To illustrate the meaning of progressive scan, let's take a look at that old analog TV in your living room. It most likely uses the interlace method to draw onscreen images. That is, the electron gun at the back of the TV tube first fires off the odd lines of the onscreen image, then during a second pass, it shoots out the even-numbered lines. This all occurs within 1/30 of a second, but what you wind up seeing is an acceptable picture that has some occasional flicker or artifacts.

To improve upon those images, sophisticated front- and rear-projection TVs have used and continue to use line doublers. Line doublers turn an interlaced NTSC picture into a progressively scanned image for big-screen home-theater use by effectively doubling the number of lines on the screen, making the scan lines that make up the picture less visible.

Newer digital HDTVs draw progressive-scan pictures. Progressive scan works in the same manner as your computer monitor. It writes one full frame of video from left to right across the screen every 1/60 of a second. And since you get an entire image drawn at one time--as opposed to an image split into two--a progressively scanned video image is better than an interlaced one. This also means you wind up with few artifacts from the interlacing process or motion artifacts introduced into the picture.

Progressive-scan DVD players will work only with digital HDTVs and are not compatible with older analog sets, due to their higher horizontal-scanning frequency of 31.5kHz. One big feature that will be in any progressive-scan DVD player worth its salt is 3:2 pull-down circuitry. This tiny bit of silicon makes all the difference with your movies, by helping differentiate between the 24fps (frames per second) frame rate of film and the 30fps frame rate of video. In plain English, it smoothes out the picture and virtually eliminates what we in the industry call jaggie artifacts.

The best example of jaggies that comes to mind is in the very beginning of the Star Trek: Insurrection DVD. The movie opens with some children playing in haystacks. Then the camera pans to a village with a number of bridges and rooftops. If you watch this scene on an HDTV with a line doubler that lacks 2:3 pull-down (and almost all of them do) and a regular interlaced DVD player, you will see these nasty jaggy artifacts crawling along the bridge railings and all around the edges of the rooftops. Of course, now that you know what to look for, you'll be haunted by them in every film-based DVD you watch from now on. (Sorry.)

The other big reason why progressive-scan DVD players deliver much better pictures is because they can read extra data tags on DVDs and the players can work their image-processing magic in the digital realm before they output the video signal in analog form. (At this time, all home-theater DVD players output an analog signal.) If you feed an interlaced DVD signal to a digital HDTV, the TV's line doubler must convert the signal to digital before processing the image, and the TV doesn't have access to the extra data stored on the DVD. For this reason, a progressive-scan DVD player can deliver a sharper, cleaner picture. The good news is that the cost of progressive-scan DVD players will be plunging this summer to the $399 to $500 price points that more of us can afford.