Different video formats 
The following table outlines some characteristics of commonly used standard analog video formats: 
NTSC: National Television Systems Committee (U.S.) 
PAL: Progressive Alternation of Lines 
SECAM: Systeme Electronique pour Couleur avec Memoire
 

Color Coding
For all PAL and NTSC formats, encoding is based on the concept of Quadrature Amplitude Modulation (QAM), where two color components are combined after being individually modulated via quadrant amplitude modulation. Since the modulation must be decoded, tracking the absolute phase requires demodulating the color information. A reference signal known as the Color Burst is inserted at the beginning of each line, positioned immediately after the horizontal sync pulse (see Figures 3 and 4 mentioned above).  
For all SECAM formats, the two color components are frequency-modulated using two distinct subcarrier frequencies, then sequentially transmitted across different video lines. SECAM formats do not require a color burst signal. 
Interlaced Scanning Concept 
All composite video systems use interlaced scanning technology to display video images on a TV screen. Figure 7 illustrates the concept of interlaced scanning.

Interlaced Scanning on a TV Screen 
Analog video signals include control pulses that manage the scanning process—moving line by line from left to right, and field by field from top to bottom. The pulse controlling line-by-line scanning is called the horizontal sync pulse (H-Sync), while the pulse governing vertical scanning is referred to as the vertical sync pulse (V-Sync). 
Two interlaced fields combine to form a complete frame. The first field is called the odd field, which scans the odd-numbered lines of the video image. The second field is known as the even field, scanning the even-numbered lines. This process is repeated for every frame.

Animated Images 
The activity video images obtained through scanning always maintain a 4:3 aspect ratio (horizontal to vertical), regardless of the video format. The color composite video signal indicates that the scanning process requires additional space on both the left and right sides of each scan line, as well as at the top and bottom of the active video image field. This extra space accommodates synchronization signals, color burst components, and other format-specific information—such as ITS data—that isn’t part of the actual active video image. Approximately 90% of all lines and about 80% of each individual line are capable of transmitting active video information. As shown in the table below, the exact percentages vary depending on the specific video format.

The active lines represent the actual number of lines used to transmit image and information. For example, in NTSC, only 480 out of every 525 lines per frame carry image data. Similarly, within each line, image information is transmitted only during the active-line sequence—this segment is shorter than the total duration of the entire line. For instance, in NTSC, the active-line period lasts just 52.2 µs out of the total 63.55 µs per line. The frame rate corresponds to the scanning speed. 
Grayscale Images and Extracted Line Spectrum Profiles 
Assuming the following conditions are met, the complete NTSC frame scan images in the next section simulate the video display that could appear on a TV screen. 
Television can display entire scan lines, not just the moving-image portion. 
Television doesn't achieve a complete image frame by interlacing two fields; instead, it scans the entire frame line by line. 
Scanning begins with a few lines representing the even-field vertical sync pattern (scanned line by line, top to bottom). An optional test signal (ITS) is inserted immediately after the vertical sync of the even field. Finally, the actual image from the odd-field activity is displayed. 
This process is repeated for even fields to form a complete frame.

Explanation: Most lines begin with a horizontal sync pulse, followed by the color burst pattern signal. The subsequent active image (or ITS) shows variations in intensity, with higher signal levels corresponding to greater brightness.

The extracted spectral line profiles at the bottom of Figures 8 and 9 show the active video signal lines obtained from even fields. For more information on video levels, refer to the previous section on video signals. 
Horizontal sync pulses are typically simple negative pulses, with levels lower than those of the luminance signal. However, the vertical sync signal consists of a sequence of pulses distributed across multiple lines, and this pulse sequence differs between odd and even fields. Figures 8 and 9 illustrate the vertical sync patterns used for two types of fields and three major video formats.