Important parameters of the LED display screen: brightness and gray level
The led display has been used everywhere in various businesses today, but there is some common sense you may not know. For example, what is the gray level and brightness of the LED display, and what is the relationship between them?
The gray level of the LED display can also be called the brightness. Gray level, also known as intermediate tone, is mainly used for transmitting pictures, with 16 levels, 32 levels, and 64 levels respectively. It uses matrix processing to deal the pixels of the image into 16, 32, and 64 levels to make the transmitted pictures clearer. Whether it is a single color, dual color or full-color LED display, it is necessary to adjust the gray level of each LED luminance. The fine degree of adjustment is commonly referred to as the gray level.
There are 2 ways to control the gray level of LED display screen:
- General LED tube allows continuous working currently in about 20 mA, except for the red LED saturation phenomenon, other LED gray level is basically proportional to the current flowing.
- Another method is to make use of the visual inertia of human eyes, and use the pulse width modulation method to realize gray level control, that is, periodically changing the width of the light pulse. As long as the repeated lighting period is short enough, human eyes can not feel the flickering pixels.
Because pulse width modulation is more suitable for digital signage control, almost all LED displays use it to control the gray level.
The LED control system is usually composed of the main control box, scanning board, and display control device. The main control box obtains the color brightness data of the screen pixels from the computer display card and then redistributes it to a number of scanning boards, each of which is responsible for controlling a number of rows (columns) on the LED display screen, and the LED display control signals on each row (column) are transmitted in a serial manner. At present, there are two methods of serial transmission of display control signals.
- One is to centrally control the gray level of each pixel point on the scanning board. The scanning board will decompose the gray level value of each row of pixels from the control box, and then transmit the opening signal of each row of LED to the corresponding LED in the form of a pulse in a serial way to control whether it is lit. This method uses fewer devices, but the amount of serial data transmission is large, because in a repeated lighting cycle, each pixel needs 16 pulses at 16 levels of gray level, and 256 pulses at 256 levels of gray level. Due to the limitation of device operating frequency, the LED display can only achieve 16 levels of gray level in general.
- The other is pulse width modulation. The serial transmission content 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, each pixel needs only 4 pulses at 16 levels of gray level and 8 pulses at 256 levels of gray level in a repeated lighting cycle, which greatly reduces the serial transmission frequency. With this method of decentralized control of LED gray levels, 256 levels of gray level control can be easily realized.
LED display gray and brightness is one of the important parameters of the product. In order to better use LED display screens, we need to understand the relationship between LED screen gray and brightness.