LED Display Grayscale and Brightness

LED display grayscale and brightness is one of the important parameters of the product, in order to better use LED display, we need to understand the relationship between the LED display grayscale and brightness

The gray level of the LED display can also be called the brightness of the LED display. Gray scale is also called midtone, which is mainly used to transfer pictures. There are 16 levels, 32 levels and 64 levels respectively. It adopts matrix processing method to process the pixels of files into levels of 16, 32, and 64 levels. The picture is clearer. Whether it is a single-color, two-color, full-color LED display, to display an image or an animation requires adjusting the luminance of each LED constituting the pixel, and the fineness of its adjustment is what we commonly call gray scale.

There are two ways to control the gray level of the LED display: one is to change the current flowing, and the other is pulse width modulation. 1. Change the current flowing through the LED. The general LED tube allows a continuous working current of about 20 mA. In addition to the saturation of the red LED, the gray levels of other LEDs are basically proportional to the current flowing through; the other method is to use the visual inertia of the human eye, with a pulse width The modulation method to achieve gray control, that is, periodically change the width of the light pulse, as long as the period of this repeated lighting is short enough, the human eye can not feel the jitter of the light-emitting pixel.

Since pulse width modulation is more suitable for digital control, today, microcomputers are generally used to provide LED display content. Almost all LED displays use pulse width modulation to control gray levels.

LED control system usually consists of three main parts: main control box, scan board, and display and control device. 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 display screen, and each row (column) The LED display control signal is transmitted in a serial manner. Currently, there are two ways to serially transmit and display control signals.

One is a method for centrally controlling the gradation of each pixel on the scanning board. The scanning board decomposes the gradation values of the pixels of each row from the control box, and then serially turns on the ON signals of the respective rows of LEDs in the form of pulses. Transfer to the corresponding LED and control it to light up. 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 the limitation of device operating frequency, generally can only make the LED display 16 grayscale.

Second, one is 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.

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