Progressive scan and LCD screens
July 14, 2007
What is interlaced scan?
Standard Television sets use anyone of the interlaced scan systems - namely NTSC or PAL. Both these systems display analog video signals that are broadcast from TV stations or from some video sources. Although the display using these scanning systems produced acceptable results, they failed to create exact images on a PC or when DVD materials are used. It is because the video images produced by these scan system always had a few limitations in terms of resolution and picture quality. In an interlaced scan system, an image is scanned in an alternate order (1, 3, 5) skipping next line. As a result, the images lack smoothness and details and also become prone to constant flickering. Although certain improvements like ‘line doubling’ have been made in this system to produce images of higher resolution, they also produced some undesirable effects like ‘motion lag’ on the screen. Some of the video processors handle these problems quite efficiently, but the display needed an entirely different scanning system to completely remove flaws of the interlaced images.
What is progressive scan?
On the other hand, progressive scan system scans images in a sequential manner (1, 2, 3 etc), from top to bottom on the screen. This scanning method renders more details and smoothness to the images, especially when some text materials are shown on the screen. Presently, progressive scan is used in DVD, Digital TV and HDTV. Progressive scan is ideal for viewing DVDs and HDTV broadcast so high end PCs and flat panel television sets use this scan system to display images.
Progressive scan with 3:2 pull down and different progressive scans
There are two kinds of progressive scans that are being used. Progressive scan and progressive scan combined with 3:2 pull down. Whether your display device uses 3:2 pull down or not, the images are definitely better in terms of picture quality when compared with interlaced video images. However, the 3:2 pull down offers a film-like image quality and is often preferred if you wish to watch some HDTV sources or HD DVDs. Based on number of lines or pixel rows scanned, there are different progress scans like 480p, 720p, 1080i and 1080p. While a typical digital TV uses 480p (480 lines progressively scanned), the rest of the scans are applied in HDTV broadcast. Thus a HDTV broadcast or DVD will have resolution of 720p or higher. So if you plan to view a DVD or HDTV materials and to get enriched visual experience, you should go for TVs that come with progressive scan inputs.
What you should look for in your LCD TV?
If you want to access progressive scan pictures from DVD or TV broadcast, your TV should have anyone or all of the following connectivity options:
- Digital Video Interface (DVI)
- High Definition Multi-media Interface (HDMI)
- Component video input
Together with these inputs, either your TV or your DVD player should have 3:2 pull down detection, so that you can view progressive scan images with reverse 3:2 pulldown.
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