of panels can only have dark spots and no bright spots, such as MVA and IPS LCD panels. Panel manufacturers will sell panels with dead pixels at a discount. Usually, no dead pixels are considered A grade, within three dead pixels are considered B grade, and within six dead pixels are considered C grade. Generally speaking, these can be shipped normally. As for lower-grade panels, when the economy is good and panels are out of stock (such as in 2000), there will still be people who buy them. This year, everyone should keep their eyes open because dead pixels cannot be repaired. If the monitor you bought has a warranty for dead pixels, you can return it to them and they will replace it for you. Mura mura was originally a Japanese word. As Japanese LCD monitors have been developed around the world, This word has become a universal word in the monitor industry. Mura refers to the phenomenon that the brightness of the monitor is uneven, causing various traces. The simplest way to judge is to switch to a black screen or other low-grayscale screens in a dark room, and then look at it from various angles. With various process defects, LCD monitors have various mura, which may be horizontal stripes or 45-degree stripes, straight squares, a patch in a corner, or a patch with no rules at all. Mura will not cause any impact on use. It is a matter of taste. Panel manufacturers will mark panels with mura as inferior products and sell them at a lower price. However, I have not heard of monitor manufacturers that guarantee no mura, and this is usually not written into the monitor specifications. So keep your eyes open before buying, and you will have to admit that you are unlucky if you buy it. Contrast The contrast of a monitor is defined as follows: in a dark room, the brightness of a white screen is divided by the brightness of a black screen. Therefore, the brighter the white and the darker the black, the higher the contrast value. Generally, LCD monitors The contrast ratio is written on the specification sheet of a panel, but this value is usually only for reference, because in order to protect themselves, panel manufacturers will write some specification values very conservatively, and contrast is one of them. For example, the contrast ratio of a certain model can reach 300, but the specification is written as typical 200/minimum 150. This is to ensure that if there is any problem during mass production that causes the black light leakage contrast to decrease, the batch of goods can still be shipped normally. If you want to compare two LCD monitors, the contrast ratios are written as 350/400 respectively , don't think that the one with 400 is really better, that's just the one that dares to write it. In fact, if the two monitors are written as 300/400 respectively, I would still doubt that they may be similar. In fact, if you are lucky, they may reach 500-600. If you care about this, you can adjust the white brightness of the two monitors you want to compare to the same, and then switch to a black screen to see which one is darker in a dark room. If you are not very picky about the image quality, I think a contrast ratio of 300 should be enough for general use. Color gamut Color saturation refers to the degree of vividness of the display's colors. The display is composed of red, green, and blue colors to form any color. If the three primary colors R/G/B are more vivid, the display can display a wider range of colors. This is because it is impossible to display colors more vivid than the three primary colors. Therefore, the three primary colors of a certain display are not vivid, and the range of colors that the display can display is relatively narrow. Color saturation is an important specification for panel manufacturers, but I don't think I have seen any monitor manufacturer write color saturation into the specifications. They all write the number of colors that can be combined. For example, if the three colors of R/G/B of a certain display can be divided into 64 gray levels (6 bits), then the display has a total of 64*64*64=262,144 color combinations. If the three colors of R/G/B of the display can be divided into 256 gray levels (8 bits), then the display has a total of 256*256*256=16,777,216 color combinations. Of course, The more grayscales there are, the more detailed the color levels will look, but it does not mean that the colors will be brighter. The color saturation is expressed by using the color gamut area of the three primary colors specified by NTSC as the denominator and the color gamut area of the three primary colors of the monitor as the numerator to calculate the percentage. For example, if the color saturation of a monitor is 71% NTSC, it means that the monitor can display a color range of 71% of the NTSC standard. 71% NTSC is approximately the current CRT TV standard. LCD monitors that can achieve this level are considered high-end in terms of color. The color saturation of the screen used in current notebook computers is about 40~50% NTSC, and most desktop LCD screens achieve 60%~65% NTSC. Of course, major manufacturers have plans to continue to develop high-color saturation monitors or have already mass-produced them. Please don't use this to argue with me. I am talking about "currently" and "mostly". When buying, put two monitors you like together and click on the same picture, and you can usually tell which one has better color saturation. Brightness refers to the brightness of the display under the white screen. The unit is cd/m^2, or nit. Brightness is an important factor that directly affects the image quality. In the laboratory, we often say: "One bright cover three ugly". A bright display may still look more beautiful even if the color saturation is poor or the color is yellowish or other unfavorable factors. The general brightness specification of the monitor currently on the market is about 250 nits, and the brightness specification of the notebook is about 150 nits. Of course, brighter products are being developed or mass-produced by various manufacturers. If it is an LCD TV, the brightness is usually 400 nits. This is because the distance when watching TV is not as close as when using a monitor, and the environment in which the TV is placed will be brighter. The LCD monitor emits light because its backlight module contains a lamp tube, which is very similar to the fluorescent lamp tube used for lighting that you can see when you look up now, but it is a little smaller. There will be one in the notebook, and two to six or more in the monitor. At present, lamp manufacturers will guarantee that the lamp life is more than 30,000 hours or 50,000 hours, which means that the brightness will drop to half after 30,000 to 50,000 hours of use. So in fact, LCD monitors are quite long-lived. If there is no other destructive action that causes failure, it should be able to last until you want to replace it. The brightness of the monitor can be adjusted by the user. Just adjust it to a brightness that you feel comfortable with. Adjusting it too bright may not only make you uncomfortable, but also shorten the life of the lamp. Viewing angle (I) Due to the inherent physical characteristics of LCD monitors, the image quality will change when the user looks at it from different angles. Compared with the straight view, when the image quality changes to an unacceptable critical angle when looking at it obliquely, it is called the viewing angle of the monitor. There are three definitions of viewing angle: 1. Contrast When looking at an LCD monitor from an oblique direction, the white part will become darker and the black part will become brighter compared to the straight view, so the contrast will decrease. Generally, the angle when the contrast drops to 10 is defined as the viewing angle of the monitor, that is, when the viewing angle is greater than this, black and white are difficult to distinguish. Generally, panel manufacturers and monitor manufacturers use this definition of viewing angle most often in their specifications. 2. Grayscale inversion In theory, the higher the grayscale number, the brighter the display should be from zero grayscale (black) to 255 grayscale (white). However, when the LCD is viewed at a large angle, it is possible to see that the low grayscale is brighter than the high grayscale, which is a phenomenon similar to black and white inversion. This phenomenon is called grayscale inversion. The maximum angle that does not produce grayscale inversion is defined as the viewing angle. That is, grayscale inversion may be seen beyond this angle, and grayscale inversion is unacceptable. The difference between this definition and the first definition is that the contrast definition only considers zero grayscale and 255 grayscale, while grayscale inversion considers all grayscales. 3. Color difference When you look at the LCD from different angles, you will find that the color changes with the angle. For example, the originally white screen becomes yellower or bluer, or the color becomes lighter, etc. As the angle increases, when the color change is already large enough to reach an unacceptable critical point, the angle is defined as the viewing angle. Regarding color difference, I have said that color can be quantified, so the difference in color can be expressed in numbers. However, there is no definite standard for what is considered unacceptable color difference, so no one uses this definition when writing specifications. However, in the laboratory, when we compare two monitors, we still care about which one has a larger color difference at the same angle. This is a taste issue that users will directly feel. The earliest TFT-LCD used a liquid crystal mode called TN. The biggest disadvantage of this technology is that the viewing angle is very small. Defined by contrast, the current viewing angle is about 45 to 50 degrees on the left and right, 15 to 20 degrees on the top, and 35 to 40 degrees on the bottom. In order to solve the viewing angle problem, several wide viewing angle technologies have been developed. There are currently three mainstream wide viewing angle technologies on the market: TN + film, MVA, and IPS. Currently, notebook LCDs on the market usually do not use wide viewing angle technology, because notebooks are for personal use and wide viewing angle is not very effective. Monitors usually use wide viewing angles, considering that when using a monitor, some data or pictures may be shown to people next to you. Viewing angle (Part 2) 1. TN + film The so-called TN + film is the original TN type TFT-LCD. A wide viewing angle compensation film is affixed to the TN+ film. This wide viewing angle compensation film is the exclusive patented technology of FujiFilm (yes, the company that makes negatives), called Fuji Wide View Film. Once this compensation film is applied, the original left and right viewing angle of about 100 degrees and the vertical viewing angle of 60 degrees, based on contrast, will immediately increase to 140 degrees left and right and 120 degrees vertically. However, TN+film still does not solve the problem of grayscale inversion. 2. MVA MVA is an exclusive patented technology developed by Fujitsu. In addition to Fujitsu, Chi Mei Electronics and AU Optronics in Taiwan have obtained authorization to produce it. MVA can achieve vertical and horizontal viewing angles of more than 160 degrees (but not every direction has such a viewing angle), and solves most grayscale inversion problems. Grayscale inversion can only be seen when viewed from a very special direction and at a large angle. 3. IPS IPS was first developed by Hitachi. IBM Japan, NEC, Toshiba, etc. also have IPS technology. In China, HannStar Display has obtained authorization from Hitachi to produce it. The vertical and horizontal viewing angles of IPS are said to be 170 degrees (but not every angle has such a viewing angle), and most grayscale inversion problems have been solved. The difference between 160 degrees and 170 degrees is actually meaningless. If you are interested, pick up a protractor to see how wide the viewing angle of 80 degrees is. Basically, beyond this viewing angle, a plane has almost become a slit, and there is no way to measure it. He dared to write 170 degrees (85 degrees on each side) because at 80 degrees, the contrast ratio may be 20 to 30, so it is certain that the contrast ratio can still exceed 10 at 85 degrees. In fact, MVA can also be used in addition to the above three wide viewing angle technologies. The more famous wide viewing angle technologies include Sharp's exclusive patented ASV, Samsung in South Korea has a variant of MVA called PVA, and Hydis in South Korea (Former Hyundai's TFT-LCD division) has IPS's deformed FFS and other viewing angles. (III) There are several reasons why notebook LCD screens do not use wide viewing angle technology. In addition to the previously mentioned notebooks are for personal use, the most important reason is that notebooks are designed to be thin and light and save power, so the backlight can only have one lamp and must be very thin (that is, it is naturally not bright). In order to obtain better light utilization efficiency, the TN type design with the highest transmittance is adopted, and MVA, IPS, ASV and other technologies are rarely used. In addition to the lower transmittance of TN + film technology than TN, the addition of two wide viewing angle compensation films will also increase the thickness and weight. The thickness and weight requirements of notebook panels have always been a nightmare for institutional engineers. The easiest way to determine whether a monitor uses TN + film is to look at the grayscale inversion. The lower viewing angle is the easiest angle to see the grayscale inversion. Cut the monitor to a pattern with different colors and brightness, put your face under the monitor and look up. If you see the phenomenon of grayscale inversion (that is, the bright areas become darker and the dark areas become brighter), you can be sure that this is a TN + film monitor. If it is a notebook LCD screen, you can easily see the left and right viewing angles. The left and right viewing angles of TN + film may be 120 degrees or 140 ~ 150 degrees (defined by contrast) depending on the design. This is because FujiFilm has launched a new generation of wide viewing angle compensation film. However, there is one thing that left a deep impression on me. Once I got a TN + film panel from a certain company. The specifications stated that the left and right typical values were 75 degrees each, but there was no minimum value. When I actually measured it, I found that it was only 60 degrees. Only then did I realize that our company was a little too honest when writing the viewing angle specifications. Not only did they write the typical values honestly, but they also guaranteed the minimum value. With a stroke of the pen, their technology immediately improved by leaps and bounds. No wonder they sell so well. For those of us who make a living in this field, the judgment of MVA and IPS is actually to take a microscope and look at the pixel design of the panel. Ordinary users can get some clues from the specification. In addition to the difference between the viewing angle specifications of 160 and 170, the response time specification of MVA is 25 ms, and the response time of IPS is about 40 ms. If the Sharp panel specification also states that the vertical, horizontal and vertical viewing angles exceed 160 degrees, then it must be ASV. MVA and IPS each have their own advantages and disadvantages . For example, MVA has a faster response speed than IPS, but the color difference is also larger than IPS. In view of their respective shortcomings, manufacturers have continued to develop and improve research and have even put them into mass production. TN + film will not disappear one day, because it is easy to make brighter, and it does not require special processes for panel manufacturers. It is a very suitable choice for low-priced monitors. Response time (I) The definition of response time is the time required for the change from black to white plus the time required for the change from white to black at the same point on the panel. LCD has a response time problem because LCD controls the grayscale brightness of light by the rotation angle of liquid crystal molecules, and it takes time for liquid crystal molecules to rotate. The purpose of general monitor use is word processing and web browsing. Under normal circumstances, the monitor will continue to display the same picture for a long time before switching to another different picture. In such a usage situation, the speed of the response time actually has no effect on the user. However, if you want to use the monitor to watch animations or videos, because the picture will continue to change without stopping, the response time will affect the picture quality. The response time is divided into rise time and fall time. For TN type panels, when the driving voltage changes from low voltage to high voltage, the screen will change from white to black (voltage rise), so the time required for white to black is the rise time, and when the driving voltage changes from high voltage to low voltage, the screen will change from black to white (voltage fall), so the time required for black to white is the fall time. MVA and IPS are just the opposite, black to white is the rise time, and white to black is the fall time. The specifications of mass-produced panels on the market currently show that the TN type rise time is about 15 ms and the fall time is about 35 ms. In fact, it is not difficult to achieve 10 ms + 20 ms. There is actually a trap here. For LCD panels, the response time from full black to full white and from full white to full black is actually the fastest, but the switching of intermediate gray levels cannot guarantee this speed. For example, when switching from 128 gray levels to 140 gray levels, the response time will be much longer than the specification value, and it is possible to be greater than 70 or 80 milliseconds. When you use a monitor It is impossible to use only black and white colors. Response time (II) The screen refresh rate of a general LCD panel is 60 Hz, which means that the screen will be refreshed 60 times per second. Regardless of whether the currently displayed image is changing or not, it will be re-displayed at this frequency. Therefore, the duration of each screen is 1/60 = 16.67 ms. If the response time is much longer than this value, you may see a blurred image when the screen is moving. Note that it is a blurred image, not a residual image. Residual image is another problem. You can test it like this: There is a "message display" in the screen saver attached to MS Windows. In the settings, you can change the background color and message content. Select gray as the background, type ++++++ as the message, select a larger font, and then let it run. If you look carefully, you can see a blurred tail behind the plus sign. This is caused by the insufficient response time. CRT does not have such a problem. This means that the current LCD monitor is not very suitable for watching movies. However, according to my actual test results, if ordinary users watch ordinary movies (such as ㄟ movies), it actually has little impact. If you want to watch action movies with flashing images, You will only notice the quality degradation if you stare very hard at some background that you normally wouldn't notice. It's not a big problem when playing games. There is another pitfall in the response time specifications of commercially available LCD monitors. Some manufacturers only write rise time for response time. So if you see a response time of only 15 ms or even lower when you buy a monitor, it's best to ask clearly. This is usually the case. It will probably take some time before products with a response time of less than 15 ms are available on the market. Some other high-end LCD response time specifications may say full grayscale switching is less than 16.67 ms, which means that no matter how many grayscales are switched to, the action is guaranteed to be completed within 16.67 ms. Note that it is not rise + fall time 16.67 ms. This is achieved by tinkering with the driving voltage. It is not common at present, but it does exist. This type of panel can be used to watch movies, and the picture quality is much better than that of traditional LCDs. Protective glass Some people will ask for protective glass when they buy LCD monitors. Whether this is good or not is a matter of opinion. I personally oppose it. But one of my colleagues bought a CRT with glass. The biggest problem with glass is that it reflects light, which is especially annoying if there is a window or light behind it. It is often difficult to see the picture. The outermost layer of the LCD surface is a polarizing film. This polarizing film is usually treated with some special surface treatments, with a relatively high hardness (generally 3 H), and has anti-glare and anti-reflection functions. Therefore, LCD will not have the reflection problem like CRT. However, once the protective glass is installed, all this will be ruined. Any trouble caused by the light source behind you to your CRT screen will be reproduced on the protective glass of the LCD, wasting the original design of the surface polarizing film and destroying the image quality. So why do people want to install glass? Because when using the monitor, fingers often point on it, and fingerprints on the polarizing film are difficult to remove. They cannot be wiped off with a cloth. If protective glass is installed, it will be easy to clean. In addition, just like the situation of my colleague, as soon as he bought it home and put it in, his two sons who were not yet in kindergarten came to press hard, which made him feel that he had made the right choice of glass. In fact, LCD is not that fragile. It will not break if it is not pressed or hit very hard, and bad pixels are not caused by touching. Unless the place where the LCD is placed is often visited by very unruly friends, it is not recommended to install protective glass. To wipe off fingerprints on the polarizer, you can use water and a little dishwashing liquid, wet the cloth and wipe it, and then use the cloth to wipe it with clean water. Lightly pressing the LCD screen will not cause the liquid crystal to flow out, which is sealed inside the panel. In the event that the LCD screen is broken (the cracked area will turn black), it must be disposed of as soon as possible and hands must be washed with soap, because liquid crystal is toxic. Do not touch it and then accidentally eat it. Afterimage Afterimage refers to the phenomenon that after the screen switches, the previous screen does not disappear immediately but disappears slowly. Afterimage and response time are not the same thing. Afterimage may take two or three seconds to completely disappear, and the response time of LCD is ten to dozens of milliseconds. A well-designed LCD monitor will not be able to completely disappear even if the response time is 15+ 35ms, it is impossible for users to see the afterimage . The mechanism of afterimage is somewhat complicated. Usually, when the same picture is displayed for too long, the charged ions in the liquid crystal are adsorbed on the upper and lower glass ends to form a built-in electric field. After the picture is switched, these ions are not released immediately, so the liquid crystal molecules do not immediately turn to the angle they should turn. Another possible situation is that the pixel electrode is poorly designed, causing the liquid crystal molecules to be arranged in disorder when the state is switched. In this case, it is also possible to see afterimages. So it is wrong to think that if the reaction time is fast, there will be no afterimages. The panel manufacturer's method of testing afterimages is to watch the black and white square picture of a chessboard at room temperature for twelve hours, and then switch to 128 grayscale to watch. The standard is that the afterimage must disappear within 5 seconds (?). When ordinary users buy monitors, they can use power point to draw some pictures with black squares on a white background and a 128 grayscale picture to switch. If it is troublesome, you can also set the screen background to 128 grayscale, and then call out the mines to explode (all black mines will be displayed). Leave it on for tens of seconds or minutes, then turn it off. If you can see a residual image (not five seconds, as long as you can see it), then don't buy it. Note that you should not stare at the test screen all the time, but switch it to another screen before you look at it. Otherwise, you may see the residual visual effect of the human eye. Color temperature (color temperature) is used to describe the color of the white color of the display. It is not limited to LCDs, but is common to all displays. When the color of the display is the same as the light emitted by a black body when its temperature is as high as a certain absolute temperature, the color temperature of the display is said to be equal to that temperature. For example, when the white color of the display is designed to be close to the color of the light emitted by a black body at a temperature of 6500 K (close to the sunlight in the morning on a sunny day), the color temperature of the display is said to be 6500 K. It doesn't matter if you don't understand the above, just remember the following three sentences: the lower the color temperature, the more yellow the color will be, and the higher the color temperature, the more yellow the color will be. The color will be more blue. When a monitor with a higher color temperature displays pictures, the entire screen will look blue. It is said that Asians prefer bluish white, while Europeans prefer yellowish white. Therefore, the default color temperature of CRT TVs sold in Japan can be as high as 9300 K or even 12000 K. The default color temperature of those sold in Europe is around 6500 K. Taiwan follows Japan. It doesn't matter if you don't like bluish white. The color temperature of CRT allows users to adjust it easily, but it is difficult for LCD. Currently, the white color of LCD panels is usually designed to be around 6500 K (the color temperature of panels used in TVs will be higher), but some are deliberately designed to be more yellowish. This is because the yellower the lamp is, the higher the brightness will be. If the brightness is blue, it will be lower. If the brightness is blue and you want to maintain the same brightness, you have to spend more money on other parts to make up for the brightness. There is no standard for good or bad color temperature. Some people like bluish and some like yellowish. When purchasing, put a few monitors you like together and click the same picture. Just pick the color you like. Gamma Curve. Gamma curve refers to the relationship curve between different grayscales and brightness. Take the grayscale from 0 to 255 as the x-axis and the brightness as the y-axis, and the resulting curve is called gamma curve. Gamma curve is usually not a straight line, because the human eye has different recognition effects on different brightness. For example, the recognition ability of low brightness is higher (a slight change in brightness can be felt), and the recognition ability of high brightness is lower. Gamma curve will directly affect the gradient effect of the display screen. For example, if the gammacurve of a display is cut too thin in high brightness areas, and the brightness of the highest grayscale levels is almost the same, then when displaying bright pictures, many places will feel white and too bright, and the gradient cannot be seen, so the user will feel that the image is unnatural. Some higher-end display cards will provide the function of adjusting the gamma curve, but if you are not a more professional user, you usually don't touch that, but directly use the original settings of the monitor manufacturer when testing. Bring a few more pictures of different types, Generally speaking, you should prepare some brighter, darker, or middle-gray pictures. It is best to prepare some pictures with large portraits, because skin color is an easily recognizable impression for the human eye. Look carefully at the picture to see if the gradient effect looks natural to you. Crosstalk LCD's crosstalk refers to the phenomenon that the picture in a certain area of the screen affects the brightness of the adjacent areas. The general crosstalk test screen is as shown in the attached file. When the background color is at 128 grayscale, draw a black square that is one-fourth the size of the screen and place it in the center. In theory, the surrounding area should still maintain 128 grayscale, but if you find that the four areas above, below, left, and right become darker, it is called crosstalk. You can also change the black square to white. If there is crosstalk, the above, below, left, and right will become brighter. The general specification of panel manufacturers is that the brightness difference of the above, below, left, and right areas when there is a black square and when there is no black square cannot exceed 4%. However, this is actually a very loose specification. Usually, the human eye can see it very clearly when it reaches 2%, so some customers will require it to be less than 1%, and this is usually also the design standard of the panel manufacturer. When purchasing, just click on the picture mentioned above. If you can see crosstalk, don't buy it.