Rear Projection TV Shopping Tips
By Shane Buettner   •   August, 2007 Shopping for a big screen TV is only slightly less daunting than hitting your local used car emporium. The sales promos say they're givin' 'em away, but hey, their job is to make money on the sale. And our job is to help you keep the scales balanced and make sure you get what you need and don't buy the set with the most bells and whistles and the least in pure performance chops.

The Features That Matter
Connections: HDMI connections are ubiquitous on new displays. You definitely want and need HDMI. Not only is an all-digital connection to the display desirable, HDMI scratches Hollywood's copy restriction itch. Don't forget that Blu-ray and HD DVD were forced by Hollywood to carry the ability to downconvert the component video outputs on players. We haven't been pinched by this "Image Constraint Token" yet, but HDMI means you don't have to worry.

The latest rage are displays that offer HDMI spec 1.3. On the video side, what HDMI 1.3 offers over its predecessors is compatibility with Deep Color and x.v.Color. But for either to provide any benefit the source must also be compatible with these new standards. At present, there are no sources we're aware of that conform to Deep Color specs, and x.v.Color is available only in a few camcorders. These video features of HDMI 1.3 might be valuable in the future when we get sources, but they're borderline vaporware as of now.

HDMI Cable

HDMI gets a bum rap, and often deserves it. But HDMI is likely to remain the connection du jour for some time. The HDMI spec is now so far above and beyond what our software is capable of delivering that it will be a long time before we bunp up against its performance ceiling. Get as many HDMI inputs as you can.

Dynamic or Auto Iris: This is the real deal. At its root level a dynamic iris opens and closes a physical iris depending on the brightness levels in the image. As the image gets darker the iris closes down, and as the image gets brighter it opens up. But it's even more complex than that. Lots of electronic processing accompanies this process, and it's tricky to make it work invisibly, but a number of manufacturers have managed this feat.

Smart implementations of this feature have brought state-of-the-art performance with blacks and contrast to LCD/LCoS displays, keeping them neck and neck with the very best DLPs in these critical regards. This feature has been so successful in LCD/LCoS designs that we are starting to see DLPs follow suit.

When evaluating a display's dynamic iris to ensure its operation is undetectable, find a scene that cuts back and forth between light and dark images. Chapter 3 in Pirates of the Caribbean: Dead Man's Chest is a perfect example. Watch this scene and see if you notice the dynamic iris opening and closing to a distracting degree.

120Hz refresh rate: Speeding up the refresh rate (in this case doubling the 60Hz refresh rate that's typical of microdisplay display RPTVs) can reduce or eliminate flicker and other motion-related artifacts. Although this feature first began to appear in LCD flat panels, to eliminate or at least minimize motion lag, it is now finding its way into microdisplay RPTVs that will debut this fall. We'll give you the word once we get a look at some of these sets.

1080p input capability: Many displays cannot properly deinterlace a 1080i film-based source. But with the advent of HD DVD and Blu-ray, true 1080p sources are upon us. If the display will accept 1080p directly, it will not have to deinterlace such a source.

1080p/60 is the most prevalent form of 1080p in sources and displays. But the number of high-definition players that can output at 1080p/24 is growing. You want 1080p/60 input capability in your PJ for sure, and if you can get it, 1080p/24 is even better. At least a little bit.

Movies are shot at 24 frames-per-second (fps). A process called 3/2 pulldown is used to convert 24fps sources to either 30Hz or 60Hz for compatibility with the displays of the past, which have typically operated at either 60Hz for progressive sources or 30Hz for interlaced material. (Displaying a progressive source at 30Hz would result in intolerable flicker).

Blu-ray and HD DVD movies are encoded at 1080p/24. Displays that can accept 1080p/24 and display it at a refresh rate (akin to frame rate) that's a direct multiple of 24- such as 48Hz or 72Hz- avoid 3/2 pulldown entirely. There is no deinterlacing involved and the time distortion, called "judder," that's required to display a 1080p/24 source at 60Hz is eliminated. This results in smoother motion and a more film-like image. It's generally a subtle improvement, but an improvement nonetheless. Get it if you can.

Traditionally, RPTVs have been monstrous affairs. They got thinner and much lighter when they changed from CRT to the new digital technologies. Now, in response to the marketing challenge and increasing popularity of flat panel displays, manufacturers are slimming them down even more. While these newest sets fit into places that older RPTVs, even digital ones, could not, you should still check carefully to be certain that the slimmer depth does not result in optical aberrations, such as curved lines that should be straight.

If you're into the whole home theater experience you will probably be using an external audio system with your new display. But there may be times when you don't want to fire up the whole system just to watch the news. If that's the case, you'll find that the sound from many RPTVs is often dramatically better than from most flat panel displays. In fact, audiophiles are likely to find most flat panel audio virtually unlistenable. Check it out. Not necessarily a deal maker or breaker, and certainly variable from set to set, but worth considering.

And finally, read the fine print: RPTVs typically have more options/features than a fully-loaded BMW. Most of these are clever ways of marketing features that are more less the same as the set sitting next to it. Many things billed as image enhancements are anything but. And let's face it- we have gorgeous 1080p HD now from Blu-ray and HD DVD, and those don't need any form of artificial enhancement to look great. So read carefully and don't pay for anything you don't need.