Progressive vs. Interlaced Scanning: A Trade-off between Quality and Expense
In this post I’ll cover the two popular methods for displaying, storing, and transmitting moving images: Interlaced and Progressive Scanning.
In modern video formats, an individual image is a frame, and each frame is composed of a series of lines. Scanning these lines is similar to the way we read, line by line, from top left to bottom right. Both interlaced and progressive scanning follow this pattern. The difference is that progressive scan captures/transmits/displays each individual line in every frame, while interlaced scanning deals with only alternating lines (half as many) in each frame.
This means that with interlaced scanning, you only updated half the lines during each frame. This saves on storage space and bandwidth, but creates blurring as the lines are never quite in sync. This blurring can be almost unnoticeable with very fast video, but becomes more noticeable as the frame rate drops and more real-world motion occurs between altering captures of odd and even lines.
Progressive scan, of course, provides a flawless clean frame every time, but at the cost of more bandwidth and storage (double) and therefore more money.
When quality and storage size are of concern, large format, high FPS interlaced scanning is the way to go, and many video capture cards support this. This allows the “illusion” of very large resolution, while each frame of video only has to capture half the information. However, when quality cannot be compromised, such as in gaming and banking applications, full progressive scan should be used. It is also preferable, in my opinion, with capture cards that provide frame rates of less than 15 FPS.
For more information, a detailed discussion on modern video formats, and some history as well, check out the following article: http://www.articlealley.com/article_12985_45.html
Keep Up With Us
