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A brief analysis of the importance of "grayscale" in LED display screens
Sep 26, 2023 View : 1323

What is called grayscale in the LED display industry can also be called LED brightness. Gray scale, also called midtones, is mainly used to transmit images, pictures, and videos. There are three methods: 16 levels, 32 levels, and 64 levels. It uses matrix processing to process the pixels of the file into 16, 32, and 64 levels. , making the transmitted pictures clearer. Whether it is a full-color screen or a two-color screen, to display images or animations, it is necessary to adjust the grayscale of each LED that constitutes the pixel. The fineness of the adjustment is what we usually call the grayscale.

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

There are currently two methods of serially transmitting display control signals:

1. Pulse width modulation. The content transmitted serially by the scanning board is not the switching 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 repeated lighting cycle, each pixel only needs 4 pulses at 16 levels of gray and only 8 pulses at 256 levels of gray, which greatly reduces the serial transmission frequency. This method of decentralized control of LED grayscale can easily achieve 256-level grayscale control.

2. The scanning board centrally controls the grayscale of each pixel point. The scanning board decomposes the grayscale values of each row of pixels from the control box (i.e., pulse width modulation), and then converts the turn-on signal of each row of LEDs in the form of pulses (lighting up). is 1, not lit is 0) is serially transmitted to the corresponding LED in rows to control whether it lights up. This method uses fewer devices, but the amount of data transmitted serially is larger, because in a repeated lighting cycle, each pixel requires 16 pulses under 16 levels of gray and 256 levels of gray. 256 pulses, due to device operating frequency limitations, generally can only make the LED screen achieve 16 levels of grayscale.

There are two ways to control LED grayscale:

1. Change the current flowing through it.

2. Pulse width modulation:

1) Change the current flowing through the LED. Generally, the allowed continuous operating current of LED tubes is about 20 mA. Except for the saturation phenomenon of red LEDs, the gray scale of other LEDs is basically proportional to the flowing current;

2) Taking advantage of the visual inertia of the human eye, the pulse width modulation method is used to achieve grayscale control, that is, the light pulse width (i.e., duty cycle) is periodically changed, as long as the repeated lighting cycle is short enough (i.e., the refresh frequency is high enough ), the human eye cannot detect the shaking of the luminous pixels. Since pulse width modulation is more suitable for digital control.

Therefore, today, when microcomputers are commonly used to provide LED display content, almost all LED screens use pulse width modulation to control gray levels. The LED control system usually consists of three parts: the main control box, the scanning board and the display and control device.



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