Our TV antenna signal cable has only two wires—there’s a thick central wire surrounded by an outer layer, which helps block interference from external signals. Of these two wires, one is the ground wire, and the other is the full TV signal line; the outer layer serves as the ground wire. 
When working with video processing, it's inevitable to encounter TV signals—and understanding the principles behind the full TV signal is essential. If we connect a TV signal cable to an oscilloscope and observe its waveform, we’ll notice that the signal appears quite chaotic at first glance. However, there’s always an underlying pattern: right after each particularly distorted section of the waveform, you’ll find a tiny, low-level pulse. These highly irregular segments actually represent the varying levels of the active pixel signals, while those small pulses correspond to the synchronization signals that keep everything in sync. 
1. Regarding the pixel clock: It operates at approximately 13.5 MHz. According to the sampling theorem, the sampled signal should be 27 MHz. The pixel clock serves to synchronize the valid pixel signals, with one pixel value being captured with each pixel clock pulse. 
2. Regarding the horizontal sync signal: As the name suggests, it’s the signal that synchronizes the horizontal scanning process. It pulses once per line and is active at a low level (for positive video signals). Each time the horizontal sync signal appears, it indicates that the current line scan has ended—and the next line is about to begin. 
3. Regarding the field synchronization signal: As the name suggests, this is the signal that synchronizes the field scan—occurring once per field, with a low-level active pulse. Each time it arrives, it signals the end of the current field scan and the imminent start of the next one. 
4. On the concepts of "field" and "frame": Scanning from the top to the bottom of the screen constitutes one "field," but this is not the same as a single "frame." A frame refers to the image data that, when combined, forms a complete picture. In interlaced scanning, one frame actually consists of two fields—odd and even fields. 
5. Analysis of CVBS Waveform Levels: (Assuming a positive TV signal) Let the minimum level be 0 and the maximum level 1. Between these two extremes, there’s a reasonable threshold value, x, where pixels are defined as those ranging from x up to 1. This interval is divided into 256 discrete steps (assuming 8-bit precision), with each step corresponding to a specific grayscale value. Here, x represents black, while 1 stands for white, with intermediate levels representing various shades of gray. Note that any level below x is not considered an effective pixel value—it essentially corresponds to black. Importantly, synchronization signals, including both line sync and field sync, are embedded within this range. Notably, the field sync signal is significantly wider than the line sync signal; each has its own precisely defined duration. This precise timing ensures perfect alignment between the transmitting and receiving ends, enabling accurate reconstruction of the original image. 
6. Regarding the concept of odd and even fields: A single frame is divided into two fields, scanned sequentially—first the odd field, then the even field—before the two fields are combined to form one complete frame. 
7. Regarding field and line blanking: Following field and line synchronization, when a scan reaches the far right edge of the screen or when an entire field completes its sweep to the bottom, the system must return to begin scanning the next line or field—but in a way that remains completely invisible to the human eye. This is how field-blanking and line-blanking signals come into play. During these periods, the scanning device briefly retraces its path; although this movement occurs during the actual scanning process, it happens so swiftly and subtly that it appears as though the process is "hidden" from view.
8. Video Signal Level 
The video signal level defines the amplitude and range of different parts of the video signal. The organization responsible for defining video signal levels is IRE (Institute of Radio Engineers). The blanking level corresponds to 0 IRE, while the white level corresponds to +100 IRE. The blanking level serves as the reference point for the video signal (typically 0 V), as illustrated in Figure 6 below; however, depending on how the signal is configured, the blanking level may differ from the black level.

For NTSC, the 7.5 IRE setting is typically applied, raising the black level to +7.5 IRE. For PAL and SECAM, the black level matches the blanking level, both set at 0 IRE. 
The following table shows different video signal levels based on video format.

Simulated composite video signals are defined as voltage sources with an output impedance of 75 Ω. When driving a 75-Ω load, the white-level sync typically measures 1 V peak-to-peak. Consequently, the signal without a load is nominally 2 V peak-to-peak.
 

That is, 140 IRE = 1 Vp-p
9. Understanding Composite Video Signals 
A composite video signal is one in which all the components required to generate a video signal are combined into a single signal. The three main components that make up a composite signal are as follows: 
Brightness signal — contains information about the intensity (lightness or darkness) of the video image 
Color signal — contains color information from the video image 
Synchronization signal – controls the scanning of signals on displays such as TV screens 
The monochrome composite signal consists of two components: luminance and sync. Figure 1 shows this signal (commonly referred to as the Y signal).

Color signals are commonly referred to as C signals and are shown in Figure 2.

The composite color video signal typically consists of the sum of the luminance (Y) and chrominance (C) components, often referred to as the Color Video, Blanking, and Sync (CVBS) signal, as shown in Figure 3. 
CVBS = Y + C
 

Figure 3: Color Composite Video Signal with Color Bars 
The two components, Y and C, can be transmitted separately as two independent signals. Together, these two signals are referred to as Y/C or S-video. 
10. Composition of Video Signals 
The concept of composite video signal 
A signal that includes the luminance signal, chrominance signal, and synchronization signals (such as field sync, line sync, and line/field blanking signals) is referred to as a composite video signal. 
Also known as CVBS, it refers to the Color, Video, Blanking, Sync, or composite video baseband signal. 
The composite video signal combines luminance, chrominance, and the synchronization signal into a single transmission channel—meaning that before sending it over the cable, the chrominance and luminance signals are "merged" into one, and after transmission, they are "separated" again to be sent to the display circuit for processing. 
During the "combination" and "separation" of chrominance and luminance signals, image quality is affected by factors such as mutual interference between the luminance and chrominance signals, as well as inherent bandwidth limitations of the composite video signal itself. Unlike RF television broadcast signals, which undergo processes like modulation, audio/video mixing and separation, amplification, detection, and demodulation, composite video signals retain relatively better image quality during transmission. However, compared to other types of video signals, their overall image quality remains inferior, with horizontal resolution typically ranging from 350 to 450 lines. 
In the waveform of a composite video signal, luminance—combining brightness with the synchronization signal—is referred to as the luminance signal Y (Luminance, Luma). Hue and color saturation are converted through a specific transformation into a color difference signal, which is then modulated onto the color subcarrier. The resulting modulated color difference signal is known as the chrominance signal C (Chrominance, Chroma). The phase of the chrominance signal indicates the hue—that is, the color itself—while its amplitude corresponds to the color saturation. 
The single-level video line signal consists of a horizontal sync signal, the trailing edge, the active pixel field, and the leading edge. Notably, the horizontal sync, trailing edge, and leading edge together form the horizontal blanking interval, as illustrated in Figure 4.

The horizontal sync (HSYNC) signal marks the beginning of each new video line. Following this is the back porch, which serves as a reference level for removing the DC component from the floating-ground (AC-coupled) video signal. This is achieved through the clamping interval of the monochrome signal. In the case of composite color signals, clamping occurs within the horizontal sync pulse; since most of the back porch is dedicated to the color burst, it effectively provides the decoding information needed to extract the signal's color components. 
Color information can be embedded within a monochrome video signal. A composite color signal includes the standard monochrome signal (RS-170 or CCIR) and adds the following components: 
Color Burst: Located at the trailing edge, this is the high-frequency field that provides reference for both phase and amplitude of subsequent color information. 
Color signal: This is the actual color information. It consists of two quadrature components, each modulated onto a carrier by a color burst frequency. The phase and amplitude of these components determine the color content of each pixel.
 

Another aspect of the video signal is the vertical sync (VSYNC) pulse. This is essentially a sequence of pulses that occurs between fields, signaling to the display device that vertical retrace has been completed and it’s ready to scan the next field. Within each field, there are typically several lines that don’t carry active video information—some contain only the HSYNC pulse, while others include both the HSYNC and VSYNC pulse sequences. These pulses were originally defined in early broadcast television systems, and since then, they’ve become an integral part of the standard, even though later hardware advancements have made it possible to eliminate the need for some of these additional pulses altogether. Figure 5 shows the composite RS-170 interlaced signal, which includes the vertical sync pulse; for simplicity, a 6-line frame is illustrated below.
 

You should understand that for images obtained from analog cameras, the vertical dimension (in pixels) is determined by the rate at which the frame receiver samples the horizontal video lines. This sampling rate, in turn, is dictated by the camera’s architecture and its vertical line rate. Additionally, the structure of the camera’s CCD array directly influences the size of each individual pixel. To prevent image distortion, you must sample the horizontal direction at a consistent rate, ensuring that the active horizontal video field is divided into the correct number of pixel points. Here’s an example based on the RS-170 standard: 
Parameters of interest: 
Lines/Frame: 525 (including 485 lines used for display; the rest are VSYNC lines between every two fields) 
Operating frequency: 15.734 kHz 
Duration: 63.556 microseconds 
Activity duration: 52.66 microseconds 
Active pixels/line count: 640    
Now, we can do some calculations: 
Pixel clock frequency (the frequency at which each pixel reaches the frame receiver): 
640 pixels/line / 52.66 µs/line = 12.15 MHz (12.15 million pixels/line) 
Pixel line length of the activity video + timing information (referred to as HCOUNT): 
63.556 × 10⁻⁶ seconds × 12.15 × 10⁶ pixels per second = 772 pixels per line 
Frame rate: 
15.734 × 10³ lines/sec ÷ 525 lines/frame = 30 frames/sec