Gray Scale Explanation of Led Large Screen

November 07, 2022

With the development and application of indoor LED display, it can be seen that LED display is more and more widely used in command center, monitoring center and even studio. However, from the overall performance of the LED display system, can these displays meet the needs of users? Are the images displayed on these LED displays consistent with human vision? Can these LED displays withstand different camera shutter angles? These are the issues that need to be considered for LED displays. However, gray scale is the key to improve the low brightness display effect of LED displays. At present, consumers have higher and higher requirements for the image quality of the display screen, and it is more and more important for LED display screen to achieve the effect of “low brightness, high gray”. So I will make a specific analysis from the perspective of the gray level that affects the LED display effect.

  1. What is gray scale?
  2. What is the impact of grayscale on the screen?
  3. There are two methods to control the gray level of led display.

1.What is gray scale?

The gray level of LED display can also be called LED brightness. The gray level of LED display refers to the brightness level that can be distinguished from the darkest to the brightest in the same brightness level of LED display. In fact, the gray level can also be called halftone, which is used to transfer image data to the control card. The original gray level of LED display can be 16, 32, 64. With the progress of technology, 256 is currently used by mainstream manufacturers. The gray level of LED display screen is processed into 16, 32, 64 and 256 levels of file pixels through matrix processing, so that the transmitted image is clearer. Whether it is monochrome, two-color or full-color screen, to display images or animation, it is necessary to adjust the gray level of each LED that constitutes the source pixel of the material. The fineness of adjustment is what we usually call the gray level.

Here is a list to make you clearer. For example, if the pure red is 255 and the brightest red is 0, there are 256 colors. If you want to display images with the same material, do you have to use 256 color transmission technology. For example, if the color value of a frame in the video is red 69, and the LED display screen has only 64 gray levels, the color in the color video cannot be displayed normally. The final effect can be imagined, and it is self-evident that the picture is meticulous and exquisite.

Tip: At present, the maximum gray level of LED display screen is 256, also known as 65536, which cannot be said wrong, because each lamp bead of full-color LED display screen is composed of RGB three colors, one color has 256 gray levels, and the total number is 65536.2.

LED Display
Application case

2.What is the impact of grayscale on the screen?

The gray level of LED electronic large screen refers to the change of different color levels between peak dark color and peak bright color. Generally, the gray scale of traditional high-definition LED display is between 14bit and 16bit, with more than 16384 color levels, which can show more detailed changes of image colors. If the gray level is not enough, the color level will be insufficient or the gradient color level will not be smooth enough, and the color of the played image will not be fully displayed. To a large extent, the display effect of the LED display screen is reduced. If the image taken with the 1/500s shutter has obvious color blocks, it indicates that the gray level of the screen is low. If you use a higher shutter speed, such as 1/1000s or 1/2000s, you will see more obvious color patches, which will seriously affect the overall picture aesthetics.

3.There are two methods to control the gray level of led display.

One is to change the current flowing, and the other is pulse width modulation.

1. Change the current flowing through the LED. Generally, LED tubes allow a continuous working current of about 20 mA. Except for the saturation of red LEDs, the gray scale of other LEDs is basically proportional to the current flowing through them;

Application case

2. The other method is to use the visual inertia of the human eye to realize the gray control by using the pulse width modulation method, that is, periodically change the light pulse width (i.e. duty cycle). As long as the cycle of repeated lighting is short enough (i.e. the refresh rate is high enough), the human eye cannot feel the light emitting pixels shaking. Because PWM is more suitable for digital control, almost all LED screens use PWM to control the gray level today when microcomputers are widely used to provide LED display content. The LED control system is usually composed of the main control box, scanning board and display and control device.

The main control box obtains the brightness data of each color of a screen pixel from the display card of the computer, and then redistributes it to several scanning boards. Each scanning board is responsible for controlling several rows (columns) on the LED display screen, and the display and control signals of LEDs on each row (column) are transmitted in a serial manner.

At present, there are two methods of serial transmission of display control signals:

1. One is to centrally control the gray level of each pixel point on the scanning board. The scanning board decomposes the gray level value of each row of pixels from the control box (i.e., pulse width modulation), and then transmits the opening signal of each row of LED to the corresponding LED in the form of pulse (1 if it is lit, 0 if it is not lit) in line serial mode to control whether it is lit. This method uses fewer devices, but the amount of data transmitted serially is large. Because in a cycle of repeated lighting, each pixel needs 16 pulses at 16 levels of gray and 256 pulses at 256 levels of gray. Due to the device’s operating frequency limitation, LED screens can only achieve 16 levels of gray.

2.One is pulse width modulation. The scanning board serial transmission content is not the switch signal of each LED, but an 8-bit binary gray value. Each LED has its own pulse width modulator to control the lighting time. In this way, in a cycle of repeated lighting, each pixel only needs 4 pulses at 16 levels of gray and 8 pulses at 256 levels of gray, greatly reducing the serial transmission frequency. With this method of decentralized control of LED grayscale, 256 level grayscale control can be easily realized.

There are many series of screens in the MPLED room that have reached the gray level of 16bit, such as ST Pro, WS, WA, etc., which can perfectly display the original color of pictures and videos. In the case of high-speed photography, the above color blocks can not appear. The screens are made of high-grade raw materials, which are high-end products in the industry. We provide a variety of pixel spacing size options, as well as a variety of project solutions. If you need to purchase a batch of small pitch screens recently, please contact us, the leader of led one-stop service–MPLED.

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