LED display key technical indicators

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The pixel out-of-control ratio refers to the proportion of the smallest imaging unit (pixel) in the display operating abnormally (out of control). There are two modes of pixel out of control: one is the blind spot, which is the blind spot. When it is bright, it is not bright, and it is called the blind spot; the second is the constant bright spot. When it is not bright, it is always on. Call it a bright spot. In general, the composition of the pixel is 2R1G1B (2 red, 1 green, and 1 blue, similarly described below), 1R1G1B, 2R1G, 3R6G, etc., and the loss of control is generally not the same in the same pixel. The green and blue lights all go out of control at the same time, but as long as one of the lights goes out of control, we think that this pixel is out of control. For the sake of simplicity, we calculate and calculate the uncontrolled pixels according to the primary colors of the LED display (ie, red, green, and blue), and take the maximum value as the pixel out-of-control ratio of the display screen.
The ratio of out-of-control pixels to the total number of full-screen pixels is what we call the "overall pixel out-of-control ratio." In addition, in order to prevent the out-of-control pixels from concentrating on a certain area, we propose the “region pixel out-of-control ratio”, that is, the ratio of the number of out-of-control pixels to the total number of area pixels (ie, 10000) in a 100×100 pixel area. This indicator quantifies the requirements of “Discrete distribution of out-of-control pixels” in SJ/T11141-2003 “General Specification for LED Displays”, which is convenient and intuitive.
At present, LED display screens in domestic countries will undergo aging (bake machine) before leaving the factory. The LED lights that are out of control pixels will be repaired and replaced. The “out of control rate of pixels in the entire screen” is controlled within 1/104, and the “Range of pixels out of control” control Within 3/104 is no problem, even some individual manufacturer's corporate standards require that out-of-control pixels are not allowed before leaving the factory, but this will inevitably increase the manufacturer's manufacturing and maintenance costs and prolong the delivery time. In different application occasions, the actual requirements for pixel out-of-control ratio can be quite different. Generally speaking, LED display screens are used for video playback, and the index requirement control within 1/104 is acceptable and can be achieved; If it is used for simple character information distribution, it is reasonable for the indicator to be controlled within 12/104.
Gray scale
The gray scale is also called the color scale or the gray scale, which refers to the brightness of the brightness. For digital display technology, grayscale is the determining factor for the number of colors displayed. In general, the higher the gray level, the richer the displayed colors, the finer the picture, and the more apt to show rich details.
The gray level mainly depends on the A/D conversion bit number of the system. Of course, the system's video processing chip, memory, and transmission system must provide support for the corresponding number of bits. At present, the domestic LED display mainly uses 8-bit processing system, which is 256 (28) gray level. A simple understanding is that there are 256 kinds of brightness changes from black to white. RGB three primary colors can be used to constitute 256 × 256 × 256 = 16777216 colors. That is commonly referred to as 16 Mega colors. The international brand display mainly uses a 10-bit processing system, that is 1024 gray levels, and RGB three primary colors can constitute 1.07 billion colors.
Although grayscale is the deciding factor in determining the number of colors, it does not mean that the larger the better, the better. Because the resolution of the human eye is limited, the increase in the number of processing bits in the system will involve changes in the video processing, storage, transmission, and scanning of the system. The cost will increase dramatically and the price/performance ratio will decrease. In general, 8-bit systems can be used for commercial or commercial products, and 10-bit systems can be used for broadcast products.
Brightness discrimination level
The brightness discrimination level refers to the brightness level of the image that the human eye can distinguish from the darkest to the whitest. As mentioned earlier, the gray scale of the display is very high, and can reach 256 or even 1024 levels. However, due to the limited sensitivity of the human eye to brightness, these gray levels cannot be completely recognized. In other words, it may be that many adjacent gray levels appear to be the same in human eyes. And the eye resolving power is different for each person. For the display screen, the level of human eye recognition is naturally as much as possible, because the displayed image is for people to see. The more brightness levels the human eye can discern, the greater the color space of the display, and the greater the potential for displaying rich colors. The brightness discrimination level can be tested with dedicated software. The general display can reach 20 or even better levels.
Grayscale nonlinear transformation
Gray-scale non-linear transformation refers to converting gray-scale data according to empirical data or some kind of mathematical non-linear relationship and then providing it to the display screen. Since the LED is a linear device, the nonlinear display characteristics of the conventional display are different. In order to enable the LED display effect to conform to the traditional data source without losing the gray level, a non-linear transformation of the gray scale data is generally performed at the later stage of the LED display system, and the number of transformed data bits will increase (guaranteed not to lose the gray scale. data). Now some domestic control system vendors called 4096 grayscale or 16384 grayscale or higher all refer to the grayscale space size after nonlinear transformation. 4096 is a non-linear transformation technique that uses 8-bit source to 12-bit space, and 16384 is a non-linear transformation technique that uses 8-bit to 16-bit. Nonlinear transformation by the 8-bit source, the conversion space is definitely larger than the 8-bit source. Usually at least 10 people. Like grayscale, this parameter is not as big as possible, and generally 12 bits can do enough transformation.
LED display common terms explained
1, LED brightness
Outdoor LED display - Shanghai Xingma - Chen Xiaoxiang The brightness of light-emitting diodes is generally expressed in terms of luminous intensity (Luminous Intensity), the unit is candela cd; 1000ucd (micro Candela) = 1 mcd (mille candela), 1000mcd = 1 cd. The light intensity of a single LED for indoor use is generally 500 ucd-50 mcd, while the light intensity of a single LED for outdoor use is generally 100 mcd-1000 mcd, or even more than 1000 mcd.
2, LED pixel module
The LEDs are arranged in a matrix or pen segment and are prefabricated into standard sized modules. Indoor display commonly used 8 * 8 pixel module, 8 word 7 segment digital module. Outdoor display pixel modules have 4*4, 8*8, 8*16 pixels and other specifications. The pixel module for outdoor display is composed of more than two LED tube bundles for each pixel, and it is also called a manifold bundle module.
3, Pixel and Pixel Diameter
Each LED light unit (point) in the LED display that can be individually controlled is called a pixel (or pixel). The pixel diameter ∮ refers to the diameter of each pixel in millimeters.
For indoor displays, a single LED is generally used, with a circular shape. Indoor display pixel diameter school common ∮3.0, ∮3.75, ∮5.0, ∮8.0, etc., of which ∮3.75 and ∮5.0 most.
In outdoor environments, in order to increase the brightness and increase the viewing distance, a pixel contains more than two cluster LEDs; since two or more cluster LEDs are not generally circular, the pixel diameter of a solid outdoor display is generally represented by the average spacing of two or two pixels. : â–¡10, â–¡11.5, â–¡16, â–¡22, â–¡25.
4, dot pitch, pixel density and information capacity
The pitch or dot pitch of the two or two pixels of the LED display; the number of pixels in a unit area is called pixel density; the amount of display content contained in a unit area is called information capacity. The essence of these three is to describe the same concept: the dot pitch reflects the pixel density from the distance between two pixels, and the dot pitch and pixel density are the physical properties of the display screen; the information capacity is the information carrying capacity of the pixel density. The unit of quantity.
The smaller the dot pitch, the higher the pixel density, the more information capacity, and the closer the suitable distance for viewing.
The larger the dot pitch, the lower the pixel density, the smaller the information capacity, and the longer the distance suitable for viewing.
5, resolution
The number of rows of LED display pixels is called the resolution of the LED display. Resolution is the total number of pixels in the display, which determines the information capacity of a display.
6, LED display (LED Panel)
The LED pixel module is assembled according to the actual needs of the size of the matrix, with a dedicated display drive circuit, DC power supply, software, frame and exterior decoration, which constitute a LED display.
7, grayscale
Grayscale refers to the degree of light and shade changes in a pixel's light. A gray color of a basic color generally has 8 to 1024 levels. For example, if the gray level of each primary color is 256, for a dual-color color screen, the display color is 256*256=64K, which is also known as a 256-color display.
8, double color
Most color LED display screens today are dual-color color screens, ie, there are two LED dies for each pixel: one is a red light die, and the other is a green light die. The pixel is red when the red light is on, green when the green light is on, and yellow when both red and green are on. Among them, red and green are called base colors.
9, full color
The combination of red and green bi-primaries plus the blue color forms three full-color colors. Since the technology for forming full-color blue tubes and pure green dies is now mature, the market basically uses full-color.
LED display technology advantages
(1) The use of imported LED high-quality die to produce full-color display: a large viewing angle, low power consumption, uniform color, thin screen thickness, light weight screen, low failure rate, easy maintenance and other advantages.
(2) Adoption of the PCTV card: This card is a multimedia display card with excellent performance, such as display, acquisition, and video capture. The card is accompanied by a Studio editing software. Studio is an award-winning software of Pinnacle Systems. It is compared with existing common common multimedia card
Outdoor LED display - Shanghai Xingma - Chen Xiaoxiang has the following advantages:
1 Enables users to create digital movies on their PC, capture video, edit and add stylized titles, transitions, and even their own music and digital video production narration.
2Studio allows users to choose to output video in the format of MPEG or AVI files and store it on a compact disc, or display on a Web site, or create video e-mail. As Studio can work with Pinnacle Systems' series of capture devices, Video capture has never been easier.
3Studio's application software is like a VCR from easy to good, better, best quality form, and how much video the computer can store. Studio automatically discovers and records scene changes, making editing a breeze
4 Using Studio for authoring is a fast and interactive process. With instant preview window you can preview the movie at any time during editing, ie what you see is what you get.
5 If you don't like the title or the effect, you can make a change and you can immediately see this change. Video editing has never been as fast and fun like this. It's free, personalized, and has background music, voice-overs, and other effects.
(3) Adopting the latest DVI interface technology: The DVI interface (Digital Visual Interface) is an industry standard for the interface between a PC and a digital flat panel display (including). As we all know, the computer is digital, that is, the information it processes is all digital. , But the most widely used CRT displays (such as TVs) are analog ones. Therefore, before the computer processed data is sent to the display, a digital/analog conversion (D/A) must be performed. Caused the loss of information and the defects of the display effect. LCDs, PDPs, HDTVs and other new generation displays are themselves digital. In the traditional way, the output of the computer graphics card (analogue) has to undergo analog-to-digital conversion (A/. D) can be sent to the display, which in turn causes new losses and troubles. Using the DVI interface, the developed LED display system can directly access the DVI interface of the PC, no special graphics such as a Galaxy card, or special The acquisition card is not limited by the PC, because there is no D/A and MD conversion process, and the loss of image details is avoided, thus ensuring perfect reproduction of the computer image in the display screen. At the same time, since DVI is an industrial standard, although the bandwidth high 83MHZ can also work well. DVI now supports all display modes from VGA (640x480) to HDTV (1920x1080) and QXGA (2048x1536). In addition to the DVI interface, LED display systems have been developed. , On the basis of stable and reliable display data, many important functions can be integrated together
For example: 1 no data loss, 2 is not limited by the PC, 3 convenient upgrade, the general display card memory is 8M, and the card memory is 128-256M, 4 window position and size adjustment; 5 frame rate up to 60HZ; 6 non Linear adjustment output, more suitable for human eyes; 7100 screen brightness control; 8 constant current drive; 9 unit board red, green, and blue light brightness are adjustable, eliminating mosaic.
(4) Adopt indoor full-color system: In addition to the display data distribution task, the feature of the chip is to convert the received 8-bit (8-bit) display data into 12-bit PWM output pulses, so that the display screen can achieve 4096 ( 12bit) level gray control, to ensure the realization of non-linear 256-level visual grayscale, to achieve full-color visual effects, can fundamentally solve the digital display system due to excessive data transmission system complexity caused by the system.
Has the following characteristics:
1 Simplicity Since the most complex data conversion part of the system is implemented in the form of internal logic of the chip, the system becomes very simple.
2 The ease of maintenance and simplicity are directly related to the ease of maintenance of the system. Due to the elimination of complicated control parts, system maintenance becomes a job that can be accomplished by junior technicians, which reduces overall maintenance costs. , And improve user satisfaction.
3 The simplicity of the high-reliability system control system brings about the high reliability of the system. This is mainly because the integrated chip technology has several times more stability than the discrete device technology.
4 cost-effective system with the most reliable performance to achieve the control of the screen color 4096 gray level, image display realistic, natural, and achieve the same display control effect.
5 Unitized, structured design is consistent with the current development direction of the industry. The large-scale display system adopts unitized design on the screen structure, and the system connection is intuitive and simple, which not only ensures that the size of the display screen can be spliced ​​and adjusted according to needs. Moreover, the installation, debugging and maintenance of the system become extremely simple, thereby minimizing the invisible failure rate of the display screen system.
6 Industrial Reliability Design system adopts unitized design, which replaces a large number of discrete devices in the traditional design, and greatly improves the reliability and stability of the system.
7 A full set of program components The system consists of data sources, transmission equipment, data processing, data distribution and software management tools, making the construction of LED displays simple and standardized. This technology has been continuously developed and improved in the actual application process and has become a set of The most mature, stable, easy to implement system solutions.
8 Equivalent CRT display effect The most important performance indicator of LED display is the gray level or brightness level achieved for each primary color (red, green, blue). The current international display standard requires that each primary color reach the visual 256 level. Grayscale. The dedicated grayscale control chip's built-in processing logic can output 4096 levels of grayscale, and select the 256-level grayscale output that fits the CRT display to make the overall image effect clearer, more realistic and full of appeal.
9 High resolution and high refresh rate In addition to gray levels, the other two performance indicators of the display are its resolution and refresh rate. Due to the characteristics and requirements of the LED display itself, traditional solutions often have to lose One or both of the criteria is used as a cost to increase the cost of the other indicator. Since the chip's data output per second per pin reaches 1 trillion, far more than the data output capability of the traditional solution, the problem is fundamentally solved. Resolved. The full-color system can simultaneously support 1024×768 screen resolution and screen refresh rate of up to 300Hz, far exceeding the performance indicators of traditional solutions, so that the display screen is stable, no flicker, no smear.
(5)Using constant current drive: The circuit technology is mature and reliable, has been widely used in full-color display, high cost performance, is currently used by many companies constant current driver chip, better solve the LED tube voltage drop discrete Sexual defects and good performance, eliminate mosaics.
(6) Optical fiber transmission, unattenuated optical fiber transmission technology:
1 Optical fiber transmission frequency bandwidth, communication capacity is large. The available bandwidth of optical fiber is about 1.25G, frequency bandwidth, and the scanning frequency and refresh frequency are increased. The full-color LED screen refresh frequency designed by our company is ≥200Hz/s.
2 Optical fiber transmission loss is low, and the relay distance is long. The maximum relay distance is up to 15,000 meters, which improves the reliability and stability.
3 Fiber-optic transmission anti-electromagnetic interference. Optical fiber is an insulator material, it is not subject to natural lightning interference, ionospheric changes and sunspot activity interference, and is not subject to electrical railway feeders and high-voltage equipment and other industrial electrical interference.
4 Optical fiber diameter is thin, light and soft. The core diameter of the optical fiber is very small, about 0.1mm, it is only one percent of a single coaxial cable; the diameter of the optical cable is also very small, the cross-sectional diameter of the 8-core optical cable About 10mm, while the standard coaxial cable is 47mm. The use of optical fiber characteristics, so that the transmission system occupies a small space, so that the construction of wiring is quick and easy.
In addition to the outstanding advantages of fiber optic transmission, it also has the advantages of strong corrosion resistance, anti-nuclear radiation, and low energy consumption.
How to evaluate the quality of LED screens
The quality of a full-color display can be mainly signed from the following aspects:
Flatness
The surface flatness of the display should be within ±1mm to ensure that the display image does not distort, and local raised or recessed leads to a blind angle in the viewing angle of the display. The flatness is mainly determined by the production process.
2. Brightness and viewing angle
Indoor full-color screen brightness to 800cd/m2 or more, outdoor full-color screen brightness to 1500 cd/m2 or more, in order to ensure the normal operation of the display, otherwise it will be too low to see the brightness of the displayed image. The brightness is mainly determined by the quality of the LED die.
The size of the viewing angle directly determines the number of display audiences, so the bigger the better. The size of the viewing angle is mainly determined by the packaging method of the die.
3. White balance effect
The white balance effect is one of the most important indicators of the display. In color science, when the ratio of the three primary colors of red, green, and blue is 1:4.6:0.16, pure white is displayed. If the actual ratio is slightly deviated, there will be a white balance deviation. Generally, it should be noted whether the white color is bluish or yellowish. Green phenomenon. The quality of white balance is mainly determined by the display's control system, and the die also has an impact on the reproducibility of color.
4. Reducibility of color
The reproducibility of color refers to the reproducibility of the display screen to color, and the color of the display screen must be highly consistent with the color of the playback source, so as to ensure the realism of the image.
5. Is there a mosaic or dead point phenomenon?
Mosaic refers to the light or dark four squares appearing on the display screen. This is due to the necrosis of the module. The main reason for this is that the quality of the connectors used in the display is not critical.
The dead point refers to the single point of the light or darkness that appears on the display screen. The number of dead spots is mainly determined by the quality of the die.
6. There is no color block
The color patches refer to the obvious color difference between adjacent modules. The color transition is based on the module. The color patching phenomenon is mainly caused by poor control system, low gray level, and low scanning frequency.
LED display FAQ
LED pays great attention to anti-static measures. The following are some explanations for static electricity and anti-static electricity:
1. Source of static electricity: The source of static electricity that affects the circuit is mainly the human body, plastic products and related equipment and equipment, among which the static power supply from the use environment has the following items:
Outdoor LED Display - Shanghai Xingma Electronics Co., Ltd. - Chen Xiaoxiang 1) Object, Material
2) Floor, work tables and chairs
3) Work clothes, packaging containers
4) Painted or waxed surfaces, organic and fiberglass materials.
5) Cement floors, painted or waxed floors, plastic tiles or floor leather.
6) Chemical fiber work clothes, non-conductive work shoes, and clean cotton work clothes.
7) Plastics, boxes, boxes, bags, trays, foam liners.
2. Electrostatic discharge failure modes: sudden failure and potential failure.
The static failure of more than 90 in the use environment is a potential failure, which manifests itself in the weakening of the circuit's resistance to electrical overstress and shortened service life.
3. Anti-static measures:
1) Training on the use of electrostatic sensitive circuit personnel for electrostatic knowledge and related technologies.
2) Establish an anti-static working area in which static-discharged floors, anti-static worktables, anti-static grounding leads and anti-static devices are to be used, and the relative humidity should be controlled to 40 or more.
3) The harm caused by static electricity to the electronic equipment may be released anywhere from the manufacturer to the field equipment. The hazard is caused by insufficient, effective training and equipment manipulation failure. LEDs are devices that are sensitive to static electricity. INGAN wafers are generally considered "first place" susceptible to interference. And ALINGAP LEDS SHI "second place" or better.
4) Devices with damaged ESD can show dimming, blurring, extinguishing, short or low VF or VR. Devices that are damaged by ESD should not be confused with electronic overloads, such as: faulty current design or driving, chip mounting, wire shield grounding or encapsulation, or common ambient induced pressure.
5) ESD security and control procedures: Most ESD and EMD companies have very similar ESDs and have successfully implemented ESD control, manipulation, and main programs for all devices. These programs are instruments that have been used to detect quality effects since ESD. The ISO-9000 certification also lists him as a normal control program.

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