Article Directory
1. Display related terms
1.1 Video memory
Definition: Also called frame buffer, it is used to store the rendering data processed or about to be extracted by the graphics card chip, and is used to store the graphics information to be processed. Principle: The display screen is composed of pixels,
each pixel 4 to 32 or 64 bit data to control brightness and color. After the display chip has processed the data, it will save the data in the video memory, and then hand it over to the display chip and CPU for allocation, and the RAMDAC (digital-to-analog converter) will read the data from the video memory and convert the digital signal into an analog signal. The result is converted into graphics and output to the monitor
Frame buffer = monitor resolution bit plane number / 8
For example: the resolution is 1080p, how many bytes of frame buffer with 24 bit planes are needed?1920*1080*24/8=6220800字节
1.2 Screen size
Definition: the length of the diagonal of the display screen (the actual size of the screen), in inches, common screen ratios are 16:9, 16:10, 4:3, etc.
1.3 pitch
Definition: The pixel pitch of a liquid crystal display (pixel pitch) generally refers to the distance between two adjacent pixels on the display screen, and the fineness of the image quality is determined by the pixel pitch
Dot pitch = panel size/resolution, and the number of pixels of LCDs is fixed, so when the size and resolution are the same, the pixel pitches of most LCDs are basically the same
1.4 Brightness
Definition: the brightness of the picture
There are currently two ways to increase the brightness, one is to increase the light transmission rate of the LCD panel; the other is to increase the brightness of the background light, that is, increase the number of lamps. The higher the resolution of the display, the darker the brightness should be adjusted.
1.5 Viewing angle
Definition: Refers to the angle at which users can clearly observe all content on the screen from different directions
1.6 Display Color/Tint
Definition: the total number of colors that can be displayed on the screen at most. For each pixel on the screen, 256 colors should be represented by 8-bit binary numbers, that is, 2 to the 8th power, so we also call 256-color graphics 8-bit picture
1.7 color gamut
Definition: The range area composed of colors that can be expressed by a certain color representation mode. The colors of the visible spectrum in nature constitute the largest color gamut space (CIE color space). Generally, there are several standards for the color gamut, and the common ones are sRGB, ARGB, NTSC, DCI-P3, Rec.709, etc. These color gamut standards are all subsets of the CIE color space
1.8 color quasi
Definition: How accurately a monitor displays colors within its gamut coverage
1.9 color depth
Definition: Color depth is the number of bits used to store the color of 1 pixel in the bitmap or video frame buffer in the field of computer graphics, and the number of light and shade changes that each display unit can display, also known as bits/pixel (bpp ). The higher the color depth, the more colors are available
2. Video interface
There are mainly four types of common display interfaces, namely DVI, HDMI, VGA, and DP interfaces.
DVI, HDMI, and DP are digital signals, and VGA is an analog signal.
2.1 DP（DisplayPort）
Both the current mainstream HDMI interface are digital high-definition interfaces, and both support one signal line to transmit video and audio signals at the same time
2.2 HDMI（High Definition Multimedia）
The high-definition multimedia interface can transmit uncompressed audio signals and high-resolution video signals. At the same time, there is no need to perform digital/analog or analog/digital conversion before signal transmission, which can ensure the highest quality audio and video signal transmission, and the longest transmission distance is 15 meters, and audio and video signals can be transmitted at the same time.
2.3 DVI（Digital.Visual.Interface）
Digital video interface, based on TMDS to minimize the transmission of differential signals, supports video, does not support audio
2.4 VGA（Video Graphics Array）
Video graphics array/D-Sub, mainly used for old-fashioned computer output, the output and transmission are analog signals
3. Display
3.1 LCD liquid crystal display
LCD liquid crystal display: Liquid Crystal Display, which uses liquid crystal to control light transmittance technology to achieve color display. Because the brightness and darkness are controlled by controlling whether the light is transmitted, when the color remains unchanged, the liquid crystal remains unchanged, so there is no need to consider the refresh rate. For a liquid crystal display with a stable picture and no flicker, the refresh rate is not high but the image is also very stable. The LCD display also uses the technical principle of liquid crystal to control the light transmittance to make the bottom plate emit light as a whole, so it achieves a truly completely flat surface. Some high-end digital LCD monitors use digital methods to transmit data and display images, so that there will be no color deviation or loss caused by the graphics card. There is no advantage of radiation at all, even if you watch the LCD monitor screen for a long time, it will not cause great damage to your eyes.
Working principle: the backlight layer is always bright white light, apply voltage to the positive circuit, and the electricity passes through the liquid crystal layer to connect to the negative circuit to form a circuit. The voltage drives the liquid crystal layer to deflect, thereby blocking the white light emitted by the backlight layer. Controlling the voltage can control the deflection of liquid crystal molecules Angle, and then control the brightness of red, green or blue (white light can be turned into light of the corresponding color through a color filter), and the desired color can be obtained by controlling the ratio of red, green and blue. It should be noted that the backlight layer is a large backlight layer shared by all pixels of the entire screen.
Limitation: If you want to display pure black, the ideal state is that the liquid crystal molecules are completely closed to completely block the emitted backlight, but the liquid crystal molecules cannot be completely closed, so when the display is black, there will be a slight white light emitted, so you can see The black is not really pure black, but a gray with greatly reduced brightness. Similarly, when the screen displays pure black, a large area of halo will appear at the border, which is called light leakage.
Classification:
- TN: fast response time, cheap, narrow viewing angle, low color gamut, suitable for gaming LCD screens, soft screens - water ripples appear when pressed
- Super TN: Mostly used by mobile phone LCD screens
- VA: viewing angle up to 178, high contrast, wide color gamut, high power consumption, slow response, viewing angle lower than IPS, soft screen - plum pattern appears when pressed
- IPS: fast response, large viewing angle, true color, excellent picture, no watermark on touch, environmental protection and power saving, accurate color, size advantage; the disadvantage is light leakage and insufficient black purity, the larger the screen, the smaller the area of light leakage at the edge bigger
3.2 OLED display
OLED: Organic Self-Emitting Diode
Working principle: The self-emitting diode can emit light when it is powered on. The more power, the higher the brightness, and the less power, the lower the brightness. Since there is no backlight layer, each pixel can be independently controlled on and off, so one of the advantages of OLED is that it can be used as an always-on screen reminder
Limitation: Using PWM dimming, adjusting the duty cycle to adjust the dimming by turning on and off, will produce stroboscopic flicker, if the PWM frequency is low, it will be captured by the human eye, which will hurt the eyes, and if the PWM If the frequency is high, the damage to the eyes will be much smaller. The OLED screen uses organic materials, and organic materials are easy to age, so OLED cannot use high-frequency PWM dimming, so only low-frequency PWM dimming can be used.
3.3 Differences between the two
- The advantages of OLED are close to infinite contrast ratio (brightness ratio of black and white light and dark of the screen), no light leakage, and short response time. The disadvantage is short lifetime (organic matter + frequent electron migration + self-luminescence)
- Since the LCD screen uses a backlight layer, the aging of the entire screen is the aging of all pixels together, while each pixel of the OLED screen is independently illuminated, so the aging speed is different with the use of different areas of the screen. For example, if area A displays blue for a long time, its blue pixels will attenuate faster. Then when solid color content is displayed next time, the blue in that area will be slightly darker, resulting in afterimages, as if the screen has been blurred. Burned on the screen, this phenomenon is called burn-in (screen color difference caused by uneven aging of pixels).