INTERLACED & PROGRESSIVE SCAN
Interlaced and progressive scan are two methods of displaying video content on a screen.
Interlaced Scan:
Interlaced scan is a display technique that originated from the limitations of early broadcasting and analog video transmission systems. It divides each frame of a video into two fields: the odd lines and the even lines. The odd lines are displayed first, followed by the even lines, resulting in a complete frame. This process happens rapidly, giving the illusion of a continuous moving image.
The interlaced scan method was developed to conserve bandwidth and accommodate the constraints of analog transmission systems, such as limited bandwidth and slower refresh rates. By displaying only half of the lines at a time, interlaced video effectively doubles the perceived frame rate, providing smoother motion rendition.
However, interlaced video can introduce certain artifacts. One common artifact is visible scan lines, where the gaps between the lines become noticeable, especially on larger screens. Another artifact is flicker, which can occur due to the rapid alternation of the odd and even lines. These artifacts are more pronounced during fast motion or when displaying fine details.
Progressive Scan:
Progressive scan is a display technique that presents a complete frame of video in a single pass. Unlike interlaced scan, where each line is displayed in two separate fields, progressive scan displays each line sequentially from top to bottom, resulting in a smoother and more detailed picture.
Progressive scan technology became more prevalent with the introduction of digital display technologies like LCD and LED, which are inherently progressive in nature. With progressive scan, there are no visible scan lines or flickering issues associated with interlaced video. Each frame is displayed in its entirety, providing a more consistent and visually appealing viewing experience, especially for static images or slow-motion content.
It's important to note that while CRT displays are primarily interlaced, multiformat and multisync CRT displays do support progressive scan signals. This means that if a progressive scan video signal is provided, the CRT display can directly display the entire frame without interlacing artifacts.
In summary, interlaced scan is the traditional method used in CRT technology, where each frame is divided into odd and even lines displayed in rapid succession. It provides a perceived increase in frame rate but can introduce artifacts such as scan lines and flickering. Progressive scan, on the other hand, presents a complete frame in a single pass, providing a smoother and more detailed image with no interlacing artifacts.