LED full-color display grayscale importance

The gray scale in the LED display industry can also be called LED brightness. Gray scale is also called midtone, which is mainly used to transfer images, pictures, video screens, there are 16 levels, 32 levels, 64 levels in three ways, it uses matrix processing to process the pixels of the file into 16, 32, 64 level To make the transmitted picture clearer. Whether it is a full-color screen or a dual-color screen, to display an image or an animation, it is necessary to adjust the gradation of each LED constituting the pixel. The fineness of the adjustment is what we commonly call gray scale.

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

There are currently two ways of serially transmitting the display control signal:

First, pulse width modulation. The content of 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. In this way, in a repetitively lit period, each pixel point needs only 4 pulses under 16 gray levels, and only 8 pulses under 256 gray levels, which greatly reduces the serial transmission frequency. With this method of decentralized control of the LED gray level, 256-level grayscale control can be easily achieved.

Secondly, the scanning board centrally controls the gray level of each pixel. The scanning board decomposes the gray value of each row of pixels from the control box (ie, pulse width modulation), and then turns each row of LED turn-on signals into pulses (lights up). 1, not lit 0) Transfer to the corresponding LED by serial mode and control whether it is lit. This method uses fewer devices, but the amount of data transferred in series is larger because each pixel requires 16 pulses at 16 levels of gray in a repetitively lit period, requiring 256 levels of gray. 256 pulses, due to device operating frequency limitations, generally only enable the LED screen to achieve 16 shades of gray.

There are two ways to control the LED grayscale:

First, change the flow of electricity.

Second, pulse width modulation:

1) Change the current flowing through the LED. The general LED tube allows the continuous working current to be around 20 milliamperes. In addition to the saturation phenomenon of the red LED, the gray scale of other LEDs is basically proportional to the current flowing through;

2) Utilize the visual inertia of the human eye to achieve grayscale control using a pulse width modulation method, that is, to periodically change the optical pulse width (ie, duty cycle) as long as the period of this repeated lighting is sufficiently short (ie, the refresh rate is high enough ), the human eye does not feel the jitter of the glowing pixels. Because pulse width modulation is more suitable for digital control.

Therefore, in the general use of microcomputers to provide LED display content today, almost all LED screens use pulse width modulation to control the gray level. LED control system usually consists of three main parts: main control box, scan board and display and control device.