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LCD (short for Liquid Crystal Display) liquid crystal display.

According to different backlight sources, LCDs can be divided into

We have known for a long time that matter has three types: solid, liquid, and gaseous. Although the arrangement of liquid molecules' centroids does not have any regularity, if these molecules are long (or flat), their molecular orientation may be regular. Then we can subdivide the liquid into many types. Liquids with no regular molecular direction are called liquids directly, while liquids with directional molecules are called "liquid crystals", or "liquid crystals" for short. Liquid crystal products are no stranger to us. The mobile phones and calculators we often see are LCD products. Liquid crystal was discovered by Austrian botanist Reinitzer in 1888. It is an organic compound with a regular molecular arrangement between solids and liquids. Generally, the most commonly used liquid crystal type is nematic liquid crystal. The molecular shape is a slender rod shape with a length of about 1nm to 10nm. Under the action of different electric current fields, the liquid crystal molecules will be regularly rotated 90 degrees to arrange the light. The difference is that there is a difference between light and dark under the power ON / OFF, and each pixel is controlled according to this principle to form the desired image.

The principle of liquid crystal display is that the liquid crystal will show different light characteristics under the action of different voltages. Liquid crystals are physically divided into two categories, one is passive (also called passive), this type of liquid crystal itself does not emit light and requires external Provide a light source, which can be divided into reflective and transmissive types according to the position of the light source.Passive LCD displays have lower cost, but the brightness and contrast are not large, and the effective viewing angle is small. Small, so the color is not bright enough. The other type has power, mainly TFT (Thin Film Transitor). Each liquid crystal is actually a transistor that can emit light, so strictly speaking it is not a liquid crystal. LCD screen is composed of many liquid crystals Arranged in an array, in a monochrome LCD screen, a liquid crystal is a pixel, while in a color LCD screen, each pixel is composed of three red, green, and blue liquid crystals. At the same time, each liquid crystal can be considered There is an 8-bit register behind it. The value of the register determines the brightness of each of the three liquid crystal cells, but the value of the register does not directly drive the brightness of the three liquid crystal cells. "Swatches" to access. It is not practical to equip each pixel with a physical register. In fact, only one row of registers is provided. These registers are connected to each row of pixels in turn and loaded with the contents of the row. Lines are driven once to display a complete frame.

Liquid crystal looks like a liquid from its shape and appearance, but its crystal-like molecular structure shows a solid form. Like a metal in a magnetic field, when it is affected by an external electric field, its molecules will produce an accurate ordered arrangement; if the arrangement of the molecules is properly controlled, the liquid crystal molecules will allow light to penetrate; the path of light penetrating the liquid crystal can be determined by The arrangement of the molecules that make up it is determined, which is another characteristic of solids. Liquid crystal is an organic complex composed of long rod-shaped molecules. In the natural state, the long axes of these rod-shaped molecules are approximately parallel. The first feature of a Liquid Crystal Display (hereinafter referred to as LCD) is that liquid crystal must be poured between two planes with fine grooves in order to work properly. The slots on these two planes are perpendicular to each other (intersecting at 90 degrees). That is, if the molecules on one plane are aligned in the north-south direction, the molecules on the other plane are aligned in the east-west direction, and the molecules between the two planes Forced into a 90-degree twist. Because the light propagates along the direction of the molecules, the light is also twisted 90 degrees as it passes through the liquid crystal. But when a voltage is applied to the liquid crystal, the molecules will re-align vertically, so that the light can be directly emitted without any twist. The second characteristic of LCD is that it relies on polarization filters and the light itself. Natural light is scattered randomly in all directions. The polarization filters are actually a series of increasingly thin parallel lines. These lines form a net that blocks all light that is not parallel to these lines. The lines of the polarization filter are exactly perpendicular to the first one, so they can completely block those that have been polarized. Only when the lines of the two filters are completely parallel, or the light itself has been twisted to match the second polarization filter, can the light pass through. The LCD is composed of two polarizing filters that are perpendicular to each other, so under normal circumstances, all light trying to penetrate should be blocked. However, because the two filters are filled with twisted liquid crystals, after the light passes through the first filter, it will be twisted by 90 degrees by the liquid crystal molecules and finally pass through the second filter. On the other hand, if a voltage is applied to the liquid crystal, the molecules will be rearranged and completely parallel, so that the light is no longer twisted, so it is just blocked by the second filter. Taking Synaptics TDDI technology as an example, the touch controller and display driver are integrated into a single chip, which reduces the number of components and simplifies the design. The ClearPad 4291 supports a hybrid multi-point in-line design, eliminating the need for a discrete touch sensor due to the use of existing layers in the liquid crystal display (LCD). The ClearPad 4191 goes a step further and utilizes the electrodes already in the LCD, thus achieving a more compact system architecture. Both solutions make the touch screen thinner and the display brighter, helping to improve the overall aesthetics of smartphone and tablet designs. For the reflective TN (Twisted Nematic) liquid crystal display, its structure is composed of the following layers: polarizing filter, glass, two sets of electrodes that are insulated and transparent, vertical and horizontal, liquid crystal, electrode, glass, polarization Filters and reflectors.

(1) Low voltage micro power consumption

(2) Small and exquisite appearance, thickness is only 6.5 ~ 8mm

(3) Passive display type (no glare, does not irritate human eyes, and does not cause eye fatigue)

(4) Large amount of display information (because pixels can be made small)

(5) Easy to colorize (can be reproduced very accurately on the color spectrum)

(6) No electromagnetic radiation (safe to the human body and conducive to the confidentiality of information)

(7) Long life (This device has almost no degradation problems, so it has a very long life, but the LCD backlight has a limited life, but the backlight can be replaced.)

(1) Since the CRT display controls the electron beam by the electromagnetic field generated by the deflection coil, and because the electron beam cannot be absolutely positioned on the screen, the CRT display often has different degrees of geometric distortion and linear distortion. The LCD will not have any geometric distortion or linear distortion due to its principle, which is also a great advantage.

(2) Compared with traditional CRTs, liquid crystals also perform well in environmental protection. This is because there are no high-voltage components like CRTs inside LCDs, so they will not cause x-rays exceeding the standard due to high voltage, so their radiation The indicator is generally lower than the CRT.

(3) The biggest advantage of LCD compared with traditional CRT is power consumption and volume. For traditional 17-inch CRT, its power consumption is almost above 80W, while most of 17-inch LCDs have power consumption around 40W. In this way, LCD has obvious advantages in energy saving.

LCD liquid crystal projector is a product of the combination of liquid crystal display technology and projection technology. It uses the electro-optical effect of liquid crystal, and controls the transmittance and

Although LCD product descriptions have "maximum number of colors", it seems that not many people notice this item. Because almost all products now have 16 million color display capabilities, no one should be dissatisfied with this. However, there are unexpected pitfalls in a "maximum number of colors".

The ideal goal of the PC LCD is to be able to fully display the 8-bit per channel (3 * 8bit = 24bit) of RGB output from the PC, and the full color data. 8bit per channel of RGB means the ability to display 16.77 million colors. The calculation method is as follows:

8bit = 2 ^ 8 = 256 colors

256 colors (R) × 256 colors (G) × 256 colors (B) = 16,777,216 colors

16,777,216 colors 16.77 million colors

I hope you remember two things. The first point,

Not all mainstream LCDs can achieve 16.77 million colors. Second, the implementation of 16.77 million color displays is not the same. At present, the maximum number of colors and implementation methods of consumer LCDs are as follows:

In the true sense, LCDs that realize 16.77 million colors display only products that use 8-bit drive and display 8-bit data for each channel of RGB, which is the first type of product in the table. In contrast to the native 8-bit display, the second and third categories of products in the table are so-called "pseudo full color" displays. While reducing the production cost, the theoretical color expression is inferior to the 8-bit driven panel.

In terms of product performance identification, the third category of products is easier to distinguish because of its color number of approximately 16.19 million colors / approximately 16.2 million colors. However, because the number of colors of the first and second products is about 16.77 million colors, it is difficult to distinguish. Because the former has advantages in image quality performance, if you need to use it in areas such as image processing, you must pay special attention when choosing.

Insert a sentence here, some products used in LCD TVs and LCDs in the commercial field are produced using 10-bit driven LCD panels. Theoretically, it can display 1,073,741,824 colors (approximately 1,073 million colors). Because it needs to cooperate with 10bit output graphics equipment and professional software, it is far from universal in the PC field.

Let's talk briefly about FRC. The so-called FRC (Frame Rate Control) refers to the technology that uses the visual retention characteristics of the human eye to control the frame refresh rate to increase the number of colors visually. As a simple analogy, if you display "white" and "red" at a very high frequency, then it will become "pink" to the human eye.

Specific to the "6bit driver panel + FRC" LCD, the number of colors that the LCD panel can display is only poor 6bit (2 ^ 6 = 64) ^ 3 = 262,144 colors. At this time, let FRC act on each RGB channel. By changing the interval of each color of the liquid crystal display, 3 kinds of false colors are generated between each two colors (4bit drive FRC). In this way, 189 pseudo colors ((6bit-1) × 3 = 189 colors) can be added for each channel of RGB. Adding these 189 colors can achieve (2 ^ 6 + 189) ^ 3 = 16,194,277 colors ( 16.19 million colors / 16.2 million colors).

Products using next-generation FRC technology are gradually increasing. Through the use of more bits than traditional FRC technology to generate more false colors, and then select other colors in the "Full Color" range to achieve 16.77 million color display.

Having said that, the factor that affects picture quality is not only an LCD panel,

Grayscale comparison diagram

Other factors (image processing chips) also have a great impact on the picture. Therefore, the difference between the "8bit drive" and "6bit drive + FRC" display modes is sometimes difficult to distinguish. It should be more obvious to distinguish by the gray scale diagram of the linear change of light and dark. This property is the same in both still images and video and game applications.

LUT greater than 8bit

Although "6bit driver + FRC picture quality is not as good as 8bit driver", it cannot be said that the color number and color gradation display of 8bit driver panel must be good. Lookup table (slightly LUT) plays an important role in improving the color expression of LCD.

The so-called LUT refers to a list in which the results of certain operations are stored in advance. In a certain system, when certain specific operations occur, the pre-calculated results can be obtained by looking up the table, which can greatly improve the efficiency. (Note: A bit similar to the familiar multiplication formula.)

Specifically, the LUT in the LCD is a function that calculates and maps the signals obtained from the PC (8bits of RGB each) and the output signals (8bits of RGB) output to the LCD in advance. Cheap LCDs usually use 8-bit LUTs, while LCDs that emphasize color performance usually use LUTs larger than 8-bits such as 10-bit and 12-bit. In the mapping process between input and output signals, internal accuracy of more than 10-bit is also used.

Let's start with the performance of LUTs greater than 8bit. such as,

A product introduction labeled "about 16.77 million colors (1,064.3 million colors)" indicates that the product has a 10-bit LUT for RGB (1024 ^ 3 = 1,064.3 million colors). Specifically, the display will first upgrade the 8-bit RGB signals input from the PC to the 10-bit signals for internal processing of the display, and then find the most suitable 8-bit output value according to the 10-bit LUT for display output. Therefore, the gamma curve can be closer to the theoretical curve, and the occurrence of problems such as banding and hue shift is greatly reduced. If it is a 12-bit LUT, a suitable 16.77 million colors are selected from 68 billion colors, which is more excellent than the 10-bit LUT in color reproduction.

Next, let's talk about the processing operations that increase the 8-bit RGB input signals to a precision of more than 10 bits inside the display. Even if the LUT is only 10-bit or 12-bit, better results can still be obtained if 14-bit or 16-bit calculation accuracy is used. Some people may doubt that the final output is only 8bit anyway, whether it is necessary to use such a high calculation accuracy. But what I want to say is that to show the correct dark part of the image, the processing accuracy inside the display is very important. Simply put, the higher the accuracy of internal processing, the closer the gamma curve of the dark part to the theoretical curve.

Throughout today's LCD displays, even relatively inexpensive products, more and more products use 10bit LUTs. However, the accuracy of operations exceeding the accuracy of LUT is still limited to a few high-end products. In particular, the ultra-high precision of the 12-bit LUT + 14 / 16-bit internal operation is only found in high-end LCDs with color management.

In fact, the difference between an 8-bit LUT + 8-bit computing product and a 10-bit or more LUT + 10-bit or more computing accuracy product is sometimes surprisingly obvious. High-end products with this level of precision usually also have high-performance image processors. Compared with entry-level products with uneven picture quality, the difference in picture quality is even more obvious. When displaying gray levels, products with high-precision LUTs / high-precision calculations usually perform smoother in the dark. The banding and hue offset of such products are almost 0, and the grayscale transition is natural.

Schematic diagram for improving the accuracy of gray-scale transitions

The contrast is also more stable. Needless to say, users who are looking for color reproduction performance. For users who are a bit more pursuit of picture quality, they also recommend purchasing products with 10bit LUT.

3D-LUT with higher accuracy

Some Hi-End LCDs use the next-generation LUT, 3D-LUT. In the traditional LUT, each channel of RGB has a separate LUT. When a certain color needs to be expressed, it is necessary to refer to the LUT of each color of RGB separately, and use the RGB color obtained from each LUT to calculate the color to be displayed. .

The 3D-LUT mixes the three RGB colors into a three-dimensional LUT (it can be understood as a cube with RGB and XYZ axes). Because the LUT has a middle-level gray scale after RGB mixing, there is an improvement in the expression of the middle-level gray scale and the correctness of the Gray scale.

Taking EIZO's widescreen LCD as an example, the ColorEdge CG242W uses a 3D-LUT. Compared with the traditional LUT, the difference between the measured value and the theoretical value of the middle gray level is very small.

3D-LUT can also exert its power when performing color space conversion in a color management environment. When 16.77 million colors in a certain color space are converted into other color spaces, the loss of the source space can be minimized, and high-precision conversion can be performed. Not only that, due to the improvement in the reduction of RGB mixing (additive color mixing), in the process of image editing that adjusts brightness, chroma, and hue, the user can linearly reflect the adjustment of various parameters to the display. This is probably the most important feature of a color management LCD that places the most emphasis on color reproduction.

In summary, the number of driving bits, LUT, and internal calculation accuracy of the LCD panel affects the color reproduction of the LCD to a large extent. Even if the monitors have the same performance indicators (Note: the same is 16.77 million colors), after actual comparison, sometimes they will find great differences. Therefore, the performance of the display is by no means clear in a manual, so I would like to recommend that you conduct an actual inspection and comparison before purchasing.