Due to the emitting light colors of LED display
and luminous efficiency associated with materials and technology of the production of LED display, there is widespread use of red, green, blue three kinds.
Due to the low voltage LED display work (
Brightness, can take the initiative to light and to a certain extent, brightness and in voltage (
Adjust, itself and impact resistance, resistance to vibration, long life,
, so in the large display devices, there is no other way of display and LED display display mode.
The red and green LED display together as a production LED display is called double color screen or a pixel color screen.
The red, green, blue three kinds of LED display tube together as a pixel or full color LED display is called three color screen screen.
Production of indoor LED display screen pixel size is generally 2 -
10 mm, often use several can produce different colors of LED display tube core is encapsulated into a whole, the pixel size of outdoor LED display screen for 12 - more
26 mm, each pixel is made up of several kinds of single color LED display, common product according to pixel tube, double color pixel tube usually consists of three red 2 green, three color pixels of tube in 2 red 1 green and 1 blue.
Whatever made monochrome, double color or 3 color LED display screen, the need to display the image pixels of each luminous brightness of the LED display must be able to adjust, the adjustment is the fine degree of LED display gray-scale of the order.
Gray-scale order is higher, such as display image is more delicate, more colorful, the corresponding display control system are more complex.
General order 256 gray-scale image, color transition is very soft, and 16 order gray color image, color transition boundary obviously.
All color LED display screen, therefore, the current requirements of more than 256 order gray-scale.
There are two ways to control the LED display brightness.
Current through the LED display is a kind of change, general LED display tube allows continuous working current is controlled in 20 ma, in addition to the red LED display have saturation phenomenon, other LED display brightness basically proportional to the flow of electric current;
Another method is to use human eye visual inertia, using pulse width modulation method to realize gray-scale control, light pulse width (cyclical change
The duty ratio)
Cycle is short enough, as long as the repeated light (
The refresh rate is high enough)
, the human eye is feeling less than glowing pixels in jitter.
Due to pulse width modulation is more suitable for digital control, so widely used in computers to provide LED display display content today, almost all of the LED display screen is use the order such as pulse width modulation to control the gray scale.
LED display control system generally consists of main control box, scan and display control device is composed of three parts.
Main box from computer display card to get a screen pixel brightness of of all kinds of data, and then reassigned to a number of scanning board, to scan each responsible for a number of LED display screen control line (
While each line (
On the LED display screen display control signal is transmitted in serial mode.
There are two types of serial transmission display control signal way: one kind is centralized control on scanning board each pixel gray, scanning board will come from the control box of the brightness values of all pixels decomposition (
The pulse width modulation)
And then all the opening of the LED display signal in pulse form (
Light is 1, not bright 0)
In line with serial transmission to the corresponding LED display screen, control whether the light.
This way using the device is less, but the serial transmission data volume is bigger, because in a repeated cycle of light, each pixel in the 16th order under the gray-scale need 16 pulse, under the order 256 gray-scale need 256 pulse, because the device operating frequency restricted, generally can only make the LED display screen do 16 gray-scale.
Another method is to scan the board serial transmission not every LED display the contents of the brightness of the switch signal instead of an 8 bit binary value.
Each LED display has a pulse width modulator to control the lighting time.
So, in a repeated cycle of light, each pixel in the 16th order gray-scale just under four pulse, just under 256 gray-scale eight pulse, greatly reduces the frequency of serial transmission.
With this kind of decentralized control LED display gray-scale method can be easily implemented 256 gray-scale control.
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