LED displays have been widely used in business today, but there are some common knowledge that you may not know.For example, what is the gray level and brightness of LED display, and what is the relationship between them?The gray level of LED display can also be called the brightness of LED display.Gray level, also known as intermediate tone, is mainly used to transmit pictures, there are 16 levels, 32 levels, 64 levels of three ways, it uses the matrix processing method will file pixel processing into 16, 32, 64 levels, so that the transmission of pictures clearer.Whether it is monochrome, two-color, outdoor full-color LED display, to display images or animations, it is necessary to adjust the gray level of each LED that constitutes the pixel, and the fine degree of adjustment is what we usually call the gray level.
There are two ways to control the gray level of LED display: one is to change the current flowing through, the other is pulse width modulation.1. Change the current flowing through the LED.General LED tube allows continuous working current of about 20 mA, except the red LED saturation phenomenon, other LED gray level is basically proportional to the current through;Another method is to use the visual inertia of human eyes, using pulse width modulation method to achieve gray control, that is, periodically change the width of the light pulse, as long as the cycle of repeated lighting is short enough, the human eyes are not felt in the light pixel jitter.
Since PWM is more suitable for digital control, almost all LED displays use PWM to control the grayscale level when microcomputer is widely used to provide LED display content.
The control system of LED is usually composed of three parts: main control box, scanning board and display control device.The master control box acquires a screen of pixels' color-colored brightness data from the computer's display card, and then reallocates it to several scanning boards. Each scanning board is responsible for controlling several rows (columns) on the LED display screen, and the display control signal of the LED on each row (column) is transmitted in a serial way.At present, there are two ways of serial transmission of display control signals.
One is to control the gray level of each pixel point centrally on the scanning board. The scanning board decomposes the gray level of each line of pixels from the control box, and then transits the LED opening signal of each line to the corresponding LED in a serial way in the form of pulses to control whether it is lit or not.This method uses fewer devices, but the serial transmission of data is large, because in a cycle of repeated lighting, each pixel needs 16 pulses under the 16 level gray level, 256 pulses under the 256 level gray level, due to the device operating frequency limit, generally can only make the LED display 16 level gray level.
Two, one is pulse width modulation.The contents transmitted serially by the scanning board are 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 cycle of repeated lighting, each pixel only needs 4 pulses at 16 gray levels and 8 pulses at 256 gray levels, which greatly reduces the serial transmission frequency.With this method of decentralized control of LED gray level, 256 levels of gray level can be easily controlled.
LED display gray and brightness is one of the important parameters of the product, in order to better use LED display, it is necessary for us to understand the relationship between LED display gray and brightness.