1. What are R, G, and B?
In nearly all video technology standards, a critical issue revolves around how color information is represented—specifically, how display devices can accurately reproduce the true colors found in nature. Research has shown that the vast majority of colored light in natural scenes can be broken down into three independent primary colors: red, green, and blue—a principle known as the R, G, B color model. (R = RED, G = GREEN, B = BLUE)
With the advancement of electronic and digital technologies, we can now represent virtually any color in the world using a fixed number or variable—RGB is just one of many color-coding systems. This encoding method allows each color to be defined by three variables: the intensity levels of red, green, and blue signals. When it comes to capturing and displaying color images, RGB encoding remains the most widely used approach. In fact, nearly all color-display devices we encounter in our daily lives—such as televisions, computer monitors, and LCD screens—rely on this very system. No matter what type of signal is initially input into these devices, they ultimately convert it into an RGB signal, which then activates either a CRT (cathode-ray tube) or an LCD (liquid-crystal display) to accurately reproduce the intended colors.
2. Color Television Transmission Method
Discussing this issue is meant to give everyone a basic understanding of the questions that follow—and to introduce some specialized terms along the way.
1) What is a TV standard?
Simply put, it refers to the methods used in processes like breaking down, transmitting, and combining R, G, and B signals—and then receiving and demodulating them back into their original R, G, and B components.
2) What is a compatible color television system?
Since the advent of color television, countries have adopted different color broadcasting standards—but all have been working to ensure compatibility with their existing black-and-white TV systems (which still dominated at the time). It turned out that a compatible color TV system must meet the following key requirements (to coexist seamlessly with black-and-white TVs):
[1] Uses the same bandwidth as black-and-white television
[2] Same audio and video carrier frequencies
[3] Same scanning frequency with composite sync signal (H/V SYNC)
[4] There is a basic brightness information (Y) that, when transmitting the same scene image, must match that of a black-and-white television image.
[5] Chrominance information (C) is transmitted as a separate auxiliary signal, making it easy to distinguish from luminance information (Y) in the television.
[6] The transmitted chrominance information (C) must not interfere with the reception of black-and-white television.
"Y" stands for luminance (or luma), which refers to the grayscale value—the variation in lightness and darkness.
Chrominance (C), which describes the color and saturation of an image, is used to specify the color of individual pixels.
To put it bluntly, back then black-and-white TVs dominated the market—making it nearly impossible to promote anything incompatible with them, much like how today’s CDMA mobile phones remain incompatible with GSM systems. At the time, the primary standard for black-and-white TVs relied on a 625-line (H) and 50-field (V) scanning system, with a brightness signal bandwidth of around 6 MHz. As a result, both luminance (Y) and chrominance (C) information had to be transmitted simultaneously within this 6-MHz bandwidth—or else compatibility simply couldn’t be achieved.
So began the fierce battle among various compatible color TV standards—ultimately leading to the dominance of three systems that came to rule the world (though we’ve digressed a bit here). These are PAL, NTSC, and SECAM, each with its own unique advantages and drawbacks. None could easily overpower the others, though SECAM is used today by only a handful of countries, such as France and the former Soviet Union—nearly unheard of in most parts of the globe. For now, let’s focus solely on PAL, the standard embraced by our great nation and most European countries, and NTSC, which remains the dominant system in the U.S., Japan, and Taiwan.
3) What is the NTSC standard?
The NTSC system is a compatible color television standard developed by the United States in 1953. Based on human color perception, it recombines R, G, and B signals and incorporates technologies such as spectral interlacing, orthogonal balanced amplitude modulation, and synchronous detection. As one of the earliest systems introduced, its main drawback is that it’s prone to color distortion (tinting) during transmission.
4) What is the PAL system?
In 1962, West Germany sought to overcome the NTSC system's tendency to produce color distortion by developing PAL—a compatible color television standard based on NTSC. PAL incorporated techniques such as line-by-line phase inversion (note: it’s line-by-line phase inversion, not progressive scanning), which avoided the need to invert the entire chrominance signal. This innovation effectively addressed the issue of color shifts, though it also made the demodulation process significantly more complex.
3. What is a Composite Synchronization Signal (H/V SYNC)?
To display a complete image on devices like TVs—where every picture is made up of individual pixels—simply having R, G, and B signals isn’t enough. You also need to instruct the TV precisely where each pixel should appear on the screen. While the R, G, and B signals determine the color of the pixel, its exact position on the screen is governed by the horizontal and vertical sync signals (H/V SYNC). For easier understanding, we won’t delve into the technical details here. Simply put, the horizontal position of a pixel across the screen is determined by the horizontal sync signal (H), while its vertical position is dictated by the vertical sync signal (V). Together, these sync signals also define the screen’s vertical resolution and the number of frames displayed per second. When the horizontal and vertical sync signals are combined into a single composite signal, it’s called the composite sync signal. It’s important to note that the specific characteristics of H/V SYNC signals vary depending on the television standard being used—for example, China’s common PAL-D system features H: 15,625 Hz and V: 50 Hz, whereas Japan’s NTSC system operates at H: 15,750 Hz and V: 60 Hz.
4. What is the decomposition rate?
The clarity of television is typically expressed using both vertical and horizontal resolution. Vertical resolution is closely tied to the number of scan lines (H)—the more scan lines used, the sharper the image (and the higher the frequency of the line-sync signal), resulting in greater resolution. In China, PAL-standard TV images have a vertical resolution of 575 lines (or 575-line format), with a line-sync signal frequency of 15,625 Hz. However, this is only a theoretical value; the actual resolution depends on the effective scanning interval and the specific scanning method employed. As a result, the vertical resolution of TV receivers actually used in China often falls below 400 lines.
The horizontal resolution, measured in lines or pixels, is determined by the upper frequency limit of the TV signal. Among all possible TV images, the most complex one is arguably a checkerboard pattern composed of alternating black and white squares. Based on this pattern, combined with the currently mandated nominal bandwidth of 6 MHz for TV image signals (PAL system) in China, we can theoretically deduce that China's TV signals have a horizontal resolution of approximately 630 lines.
The NTSC system has a theoretical horizontal resolution of approximately 525 lines (with a bandwidth of 4.5 MHz), and a vertical resolution of about 580 lines (with a line-sync signal frequency of 15,750 Hz).
5. What is a composite video signal?
The full TV signal is defined as a single analog signal that includes luminance (Y), chrominance (C), composite sync signals (H/V), and the audio signal. Because of the presence of the chrominance signal—determined by the specific TV system used for encoding—the full TV signal varies depending on the television standard (PAL or NTSC).
6. What is a Composite Video Signal (AV)?
The Composite Video signal is essentially the video signal derived from a full TV signal after separating the audio component. At this stage, the chrominance signal is still interleaved at the high end of the luminance signal. Because the luminance and chrominance in composite video are interwoven, it becomes challenging to perfectly reconstruct the original colors during signal playback. Additionally, due to limitations imposed by the performance of the subsequent luminance (Y) and chrominance (C) separation circuitry, the signal bandwidth tends to be relatively narrow—typically supporting a horizontal resolution ranging from approximately 240 to 350 lines. Since the video signal no longer includes the audio component, an audio port is usually provided separately for synchronized transmission of sound. In some cases, the composite video interface is also referred to as the AV (Audio Video) port.
7. What is an S-Video signal?
S-Video is a two-component video signal that separates the luminance and chrominance signals from a composite video signal into two independent analog channels, transmitted via separate wires. Not only does this type of signal feature wider bandwidths for both luminance and chrominance, but by transmitting these components separately, it minimizes interference between them—allowing for a horizontal resolution of up to 420 lines. Compared to composite video, S-Video delivers superior color reproduction.
8. What are color difference signals or component signals (Y, Cr, Cb / Y, Pr, Pb)?
"Y brightness" is created using the RGB input signal by superimposing specific components of the RGB signals together. "C chroma," on the other hand, defines two aspects of color—hue and saturation. Specifically, C chroma is extracted by demodulating the Cr and Cb signals according to the decoding method appropriate for the respective TV format. Here, Cr represents the difference between the red component of the RGB input signal and the overall brightness value of the RGB signal, while Cb reflects the difference between the blue component of the RGB input signal and the RGB signal's brightness level. These are what we refer to as the color difference signals—or, more commonly, the component signals (Y, R-Y, B-Y).
9. How to obtain R, G, B signals
If you’ve carefully read the explanations in points 5, 6, 7, and 8 above, you’ll notice that (5) → (6) → (7) → (8) represents the flow of a single signal. As previously mentioned, the R, G, and B signals are ultimately what we need. But how do we convert the component signals (Y, R-Y, B-Y) back into RGB? It turns out that, originally, to ensure backward compatibility with black-and-white TVs, the Y luminance signal was created by adding the R, G, and B signals together according to specific proportions. For simplicity here, let’s assume Y = R + G + B—though in reality, the ratio is closer to R:G:B = 0.3:0.59:0.11. With this setup, all we need to do is feed the three signals—Y, R-Y, and B-Y—into a simple mathematical matrix operation, and voilà, we’ll instantly obtain the desired R, G, and B signals. The relationship among them is straightforward:
Y + (R - Y) = R
Y + (B - Y) = B
Y - (B - Y) - (R - Y) = -B - R + Y = -B - R + R + G + B = G (Y = R + G + B)
10. The Relationship Between Various External Input Terminals and the TV Signal Flow
Let me illustrate with a diagram—(the reason we’re using the decoding process specific to Japan’s NTSC 3.58 TV standard is twofold: first, PAL decoding is far too complex and could easily confuse everyone; second, most of the game consoles we have on hand are NTSC-based. To keep things simple and easy to understand, we’ve skipped over the line-and-field synchronization details.)
The Question Section
11. Next, let’s discuss the issue of interlaced versus progressive scanning, which has recently become a topic of considerable sensitivity among everyone.
As usual, let's start with some basic knowledge.
Most of you probably already know that, to create the illusion of motion in movies and TV, several still images are rapidly played one after another—this makes it seem as though the objects in those frames are moving continuously.
We refer to each "still" image as a "frame." Movies typically use 24 frames per second, PAL-based TV systems run at 25 frames per second, while NTSC systems operate at 30 frames per second.
As previously mentioned, each frame of a television image is composed of multiple horizontal scan lines—625 lines per frame in the PAL system, and 525 lines per frame in the NTSC system.
If all the lines in this frame are completed continuously, one after another from top to bottom—or in other words, if the scanning sequence is 1, 2, 3…525—we refer to this scanning method as progressive scan.
However, in reality, taking PAL as an example (NTSC works similarly), it’s impossible to scan 50 complete 625-line frames per second when the line frequency is 15,625 Hz and the field frequency is 50 Hz. (The conversion formula is omitted here.) That’s why a single full TV frame is actually created by two separate scanning passes: the first pass scans only the odd-numbered lines—lines 1, 3, 5, and so on, up to 525—and the second pass focuses solely on the even-numbered lines—lines 2, 4, 6, and so forth, down to 524. This method of scanning is known as interlaced scanning. To achieve progressive (non-interlaced) scanning, the line frequency would need to double to 31.5 kHz. Yet, due to the requirement of backward compatibility with black-and-white TV standards, the line frequency in television systems cannot be altered.
A single image containing only the odd or even scan lines is referred to as a "field." Therefore, the actual scanning frequency for PAL television is 50 fields per second, while NTSC operates at 60 fields per second. Although the two fields in interlaced scanning appear on the screen alternately—each being an incomplete picture—they blend together so quickly that we perceive them as a single, complete image.
12. The main disadvantage of interlaced scanning is:
1) The grating structure appears coarse and sparse; in some images, you can even see scan lines.
2) Vertical resolution is severely compromised, standing at roughly half of the horizontal resolution (350 lines);
3) The screen has a flickering effect;
4) Most importantly, it will cause combing artifacts (also known as feathering or zipper effect) and line jitter on the screen.
13. Why is interlaced scanning still used?
It's very simple—line-by-line scanning overcomes the drawbacks of interlaced scanning mentioned above.
14. Currently, those devices output both interlaced and progressive scan.
Among the devices we commonly encounter, standard TV and radio receivers, VCRs, most video cameras, as well as VCDs and LD players, all use interlaced scanning. In contrast, the new generation of digital TVs will feature progressive scanning, while today’s computer monitors—both CRT and LCD—are almost entirely equipped with progressive scanning technology.
Here, it’s important to note specifically: in fact, DVDs are inherently interlaced—meaning the video format used when creating DVD specifications was designed with interlacing in mind. The video images on DVD discs are stored in an interlaced format, and this is a key detail to keep in mind. Interlaced-to-Progressive (I2P) technology was developed precisely to address the limitations of interlacing, with the primary goal of converting the interlaced frames from DVDs into smooth, progressive scans.
Alright, with the support of those challenging principles we just discussed, let me address some common questions.
1. Why are the clarity rankings of various video connectors listed as RGB > YPrPb > S-video > Composite video?
To explain this issue, let’s take another look at the NTSC TV signal flow diagram above. Each blue box in the diagram represents a conversion or separation circuit. As we learned in high school physics, no energy conversion in the world is 100% efficient—there’s always some loss, some degradation of information involved. From the signal path shown in the diagram, we can see that the composite video signal passes through the most conversion boxes on its way to RGB, followed by S-video, while YPrPb encounters the fewest. RGB, meanwhile, doesn’t involve any conversion steps at all. Theoretically, then, the clarity ranking of these video connectors would be: RGB > YPrPb > S-video > Composite video. Of course, in reality, today’s advanced electronic technologies have significantly improved the efficiency of these conversion and separation circuits, leading to much lower signal losses and reduced information degradation. As a result, the gap in image quality between these output terminals has gradually narrowed—especially when dealing with lower resolutions (below 480 lines). The reasons behind this phenomenon will be explained later.
From another perspective, we can also observe that reversing the order of these four input terminals—RGB > YPrPb > S-video > Composite video—mirrors the chronological sequence in which various input options first appeared on our TVs. Early color and black-and-white televisions didn’t come equipped with any video input ports at all. Later, with the introduction of Fc devices alongside home video recorders, and subsequently VCD players, some imported color TVs—and eventually even domestically produced models—began incorporating AV, or composite video, input ports. Consumers were quite pleased with the display quality at the time. Then came the N64, SS, and PS consoles, along with early DVD players, bringing higher-resolution signal sources (around 350 lines). This shift highlighted an issue: the common problem of color bleed often seen with composite video inputs. In response, TV manufacturers swiftly developed the S-video port to address this challenge, and output-device makers quickly followed suit, enabling both PS and SS consoles to feature S-video output cables, while DVD players adopted S-video output jacks. Fast forward to recent years, as gaming consoles like the PS2 and NGC emerged, coupled with advancements in DVD decoding technology, we now had access to even higher-resolution video sources—approaching 480 lines. Yet, it soon became clear that delivering images at this level remained a significant technical hurdle due to the limitations imposed by TV standards (PAL: 6 MHz, NTSC: 4.5 MHz) regarding video bandwidth. Pushing beyond these constraints to achieve resolutions higher than 480 lines seemed virtually impossible. Thus, the only viable solution appeared to be developing a new high-definition video interface—one that would no longer be constrained by traditional TV standards yet still support seamless transmission of both high-resolution input and output signals. Naturally, this led innovators back to the long-established D-Sub 15-pin RGB output interface originally designed for computers. However, this particular interface was tailored specifically for progressive-scan RGB signals, whereas most consumer-grade video output devices at the time hadn’t yet embraced progressive-scan technology. Moreover, the D-Sub 15-pin connector itself came with stringent technical specifications, making it far too cumbersome and complicated to integrate directly into standard TV designs. (In fact, some domestic TV manufacturers’ adoption of computer-grade VGA ports turned out to be an unconventional—and ultimately problematic—practice.) Faced with these challenges, the industry took a step back, opting instead for a more practical solution: the development of the component video interface, capable of handling both progressive and interlaced scanning formats while delivering superior image quality.
2. Why is it said that S-video and composite video cannot output high-resolution images (>480 lines) or signals with progressive scanning?
The reason is that both S-video and composite video carry a color signal (C), and the encoding and decoding of this color signal are tied to specific television standards. In other words, both S-video and composite video inherently include signals formatted according to standard TV systems—PAL or NTSC. Since the bandwidth of these signals is strictly regulated by the particular TV standard being used—6 MHz for PAL and 4.5 MHz for NTSC—the resolution of the resulting image is naturally constrained within a certain range. This is why S-video and composite video cannot output images with very high resolution (beyond 480 lines).
Similarly, the frequencies of the sync signals for S-video and composite video are fixed by the television standards and cannot be altered—PAL: H = 15,625 Hz, V = 50 Hz; NTSC: H = 15,750 Hz, V = 60 Hz. In contrast, the line sync signal for high-resolution, 480-line progressive-scan video is 31,500 Hz. Therefore, neither S-video nor composite video can output signals with progressive scanning.
Also, some might challenge me by pointing out that my PS2 was connected to the TV using either an S-video or composite video cable—and TVs today inherently operate in progressive scan mode. So how can you claim that S-video or composite video cables can’t output signals compatible with progressive scanning? Actually, this is a common misconception. First of all, having a high-quality TV matters: many modern, premium models come equipped with built-in circuitry that converts interlaced signals into progressive scans—some even feature advanced upscaling capabilities. No matter whether the input signal is interlaced or already in progressive format, these TVs will process it to deliver a smooth, progressive display. Of course, the quality of the final picture depends on how well the TV’s internal interlace-to-progressive conversion circuitry performs—this is where technologies like Sony’s DRC truly shine.
3. Why does my PS2, when connected to a domestically produced old TV via S-video or composite video, produce a picture with no color or flickering?
This situation occurs if your TV doesn’t support both international or PAL/NTSC dual-standard signals, and the video format output from your PS2’s S-video or composite video connection doesn’t match your TV’s native signal standard. The easiest solution is to add a TV format converter (PAL<>NTSC), often referred to simply as a "format converter."
4. Do color difference signals and RGB signals differ between PAL and NTSC standards?
Theoretically, no—unless the signal source differs, such as an NTSC-format DVD or PS2 game disc from Japan's Region 2, or a PAL-format DVD or PS2 game disc from Europe's Region 2. In these cases, the resolution and synchronization signal frequency of the component video output may vary compared to RGB signals. Don’t believe it? Does your computer monitor even distinguish between PAL and NTSC? Or does your graphics card make such distinctions? Of course, this doesn’t apply to devices with built-in TV output capabilities.
5. My home TV is too old—it doesn’t even have an AV port.
Sure, here's the translation: "Indeed, it’s quite old. Just buy an RF modulator—this will convert the AV signal into an RF signal, which you can then feed into the TV’s antenna port. But if your TV doesn’t even have an antenna port, well, then it’s not really a TV anymore. Of course, in that case, you’d typically need to purchase an additional converter—unless your PS2 happens to support the same TV format as your old set."
Currently, coaxial cables are still used for transmitting analog video signals, with the central signal wire surrounded by a shielding layer that serves as the ground. However, the connectors for different types of signals often vary, frequently causing confusion among the general public and inadvertently giving unscrupulous vendors opportunities to exploit the situation.
Here's a brief introduction to commonly used methods for transmitting analog video signals:
RF — Radio Frequency signal, the same TV signal you watch every day. This type of signal modulates both video and audio together and is transmitted using a 75-ohm coaxial cable.   
CV — Composite Video: This type of signal is transmitted via a single coaxial cable, which is the standard video output commonly seen in everyday use. In consumer applications, RCA connectors are typically used, while in professional settings, BNC connectors are often preferred to ensure superior connection quality. The signal quality of composite video surpasses that of RF (Radio Frequency) signals.
YC — YC video, commonly known as S-VIDEO, uses two separate coaxial cables to transmit the luminance (Y) and chrominance (C) signals individually, preventing cross-talk between brightness and color information. In consumer applications, a Mini 4-pin connector (commonly called the "S-terminal") is typically used, while professional setups often rely on two BNC connectors for connection. This method delivers superior signal quality compared to composite video.
YUV—Component Video, also known as Chroma Subsampling Video or simply the "DVD connector." This video signal builds on YC video by splitting the chrominance signal into two separate components, transmitted via three independent coaxial cables—resulting in superior quality compared to YC video. In consumer applications, it’s typically connected using three RCA jacks, while in professional settings, BNC connectors are still preferred.
RGsB — Green Synchronized RGB signal, SOG (Sync On Green). This signal is significantly superior to the ones mentioned above, as it transmits the RGB red, green, and blue components separately while modulating the synchronization signal onto the green channel. This approach dramatically improves image quality, enabling high-resolution signal transmission—a feature that was commonly used in early workstations. Connection is typically achieved via three BNC connectors or a DB9 pin header (similar to a serial port). However, the resulting image may exhibit a slight green tint.
RGBS — Composite Sync RGB signal, featuring a CS signal (Composite Sync) that transmits the RGB primary color signals separately while combining the horizontal and vertical sync signals into a single composite stream. It uses a 4-wire BNC connector, commonly found in workstation video signals, and is compatible with high-end computer monitors equipped with RGB terminals. Alternatively, it can also be connected via the standard HD15 connector (commonly known as the VGA head), though Sun and SGI computers often use the 13W3 connector instead. The signal quality remains excellent.
RGBHV — a method that separates the RGB signals along with their respective sync signals. This transmission technique represents the pinnacle of analog video signal delivery, as it transmits the R, G, B, horizontal sync, and vertical sync signals entirely independently. Widely adopted in consumer applications, this method is what ensures every comrade’s computer screen displays images clearly—typically using an HD-15 connector (commonly known as the VGA head). In professional settings, however, the 5-wire BNC connector remains the standard for handling extremely high-resolution signal transmissions.
For analog signals, the more cables used, the better the signal quality. Just like a highway—on a road shared by both pedestrians and vehicles, speed naturally can’t increase. You might find this helpful to refer to.
Currently, two types of digital video signal transmission are still commonly seen: DFP (Digital Flat Panel) and DVI (Digital Video Interface). Both signals use the same digital format, though they differ in their connectors—this distinction, however, is beyond the scope of this discussion.   
Additionally, media such as network, USB, and IEEE 1394 can all transmit video signals. Stay tuned!