Mobile / WhatsApp:+86-13553831871 email@example.com
May 31,2021| LED Knowledge
LED gray scale can also be referred to as LED brightness.
Gray level is also called half-tone. It is mainly used to transmit pictures. There are three methods of 16, 32, and 64 levels respectively. It uses matrix processing to process the pixels of the file into 16, 32, and 64 levels. Layers to make the transmitted pictures clearer. Regardless of whether it is a single-color, two-color, or full-color LED display, to display an image or animation, it is necessary to adjust the luminous gray level of each LED constituting the pixel. The fineness of the adjustment is what we usually call the gray level.
There are two ways to control the grayscale of LEDs: one is to change the current flowing through, and the other is pulse width modulation. 1. Change the current flowing through the LED. Generally, the continuous working current of LED tubes is about 20 mA. Except for the saturation of red LEDs, the gray scale of other LEDs is basically proportional to the current flowing; the other method is to use the visual inertia of the human eye and use the pulse width.
The modulation method is used to achieve gray scale control, that is, the light pulse width (that is, the duty cycle) is periodically changed. As long as the period of repeated lighting is short enough (that is, the refresh frequency is high enough), the human eye will not feel that the light-emitting pixels are in Jitter.
Because pulse width modulation is more suitable for digital control, today when microcomputers are commonly used to provide LED display content, almost all LED display 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 control device.
The main control box obtains the brightness data of each screen pixel 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 and control signal of the upper LED is transmitted in a serial manner.
There are currently two ways to serially transmit display control signals:
1. One is to centrally control the grayscale of each pixel on the scanning board
The scanning board decomposes the gray value of each row of pixels from the control box (ie pulse width modulation), and then the turn-on signal of each row of LEDs is pulsed (lighted as 1 and unlit as 0) in a serial manner by row It is transmitted to the corresponding LED to control whether it is lit.
This method uses fewer devices, but the amount of serially transmitted data is larger, because in a repeated lighting cycle, each pixel needs 16 pulses in 16-level grayscale, and requires 256-level grayscale. 256 pulses, due to the limitation of the device's operating frequency, generally the LED screen can only achieve 16 levels of gray.
2. One is pulse width modulation
The content of the serial transmission of the scanning board 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 needs only 4 pulses in 16-level grayscale and only 8 pulses in 256-level grayscale, which greatly reduces the serial transmission frequency. With this method of distributed control of LED grayscale, 256-level grayscale control can be easily achieved.