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LED display grayscale and brightness relationship
LED gray scale can also be called LED brightness. Gray level is also called half-tone. It is mainly used to transfer pictures. There are 16 levels, 32 levels and 64 levels. It uses matrix processing to process the pixels of the file into 16, 32, and 64 levels. The level makes the transmitted picture clearer. Whether it is a monochrome, two-color, LED full-color display, to display an image or animation, it is necessary to adjust the illuminance of each LED constituting the pixel, and the degree of fineness of the adjustment is what we usually call the gradation.
There are two ways to control the gray level of the LED: one is to change the current flowing, and the other is pulse width modulation. 1. Change the current flowing through the LED. Generally, the LED tube allows the continuous working current to be around 20 mA. In addition to the saturation of the red LED, the other LED gray scale is basically proportional to the current flowing through; the other method is to use the visual inertia of the human eye, using the pulse width Modulation method to achieve gray control, that is, periodically change the optical pulse width (ie, duty cycle), as long as the period of repeated lighting is short enough (ie, the refresh frequency is high enough), the human eye does not feel that the luminescent pixel is shake. Since pulse width modulation is more suitable for digital control, in today's widespread use of microcomputers to provide LED display content, almost all LED displays use pulse width modulation to control gray levels. The LED control system usually consists of three main parts: the main control box, the scanning board and the display control unit.
The main control box obtains the brightness data of each layer of pixels from the display card of the computer, and then re-allocates the data to a plurality of scanning boards, each of which is responsible for controlling several rows (columns) on the LED screen, and each row (column) The display control signals of the upper LEDs are transmitted in a serial manner.
There are currently two ways to serially transmit display control signals:
1. One is to control the gray level of each pixel point on the scanning board, and the scanning board decomposes the gray value of each row of pixels from the control box (ie, pulse width modulation), and then turns the turn-on signal of each row of LEDs into a pulse form. (Lighted to 1, not lit to 0) Serially transmitted to the corresponding LED by line to control whether it is lit. This method uses fewer devices, but the amount of data transmitted serially is larger because each pixel requires 16 pulses at 16 levels of gray during a repeated lighting period, requiring 256 levels of gray. 256 pulses, due to the device operating frequency limit, generally only enable the LED screen to achieve 16 gray levels.
2. One is pulse width modulation. The serial transmission of the scan 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. Thus, in a period of repeated lighting, each pixel point requires only 4 pulses in 16-level gray scale, and only 8 pulses in 256-level gray scale, which greatly reduces the serial transmission frequency. With this method of controlling the gradation of the LED, it is convenient to implement 256-level gradation control.