First of all, we need to know what an LCD screen is:
LCD (short for Liquid Crystal Display) liquid crystal display.
You often hear LCD TVs, LCD screens, but what exactly is LCD?
LCD light-emitting principle
First thing to know:
-
Liquid Crystal: Liquid crystal is a liquid crystal, an almost transparent substance that cannot emit light
-
Light source: The light of the LCD screen comes from the light source emitted by the backlight panel at the bottom of the screen
-
Polarizer: A lens that allows only light in a specific direction (vertically polarized light) to pass through, while light in other directions cannot pass through
-
When the fence angles of the two polarizers are perpendicular to each other, the light cannot pass through at all
The physical properties of the liquid crystal are: the degree to which the liquid crystal controls the passage of light is controlled by the strength of the voltage applied to the liquid crystal. When the power is turned on, the arrangement becomes orderly, so that the light can pass easily, and the light path does not change; when the power is not turned on, the arrangement is chaotic, preventing the light from passing through and changing the light path.
Composition of LCD screen:
The upper polarizer and the lower polarizer, so that the light from the backlight can only pass through the lower polarizer, not the lower polarizer
Color filter: After the light of different intensities passes through the red, green and blue three-color filters, various colors will be formed
Liquid crystal layer: The molecular arrangement of the liquid crystal is controlled by energizing, thereby changing the path of the light emitted by the backlight source. If energized, the path will not be changed, and the light cannot pass through the upper polarizer. polarizer for display.
TFT substrate: thin film transistors arranged in an orderly manner, each thin film transistor can adjust its voltage, so that the liquid crystal can display different brightness and color within the range of a single transistor, which is what we call pixels
Backlight: Provides uniform background light
That is to say: if you want the LCD screen not to display, you only need the light from the backlight not to pass through the upper polarizer. If you want the LCD screen to display characters, the light from the backlight needs to pass through the upper polarizer, and whether it can pass through the upper polarizer. When you pass the polarizer, you need to see the molecular arrangement of the liquid crystal layer, and the molecular arrangement of the liquid crystal layer is controlled by the voltage applied to the liquid crystal.
That is to say, in the end, we only need to control the voltage of each pixel to achieve the effect of LCD screen display. In this way, the liquid crystal can be rearranged to display various graphic images and characters through voltage control in different areas.
Difference between LCD and OLED:
LCD (short for Liquid Crystal Display) liquid crystal display.
OLED (Organic Light-Emitting Diode, OLED) is essentially an LED light-emitting diode. When a forward voltage is applied to both ends, the carriers in the semiconductor recombine and cause photon emission to generate light, also known as organic electric laser display.
Simply put, LCD and LED are two different display technologies. LCD is a display screen composed of liquid crystals, while LED is a display screen composed of light-emitting diodes. The second essential difference is that LCD needs a backlight to light up, while OLED is self-illuminating with light-emitting diodes and does not require additional light sources.
Color LCD
Before the formal discussion, it is still necessary to understand the color generation principle of TFT liquid crystal display. It is based on the familiar principle of red (Red), green (Green), and blue (Blue) three primary color light mixing principle , for example, green + red = yellow , green+blue=cyan, red+blue+green=white, as shown below:
Red, green, blue three colors (primary colors), adjust their brightness ratio, you can get the colorful you want, and the number of colors obtained is called color depth (Color Depth)
RGB mode
According to the adjustment level of each primary color, it can also be divided into many color modes. The more commonly used one is that the three primary colors occupy 8 bits each, that is, each primary color has 2 to the 8th power (1111 11111~0000 0000) 256 kinds of brightness changes, the corresponding color The depth is 256*256*256=16777216 (commonly known as 16 trillion color), we call it RGB888 mode.
RGB color matching is usually represented by RGB (rr, gg, bb). For example, RGB (0xFF, 0x00, 0x00) means red, and RGB (0xFF, 0xFF, 0xFF) means white.
Of course not all monitors need 16777216 color levels, so this was born:
- RGB565 is R-5bit, G-6bit, B-5bit
- RGB555 is R-5bit, G-5bit, B-5bit
- RGB888 is R-8bit, G-8bit, B-8bit; in fact, this is RGB24
Equal RGB format
LCD display color principle
The LCD panel under the magnifying glass is as shown in the figure below. Add a color filter film on the LCD panel . Each pixel on the filter film is composed of three sub-primary colors of "red", "blue" and "green" (this is the so-called three primary colors. That is to say, these three colors are used). We divide the three colors of RGB into three independent sub-pixels (SubPixel), and then use the three adjacent sub-pixels, namely RGB, as the basic unit of display , that is, the display pixel pixel . Then this pixel , you can have different color changes. This screen can be displayed correctly.
From the above we know that for a color LCD, its columns are arranged in RGB mode, ( one display pixel for three columns of RGB sub-pixels )
For a TFT-LCD screen with a resolution of 240 columns and 320 rows, it requires 240 3 = 720 column drive (320 row drive) pins. Each display pixel will correspond to an address in the graphics memory (Graphics RAM, GRAM) in the driver chip. The GRAM address corresponding to a TFT screen with a resolution of 240 320 should be 240*320=76800, and the specific capacity depends on the chip. Supported RGB modes
