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Brief Analysis the Importance of LED Display Gray Level

Tag: LED display board price, how to make a LED display board, LED display gray level

Gray scale also called LED brightness in LED display industry. We also named it neutral color which is mainly use for transmitting images, pictures and videos, respectively in grade level 16, 32 and 64 three ways. It uses a matrix approach processing the file into level 16, 32 and 64 to make a clearer picture. Whether it's a full color screen or dual-color screen, they both need to adjust the composition of each LED light gray pixel. The level of the adjustment is the grayscale.

 

high-gray-level-indoor-p5-led-display-screen

 

The main-control box get screen pixel brightness data from computer video card. And then reassign the number of scan panels to make each scan board took control of few row (column) on LED display board. The signal use SPI to transmit.


At present, there are two serial transmission of control signals display mode:

1.Pulse-duration modulation. The transmission content of scanning board serial is not a switching signal for each LED but an 8-bit binary gray scale value. Each LED has its own pulse width modulator to control the lighting time. Thus, If you repeated lighting a LED, each pixel in the 16 gradation need only four pulses and 8 pulses at 256 gray scale, which greatly reducing the frequency of the serial transmission. This kind of distributed control method of LED gray could help to achieve 256 gray scales easier.

 

2. Centralized control each pixel grayscale on scan panel. Scan board decomposed each row of pixel grayscale value comes from control box (i.e., pulse width modulation), and then open each row of LED signal pulses ( lit for 1 , off = 0) by using serial mode transmission to the corresponding LEDs to control the light. This method uses fewer components, but the larger the amount of data serial transmission. Because in a repeating lighting cycle, each pixel needs at 16 gray 16 pulse, 256 pulses at 256 gray scale. Owing to the device operating frequency limit, generally the LED display board only achieve 16 gray levels.

 

AIPAS_LED_parking_sign


There are two ways to control LED gray level:

 

1. Changing the current flowing.

 

2. Pulse-duration modulation.

a. Changing the current flowing through the LED. Usually the LED allows continuous current of about 20 mA. Besides, red LEDs have saturation phenomenon, the grayscale of other LEDs like green and blue lights are in proportion to the current flowing.

b. Using human visual inertia and pulse width modulation method to achieve gray control, that is periodically changing the light pulse width (i.e. duty cycle). As long as the repeated light cycle time is short enough (i.e., the refresh rate is high enough), then human eyes are not be able to feel the light-emitting pixels in jitter. By the way, pulse width modulation is more suitable for digital control.

 

That is why almost all LED display board are using pulse width modulation to control the gray level.

 

High gray scale LED display screen


 

PS: LED control system are generally consists of main control box, scan board and display control devices.

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