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What Is The Relationship Between The Grayscale And Brightness Of LED Display?
Jun 27, 2018

LED grayscale can also be called LED brightness. Gray scale is also called Half-tone, which is mainly used to transfer pictures. There are 16 levels, 32 levels and 64 levels respectively. It adopts matrix processing to process the pixels of files to level 16, 32 and 64. Levels make the transmitted images clearer. Whether it is a single-color, two-color, or three-color screen, to display an image or an animation requires adjustment of the luminance of each LED constituting the pixel. The degree of fineness of adjustment is what we commonly call gray scale.

 

There are two ways to control the gray level of the LED: one is to change the current that flows, and the other is pulse width modulation. 1. Change the current flowing through the LED. The general LED tube allows the continuous working current to be around 20 mA. Besides the saturation of the red LED, the gray scale of other LEDs is basically proportional to the current flowing through; another method is to use the visual inertia of the human eye, with pulse width The modulation method to achieve gray control, that is, periodically change the width of the light pulse (ie, the duty cycle), as long as the period of this repeated lighting is short enough (ie, the refresh frequency is high enough), the human eye cannot feel the light-emitting pixels. Jitter. Because pulse width modulation is more suitable for digital control, today, microcomputers are generally used to provide LED display content. 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.

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:

One is that the scanning board controls the gray level of each pixel in a centralized manner, the scanning board decomposes the gray value of each row of pixels from the control box (ie, pulse width modulation), and then the LED of each row is turned on in the form of a pulse. (Lights up to 1, does not light up to 0) Lines are transmitted serially to the corresponding LED, controlling 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.

 

2. 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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