DVDO's PureProgressive™ technology converts video streams from standard interlaced video to progressively scanned video. The following article describes why progressive scanning is inherently superior and how DVDO's exclusive PureProgressive™ performs this conversion with maximum video quality.

Interlace vs. Progressive Scanning

Interlace scanning is used in today's standard analog televisions. An interlaced TV "paints" the lines of a frame in two separate passes. Half of the lines are drawn in the first pass (the even lines), and the other half (the odd lines) are drawn in the second pass. First devised so that early TVs could have decent resolution with the limited transmission technologies available at the time, interlaced scanning has several unfortunate side effects which are discussed below. Progressive scanning paints all of the lines of a frame in one top to bottom pass. This is used where transmission bandwidth is not an issue and where the highest quality image is required. None of the interlaced side effects are present with progressive scanning.



The first major problem with interlaced scanning is that the image may visibly flicker if the screen is large enough that it represents a significant portion of a person's viewing angle. Even with small screens, sharp edges on objects may flicker. In addition to the flicker, vertically adjacent horizontal lines are not from the same field so motion occurring over time causes a spatial displacement on the display.
This motion displacement over time is usually not noticeable to most television viewers because the time displacement of the fields causes the "older" field to fade in intensity. However, on high resolution displays or on devices such as LCDs or plasma panels which do not fade, an interlaced image will contain noticeable motion artifacts. Just as critically, this displacement means that, during motion, the screen is only able to resolve half as many lines as it can for still images. For a standard TV, that means that the theoretical vertical resolution of approximately 480 lines actually translates to more like 240 lines during movement. For a medium that is designed for movement, this is a severe limitation.