EXPECT to be bombarded with reasons why, if you've not done so already, you should buy a high-definition television set during the coming holiday season. By the end of the festivities makers will hope to have turned at least one in three American home-owners (up from one in ten in 2004) into the proud owner of a new super-telly displaying breath-taking pictures with pin-sharp images and pristine sound. The set-makers and big-box retailers emphasise three reasons why couch potatoes should buy an HDTV set now. What they are failing to mention, of course, is the one good reason to wait awhile.

The first reason to buy is that prices have fallen dramatically over the past year—down another 30% after a similar drop the year before. Sets may continue to get cheaper, but the really big falls have probably worked their way through, as manufacturers have ironed the last wrinkles out of their production processes. An American shopper can expect to find a wafer-thin 37-inch liquid-crystal display (LCD) set for little more than $1,000. Barely thicker 42-inch sets with plasma display panels (PDP) are going for around $1,500, and somewhat fatter 50-inch digital light-processor (DLP) versions for less than $2,000.

Another argument for taking the plunge is that big improvements have been made to all three display technologies used in modern HDTV receivers. Today's LCD models produce strong blacks, in place of the wishy-washy greys of a few years back, and there is much less in the way of ghost-like trails when images move rapidly across the screen. Plasma models have overcome the “burn-in” problem that left the outline of stationary images etched into a PDP screen. Better still, the life expectancy of PDP screens, once their biggest drawback, now matches that of the best of the traditional cathode-ray tube sets.

A third reason to buy now, say boosters, is the flood of high-definition content hitting the market. The number of American television networks offering high-definition programming has increased ten-fold, to 55, in the past four years. Then there's the arrival of high-definition video players such as Toshiba's $500 HD-DVD machine and Sony's $1,000 Blu-ray rival, both of which were launched with a stack of movies on high-definition DVDs. Video-game consoles, such as Microsoft's Xbox 360 and Sony's PlayStation 3, have gone high-definition as well.

AP

Do you have it in a larger size?

To see this new high-definition content at its best, you need a television set that paints its picture with no less than 720 lines (and preferably 1080 lines) running across the screen from top to bottom. (Ordinary television sets in North America and Japan have 525 lines, while those in Europe and elsewhere use 625 lines.)

But picture quality depends not only on line count. Broadcasters can beam their high-definition signals one complete frame at a time in a so-called “progressive scan”. Alternatively, they can use the old cheap-skate method of sending first only the odd lines in the picture for one frame, and then the even lines for the next frame, and so on.

The aim of “interlacing” like this is to trick the brain into thinking that it's seeing the whole picture all the time, though only half is available at any instant. Unfortunately, the brain isn't conned completely. Moving objects, in particular, tend to be seen as images with jagged edges. Also, the interlacing produces an irritating flicker that can induce eye-strain and headaches. That's why computer monitors long ago swapped interlacing for progressive scanning.

Broadcasters have been pushing 720 lines progressive (720p) for high-definition sports programmes that include lots of moving objects, and 1080 interlaced (1080i) for everything else. Both, they say, are good enough for what they have to do.

But good enough is the enemy of better still. Anyone who has seen a 1080-line progressive-scan display knows there's no comparison. And what the shills aren't saying is that stunning and affordable 1080p sets are in the works. Those who buy HDTV models offering only today's interim standards will be kicking themselves in six months.