What is the principle of video display?

The Principles of Picture Tube TVs and LCD TVs Hello! Let's explore the fundamental principles behind how TVs display images. First, let’s take a look at CRT (Cathode Ray Tube) televisions, which might bring to mind words like "bulky," "vintage," or "old-school." While they may seem outdated, CRT TVs still hold a surprising presence in the market, even today. Their appeal lies in their ability to deliver high-quality images, though they are indeed quite large. One of the most striking features of CRT TVs is their sheer size. Even when not considering the screen dimensions, the overall bulkiness of these TVs is hard to miss. Inside every CRT TV is a "big package" housing various essential components. What exactly is inside this "package"? To understand why CRT TVs are so large, we must delve into the inner workings of the picture tube. Imagine a detailed sketch illustrating the structure of the CRT: Its key components include the cathode, focusing coil, deflection coil, vacuum tube, and phosphor. When an electrical signal enters the CRT, it is transformed into an electron beam emitted from the cathode. This beam is then directed towards the focusing coil, which helps concentrate the beam. Without a deflection coil, the electron beam would simply create a single bright dot in the center of the screen, which isn't very useful for displaying a full image. Deflection coils play a crucial role in shaping the electron beam. They generate a magnetic field that transforms the circular electron beam into a horizontal line. Horizontal and vertical deflection coils work together to create a grid-like pattern on the screen. This process is known as "scanning," and it's how TVs refresh the picture. In a CRT TV, scanning involves drawing one line at a time. In China's PAL-D system, each image consists of 625 scan lines. There are two main scanning methods: progressive and interlaced. Progressive scanning involves scanning all lines consecutively, whereas interlaced scanning alternates between even and odd lines. China uses interlaced scanning, allowing for 50 fields per second. Since interlaced scanning requires two scans to form a complete image, the frame rate is 25 frames per second, which aligns with the standard TV signal frame rate in China. Now, let's consider how the electron beam becomes the colorful images we see on the screen. The glass screen of a CRT TV is coated with phosphors, which glow when struck by the electron beam. Different phosphors emit different colors, creating the vibrant images we enjoy. CRT TVs come in both black-and-white and color varieties. Black-and-white TVs use simpler electron guns that focus on brightness, while color TVs employ more complex electron guns capable of transmitting color information. The phosphors in color TVs can emit blue, white, gray, and yellowish-white light. As a child, I often touched the screen of our CRT TV and felt a static charge. Now that I understand the technology behind it, I realize this was due to the constant bombardment of electrons, which naturally generates static electricity. Flat TVs: The Future of Display Technology With advancements in technology, TVs have become slimmer and more efficient. Modern TVs in stores are mostly flat-panel displays, including plasma, LCD, and OLED models. For this discussion, we’ll focus on TFT-LCD and OLED technologies. The Principle of TFT Display TFT stands for "Thin Film Transistor," which translates to "thin film transistor" in Chinese. Understanding the principle of TFT display begins with its structure. Let’s visualize a simplified TFT panel: A typical TFT screen includes a backlight, polarizers, a thin-film transistor layer, color filters, and a transparent substrate. The backlight emits white light, which passes through the polarizers and liquid crystals. Liquid crystals are unique materials that alter their properties based on temperature changes. Their molecular structure resembles aligned matchsticks. When the alignment of these molecules shifts, the amount of light passing through them also changes. Think of the liquid crystals as shutters whose openings are controlled by the thin-film transistors. After passing through the liquid crystals, the light’s intensity forms the brightness of the image. Adding color comes next, as the light interacts with color filters. The final step involves scattering the light with polarizers, allowing us to see the vivid colors on the screen. OLED Imaging Principle Unlike TFT-LCDs, which rely on external light sources, OLEDs are self-emissive, meaning each pixel can produce its own light. This allows OLED screens to display deep blacks when pixels are turned off. OLEDs also offer better viewing angles since they don’t require polarizers. An OLED panel comprises an anode, electron injection/transport layer, organic light-emitting layer, hole injection/transport layer, cathode, and transparent substrate. The organic light-emitting layer is a semiconducting film that emits light when electrons and holes combine in the presence of an electric current. Sub-pixel arrangements differ between LCDs and OLEDs. LCDs typically use a standard RGB arrangement, while OLEDs adjust their sub-pixels to compensate for the shorter lifespan of blue pixels. This results in an RGB-Pentile arrangement where blue sub-pixels are shared among multiple pixels. Despite some drawbacks, such as color accuracy issues, OLEDs excel in contrast and viewing angles. Over the years, improvements have significantly reduced these issues. Reflecting on the past, massive CRT TVs were once expensive. Today, affordable LCD TVs are widely available, showcasing the incredible progress in technology. That’s all for now. Stay tuned to IT House for more tech insights and practical guides! IT Home: [Insert Website Link]

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