LED screens are divided into graphic screens and video and film screens, both of which are composed of LED matrix blocks. The graphic screen can display Chinese characters, English text and graphics synchronously with the computer; the video screen is controlled by a microcomputer IC, and the graphics, text, and movies are combined. Various information can be displayed in real-time, synchronized, and clear information dissemination. It can also display 2D, 3D animation, video, TV, DVD/VCD programs and live streaming. Its advantages: high brightness, low working voltage, low power consumption, miniaturization, easy to match with integrated circuits, simple drive, long life, impact resistance, and stable performance. It is widely used in stations, docks, airports, shopping malls, hospitals, hotels, banks, securities markets, construction markets, industrial enterprise management and other public places. Some other display technologies, such as LCD, electromechanical screens and light bulb displays have certain uses in some specific occasions, but LED screens have proven to be the most reliable, efficient, energy-saving, bright, and technically the most convenient to implement .
LED is light emitting diode, the abbreviation of light emitting diode, abbreviated as LED. The principle of LED luminescence technology is that certain semiconductor materials emit light of a specific wavelength when current is applied. The conversion efficiency of this electricity to light is very high. Various chemical treatments can be performed on the materials used to obtain various brightness. And viewing angle LED. It is a screen used to display text, graphics, images, animation, market quotations, videos, video signals and other information by controlling the display mode of semiconductor light-emitting diodes.
The following is an explanation of the standard terms and concepts commonly used in LED screens, I hope it can be helpful to everyone:
Pixel (PIXEL)
It is the smallest unit that can be independently controlled on the screen. PIXEL is the abbreviation of picture element. On a three-primary-color screen, the pixel is composed of three parts: red, green, and basket. Each part is composed of one or several LEDs. In theory, respectively Adjust the brightness of red, green, and blue to show any color.
Pitch (PITCH)
The distance between the centers of adjacent pixels. The smaller the spacing, the shorter the viewing distance.
Resolution
It is usually used in digital display devices to indicate the total number of pixels. It is generally written in the form of width X height, such as 800X600.
Viewing Angle
When the observer faces the LED, the maximum brightness of the LED can be seen. When the observer moves to the left or right, the brightness will be reduced. When the brightness is reduced to half of the maximum brightness, the angle at this time will increase. The sum of the angles obtained by moving up to the opposite direction is called the horizontal viewing angle, and the vertical viewing angle is measured in the same way. The viewing angle of the LED will be given by the manufacturer.
Brightness
Brightness is the most important parameter in any display device. The main unit of brightness is called candela, which is represented by CD. The brightness of a single LED is usually millicandelas, MCD, which is one thousandth of CD. Add the brightness of one square meter of LED together to get the brightness per unit area. Special (NITS) means that 1 NITS = 1 CD/m2
Viewing Distance
For various display devices, the best viewing distance should be the minimum distance at which the human eye cannot distinguish pixels, which is about 3400 times the dot pitch. The observation distance of TV and computer is usually less than this requirement, but the acceptable distance cannot be less than 1700 times of the dot pitch.
Screen refresh rate/Refresh Rate
The screen image update rate, usually expressed in Hertz (Hz), is different from the frame rate.
Frame Rate
The number of image frames displayed on the screen per second usually depends on the input signal (25 fps for PAL, 30 fps for NTSC)
Field
Half of the frame of PAL and NTSC, because PAL and NTSC are interlaced scanning, only half of the frame image is displayed for each refresh.
Pure green and true green
In the past 30 years, various color LEDs have been developed. First, red, yellow, yellow-green, blue LED and pure green LED were invented by Nichia engineers in the 1990s. So far, it has become possible to manufacture LED full-color screens. Play The video LED screen must be made of pure green. If it is made of yellow and green, the color is definitely not true. If the number of green tubes in a pixel is more than the number of red and blue tubes, it must be a yellow-green tube, because yellow The brightness of green is not enough, more than one must be used, but the price of yellow-green LED is low. This kind of screen is commonly known as a pseudo-color screen.
Color temperature
The brightness of the red, green and blue must be balanced to accurately restore the true colors. In other words, the white of the LED must be white, not pink. If red, green and blue are at the highest brightness, the mixed color is usually not white. In order to get white (usually called 6500K color temperature), one or two of the red, green and blue must be lowered in brightness. In order to obtain the correct white color, you must Repeated measurement and adjustment of brightness, this process is called white balance.
Gray Levels
The number of colors that the LED screen can express depends on the gray level of the RGB three colors. In a standard full-color screen, it is 256 gray levels. For the stadium's full-color LED system, 256 gray levels are not enough and cannot be accurately restored. Restore colors. Also called color depth, it refers to the number of different brightnesses. Red, green and blue have their own gray levels. In a full-color system, it is generally 256 gray levels, which can produce 256X256X256=16,777,216 colors. It is called 24-bit color in PC. It is called 8-bit system in LED display system.
Gamma correction
This is a way to reduce the number of grayscales through a transformation function, thereby producing a color and contrast closer to the real environment. The actual color displayed by the full-color screen is subject to many restrictions. At night, the brightness of the screen must be reduced, and the display can be displayed at this time. The color will be reduced. Therefore, the color of the digital RGB display is definitely less than 16M colors. In order to solve this problem, a higher level of gray is required. The 1Bill color system (red, green and blue each of 1024 colors) can express more realistic colors. , Because the gray scale is expanded from 256 to 1024, which greatly enriches the number of colors that can be expressed.
Virtual Resolution
Also known as shared pixels or dynamic pixels, the pixels that are 4 times the physical pixels are quickly sent to the physical pixels according to the odd-even column and the odd-even row 4 times for display. The effect is equivalent to reducing the pitch by half, and the cost is basically the same as the traditional method. The ratio is basically not increased, but it can achieve 4 times the original resolution.
Uniformity
The quality of the entire picture largely depends on the consistency of the LED. The problem of consistency is an inherent problem of LEDs when they are produced. Their brightness, viewing angle, and other characteristics are actually not uniform. These parameters are distributed in a certain range. The better the manufacturer's process control, the smaller the range. Choosing LEDs provided by high-quality manufacturers can reduce the workload of debugging. The human eye is very sensitive to color and brightness, and it is easy to perceive the difference between LEDs. Especially in high-brightness display systems, this difference is even greater. Designers must use various techniques to eliminate this difference. , Increase consistency.
Color Shift
The LED screen is composed of red, green and blue to produce various colors, but these three colors are made of different materials, the viewing angle is different, and the spectral distribution of different LEDs are changed. These differences that can be observed are called Chromatic aberration. When observing the LED from a certain angle, its color changes. The human eye's ability to judge the color of the real picture (such as a movie picture) is better than observing the picture produced by a computer.
