There is a lot of understandable confusion over component video, and whether progressive scan 480p output from a DVD player is better than interlaced output, 480i. One reader writes:

If I have a DVD player that is 480i (non-progressive) and I used it with a projector that has a line doubler to display it in 480p, will I get the same result as if I would feed the projector direct 480p?

Good question. First, let's clarify one item--all digital projectors have deinterlacers (line doublers) on board. LCD panels, DLP chips, and LCOS chips are all exclusively progressive scan devices. They cannot operate any other way. So when a projector receives an interlaced signal either through the composite, S-video, or component ports, it must deinterlace it internally prior to sending it to the display device.

Now, if you have a DVD player that outputs both interlaced 480i and progressive scan 480p, do you end up with the same result either way? The answer depends. Frequently, as you've probably heard, the 480p signal from the DVD player is better.

Why? A DVD is encoded in digital component interlaced format. Frames must be assembled into sequential progressive scan format within the DVD player for it to output a 480p signal. This deinterlacing happens in the digital domain before the information is converted to analog for transmission. So in theory a good deinterlacer in the DVD player has the best chance of assembling the cleanest signal.

Meanwhile, if you switch your DVD player to interlaced 480i output, the DVD player foregoes the deinterlacing step. It simply converts the signal to analog for transmission to the projector (unless it has DVI output, which almost none of them have at the moment). The projector then converts the incoming analog signal back to digital and does the deinterlacing internally. In theory the two D/A conversions can compromise the signal, leaving the projector with less precise data with which to accomplish the deinterlacing.

However, these days D/A conversions are much cleaner than they used to be. Furthermore, it is quite possible that the projector has more comprehensive deinterlacing and video processing logic on board than does the DVD player. By using 480i, you take advantage of the projector's deinterlacing capability. On the other hand, using 480p bypasses it. So when the projector's internal video processing electronics are more powerful than those in the DVD player it is possible to get a better picture using 480i than 480p.

Bottom line...ignore all conventional wisdom. Set it up both ways, and trust your eyes. Depending on the DVD player and projector that you have, you may or may not see a difference between 480p and 480i. (Keep in mind that if you have two different input ports for 480i and 480p the projector may be calibrated differently on those two ports--don't confuse differences in calibration with differences attributable to 480i vs. 480p.) If you do an A/B test with the same calibration settings and you see a difference in picture quality, go with the one you like best. Don't go with 480p just because it is supposed to be the best. In may not be. Given the vast improvements we've seen in the deinterlacing capabilities on projectors, there are no absolute right answers anymore.

(note: to send this article to a friend, click the link below)